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Thread: Reducing neck tension, case taper and sharpening shoulders...is it really "Improved"?

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    Member mainer_in_ak's Avatar
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    Default Reducing neck tension, case taper and sharpening shoulders...is it really "Improved"?

    When you make the neck shorter, you reduce neck tension. When you take away case taper, you increase extraction effort, when you sharpen shoulders, you run the risk of feeding problems. Why do some gunsmiths have to do work to the feed areas of an action if this were not the case (referring to the combo of sharper shoulders and reduction of case taper)?

    Do these things really "Improve" the cartridge?

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    The neck of a cartridge needs only to be slightly longer than the bullets diameter to maintain a proper hold on the projectile. Anything extra is just extra length that holds the bullet out of the powder chamber, increaseing case volume.
    A tapered case acts much like a splitting wedge. Straightening the cartridge case taper out reduces rearward thrust on the bolt and bolt face, also reduceing reward thrust on the bolt lugs. BUT all improvements may or may not actually be an improvement; some may increase velocity yet decrease accuracy or the ability to operate in certain types of firearms.
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    Default thrust on bolt face

    In reality, the case walls aren't near strong enough to do much to reduce the bolt thrust - they just stretch until the base of the case is supported by the face of the bolt. Actions that stretch like the Lee-Enfields shows this effect in the short case life caused by stretching cases. Cases with minimum taper will hold more power but as you note, other problems like difficult extraction may result.

    Quote Originally Posted by brav01 View Post
    The neck of a cartridge needs only to be slightly longer than the bullets diameter to maintain a proper hold on the projectile. Anything extra is just extra length that holds the bullet out of the powder chamber, increaseing case volume.
    A tapered case acts much like a splitting wedge. Straightening the cartridge case taper out reduces rearward thrust on the bolt and bolt face, also reduceing reward thrust on the bolt lugs. BUT all improvements may or may not actually be an improvement; some may increase velocity yet decrease accuracy or the ability to operate in certain types of firearms.
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    I don't know...all I can say is that I'm dubious of most of the "improved" cartridges. I'm not sure many of them actually do much more than burn more gunpowder and many come with a list of drawbacks that (IMHO) outweighs the slight gains in velocity.

    I've got a couple of the newer cartridge designs that I like very much but I can't actually say they're better in any way that doesn't qualify as minutiae.

    I'm a big fan of the .300WSM- but I've also had a stuck case with a factory load. I also like the .375 Ruger but I look at that straight sided bottle and wonder about it a little. I don't generally regard cartridge variations as progress in rifle making...sure interesting to think about but we're a long way down that road already. I wish rifle makers would concentrate on better shooting iron and less on different shaped powder bottles but it does keep things different.
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    Quote Originally Posted by brav01 View Post
    The neck of a cartridge needs only to be slightly longer than the bullets diameter to maintain a proper hold on the projectile.
    I used to think the same thing. However two cartridges I am currently working with have shorter necks than bullet diameter. The .243 Win and the .375 Ruger both have short necks, less than the bullet diameter and they both work well.

    Hornady TAP ammo in 110gr .308 Win is factory seated to a bullet depth of less than .130, that opened my mind to the reality of not needing to seat to a depth that equaled or exceeded bullet diameter.

    In closing, I also like to seat at least bullet diameter deep but it does hurt not to. After all, some very proven designs have short necks even prior to trimming .010 back of SAAMI spec which is a fairly common practice.

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    Some are worth it, some aren't. 30/30 AI, pretty big gain in case capacity on a percentage basis, and none of the Marlins I've converted needed any feed work. 30/06 AI, probably a waste of time if you're hunting increased performance, but could be useful to clean up a sloppy chamber or just to have something your buddies don't. To properly cut an "Improved" chamber in a rimless cartridge that headspaces on the shoulder, one needs to set the barrel back a turn if reaming out an existing factory chamber, so I guess with that amount of work already going into the project, I never thought twice about going ahead and making sure the darn thing would feed. Not sure why an Improved would have less neck tension, unless your dies were screwed up. But as Marshall pointed out, it only takes so much. My favorite 257Wby load only has me seating the bullets .225 in the neck, but I'm not going to argue with 5/8" for 3 shots at 100 on a regular basis. Another big benefit of the AIs is the reduced frequency of trimming the brass, I HATE trimming brass, but have a pal who gets about 12-15 firings out of 243AI cases without needing to trim. Once they need to be trimmed, he just tosses them and starts with a new batch of 100.

    Bottom line to me is, it isn't going to turn your rifle into a magic magnum, but there are some benefits. It's up to you as to what you think is best for your gun.

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    Quote Originally Posted by brav01 View Post
    A tapered case acts much like a splitting wedge. Straightening the cartridge case taper out reduces rearward thrust on the bolt and bolt face, also reduceing reward thrust on the bolt lugs.
    Thrust forces on the bolt face (or any other part of the chamber) is a direct product of chamber pressure acting on surface area. No mater the chamber shape the thrust force on the bolt will always be the sane unless as long as the bolt face area the pressure acts on is the sane. Enlarging the chamber may reduce pressure thus reducing the force in that way, les PSI less force on everything.


    The case doesnít push or wedge back but rather inflates inside the chamber like an inner tube inside a tire. The case becomes glued to the chamber walls in all directions from the pressure inside inflating it, it isnĎt linier but pushes in every direction equally all at once, forward, backward, left, right, up, down equally.


