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Thread: What Causes leading in revolvers???

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    Default What Causes leading in revolvers???

    Actually I've been casting and shooting cast bullets in revolvers for nearly 50 years now.

    Many of these bullets cast were from salvaged bullets I've dug out of dirt backstops at numerous ranges around the country. In examing these bullets from probably thousands of guns in many different calibers I don't recall ever seeing one that ever showed any signs of being melted or damaged by the heat of the burning powder. I've also picked up lots of bullets from the range here in Alaska when the snow melts in the spring; most of these bullets look like new other than being fired as the snow stops them without damaging them. Again - no signs at all of any damage from the heat of the powder. I have found numerous bullets however that showed evidence of the powder granules being blasted into the exposed lead base of the bullets but again there was no sign of heat damage.

    I suspect that the plastic residue in your bores is from friction and smearing. If you check the edges of the sabots or wads on shotgun wads I think you will agree that there is no signs of melting. Heck - even look at paper patched bullets or the cloth patches from your muzzle loaders- they aren't even scorched!

    Cutting my hot gases and/or high velocity particles is a destuction process. I've seen high velocity air with water particles in it cut right through thick forged steel elbows on pipe and high pressure gas wells tht produce sand will cut out piping in a very short period of time. High pressure steam is a bad actor; I've seen it cut through hardened steel in a few hours or less. The throat errosion could be caused by hot powder particles as I mentioned before or perhaps something else or a combination of factors. i really don't know.

    I suspect any lead evident around the gap in a relover comes from particles sheared off the edges as it passes through the gap but there is no way to tell where it comes from in my experience.

    I don't know why GCs would cause any faster gas cutting of the top strap - I don;t recall hearing that before but I may have forgotten. At first though it sounds similar the Lil'gun errosion talk.


    Quote Originally Posted by Murphy View Post
    Have either of you two guys shot cast lead bullets from any of your revolvers?
    Where does that splash of lead come from that is on the forcing cone and the top strap and the face of the cylinder??

    Why do plastic sabots leave plastic in the bore of my muzzle loader?

    How do plastic shot wads leave plastic in my shotgun??

    Why do some folks say GC bullets lead to premature gas cutting of the top strap?

    I had a cheap S&W 686 and shot it with mostly 38 specials. It actually cut thru the top strap with 125 grain JSP bullets anter ony a couple hundred thousand rounds. Why?
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    I started in about 1958, I have 21 pistol molds and 3 lead pots and 2 electric furnaces and 2 propane burners for casting and I don't have time to cast to keep up with my shooting so I buy cast bullets as well...by the 5,000 usually or the cheapest shipping rate.

    I don't have an answer to the questions posed but I am willing to discuss it in a civil manner.
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    The smearing of lead, or plastic down the bore is not from wiping but from hot gases getting past the bullet (or sabot) and melting very slight lead (or plastic) which adheres to the bore, thus the need for a tight fit of bullet to bore. If it were from just smearing (wiping) the lead down the bore, the solution would be to just use loose fitting bullets. When you try that you will find very significant amounts of lead on the bore. Regardless of how hard, what BHN number the bullet, lead has a low melting temperature. The alloy not the BHN will determine melting temperature and that is usually no more than 500 F, Typical powder burn temp is about 3200F. When fully enclosed in a barrel (without a cylinder gap) powder is much cooler. Powder burns because it creates it's own oxygen from the nitrates (NO3) in the powder (Nitrocellulose and Nitroglycerine) When unburned powder exits the barrel the new found oxygen increases this burn at the muzzle.

    In a revolver with a cylinder gap, a fresh dose of oxygen is found as the burning powder column passes through. This creates special needs for cast bullets in revolvers because it is the hottest point in the path down the barrel. The term here is vapor blasting of the lead from the base and edges of the bullet at this juncture. It actually is lead particles, but they are hot and adhere to the steel surrounding area easily because they are at, near or above the melting point of the lead alloy used. Gas checks definitely help to reduce this lead deposit around the cylinder gap but do not eliminate it because gas is getting around the bullet at the cylinder throat. Lead is then eroded away from the sides of the bullet and deposited on throats, etc. Here again we use the right lube and that helps. Now we can talk about gas cutting of the cylinder throats. (this is the FA problem) The gas cutting or normal wear and tear, as the bullet plugs the forcing cone with all the hot gas pushing it, can wear/damage the barrel extension, usually rounding and notch cutting the the outside diameter of the forcing cone. Reshaping the inner cone will help this because the bullet enters more easily (quicker) and will have less yaw at that point. And of course making a smaller cylinder gap helps this situation but brings other issues as well.

