Bullets, Bores and Throats...

[Murphy]

This is a subject that I've seen discussed here but found an old PM about from an old handgunner so thought I'd elaborate on the subject.

We speak here of cast bullets for revolvers. Bullet size vs bore size vs cylinder throat diameter.

I know Snyd and BFR shooter are some of the experts on this subject and a few others have experience as well. The dimensions of these three do matter from the stand point of accuracy and lead fouling and are important considerations when using hard cast bullets in a revolver. Slugging the bore to obtain accurate bore diameter and cutting the throats to the correct diameter will help when making happy loads.

I like to round up the bullet diameter to slightly greater than bore diameter.

Bore slugged and miked at .4305" I size bullets to .4310".

Cylinder throats will be cut to .4320" or .4330".

(Bullet sizing and throat cutters are usually even thousandths.)


What are your thoughts on these dimensions?

[tvfinak]

To be honest - I've never given much though to diameters on my S&W revolvers - they all seem to shoot great and I've never had any real leading issues with any of my .44s and larger. I normally shoot .430 in my .44s now although I may try some .429s again to see if can seat them out further - getting the maximum length before the bullets jam into the throat is my only issue and it is not a major one.

Perhaps the issue is more of a Ruger thing? I keep hearing all the talk about reaming Ruger cylinders but very little of messing with S&Ws.

This is a subject that I've seen discussed here but found an old PM about from an old handgunner so thought I'd elaborate on the subject.

We speak here of cast bullets for revolvers. Bullet size vs bore size vs cylinder throat diameter.

I know Snyd and BFR shooter are some of the experts on this subject and a few others have experience as well. The dimensions of these three do matter from the stand point of accuracy and lead fouling and are important considerations when using hard cast bullets in a revolver. Slugging the bore to obtain accurate bore diameter and cutting the throats to the correct diameter will help when making happy loads.

I like to round up the bullet diameter to slightly greater than bore diameter.

Bore slugged and miked at .4305" I size bullets to .4310".

Cylinder throats will be cut to .4320" or .4330".

(Bullet sizing and throat cutters are usually even thousandths.)


What are your thoughts on these dimensions?

[Snyd]

....What are your thoughts on these dimensions?

They are all too small! They need to start with at least .45 or .47

Welcome back Murphy

I'm far from being an expert but I've been learning a little. It seems that as long as the throats are larger than the bore we need to size for the throats. Here's my latest project/experiment. 435gr .458 sized down to .454 shot through .454 throats into a .451 bore. Zero leading for 24 rounds and excellent accuracy. At least in my first test loads yesterday.

No-nos.... boolits smaller than bore or larger than the throats.

[Smitty of the North]

OK, bore, then the bullets, and then the throats.

Murphy, you've described these dimensions before, and I've TRIED to remember them.

What is an easy way to slug the bore? Do you need soft/pure lead, and how beeg in relation to the bore does it hafta be to start with?

Can you measure the cylinder throats with a Caliper, or do you slug them too?

It seems to me, that you would need something stronger than your normal cleaning rod.

My ignorance of these things is why I've never done it. Either, Ignorance is Bliss, or it would be good to know if I have a problem in my 357 BH, and 44 Mag. Mdl 29 .

Thanks
Smitty of the North

[evandailey]

I was just thinking last night when reading Snyd's other thread that I would like for someone to go over this process and explain it better so this is timely for sure.

Would one of you experienced guys please explain this whole process and the theory behind it in depth for those of us with less casting/custom handgun experience?

Thanks.

[rbuck351]

Basicly the bullet needs to start out either at throat size or slightly smaller so that it isn't being sized in the cylinder yet not too small so that it's not tipping before it gets to the forcing cone. Once past the throat it needs to be slightly larger (.0005/.001 ) than groove size in the barrel so that it completely fills and seals the barrel. The throat needs to be slightly larger than groove size so that bullets won't be reduced in size below groove size before it inters the barrel. If the bullet starts in the barrel ANY smaller than grove size, hot gasses blasting past the bullet will cut off lead and deposit it in the barrel. So, groove size needs to be the smallest of the three. Ideally, the bullet and throat size would be the same at about .0005/.001 bigger than the groove size. I would think you could get gas cutting in the the throat if the throat was much bigger than the bullet.

[evandailey]

Basicly the bullet needs to start out either at throat size or slightly smaller so that it isn't being sized in the cylinder yet not too small so that it's not tipping before it gets to the forcing cone. Once past the throat it needs to be slightly larger (.0005/.001 ) than groove size in the barrel so that it completely fills and seals the barrel. The throat needs to be slightly larger than groove size so that bullets won't be reduced in size below groove size before it inters the barrel. If the bullet starts in the barrel ANY smaller than grove size, hot gasses blasting past the bullet will cut off lead and deposit it in the barrel. So, groove size needs to be the smallest of the three. Ideally, the bullet and throat size would be the same at about .0005/.001 bigger than the groove size. I would think you could get gas cutting in the the throat if the throat was much bigger than the bullet.

