Smith Carbine Bullet size

[Michael Bodner]

OK - Riddle me this....

Most folks are shooting a 0.515 in their Smith Carbine. I just used pin gauges in my Smith and the barrel is LESS than 0.501" (I need to borrow smaller pin gauges).

So, why do we use such a large bullet??? Of course, the depth of the lands/grooves will come into play, but how much should we add to the pin gauge to come up with the 'correct' bullet diameter?

I'm learning every day....

Thanks!!

-Mike

[ian45662]

The pin gauge only tells you what the bore diameter is. Most people will size breach loading bully's at or slightly over groove diameter. One way to tell what your groove Diameter is would be to slug your barrel. Push an over sized roundball or bullet through the barrel and measure what you got.

[Michael Bodner]

Thanks for the answer, but it's not the question I asked....

WHY do we shoot a bullet that is 0.015" bigger than the pin size?

For instance, we size our muzzle-stuffer bullets about 0.001" smaller than the pin gauge. Why are we 0.015" BIGGER for a carbine?

In addition, there is a lot of guesswork determining the measurements of the slug since there are non-opposing lands and grooves....

-Mike

[ian45662]

An unscientific but efficient way to determine the groove diam in a breachloader with an odd # of lands and grooves would be to slug it and then take some thin material and wrap around the slug then measure that. I like to use a pop can. I'll cut out a sliver if it then measure the thickness which is around .004 if I remember correct. I will take that sliver and wrap it around the slug measure that then subtract twice the thickness of the material that is wrapped around the slug. With a carbine that you are loading from the breach and not the muzzle I don't think a pin gauge will be of much use to you. You should be looking for groove diam not bore diam like we do with the front stuffers.

[BobbyHannula8450v]

Reason 1 - cause that's what the old timers said you do, and you don't doubt the wisdom of old timers.
Reason 2 - Since the bullet doesn't have a base cavity to expand, it ensures a good seal.

[henrymstr]

Dont over think it. Just try it. Shoot groups off the bench for tightest groups. Borrow moulds if you can ect. I use a .520 in my yeck smith. All 8 shots are touching off the bench, 1 1/2 group or so. Of course there are a few more secrets in there............but nothing no one else doesnt do or has suggested in carbine shooting.

Sent from my SM-T217S using Tapatalk

[Michael Bodner]

Dont over think it. Just try it. Shoot groups off the bench for tightest groups. Borrow moulds if you can ect. I use a .520 in my yeck smith. All 8 shots are touching off the bench, 1 1/2 group or so. Of course there are a few more secrets in there............but nothing no one else doesnt do or has suggested in carbine shooting.

Sent from my SM-T217S using Tapatalk

Been shooting it for 16 years with a .520 Rapine sized to .517. WAY overpressured.... Blown out clean-out screws and it tends to lead up.

[jonk]

It's hard to slug an odd number of lands and grooves, but nominally, these should run in the .515 to .520 mark across the grooves. So the bullet isn't oversized at all, any more than a .308 is in a modern gun that measures .300 across the rifling raised lands. Black powder guns are no different, you size a bit over groove diameter if a breechloader. Leaving unfilled grooves leads to blow by and that blows off lube, etches lead with gas, etc... bad juju.

If you ran a .501 minie in your smith, it would swell up and be a non issue, just like a muzzleloader.

Most breechloaders also have a LOT deeper rifling than muzzleloaders.

[Michael Bodner]

Regarding comments about the grease: After slugging the barrel with the bullet I use, there IS NO grease grove left. The obduration of the bullet displaces sufficient lead to basically obliterate the groove...

Hence the reason that I have to keep lots of lube on the front of the bullet to get sufficient accuracy.

Keep those comments coming...

-Mike

[Maillemaker]

WHY do we shoot a bullet that is 0.015" bigger than the pin size?

For instance, we size our muzzle-stuffer bullets about 0.001" smaller than the pin gauge. Why are we 0.015" BIGGER for a carbine?

disclaimer: I don't have a breech loading black powder gun.

Front-loading military guns utilize an under-size bullet so that the will load easily without having to pound it down the barrel. This was the genius of the expanding ball bullet.

With a breech-loading design, the bullet does not have to be undersized because it will be forced into the rifling no matter what. You don't have to rely on deformation of an under-sized bullet to take up the rifling because the rifling cuts its way through the bullet as the bullet engages the rifling at the breech.

As someone else said above, it's probably a good idea for the bullet to be at least the same diameter as the groove diameter.

Steve

[PoorJack]

Mike before you rely on any measurements from slugging the bore, clean out any leading first. Run a patch through soaked with Kroil, let it sit a day, repeat, let it sit then brush out the leAD. Then slug and measure.

[Michael Bodner]

Does anyone have the throat of the barrel coned? Put another way, since the bullet is way-bigger than the bore, going from the chamber to the barrel in an abrupt step seems like a 'bad idea'

Thoughts/comments??

-Mike

[Jud96]

Does anyone have the throat of the barrel coned? Put another way, since the bullet is way-bigger than the bore, going from the chamber to the barrel in an abrupt step seems like a 'bad idea'

Thoughts/comments??

-Mike

Sounds like a good idea to relieve pressure. High power rifles that have custom chambers sometimes have a longer throat cut in them. The longer throats or throats with a different lead serve a couple purposes. In modern cartridges when using a long and heavy for caliber bullet, the slug often contacts the rifling unless the bullet is seated deep into the case robbing excess powder capacity. When a longer throat is cut it lets you seat the longer projectiles further out without touching the lands which allows for more powder space but most importantly, less pressure. It may be beneficial for you to have like a forcing cone or some free bore cut into the back of your barrel, this will remove the pressure spike like you are talking about and will be beneficial. You may also want to try and find the smallest sizing die that won't take too much off the bullet and wipe away the grease grooves, but will be a few thousandths smaller than what you have now. Just some thoughts.