    I run pressure, temperature and velocity measuring equipment every week. I see lots of useful information flash before my eyes on very expensive test equipment. I think my theory is valid.
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    There must be vaporized lead because:
    Lead vapor is a major consideration in indoor shooting range design for air quality.
    There is lead in the powder residue that gets all over a revolver shooting cast.

    And the amount of lead vapor seems to be linked to heat, pressure, or both since there is more lead in the residue on my revolvers that run hot high pressure rounds than those that donít.


    I suspect Murphy is correct here. Iíve been around plaiting processes where things like zinc are vaporizes into gas. In these processes the sacrificial donor bar of metal just gets smaller, doesnít look at all melted, changed, or blemished just reduced in size but the part becomes magically plated as it attracts the vaporized mettle floating around it.
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    What Andy said sure makes sense and it makes my head hurt.

    If anyone has ever looked inside a .22 caliber suppressor there is lead smeared all over the baffles just as it is on the frame, barrel and cylinder on a revolver. I could be wrong and have been before, but 22lrs are softer bullets and probably lower temps and they still leave a bunch of lead behind when they are fired.

    The plastic sabot/wad issue is difficult to address without knowing the temp at which they soften/melt and what temp the powder burns. My old Browning trap gun had a chrome bore and picked up pretty much no plastic residue. My Superposed skeet set would strip plastic off AA wads and it had to be cleaned every 200-300 rounds or it would change patterns. A tornado brush always solved the problem and I figured it was barrel friction that caused the plastic build-up....never thought of heat being the culprit. Never had that problem when we were shooting fiber wads.
    Something I found when I Googled "plastic residue in shotgun barrel": I have a small bottle of Powdered Teflon that after Im done cleaning the barrel I put on a clean, dry patch and pass it through the barrel around ten times. This really seems to make a difference, after all that shooting, there seem to be very little residue build up of any sort, plastic, powder, lead, and the cleaning is a lot easier and faster. I also use it on all the working parts of my gun including the trigger group and so far have never encountered any major problems or wear. I have noticed that the inside of my guns are a lot cleaner probably due to there not being any oil for the dirt to adhere to.

    I'm not just posting this to support my friction idea, but it is the only thing that I found that related and we all know....Google knows all.
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    There is no doubt that lead get removed from the bullets in very small particles; the question is how.

    One source of lead in shooting ranges is from the use of standard primers; we now have lead free ones in some ammo. The lead from the primers is indeed a hazard on indoor ranges as is the bullets impacting on the steel backstop. If you have examined a steel backstop or target the lead is smeared in very very fine particles on the steel; heat from the powder is obviously not present at that point.

    Based on the examination of many many recovered bullets and finding no signs of melting or damage to the base of any bullets I maintain that the lead is primarily stripped from the bullets by mechanical means as it passes through the cylinder gap. We find similar lead particles in the gas ports of gas operated firearms even way up on the barrel like the M-1 Garand. In my M-2 carbine I have to pull the gas plug periodically to remove packed in lead, the lead is bright and shiney instead of dull gray like it would be if it had been heated. In my experience lead "shaved" from firing .22 rounds is also bright as if mechanically removed; Lowrider finds the same thing in a suppressor as the lead is wiped or shaved from the bullets - not melted from tjhe relatively low amount of heat produced by a few grains of powder in a .22 RF.

    I'll have to try it but I'll bet I can put a cardboard wad behind a revolver bullet and still get lead particles in the cylinder/barrel gap and still recover the cardboard wad intact; the base of the bullet is obviously not being melted by the hot gases. Actually cardboard wads and even paper patched bullets are used frequently in rifles with no signs of any scorching to the paper. The base of the bullets just doesn't get hot enough to scorch paper or melt plastic yet alone melt lead. In examing many many bullets from a very large number of different guns I have yet to find any evidence of a bullet base that has gotten heated to any visiable degree. As previous mentioned I also find numerous paper and plastic wads and sabots - not have ever shown any signs of melting or scorching yet I can easily and quickly damage them with a match even though a match won't begin to melt a bullet base. We also have plastic cases for handguns and even for the .223 - even they don't get melted from a single firing.

