.40 vs 10mm primers: case strength question

[afrederick]

I just picked up a G20sf and am now interested in learning more about the capabilities of the 10mm. I read on this forum that a .40 S&W case can handle higher pressures than a 10mm case because the .40's small primer pocket weakens the case less than the large primer pocket of the 10.

Assuming that is true, it seems quite paradoxical that in search of greater power you add more gunpowder to a cartridge, at some point that greater amount of powder necessitates a bigger primer - but in making room for a bigger primer you weaken the case and thus limit the power you can get out of the cartridge.

If a pistol round has too much powder for a small pistol primer wouldn't it be a better idea to just use small rifle primers instead of weakening the case by drilling the bigger hole needed for the large pistol primers?

Yes, rifle primers are tougher to set off than pistol primers but wouldn't it be pretty simple and cheap to make pistol firing pins strike the primers harder?

I enjoy shooting but I must admit that I have never reloaded and I am certainly no engineer. This post is based on things I read and my own ponderings so please point out any faulty assumptions I have made.

 

[Match10]

First... the 10 mm came first. It did not necessitate "making room for a bigger primer". The 10 is loaded for higher pressures and the cases are designed and manufactured to do so. (In fact, I have 10 mm cases with both the large adn some with small primers.)

The .40 Short & Wimpy is the newer cartridge, and has a different web taper inside that cartridge.

 

[greenlion]

In all my years of reloading, I have never seen a case fail because of the primer pocket. I've seen splits and cracks in the case walls, and I've seen the entire rim come off one or two, but I've never seen anything to suggest a primer pocket is a weak spot. I don't even think its an issue in .32 caliber, where the primer takes up most of the space on the bottom of the cartridge.

 

[readyeddy]

I have no idea whether a small primer pocket would increase the strength of the case. I will say that I have had 10mm brass start splitting after 3 or 4 warm reloads.

As far as a harder firing pin strike to ignite a rifle primer, the increased inertia would likely interfere with accuracy in a striker fired gun. That's why some people install titanium firing pins and/or reduced striker springs.

 

[R.W.Dale]

It theory yes given the same case head the small primed case will be stronger than the large primed one.

Some reloaders (not me) go so far as to use 40 cases with 10mm level loads in 10mm guns with 40 caliber conversion barrel throated to accept 10mm COL

 

[DesertFox]

As an old guy reloader, I much prefer working with large primers. 10mm and 44 Mag mostly with a little 357 Mag for good measure. I do reload 9mm and 38 Special but don't do 5.56x45 because of the small primer and small bullet.

Never seen a case failure due to primer pocket either. Load lots of light target loads for practice and some mid-hot for real applications. But I tend to stay away from the super-hot or crazy-hot loadings as to not have a KB!

If you need a bigger "BANG", buy a bigger gun.

 

[R.W.Dale]

As an old guy reloader, I much prefer working with large primers. 10mm and 44 Mag mostly with a little 357 Mag for good measure. I do reload 9mm and 38 Special but don't do 5.56x45 because of the small primer and small bullet.

Never seen a case failure due to primer pocket either. Load lots of light target loads for practice and some mid-hot for real applications. But I tend to stay away from the super-hot or crazy-hot loadings as to not have a KB!

If you need a bigger "BANG", buy a bigger gun.

Where are you finding large primed 357 mag cases? I'd genuinely like to have some

 

[hentown]

This thread was started based on bad information on the part of the OP. However, I would add that I use small rifle primers, exclusively, for 9mm reloading and used them, exclusively, for .40 Super reloading.

 

[GLOOB]

Some reloaders (not me) go so far as to use 40 cases with 10mm level loads in 10mm guns with 40 caliber conversion barrel throated to accept 10mm COL

Even if your 10mm cases AREN'T failing prematurely due to primer pocket enlargement, this seems like it would be a good strategy in order reduce the cost of your brass! It would also mean you could shoot 40SW out of your gun with no change if the gun will cycle reliably. Or a spring swap at the most. The only downside would be you can't load to full OAL with some of the light weight bullets.

This thread was started based on bad information on the part of the OP.

I think this info came from some posts by Clark. They were way over pressure loads. So you might call that bad info. But if you believe his results, it shows that the large primer pocket in such a small diameter casehead actually weakens it in one specific aspect. And the problem wasn't catastrophic case failure. When overcharged, the 10mm case heads were measurably expanding before the 40SW cases. Which simply boils down to the fact that you can apparently load 40SW cases to 10mm levels (using 10mm OAL) out of a 10mm platform WITH FULL WEB SUPPORT. And push comes to shove, the 40 case might even be able to be pushed higher - again, out of a gun with full web support. Now in a gun without full support, the 40SW case might fail, first, due to the different web specification. All this means is, that out of the right firearm at beyond recommended pressures, the 10mm large primer pocket could be the first weak link, rather than the 40SW thinner case head/web.

