.223 Primer protrusion after firing

[Skoodifoo]

I encountered a problem with my previously good load in .223. The load is 1,57G N135 behind 52gr SMK, OAL 55,6mm, case is 2 x fired Lapua Match full body sized.

I noticed that primer protruded 0,15-0,2 mm after firing, enough to be noticed by naked eye. I've never encountered such a problem with my loads. The primers were not flattened at all and had still round edges. No hard bolt lift and all of the cases had fouling on the necks and not on the shoulders after firing, which should indicate that the load was in proper pressure window. Bolt face doesn't show anything wrong, it was clean after firing so no primer leakage either.

I have no idea what could cause this, as I've used this load before with great success and even with the primer problem yesterday it still did 10mm groups at 100m out of my CZ's clean barrel.

I try to take some pics today, it should be the easiest way to determine if there's something going on.

 

[mikecr]

I don't see it as a problem

 

[SmokinJoe]

I would recommend that you check the shoulder bump back you are getting with your "full body sized" brass. You may be creating a bit of excess headspace.

 

[Preacher]

Plus 1 for what SmokinJoe said....
The case is being held foreward in the chamber when it's fired and the primer is backing out...
Reset your FL die and the problem will go away..

 

[Minesweeper3433]

I have had this on very low pressure loads out of a 6.5swede when shooting gallery loads. I just ignored it as it went away when I bumped up the charge.

 

[BoydAllen]

What you are seeing is an indication of a load that is fairly low in pressure. If you shoot this load repeatedly, in the same cases, you will probably see the primers sticking out a little more with each firing. When using a caliber that has a rimless case, it is always better to use loads that leave the primer flush. The reason being that if you use your light load over and over, the shoulder will be set back a little more with each firing, eventually leading to a situation where even though the case length is within spec, the neck will be so long that it will start to be forced into the bullet, by the angle at the end of that part of the chamber, during firing. Also, if a higher pressure load is then used in one of these cases (that have been fired repeatedly with a low pressure load), an incipient separation will occur, showing up as a bright line just in front of the case head, with a corresponding thinning of the case at that point. Any case that shows this thinning should be discarded, with its neck crushed, to prevent someone, who is not aware of its history, from using it.

 

[jonbearman]

Boyd you are right on.I had it happen with reduced loads in an 06.Once I bumped it back up to normal pressures problem was solved.I have seen oversized brass where you bump that shoulder so far that the primers were falling out of this fellas m1 garand.I told him to start over and discard that brass.Next time I saw him all was normal.

 

[bigedp51]

The primer can back out by the amount of head clearance or air space between the rear of the case and the bolt face. At low pressures the case will headspace on the primer and the primer will protrude, as the pressure is increased the primer will be seated flush with the rear of the case.

Below, low pressure reduced load and protruding primer.

 

[BoydAllen]

The difference between the rimmed cases that you show, and rimless, is that the rimless have only the shoulder to control headspace, and repeated use of low pressure loads, can increase primer protrusion with each firing, assuming that there are not intervening loads of higher pressure. I have done the actual testing on this, it is not conjecture.

 

[bigedp51]

Mr BoydAllen

The reloading manuals warn against using cases that were used in reduced loads again with full power loads because of the increased cartridge headspace as you stated above.

I simply used photos of rimed .303 cases because they are the only photos I have on this subject.

 

[BoydAllen]

Your explanation and the video are first class. I was just emphasizing my first point, so that there would be no confusion. Given the superior nature of your post, I was sure that you already knew. Sorry if I offended. Sometimes I rattle this stuff off a little too quickly.
Boyd