    Also, I'll have to disagree with the assumption that the presence of oxygen at the cylinder barrel gap creates a hotter flame at that point. The oxygen for the burning of the powder is totally contained in the powder and no additional oxygen is required for complete combustion. Also the gases produced by the burning powder are generally inert (CO2, H2O, and N2) and won't burn anyway so the presence of oxygen is just not significant.

    As to throat errosion there are probably many factors involved. The throat is obviously blasted by the flame and burning and unburnt powder granules especially with heavy loads and slower burning powders. Remember that we find unburnt powder gradules and/or ash in the barrel and sometimes on the bench in front of where we are firing. As to Lil'gun causing more errosion - if it does - it could be burning hotter from the added nitrogylcerine or it may a number of other factors. I can only guess on that one!

    Enough for one night. I'll see if I can dig out some undamaged fired bullets tomorrow.


    Quote Originally Posted by ADfields View Post
    There must be vaporized lead because:
    Lead vapor is a major consideration in indoor shooting range design for air quality.
    There is lead in the powder residue that gets all over a revolver shooting cast.

    And the amount of lead vapor seems to be linked to heat, pressure, or both since there is more lead in the residue on my revolvers that run hot high pressure rounds than those that donít.


    I suspect Murphy is correct here. Iíve been around plaiting processes where things like zinc are vaporizes into gas. In these processes the sacrificial donor bar of metal just gets smaller, doesnít look at all melted, changed, or blemished just reduced in size but the part becomes magically plated as it attracts the vaporized mettle floating around it.
    Living the urban lifestyle so I can pay my way and for my family's needs, and support my country. And you?
    ".. ask not what your country can do for you, ask what you can do for your country" JFK

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    We are way off the 45LC loading but...

    I found something else last night on one of the shotgun forums that further supports my idea that it is friction and not heat that causes plastic to be deposited on shotgun (and muzzleloader) barrels. There was an article about burnishing the bore of a shotgun to dramatically reduce the plastic deposits. It was done with OOOO steel wool and dowel rod on a drill. Apparently, it did a great job of smoothing the metal in the bore and that pretty much did away with the plastic residue from wads.

    That follows what I used to see in my old trap gun with the chrome bore...no plastic to speak of.

    I'm not completely convinced that heat from the powder does not have some contributing factor but I'm pretty well convinced that it is a "rough" bore that picks up plastic in a shotgun or ML. It may look smooth but microscopically it is not. I'm not a big fan of chrome in rifle bores because it rounds out the rifling and takes away some of the "purchase" the rifling has on the bullet hurting accuracy...but...it sure makes the barrel easier to clean.

    I wonder why no one chromes the inside of there pistol/revolver barrels...at least I'm not aware of anyone who does??
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    Quote Originally Posted by tvfinak View Post
    There is no doubt that lead get removed from the bullets in very small particles; the question is how.

    One source of lead in shooting ranges is from the use of standard primers; we now have lead free ones in some ammo. The lead from the primers is indeed a hazard on indoor ranges as is the bullets impacting on the steel backstop. If you have examined a steel backstop or target the lead is smeared in very very fine particles on the steel; heat from the powder is obviously not present at that point.

    Based on the examination of many many recovered bullets and finding no signs of melting or damage to the base of any bullets I maintain that the lead is primarily stripped from the bullets by mechanical means as it passes through the cylinder gap. We find similar lead particles in the gas ports of gas operated firearms even way up on the barrel like the M-1 Garand. In my M-2 carbine I have to pull the gas plug periodically to remove packed in lead, the lead is bright and shiney instead of dull gray like it would be if it had been heated. In my experience lead "shaved" from firing .22 rounds is also bright as if mechanically removed; Lowrider finds the same thing in a suppressor as the lead is wiped or shaved from the bullets - not melted from tjhe relatively low amount of heat produced by a few grains of powder in a .22 RF.

    I'll have to try it but I'll bet I can put a cardboard wad behind a revolver bullet and still get lead particles in the cylinder/barrel gap and still recover the cardboard wad intact; the base of the bullet is obviously not being melted by the hot gases. Actually cardboard wads and even paper patched bullets are used frequently in rifles with no signs of any scorching to the paper. The base of the bullets just doesn't get hot enough to scorch paper or melt plastic yet alone melt lead. In examing many many bullets from a very large number of different guns I have yet to find any evidence of a bullet base that has gotten heated to any visiable degree. As previous mentioned I also find numerous paper and plastic wads and sabots - not have ever shown any signs of melting or scorching yet I can easily and quickly damage them with a match even though a match won't begin to melt a bullet base. We also have plastic cases for handguns and even for the .223 - even they don't get melted from a single firing.

