pushed primers

[78stw]

this seems the most appropriate place to post this. I am breaking in a barrel and doing load development on a belted mag and i am getting some primers that back out flush or just past (.001) this is new or 1x fired brass. I also loaded a few in WRA brass from the 1940's and they backed out .005-.007 without more detail does anyone have insight? thank you. I am a new to this great site so please indulge me if this is a redundant question

[earl39]

Without more information this would seem to be one of two things. You have loose primer pockets (not likely since it happened with different lots of brass) or you are running into high pressure for some reason.
There is a third reason and that would be badly dished out bolt face allowing the primer to be forced back against the bolt face when fired and the differences you see in measurements with different brass would be due to how tight the primer pocket is.
My money would be on the high pressure.

Gary

[DanSavage]

If your starting out with a light charge there could be the possibility that your head space is a little to excessive. Tell us about the rifle, obviously the barrel is new because your breaking it in. Who put the barrel on and who head spaced it. I would re check the head space with a no go gauge and make sure the bolt does not close on it.

Dan

[thirty06]

Your headspace is probably a little loose in the shoulder area because it's headspaced off the belt.
Try just neck sizing some that have been fired in that rifle and see if it stops the primer from trying to back out.

[78stw]

thanks for the quick replies. Ok the rifle is a custom build by me starting with a LH model 111. the barrel is a factory savage 375 H&H safari weight cut down from 25 to 20.5 recrowned with an 11`. headspaced with both forster gages. I checked and re-checked and ..........before and after I gave the NUT it's final "rap" . the charge is approx. 80% rl15 (65.6gr) 215M and a hornady 225 sp. i shot 9 rounds last week and did not notice any issues. yesterday i shot 14 rounds and got pushed primers. Thirty mentioned "loose at the shoulder " this might be an issue of sorts as I have another belted mag with an awfully long chamber, or so it seems. let me know if this info sparks more insight. thanks

[earl39]

That charge is a full 2 grains below the minimum shown in my Hornady load book and about 6 below in my lee book. If it is headspaced on the belt you may be too light to get a good seal on the chamber wall and pressure is trying to get out thru the primer and lifting the brass off the bolt face. If you did the headspace off the belt and feel like breaking the nut loose then try to headspace off the belt on a few different pieces of brass. Take this all with a large grain of salt as i am just trying to make an educated guess since i have no belted magnums.
Notice it is still a pressure problem just sounds more like low pressure.

Gary

[bigedp51]

Any time you shoot low pressure loadings or start at the suggested starting load you "WILL" see the primers back out of the primer pockets. If you take the time to read the front of your reloading manuals you will also see warnings to "NOT" use cartridge cases that have been used for reduced loads with full power loadings. The reason for this is excessive "cartridge headspace" caused by the firing pin driving the case foreword and actually pushing the shoulder of case backward increasing headspace.

At low pressures the primer will back out of the primer pocket and the chamber pressure is not great enough to push the cartridge case against the bolt face. This is called headspacing on the primer and the primer can back out by the amount of head clearance you have. Head clearance is the "air space" between the rear of the case and the bolt face, and "why" you fireform cases to your chamber.

Watch the animated image below and the primer backing out of the primer pocket, first chamber pressure builds and causes the case to grip the chamber walls. Then as the pressure gets higher the primer is pushed from the primer pocket, then as the pressure reaches the yield strength of the brass case the base of the case stretches to meet the bolt face. This is one of the reasons that military ammunition is thicker in the base web area and has staked or crimped primers to keep them from backing out of the primer pocket at the longer military headspace settings.



Below a .303 British cartridge case used to shoot cast bullets at "reduced" pressures, the primer has backed out the exact same amount as the head clearance will allow. (headspacing on the primer)

[img width=600 height=272]http://i122.photobucket.com/albums/o254/bigedp51/9-1.jpg[/img]

Now to your 7mm Remington magnum, the SAAMI manufacturing tolerances allow the belt to vary .008 in length. This means the case when new can be .008 shorter than the GO headspace gage. Add this .008 to how far your headspace is over or longer than GO gage it is possible to have the primer protruding from the case .014.

When fire forming cases one method to prevent this from happening is to seat your bullet long jambing them into the rifling to hold the case against the bolt face when fired at the lower pressure loadings.

[bigedp51]

Just a further note, all my 30-30 fired cartridge cases have the primer protruding from the primer pocket .004. This is due to the 30-30 lower chamber pressure of 38,000 cup which is lower than the yield strength of the Winchester 30-30 cases. Simply put the 30-30 chamber pressure is not great enough to cause the case to stretch and these cases all headspace on the primer just like reduced loadings.

Also all of what I have said above is in the front of your reloading manuals....................

"All the information in the world is written in books and all you have to do is read"

[78stw]

thanks guys. I did go back and read that "lowpressure/pushed primer" bit in my hornady manual. To be honest I forgot all about that and I have read all of my manuals several times. Also, the charge I used, being a "fast" powder should be ok. Lesson learned. I will crank it up a bit and hope I get good accuracy without getting too high velosityas I am trying to create a 35 whelen/350 rem mag/375 win type round. thanks again for your help. Matt