Spent Primer Pushed Out on Reduced Loads... HELP!

[WB300]

I worked up some reduced .308 loads as per Hodgdon's site using H4895, 125 grain SST's, Hornady Brass, and Fed Large Rifle Primers. My test loads were 34 to 35 grains of powder which put me about 74%-76% of max load. Hodgdon recommends going no lower than 60% of max, so I should be good there.

Brass was once fired from my Rem LTR, and the shoulder was bumped back about .003".

The rifle I fired these rounds in is a Marlin XS7 youth that started as a .243, but I had a factory .308 barrel for the same model installed (I don't reload for .243). The head space was set using sized and unsized brass from the LTR. The bolt closes on the sized brass, and is snug to close on the unsized brass.

I seat the primers just below flush. When fired, the primers are just barely sitting above flush. It's enough to see and feel. When I fire these same rounds in my Rem LTR, this does not happen.

The bolt face on the Marlin looks fine.

Can anyone shed some light on what is causing the primer to back out?

Thanks in advance.

Bill

 

[gunsnjeeps]

What happens with a normal .308 load? With some ammo the case doesn't get set back onto the primer after the round fires, When you fire a round the primer sets back out of the case and the powder ignition sets the case back onto the primer.

 

[buffybuster]

Headspace is probably on the loose side and the pressure it too low to blow the case out to the boltface.

 

[MarinePMI]

Headspace is probably on the loose side and the pressure it too low to blow the case out to the boltface.

This ^^^^^

The shoulder is being bumped back a bit when resizing, and upon firing, the case is being pushed forward against that shoulder by the firing pin strike, and then the case is adhering to the chamber wall upon ignition. With a gap now at the back of the case, the primer ends up backing out a bit.

 

[jonbearman]

One thing I noticed is you said the brass came from a rem 700 LTR and you set the shoulder back .003 thou. You just induced headspace by bumping the shoulder back when it (LTR Brass) may have fit your marlin with only neck sizing . You don't set headspace with fired or unfired cartridges because they flex. You need a go gage at least. Sometimes you can get away with brass to set headspace but it is wrong and not a good practice to try and save 25.00. You should buy or rent a gage or go to your local smith and have a go gage tried in it to see where you really are. If the primers are backing out you have a headspace issue that could be dangerous and will eventually stretch the brass till you have head separation. This is not a good thing. If you have never had head separation it is unpleasant and can damage your eyes permanently. Start over with the headspace gage and your troubles will go away. What are you using to measure how much bump you think you need?

 

[WB300]

All makes sense so far.

I fired some Hornady full factory loads at lunch today and the primers are all seated flush and not sticking out. when I get home tonight, I will drop those cases into a Wilson Case Gage and see how they compare to the others shot from the LTR as well as those that have been sized.

 

[M40_A1]

If your brass will be dedicated to reduced loads, then an old trick is to drill the flash hole larger.

 

[WB300]

OK so I checked the sized brass against the factory fired brass and reduced load fired brass with the Wilson Gage. There are 2 levels on the gage that measure .005" apart. I set up the sizer die so that the sized and fired brass fall between that range, so I know I am not bumping the shoulder back more than .005". Interestingly, the cases fired in the Marlin that were factory loads measure the same as the ones with my LTR, which means the shoulder is being bumped back after sizing about .003", so all is well there. But the fired reduced loads seemed to have the shoulder pushed back instead of blown outward. When I dropped the fired case into the gage, it actually dropped lower than the level, which indicates more than .005". Is it possible that the firing pin and primer detonation is pushing the case hard enough to bump the shoulder back just a hair, then the ignition of the powder is sealing the case against the chamber, but does not have enough force to push it back against the bolt face???? Could the primer actually be pushing the case hard enough to create more headspace??? And then the primer is backing out that amount???

I guess if this were true, it would explain undercharged loads and excessive headspace as noted above.

I use a Lee hand primer and the primers seat with a little force, so I know the pockets are not loose. And why would this happen in the Marlin, but not the Remington?

Does this make sense? Or should I just start drinking???

Bill