    Also, I'll have to disagree with the assumption that the presence of oxygen at the cylinder barrel gap creates a hotter flame at that point. The oxygen for the burning of the powder is totally contained in the powder and no additional oxygen is required for complete combustion. Also the gases produced by the burning powder are generally inert (CO2, H2O, and N2) and won't burn anyway so the presence of oxygen is just not significant.

    As to throat errosion there are probably many factors involved. The throat is obviously blasted by the flame and burning and unburnt powder granules especially with heavy loads and slower burning powders. Remember that we find unburnt powder gradules and/or ash in the barrel and sometimes on the bench in front of where we are firing. As to Lil'gun causing more errosion - if it does - it could be burning hotter from the added nitrogylcerine or it may a number of other factors. I can only guess on that one!

    Enough for one night. I'll see if I can dig out some undamaged fired bullets tomorrow.
    There are several points here where science is over ruled but I'll stick to a couple of obvious points.
    A bullet doesn't touch any point inside a can. What is scraping?

    Which part of the bullet, of your carbine (M1, M2) touches the gas port? If you refer to an M1/M2carbine, how do you see inside the captive piston house?? Do you shoot cast, unjacketed lead in these guns?
    There is lead in the cans on my pistols and Carbines from FMJ bullets, from the exposed base which doesn't scrape past any gas port.

    Do you forget what I do now??

    I set up electronic equipment to measure temperature, pressure and velocity on various types of guns and test chambers. Neither you nor anyone else can tell me that cylinder gaps aren't hot.

    How, with your theory can you explain how rifle barrels are eroded, gas cut or what ever term you choose to use??
    If there isn't enough heat and pressure to erode lead from a bullet, how could there be enough to erode steel??
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    Yip...sorry if I implied that the suppressor scraped or otherwise stripped the lead off the bullet. Bullets do not touch the inside of most modern suppressor as they pass thru it. There are suppressors that use "wipers" and rubber seals to help keep gas inside the can but these are not what I was talking about when I saw lead smeared on the baffles and inside the expansion chamber of 22 LR cans.

    I can sorta buy the idea of heat causing this leading on short barreled pistols but we also see this on suppressors on 16"-24" rifle barrels as well and I find it hard to believe the gases are hot enough from a sub-sonic .22LR at that distance to melt lead. On some 22 rifles you will see lead smeared on the face of the muzzle too.

    We may be beating a dead moose here but I would be interested in knowing what is really happening and what is causing leading...especially in .22's,.
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    Iím interested too, take some lab experimenting to positively find out.

    Iím interested enough that I just went out and fired off some 22lr from my Henry rifle that lives next to the front door. In the dark I get 4 to 6 inches of yellow flame and some sparks out the muzzle. So if it was hot enough at any point in there to melt lead Iím sure itís still melted at the muzzle. It isnít likely to solidify surrounded by an approximately 1100*f yellow flame. It adds up to me that there would be lead solidifying at the muzzle, as the bullet exits pressure will rapidly drop off. A rapid decree in pressure will have a rapid cooling effect (thatís what makes a refrigerator work) and also at that point itís mixing with the cooler air.
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    Andy,

    Them be some fierce .22LR's you're shooting!! I just did the same thing with my "by the door" gun, a CZ 452 16" with and without the suppressor shooting Aguila sub-sonics and there was no flame or sparks from that ammo. Your results must be because you are shooting high velocity stuff. I tried my 16" 17M2 without the suppressor and got a 2" flame so that is similar to your experience with your henry. Stepping up to a 20" 22 mag I got probably a 6" flame and ringing ears since I forgot my ear plugs.

    Perhaps I spoke too soon about the .22 LR not having enough heat to melt the bullet base. I put a cotton tee shirt over the muzzle of the 17M2 to see if I could see any burn marks and it ended up black but it is anybodys guess as to whether it is powder residue or burn marks...just looks black but did not catch on fire.

    I learned something from this but I still wonder if the couple grains of powder in a 22 lr is hot enough to melt the base of the bullet.