Sure, Clark is just one guy doing some strange things. But if you think this is wrong, I'd like to see your testing. For 99.9% of us it doesn't matter, since we stick to the books. Well, other than perhaps the cost of brass.

Assuming that is true, it seems quite paradoxical that in search of greater power you add more gunpowder to a cartridge, at some point that greater amount of powder necessitates a bigger primer - but in making room for a bigger primer you weaken the case and thus limit the power you can get out of the cartridge.

If a pistol round has too much powder for a small pistol primer wouldn't it be a better idea to just use small rifle primers instead of weakening the case by drilling the bigger hole needed for the large pistol primers?

What's paradoxical is that they decided to use a large primer in the first place. The 357 magnum started out with a large primer. And they switched to small, because it wasn't necessary. The 45ACP unnecessarily uses a large primer. But the 45GAP uses a small primer. Federal is also making 45ACP with small pockets, these days, and plenty of reloaders are reusing them with no issues. Some reloaders have actually chronied the difference and found the small pocket brass produces tighter ESD.

 

[hogshead]

Seems like a good way to cause a kb to me.

 

[GLOOB]

Shooting certain manufacturer's 10mm loads/brass is a good way to get a KB. See the recent threads of Colt Deltas kb'ing due to a certain manufacturers brass being crap. So much for the "10mm brass has a stronger web" argument.

 

[MachIVshooter]

See the recent threads of Colt Deltas kb'ing due to a certain manufacturers brass being crap. So much for the "10mm brass has a stronger web" argument.

Bad brass is just bad brass, nothing more. If it was failing in 10mm, it would fail in .40 too. The 10mm case does have a thicker web, but that won't mitigate bad metallurgy combined with a lack of support.

 

[hentown]

Hahahahaha! There's a GOOD reason that Clark's been banned from a bunch of forums. Scientific testing?? That's the joke of the century!!!

 

[weemsf]

I actually have some 38 Special cases with large primer pockets.

 

[MachIVshooter]

Hahahahaha! There's a GOOD reason that Clark's been banned from a bunch of forums. Scientific testing?? That's the joke of the century!!!

Clark knows what he's doing, and provides useful and entertaining information for the rest of us. He does NOT suggest using any of his over-pressure loads in production guns; His testing is done in barrels and receivers that he has built himself, and reinforced/shielded to handle what he's putting in them.

Unless you're able to do what he does (I highly doubt it), who are you to judge?

 

[R.W.Dale]

In the old days Clark would blow something to pieces and the only thing you could learn from his findings were "yeah it blowed up"

But over the years he's developed some methodology and safety precautions behind what he does and his comparisons of components or firearms for a given chambering are indeed quite valid.

This coming from a guy who used to flame Clark to a crisp years ago

 

[ArchAngelCD]

Just as a side note, there's no reason to go to a small rifle primer if you need more ignition, just use a small pistol magnum primer instead.

I have to agree, in all the reloading I've done over the years I have never seen a piece of brass fail because of the primer pocket.

 

[atblis]

Just as a side note, there's no reason to go to a small rifle primer if you need more ignition, just use a small pistol magnum primer instead.

I don't believe people use small rifle primers for that reason.

 

[ArchAngelCD]

I don't believe people use small rifle primers for that reason.

I was answering the first post where the OP said exactly that.

 

[2zulu1]

The 10mm is fully capable of destroying any 40 S&W JHP bullet before you get into 10mm brass pressure issues. My G20 SF and G20 both have fully supported Lonewolf barrels, then there's a 6"/KKM barrel for uber fast velocities.

I like 200gr WFNs for when I carry the 10mm at my place or trail and 180gr Gold Dots @1265 fps for social occasions; Starline brass.

 

[Swampman]

IIRC, when the .454 Casull first came out, all of the cases were made for a large magnum pistol primer. Sometime around the mid 80s they changed them to a small rifle primer.
There must have been some reason for this, although I never had any problems with the larger primers.

 

[ArchAngelCD]

IIRC, when the .454 Casull first came out, all of the cases were made for a large magnum pistol primer. Sometime around the mid 80s they changed them to a small rifle primer.
There must have been some reason for this, although I never had any problems with the larger primers.

The reason was pressure. Most handgun primers are designed to withstand pressures that don't exceed 40,000 CUP. The 454 Casull generated pressures up to 50,000 CUP so a rifle primer that is designed to withstand pressures up to 65,000 PSI is safer.