primers

[casullman]

I have a few fired cases that the primers have backed out .001-.004 past flush with the head ( you can just catch you fingernail on it) what could be some causes ?

[Paul B]

I have a few fired cases that the primers have backed out .001-.004 past flush with the head ( you can just catch you fingernail on it) what could be some causes ?

Gosh! I always love it when a question gets asked and no real details. Was this in a handgun? Rifle? Straight walled case or bottleneck?

Well, the simple answer is it's possibly a headspace problem. Whether it's in the gun un question or shooter induced is something else. All guns have headspace. If they didn't, they wouldn't work. With most straight walled cases it's based on the rim. Some like the .30 US Carbine or .45 ACP on the mouth of the cartridige case. Bottlenecked rounds on the shoulder and belted cases on the belt.

As I don't know what type of case we're discussing I'll have to be somewhat general here. IIRC, headspace measurements less that .006" is considered OK and more than .006" bad. It's just been way too long since I was working for a gunsmith. He died in 1976. Anyway, when the firing pin ignites the primer, some of the force of the explosion drives the case forward. The igniting powder freezes the case to the walls of the chamber and the primer is then pushed back against the bolt, recoil shield or slide depending on the type of firearm. If the force of firing does not push the case rearward and reseating the primer, it will protrude somewhat depending on the gun's headspaing measurement.
One example of this is when shooting light or gallery type loads in a rifle using bottlenecked cartridges. Every time you shoot the load in a particular case, the primer drives the case forward pushing the shoulder back. It doesn't take many reloads with that light load to push the shoulder back to a point where headspacing with that cartridge is beyond that .006" cut of point. In fact, some consider that .006 to be excessive. That brass will continue to be safe with those gallery loads until the shoulder is pushed so far forward that you get misfires. After the first firing BTW, that brass will not be safe for full power loading.
Dunno if that answers your question or not but without more details, it's the best I can do.
Paul B.

[casullman]

Thank you Paul. Sometimes vagueness helps to broaden the thought process. In any case your reply helped me as I am working load development on a belted cartridge and I just need to increase charge weights as i probably started a little too light.

[Paul B]

Thank you Paul. Sometimes vagueness helps to broaden the thought process. In any case your reply helped me as I am working load development on a belted cartridge and I just need to increase charge weights as i probably started a little too light.

That may not be the case at all. (no pun intended) The clue is "belted cartridge". I know they are supposed to headspace on the belt, but measure those belts sometime. Not the circumference but the with of the belt itself. It's not too easy as it's hard the get a caliper or micrometer on them but the varience in the width is something else.
When I work with belted cartridges, 7MM Rem. Mag, .300 Win. Mag. .375 H&H and a .375 taylor wildcat (.375x338 Win. Mag., the .338 case necked up to take .375 caliber bullets) I adjust my dies to headspace on the shoulder, just as I would do with rimless bottleneck cartridges. The fact that you showed diffeent protrusions of the primers leads me to believe that is the source of your problem. it's just the variable in the width of the belts. To eliminate this, try setting your sizing die up so the shells headspace on the shoulder.

This is how I set up my sizing die for bottleneck cartridges.

1. Take a once fired factory round and blacken the neck and shoulders with a Magic Marker or Sharpee pen. Some people like to smoke the neck and shoulder, but I find the Magic Marker/Sharpee pen a bit better.

2. Carefully lubricate the case.

3. Loosen the lock ring on the sizing die and back off about two turns from when the die is set to touch the shell holder.

4. Size the case. Note where the marks are on the case and turn the die down about a half a turn and size again. Turn down some more, and resize again. What you are looking for is the marks on the blackening just touching the shoulder.

5. Clean the lube from the case and try it in the rifle. It may chamber just a bit on the snug side. If so, turn the die down ever so slightly, lube and size again. Wipe off the lube and try in the rifle. If it slides in as easily as a factory round, you should be good to go. If not, usually one more very slight adjustment should fix the problem.

6. Tighten the locking ring for the die and you're done. You have just set your sizing die up for a custom fit to your specific rifle, rather than a generic one size fits all guns.

Paul B.

[casullman]

I have a body dies and generally neck size for most of my cartridges, but this one (375 H&H) I cannot find a body die for so I will have to try your method after a few firings as I have new brass which seems to take at least two firings before reaching it's full shoulder datum length. Maybe because of light loads. thanks again

[fryboy]

also often with a light load when the firing pin hits the primer it pushes the case as far forwards as it will go , if there isnt enough pressure or the case is gripped in the chamber the case doesnt return to the rear and leaves the primer sticking out a bit ( as opposed to the case head slamming back into the bolt and re-seating the primer fully )

[versifier]

With a belted or a rimmed case, if the rim/belt thickness is correct for the headspace, the primer cannot protrude at all. When it is too thin, then it is a fair assumption that the cause may be low pressure, but it's not such a clearcut situation as it would be with a rimless case. The rimmed or belted case is not supposed to move in the chamber like a rimless one is designed to, which contributes to case stretching as the shoulder and neck obturate (fireform) to the chamber. This often results in limited case life, especially in bottleneck cases that are full length resized. Your rifle was chambered for brass with a thicker rim than what you are using. Initial fireforming with a load of sufficient pressure then neck sizing until you have to set the shoulder back will give you best case life. The lower working pressure of the .375H&H will give you better case life than the hotter belted magnums, but how much better depends on the rifle and your loading technique.

IMO a body die is useless for a tapered case like the .375H&H. I would go with a collet neck sizer.

[Paul B]

"With a belted or a rimmed case, if the rim/belt thickness is correct for the headspace, the primer cannot protrude at all. When it is too thin, then it is a fair assumption that the cause may be low pressure, but it's not such a clearcut situation as it would be with a rimless case. The rimmed or belted case is not supposed to move in the chamber like a rimless one is designed to, which contributes to case stretching as the shoulder and neck obturate (fireform) to the chamber."

Exactly. However, if you measure the belt on various cartridges, you can see as much as .003" plus or minus which you might as well call slop in the chamber. That brass that I measured were all from the same box of new factory ammo.

By setting up the sizing die to headspace on the shoulder rather than the belt, case life is much improved. You can just neck size up to a point but eventually you will have to do a full length resize. Just how often would depend on just how hot you're loading that brass.

My .375 H&H is on a Ruger #1 and I neck size for four reloads, anneal the necks and do a full length resize for the fifth reload with the die set up as described earlier. Using only one box of brass, I have reloaded that brass 20 times so far and they're still going strong. two things that helped them last is the load is fairly a mild one that shoots a 290 gr. cast bullet at 2050 FPS. As my rifle is a single shot, I don't have to crimp the loads which also aids in longer case life.
Paul B.