    Anyone else have any ideas?
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    I tried the CCI Mini-Mag that I keep in it, some Federal Lightning, and Peters high velocity lead that I had handy around. I don't have any sub-sonic around sence I don't need quiet, well I got some shorts someplace around I'll try if I can find. I can't walk past a brick of cheap 22 without it latches onto my hand but I just love those Mini-Mags for any real job, they are hot little suckers.
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    There was some further clarifications on the can so I'll pass on that for now.

    I shoot both cast lead and jacketed bullets thru my M1/M2. Most of the time with jackeded bullets the gun can be shot for thousands of rounds without ever pulling the gas cylinder - it is really not made to be readily removed. Shooting gas checked cast lead bullets - usually Lyman #311359 - I'll have to pull the gas nut and plug and scrape the lead out of the cylinder- the pistol freezes up from all the lead that accumulates. I've recovered a lot of the bullets and the gas checks are still bright and shiny and there is no signs of melting of the lead at all- the lead is still bright and lube is still in the grooves. Like the revolver a relatively soft bullets is scrapped over a gap and a portion is simply scrapped away. And as Andy pointed out - even very smooth bores are quite rough - and abrasion of the lead by metal is a very real probability.

    As explained before one simple explaination for the errosion of the throat and cylinder is simply one of numbers: the base of the bullets is exposed only once and for a very brief time period to the heat, gases, and particles from firing while the throat/gap is exposed for a relativley longer period for many many thousands of exposures. The gas/particles make a right angle turn at the cylinder gas also - gas flowing over a sharp angle can errode the corner relatively fast especially if particles are involved. Also remember even brass cases aren't damaged by the heat even though they be fired a dozen or so times.

    Since you brought up the subject - I spent the last few days myself involved in project using piezo pressure transducers, accelerometers, and strain gages to study high energy flow in some piping. Lots more complicated that firearms but many of the same principles still apply. Actually I've spent many of the last 40+ years involved with pressure, temperature, flow, strain etc. measurments and data acquistion / logging - that is a big part of what I do. I also get involved with the errosion of piping and valves by hot gases, particles, high velocity fluids and gases etc - I'm not stranger to errosion and high energy cutting of metals. I've also got a PE license in control systems for whatever that title means to you.

    BTW -Have you fooled around much with choked flow in piping? I've did some interesting calculations as how that applies to firearms that you may be able to verify with your equipment.


    Quote Originally Posted by Murphy View Post
    There are several points here where science is over ruled but I'll stick to a couple of obvious points.
    A bullet doesn't touch any point inside a can. What is scraping?

    Which part of the bullet, of your carbine (M1, M2) touches the gas port? If you refer to an M1/M2carbine, how do you see inside the captive piston house?? Do you shoot cast, unjacketed lead in these guns?
    There is lead in the cans on my pistols and Carbines from FMJ bullets, from the exposed base which doesn't scrape past any gas port.

    Do you forget what I do now??

    I set up electronic equipment to measure temperature, pressure and velocity on various types of guns and test chambers. Neither you nor anyone else can tell me that cylinder gaps aren't hot.

    How, with your theory can you explain how rifle barrels are eroded, gas cut or what ever term you choose to use??
    If there isn't enough heat and pressure to erode lead from a bullet, how could there be enough to erode steel??
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    TV,

    You are about 5 light years ahead of me on this and I am very interested in your findings if you can find some answers to what is happening here. My theories seem to be vaporizing like the lead. I wait with great anticipation.
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    TV,

    I 'm not sure you understand my position on this at all. You keep using the word melted. I have used that term but don't mean in the traditional sense of liquid lead. Obviously the bullet isn't melted, but does it not make sense to you that if you expose an alloy with a melting point of about 470 F to a temperature of about 2000 F, even for a few milli seconds that some of the surface could reach a temp above 500F?? Maybe not couple this with an expanding gas pulse of approximately 30,000 psi that pushes this lead slug into the cylinder throats where the fit is loose and the gas can now escape around the sides of the bullet, doesn't it seem quite logical that part of the hot surface on the base and now sides of that bulled will be .....pick a word here, melted/eroded/blasted/removed from the bullet surface, in some manner and propelled out the cylinder gap on to the surrounding surface of the cylinder face, the barrel extension (the part inside the cylinder frame window) and the cylinder frame.
    Your theory also contends that there is nothing between the surface and the bullet such as lube or gas rushing by.

    Throughout this discussion you have maintained all this lead is mechanically removed (scraped/smeared/wiped) from the bullet.
    If that is you position, and theory, we'll just agree to disagree on this lead and revolvers point.

