Revolvers, Brass, and Primers

[HTRN]

According to my handy-dandy Starrett calipers, large pistol primers measure 0.121 from front to back. Large rifle primers measure 0.128. Rifle primers tend to be helluva lot harder than pistol primers, which may explain the need for multiple strikes to get ignition.

I thought this was common knowledge - the Small Rifle and Pistol primers have the same outside dimensions, but the Large Rifle and Pistol primers have the same diameter and different heights. See here.

My next step was going to be to cut down .308 to use with the large rifle primers.

Or, you could do the sane thing, order a primer pocket uniformer, and ream all the existing depths to Rifle depth..

[PawPaw]

As I did this, I noticed that the cylinder would become hard to turn/not turn at all. The primer would back out of the pocket after firing, sometimes to the extent that it would require a plastic hammer to get it loose.

Yeah, that's your primer backing out. It's a regular occurrence in low-pressure loads, and you can't get much lower pressure than a primer-only load.

What happens when firing a regular cartridge is that when the firing pin hits the primer, it pushes the cartridge forward before it ignites the primer. There are two different things happening. The tiny bit of flash powder in the primer ignites, but before the main charge lights the primer unseats and goes back to the recoil shield. More pressure as the main charge lights, and the cartridge case slams back against the recoil shield, which re-seats the primer. About that time, the pressure builds more, the cartridge case expands to grip the chamber wall and the bullet releases. By the time you hear the boom, all this is over and pressure returns to normal. The primer is re-seated and the case is again "loose" in the cylinder.

What happens in a primer-only load is that the primer unseats under pressure, but the cartridge doesn't generate enough pressure to slam back against the recoil shield. That ties up the cylinder.

All this to say that primer-only loads routinely tie up the cylinder. I would expect it almost every time even if the cartridge case is empty. There's no pressure tore-seat the primer.

Because we shoot a lot of very low pressure loads in Cowboy Fast Draw, we've developed some special techniques to deal with this issue. The most garage-friendly technique is to drill the flash-hole. I normally use a 5/32 or 3/16 bit to drill out the flash hole. Then I seat a regular primer, put 3 grains of Triple7 powder and seat a wax bullet (this for .45 loads). This load is very safe, it will dent, but not penetrate 1/2 inch plywood. The bullet will fly about 30 yards unimpeded before it runs out of momentum and falls to the ground.It's a very safe load for testing revolvers in a suburban area.

[JAG2955]

What happens when firing a regular cartridge is that when the firing pin hits the primer, it pushes the cartridge forward before it ignites the primer. There are two different things happening. The tiny bit of flash powder in the primer ignites, but before the main charge lights the primer unseats and goes back to the recoil shield. More pressure as the main charge lights, and the cartridge case slams back against the recoil shield, which re-seats the primer. About that time, the pressure builds more, the cartridge case expands to grip the chamber wall and the bullet releases. By the time you hear the boom, all this is over and pressure returns to normal. The primer is re-seated and the case is again "loose" in the cylinder.

So why doesn't the cartridge stay against the recoil shield when a regular load is fired? Does the brass obturate, then return to its pre-elastic size, and is that enough to allow it to slide along the recoil shield?

[Denis]

I thought this was common knowledge - the Small Rifle and Pistol primers have the same outside dimensions, but the Large Rifle and Pistol primers have the same diameter and different heights. See ...

I didn't know that, and I thought I lived pretty deep in the gun-nut forest. Here's the image again, since tinypic often doesn't work for me.

primer sizes.jpg

[PawPaw]

So why doesn't the cartridge stay against the recoil shield when a regular load is fired? Does the brass obturate, then return to its pre-elastic size, and is that enough to allow it to slide along the recoil shield?

Yeah, pretty much. I'm sure that a metallurgist or ballistician could explain it better than I, but at the instant of firing a standard cartridge, when pressure is at its max, the cartridge case is firmly against the recoil shield, the case is expanded against the chamber walls, and the bolt is locked in the cylinder notch. The revolver is locked as tight as it's going to get. Thankfully so. By the time you feel the recoil, the brass has relaxed against the cylinder wall and is free to move that tiny fraction of an inch that lets the cylinder move freely to the next cartridge. All of this happens in a millisecond.

With an extremely low pressure load, the firing pin pushes the cartridge into battery, then pops the primer. The primer flows back against the recoil shield and it's over. Nothing else happens. That's what ties up the revolver. There is not enough pressure to make the casing flow back to the recoil shield and re-seat the primer.

[JAG2955]

Ugh.

Took it back to the range today. More light strikes. Even on WWB .45ACP. I'm calling Smith. Hopefully they'll still look at it even though I had Clark Custom cut the cylinder. I did get the last round I had of Buffalo Bore's .460 Rowland FMJ to fire on the second strike. It may have pierced the primer, I'll have to look at it with a magnifying glass. I can see soot in the dimple.

I had the Apex XP firing pin installed, which is not longer, but allows for more travel. Definitely glad I didn't put in the Cylinder & Slide extended firing pin that I also have.

On the upside, my Saker 762 works great.

[HTRN]

I thought I lived pretty deep in the gun-nut forest.

Do the trees look like this?

If not, keep going, you're not deep enough.

[PawPaw]

Took it back to the range today. More light strikes. Even on WWB .45ACP. I'm calling Smith. Hopefully they'll still look at it even though I had Clark Custom cut the cylinder.

Why not send it back to Clark? Tell them that you're getting light strikes and have them look at it. I haven't dealt with Clark in 15 years, but they used to have really good customer service. I'm sure if there is a problem with the gun, it's a small, minor thing and they can work it out fairly easily.

But, I agree that there is nothing more aggravating than a gun that won't go BANG on demand.

[JAG2955]

Smith sent me a label. They said that they may or may not do work on it since I performed "modifications" to the revolver.

This sucks. The damn thing so far is the biggest letdown in my gun collecting career. Hell, that looks like fodder for another thread.

[First Shirt]

Just suggestions, which are worth about what you paid for them.

(a) Send it to Smith. If they fix it, great. If not, at least you know, and then you can...
(b) Send it to Clark. They will fix it, and probably not charge too much for the repair. Or...
(c) Let me know what you want for it. (You shouldn't have flaunted it while you were here!)