[jonk]

Sounds like a good idea to relieve pressure. High power rifles that have custom chambers sometimes have a longer throat cut in them. The longer throats or throats with a different lead serve a couple purposes. In modern cartridges when using a long and heavy for caliber bullet, the slug often contacts the rifling unless the bullet is seated deep into the case robbing excess powder capacity. When a longer throat is cut it lets you seat the longer projectiles further out without touching the lands which allows for more powder space but most importantly, less pressure. It may be beneficial for you to have like a forcing cone or some free bore cut into the back of your barrel, this will remove the pressure spike like you are talking about and will be beneficial. You may also want to try and find the smallest sizing die that won't take too much off the bullet and wipe away the grease grooves, but will be a few thousandths smaller than what you have now. Just some thoughts.

Yes and no. Some high power rifles do have a longer throat, but that has the dual benefit to permit seating longer heavier bullets for longer range, without seating the bullet so deeply as to cause excessive pressure or lower velocity. In fact, burnt out throats are one of the reasons to REPLACE a high power rifle barrel; and some, such as the Swiss K-31, have very abrupt throats that rely on bullet design to guide the bullet into the throat.

On something like a sharps with the Christmas tree design, this works fine with no throat as the bullet provides that taper. If you were to fire a full wadcutter in a sharps or smith or whatever, then the idea of having a coned throat makes good sense.

If someone has a bullet that slugging the bore results in obliterated grease grooves, that bullet is too big, throat or no. As said though, don't overthink this. Try some different bullet designs and diameters that are in the ballpark of what slugging reveals. The standard for a lead bullet in a cartridge or otherwise breechloading weapon is 1-2/1000 over groove diameter. You can go AT groove diameter or maybe 1-2/1000 under with SOFT lead that upsets into the rifling, but I wouldn't push it past that or you will get leading.

[Jud96]

Yes and no. Some high power rifles do have a longer throat, but that has the dual benefit to permit seating longer heavier bullets for longer range, without seating the bullet so deeply as to cause excessive pressure or lower velocity. In fact, burnt out throats are one of the reasons to REPLACE a high power rifle barrel; and some, such as the Swiss K-31, have very abrupt throats that rely on bullet design to guide the bullet into the throat.

On something like a sharps with the Christmas tree design, this works fine with no throat as the bullet provides that taper. If you were to fire a full wadcutter in a sharps or smith or whatever, then the idea of having a coned throat makes good sense.

If someone has a bullet that slugging the bore results in obliterated grease grooves, that bullet is too big, throat or no. As said though, don't overthink this. Try some different bullet designs and diameters that are in the ballpark of what slugging reveals. The standard for a lead bullet in a cartridge or otherwise breechloading weapon is 1-2/1000 over groove diameter. You can go AT groove diameter or maybe 1-2/1000 under with SOFT lead that upsets into the rifling, but I wouldn't push it past that or you will get leading.

I said the same thing in my post. I am a big long range shooter and hunter outside of the N-SSA shooting competition and I understand how these types of things work. Burnt out throats are caused by the spike in pressure and can somewhat be controlled by your powder burn rate but no matter what they start to get fire cracking in them and burn out no matter the throat dimensions or powder used. But this is a discussion for another time.

But I agree with the best solution to Boot's problems is to find a bullet that you can size to .001-.002 oversize without smearing off all of the grease grooves. He was talking about relieving some of the pressure from the instant jamming of the bullet into the lands, so that is why I said a forcing cone or longer throat could be used. But I do not believe it is really a must given the loads we shoot and the relatively low pressures.

[Michael Bodner]

The fly in the ointment is that everyone shoots either a .515 or a .520 in their Smith. I have not heard of any other sized mold.

Has anyone else??

-Mike

[Hal]

Probably not what you're asking, but I have a .518 I use in an original Smith. I believe it to be a special order Lee mold, the same design as their .515, but .003" bigger. Got it from one of the suttlers. Lodgewood, I think, but maybe S&S or Dixie Gun Works. Like I say, I think it is something that vendor has special made for htem by Lee, as I don't see Lee listing that particular mould on their website, nor do ordinary vendors like Midsouth Shooters or Midway USA have it in their catalog.

[Michael Bodner]

On my Facebook posting regarding this topic, folks stated that the Originals were much larger in bore - Hence the bigger sized bullets. Its the Italian repros that are true 50 cal...

-Mike

[henrymstr]

You are correct then....way to much pressure. Can you still see grease rings after you slug the barrel? If not, you are way oversized. Soft lead of course? But step it dwn in size. Cut a new crown if the group has opened up. Start fresh and regroup some charges. Should still be the same load or real close. I find it real easy to over think blackpwdr shooting. Good luck.

Sent from my SM-G920P using Tapatalk

[Chris Sweeney]

OK - Riddle me this....

Most folks are shooting a 0.515 in their Smith Carbine. I just used pin gauges in my Smith and the barrel is LESS than 0.501" (I need to borrow smaller pin gauges).

So, why do we use such a large bullet??? Of course, the depth of the lands/grooves will come into play, but how much should we add to the pin gauge to come up with the 'correct' bullet diameter?

I'm learning every day....

Thanks!!


-Mike

I'm not sure how deep the grooves are on a repro Smith, but assume that they are .005 deep. If you have a nominal bore diameter of .500 then you need a bullet of AT LEAST .510 to fill the grooves. most folks like to have .002 over that if using soft lead. If the grooves were .007, then a 515 would be minimum.

And another thing . . .

The diameter of the Lyman Smith bullet inside the grease grooves, is about .463. If you are really wiping out all of the grease grooves when you slug the barrel, that a 45 cal. barrel!!