    I wasn't aware that folks used cast bullets in an M1 carbine but I guess some do. But what do you think the pressure is at that gas port? You didn't say how you get that lead out...if you mechanically scrape it out of course it would be bright!! I don't know of a way of getting the lead out of the house without vinegar and hydrogen peroxide and that would only tell you if it is lead. I'v found if the nut is fully bottomed out and the piston staked in place there will be lots of buildup under the nut.

    Your work sounds interesting. What gas and what pressure do you run through your pipes? Fluid dynamics is quite different and will cut at much lower pressure. Gas seems to be accelerated when the metal is hot, would you agree.

    I haven't worked with piping except barrels and all my work in this field has been with guns, universal receivers, and test fixtures for piezo crystal, copper crusher cylinders and strain gages to measure the pressures of these single stroke, thermodynamic devices we call a gun.

    I look at PT curves or PD curves as it translates to barrel length (distance) and notice that peak pressure is at about .5 milli-seconds after ignition. I see lots of these curves and watch how they differ from powder burn rates. I see these in relation to bullet movement and position by watching the thermal signature of the barrel as the bullet moves down the barrel. The heat is from the hot gas pulse chasing the bullet down the barrel. Can you explain the 200C thermal jump at the cylinder gap?

    Another question for you, and others, I have a 300 Winchester, SAKO barrel that had exactly 600 rounds of run through it. I re-barrelled the rifle to another caliber and had Gunbugs mill out the barrel to expose the chamber , throat and a few inches of the rifling. There was never any lead bullets shot down the barrel, even though it was cleaned before the milling, there is copper on the rifling, scraped there from the bullet I presume, but what do you think the throat looks like after 600 magnum rounds? (300 WM) This would be just gas erosion, we would agree on that right? I can send a picture of this I think.
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    I think I shall avoid all such pissin' contest as this in the future. I'm just going to presume everyone out there disagrees with me and let it go at that. That makes it easier on me. I have to go to work before I forget what they pay me for!!
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    Default Don't take it so hard!

    I don't take it personally or consider it a pissing contest when someone disagrees with me - that is what a forum is all about isn't it?: a place to discuss and trade ideas? There are many members on here with good and bad (to me) ideas but the ideas represent a lot of experience and observations. I've learned a great deal and I hope I'll pass on some things I've learned to others.

    I'm very interested in some of your observations like the temperature rise at the cylinder gap. While we may disagree on the cause information like that can lead to some interesting theories. Incidently - how did you measure the rise and did you get a corresponding increase in pressure that would come from a pressure rise?

    In any event we should probably start a new thread instead on continuing it under this one. Can you swap the appropriate post to another threat and give it a good title?

    Thanks!


    Quote Originally Posted by Murphy View Post
    I think I shall avoid all such pissin' contest as this in the future. I'm just going to presume everyone out there disagrees with me and let it go at that. That makes it easier on me. I have to go to work before I forget what they pay me for!!
    Living the urban lifestyle so I can pay my way and for my family's needs, and support my country. And you?
    ".. ask not what your country can do for you, ask what you can do for your country" JFK

  18. #18
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    Quote Originally Posted by tvfinak View Post
    I don't take it personally or consider it a pissing contest when someone disagrees with me

    That's probably a good thing considering your opinions... just an observation.

  19. #19
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    I think a lot of folks don't understand the causes of leading and particularly in the revolver we have an additional issue which is unique to the revolver.

    I've been loading, shooting and testing big bore revolvers with cast bullets since 1978. Here are some things I've discovered.

    The cause of most leading is gas escaping around the bullet in the barrel because of poor fit or lack of full obturation of the bullet in the barrel. It isn't that the bullet is too soft, in fact it may be that the bullet is too hard. Yes that's right, too hard. A hard bullet that cannot obturate in the bore, cannot seal the bore and prevent hot gas from ripping small particles of lead from the bullet and depositing them on the surface of the barrel. It isn't always caused by a velocity that is too high, quite the opposite, it may be the velocity is too low. Well, not the velocity but the pressure is too low to obturate the bullet. Basically it comes down to fit. The bullet must fit the bore tight to keep gas from leaking by. We can make the bullet fit tight by casting of a softer alloy (Lyman #2) and firing in a load that gives enough pressure to obturate the bullet. One way of increasing this needed pressure is to use heavier bullets over a moderate to heavy powder charge. Or we can make a tight fit by slugging the bore and making high BHN bullets .001" to .002" over bore slug size. This is generally the technique used for revolvers because we want what is essentially a heavy solid bullet for hunting in a relatively low velocity handgun.