Thanks rbuck351, that was a god description and reinforced what I thought I knew about it. Could you elaborate on your measuring methods for all of those dimensions?

[Snyd]

Slugging the Bore...

Use only soft lead. Egg sinkers work good as do round balls. Just make sure they are pure lead. Clean your bore and run a patch of oil down it. Set the egg sinker on top, tap it in with a hammer, it will mushroom and flatten on top. Then take a rod or dowel of some sort ( I used a shotgun cleaning rod) and tap-tap it through. Pay attention to how it feels, you can identify bore restrictions. Then measure it. Here's a couple pics, .451 is from my Redhawk, .452 is from my Puma 454.

[evandailey]

Use only soft lead. Egg sinkers work good as do round balls. Just make sure they are pure lead. Clean your bore and run a patch of oil down it. Set the egg sinker on top, tap it in with a hammer, it will mushroom and flatten on top. Then take a rod or dowel of some sort ( I used a shotgun cleaning rod) and tap-tap it through. Pay attention to how it feels, you can identify bore restrictions. Then measure it. Here's a couple pics, .451 is from my Redhawk, .452 is from my Puma 454.

Great pics Snyd! Thanks.

Are you just clamping the gun in a vise of some sort to do that?

[Steve8261948]

Snyd, I find dial calipers too easy to turn into a C clamp, I must prefer a micrometer(preferable in tenths, ten thousands of an inch) for this type of measuing. They give me a better feel.
Steve

[Snyd]

Ya, I really should buy a mic.

evandailey. I didn't use a vise but I guess you could.

[Murphy]

OK, bore, then the bullets, and then the throats.

Murphy, you've described these dimensions before, and I've TRIED to remember them.

What is an easy way to slug the bore? Do you need soft/pure lead, and how beeg in relation to the bore does it hafta be to start with?

Can you measure the cylinder throats with a Caliper, or do you slug them too?

It seems to me, that you would need something stronger than your normal cleaning rod.

My ignorance of these things is why I've never done it. Either, Ignorance is Bliss, or it would be good to know if I have a problem in my 357 BH, and 44 Mag. Mdl 29 .

Thanks
Smitty of the North

Smitty,

Lead balls or egg sinkers (best), must be pure lead, CLEAN bore, light oil patch. I would say at least .10" bigger than expected groove diameter would be good. I use a rawhide mallet, wood will work well. I measure across each pair of grooves, (six grooves, three measurements) to get a good average of the groove width. Technically a good dial caliper is only accurate to with in .001" but you can generally see when it is .451+?". Which is enough to tell you to size bullets to .4520" or .4530". I have found large variations in throats from some 357 revolvers, Ruger is notorious for inconsistent throat diameters. I have a top of the line M27-2 S&W that has two throats that measure .3565"ish and four that are about .358+" I have a set of gages, I think they are called pin gages, to measure the throat diameters. You can use the back side of a dial caliper to get a good idea about throat size. I do think that if you are serious about shooting hard cast lead in high performance ammo you should cut the throats to appropriate size. This cutting will leave throats perfectly round, or at least more nearly round, that is a problem for some guns.

My old 6" M28 S&W has had the throats cut to .3610" and the forcing cone cleaned up. I shoot 180 and 200 grain hard cast bullets sized to .360", I think the groove of that very smooth barrel is about .358" It will shoot a full cylinder into 3" group at 100 yards. I have hit the 16" gong at 300 yards, with six of six shots from prone, many times. Its fun to watch, and yes that is with the original iron sights. A nice thing, for me, shooting the 357 is that recoil doesn't takes its toll on my ability to hold still like the heavy hitters do. I shoot nothing but hard cast bullets through this old gun, and it couldn't be better.

[Murphy]

Ya, I really should buy a mic.

evandailey. I didn't use a vise but I guess you could.

Nice demo Perry, now everyone knows why I called you expert.

And a very good explanation rbuck351.

[Smitty of the North]

Thank You Murphy: Again

Smitty of the North

[rbuck351]

Snyd showed an excellent method of slugging a bore. Small holes are difficult to measure accurately without some fancy equiptment that most people just don't have access to. But you can slug the throat just like the barrel except from the rear. You may have to roll a sinker between two pieces of flat steel to get it small enough to fit in the chamber, then just drive it through with a wood dowel and measure the slug.