    This adhering of the case to the chamber wall is well known to stretch brass at the base of the case with excessive head space. Firing pin strikes primer and drives case forward within the headspace, powder ignites causing pressure to freeze the case to the chamber walls. The pressure then moves the only un-supported part of the case, the head, until it becomes supported. Since the case walls are frozen to the chamber walls by the pressure and cant move the portion of the case wall right at the head stretches and thins as the case head moves back into the bolt face.
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    Quote Originally Posted by hodgeman View Post
    I don't know...all I can say is that I'm dubious of most of the "improved" cartridges. I'm not sure many of them actually do much more than burn more gunpowder and many come with a list of drawbacks that (IMHO) outweighs the slight gains in velocity.
    Thatís about where Iím at too. What chamber is more about component accessibility to me, if I want more power Iíll just step up to a bigger round rather than trying the do more with less game. Some of it may be improvements and Iíll care when they been around long enough that components get cheap and plentiful.
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    Quote Originally Posted by marshall View Post
    In closing, I also like to seat at least bullet diameter deep but it does hurt not to. After all, some very proven designs have short necks even prior to trimming .010 back of SAAMI spec which is a fairly common practice.
    I meant to say it doesn't hurt not to. It sucks not being able to fix typos after you catch them in the morning...

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    Quote Originally Posted by marshall View Post
    I used to think the same thing. However two cartridges I am currently working with have shorter necks than bullet diameter. The .243 Win and the .375 Ruger both have short necks, less than the bullet diameter and they both work well.

    Hornady TAP ammo in 110gr .308 Win is factory seated to a bullet depth of less than .130, that opened my mind to the reality of not needing to seat to a depth that equaled or exceeded bullet diameter.

    In closing, I also like to seat at least bullet diameter deep but it does hurt not to. After all, some very proven designs have short necks even prior to trimming .010 back of SAAMI spec which is a fairly common practice.
    WELL most of this is semi-correct but mostly WRONG ! The current rimless, non-belted, centerfire cartridges used by civilians are the result of R&D done for military rounds. These rounds require that the projectile be held firmly when operated in bolt guns, semi-autos, full autos and belt-fed weapons. The neck not only has to hold the bullet in the case but also has to be able to hold the case when linked. The current 7.62x51 round had to have a neck long enough to support the Browning MG links (which were in current use at it's adoption). When autos cycle the bullets can be pulled from the case or driven back into the case. In civilian use a cartridge has to function in all available actions that it fits in, lever,auto,semi-auto, and bolt actions without incurring problems.
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    yes, brav you are right there. Briskly Shuck a cartridge through a lever rifle, and take measurements of the COAL. It changes, sometimes drastically so. Barnes X bullets and compressed loads......even with standard cartridges, the neck tension isn't enough. I refuse to use banded barnes bullets in a lever action from my own personal experiences. Recoil can oftentimes change the COAL of a cartridge too.

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    Quote Originally Posted by brav01 View Post
    WELL most of this is semi-correct but mostly WRONG ! The current rimless, non-belted, centerfire cartridges used by civilians are the result of R&D done for military rounds.
    Well gee-wizz. The original poster wasn't asking about belt fed super duper automatic combat weapons or the history of their development. He just referred to making the neck shorter and reducing neck tension and other issues that interfered with feeding.

    I simply referred to production cartridges that have less neck length than bullet diameter and a proven Law Enforcement .308 Win load that is seated less than half it's diameter and the fact that they function just fine.

    Please don't fart in my general direction...

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    [QUOTE=marshall;1205827]Well gee-wizz. The original poster wasn't asking about belt fed super duper automatic combat weapons or the history of their development. He just referred to making the neck shorter and reducing neck tension and other issues that interfered with feeding.

    I simply referred to production cartridges that have less neck length than bullet diameter and a proven Law Enforcement .308 Win load that is seated less than half it's diameter and the fact that they function just fine.

    SORRY GUYS ! That's not what I meant.
    HISTORY; The 308 started life as the US Military T65 round(300 Savage) in 1946. It was determined the T65 had too small a rim diameter and was modified to .473 (same as 06'). The T65 had too much case taper and was modified. The T65 rim was too thin for automatic weapons and was modified. The T65 neck failed to hold projectiles effecting feeding under automatic weapons testing and was lengthened. The T65 shoulder angle was modified 3 times before the current angle was accepted. These modifications over 7 or so years produced the T54 round used in the military trials for it's then new M14 battle rifle in 1954 and the new M60 machine guns under developement to replace the Browning 30 cal.
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    FLs are crimped. Also, Military rounds. At least, I've never seen one that wasn't. Sometimes you gotta look close.

    That helps to insure adequate neck tension for function in all kinds of arms.

    I think that short necks are a poor design, and that includes the 300 WM, and 7mm RMs. The reason you see short necked cartridges, particularly in so-called "improved" ones, is that the designers have compromised neck length to increase case capacity, or to meet OAL requirements. Most "improvements" with cartridges compromise something, so I agree with Mainer on that.

    Then you couple it with the fact that most cartridges are based on the same case heads, as many others. So what is the best case design, for all around use, accuracy and function?

    I'm thinking, that, the 6.5 Creedmoor is a near perfect design.

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    Also in all military designed ammunition the projectiles are required to be sealed in with an asphaltic laquer, which holds the bullet as well.
    " Americans will never need the 2nd Amendment, until the government tries to take it away."

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