    Too high of a velocity will have the same effect as too little or the wrong lube. This is called galling. The bullet is literally scraped against the barrel and large scalds of lead are left on the bore surface. Similar to the way two sheets of aluminum might do under light pressure when rubbed together. There is a limit of velocity for any gun/cartridge combination but we know we can exceed 2200 fps in rifles with bullets of BHN of about 16. There are many factor that can limit this such as bore smoothness and concentricity and this applies universally to all guns and all cast bullets. And much has been written about using the right lube for the bullet application. Much like using the right motor oil for a precision racing engine. But bullet fit is paramount, regardless and the bullet must make a tight seal, plug the bore and prevent any blow gasses from escaping around the bullet.

    A revolver presents all these issues with cast bullets but also an additional issue. This issue is also related to fit of bore and bullet, that is still a must. In addition, the cylinder throats must allow the bullet to pass through freely, without swaging it down with accuracy robbing deformation. All this and yet the fit must be such to allow no gas blow by. This is a primary cause of leading at the cylinder face, cylinder throats and forcing cone. (barrel throat) That of course is an impossible task but we can take steps to move closer to this goal. A bullet that seals a cylinder throat, and prevents gas blow b, will be swaged, resized in that throat which will cause accuracy problems and possibly leading problems in the barrel because it doesn't fit the barrel any longer. This again is further emphasized when using hard cast (BHN 18-22) as is used in most big bore revolvers for hunting and wilderness defense because they will not obturate in the bore at revolver pressures. Generally, at revolver pressures of about 40,000 psi and less, (most magnum calibers fit in here) a bullet of BHN of 22 will not obturate to fit the bore. Higher pressures guns such as the 454 Casull, 475 Linebaugh, and the 500 S&W, can obturate even a BHN 22 bullet. These pressures do add more leading and gas blow by issues and some find the use of bullet gas checks help with leading at the cylinder gap in these revolvers.

    The best solution for revolvers and cast bullets would be a compromise. These steps should help to optimize cast bullet performance in revolvers.

    1. Slug the bore and and size bullets to at least .001" over bore size. (.001" to .002")

    2. Cut cylinder throats to uniform size of no more than .001" larger than the bullet. (.0005" to .001")

    3. Use bullets and lube specifically designed for revolvers.

    It is actually common for cylinder throats to be oversized. This will require adjustment to the above steps.
    If you shoot a 45 caliber revolver and the cylinder throats are .454" and the bore is .451" you would be well served with bullets of .453" Typically we would cut throats to .4525" for a bullet size of .452" but if they are larger than that we may just have to try to make them as uniform as possible and live with the excess slop. This will cause more leading at the cylinder gap and require more cleaning which isn't a problem but it could also cause more gas cutting around the cylinder gap which could lead to a premature retirement of the revolver. Custom fitted, line bored cylinders can be made by several custom gunsmiths and may be a worth while investment if you are serious about shooting of your big bore revolver.
    Mike
    _______________________________________
    "The rifle brought man out of the mud". Cooper

  20. #20

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    Quote Originally Posted by Murphy View Post
    Lets explore some causes.
    Entry angle of the barrel throat is a big concern in my experience. Dunno how current my info is because I haven't measured any current revolvers, but at one time it was way too steap. I "cured" it by reaming the barrel throats on my revolvers to a gentler entry angle. It all started about 40 years ago when I was forced to shoot swaged bullets and lots of them from Remington, Winchester, Hornady and Speer. I was separated from my casting gear for a couple of years and could buy lots of swaged bullets cheap.

    I was only shooting midrange and lighter loads, but especially when shooting rapid fire I'd get terrible lead smearing from the throat forward and again at the muzzle. Reaming the throat took care of it unless the guns got really hot, at which point I'd start seeing it again toward the muzzle.

    Fast forward to when I got back near wheel weight and harder bullets and tried higher velocities, and the benefits extended there. No loss of accuracy with hard cast or jacketed, and at the time I was doing it I beat the deterioration in accuracy as the leading built up over the course of a shoot.

    Dunno what current throat angle standards are, but it's the first thing I suspect when I hear someone wailing about leading.

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