Primer backout problems

[Wayfaroff]

Using Sierra 168, Gm210m, FC case, 41 grs H4895 and noticed
about half of the 30 I fired the primer had backed out 3-5
thousandths. It's a 700 PSS .308. Any concern with this or
forget about it?
Thanks

 

[davewilson]

not sure if it's a concern, but you might not have enough pressure to slam the case back against the bolt.what do the primers look like after firing?

 

[sniper2]

Yep load too lite!!!

 

[Wayfaroff]

Primers are starting to become flattened. Could it be loose
primer pockets, federal brass, after 2-3 firings?

 

[257speed]

It is possible that you could be sizing the shoulder back, creating a slight headspace problem. Just an idea. The whole concept of "slamming the case back against the boltface" does not make good sense, since it shouldn't need to be slammed anywhere.

 

[Neverlost1]

Doing a quick check of Hodgen's load data, your load is just fine. They list 43.5 grs H4895 as a max load with a 168 gr bullet.

There are so many variables with reloading it's difficult to diagnose a problem to a single cause. Backed out primers are "normally" an indication of a light load. You also mentioned that some primers are flattened?, which could be an indication of a hot load. Since the load you are using is less than a max load, but you're seeing both pushed back primers and flattened primers with the same load, my first suspect would be uniformity. My second suspect would be the brass. Here's a few ideas of what I would check:

How do you measure your powder for each load? Are you weighing each load or dispensing from a powder measure? You should probably carfully weigh each load.

Are you using a hand priming tool or using the ram on the press to seat the primers? You will easily feel the difference between a normal and a loose primer pocket using a hand tool. You may want to try a different brand of primers, brass, or both.

Are you checking case length and trimming to a uniform length? If crimping bullets this is critical for uniformity.

Is bullet seating depth uniform? Touching the lands, just back from the lands or set to recommended OAL?

How does the accuracy of your handloads compare to factory ammo?

Do you have a chronograph? Measuring your velocities may be the best indication of how uniform your loads are and a low velocity would also show you if this load just happens to be very light in your particular rifle.

These are just a few ideas to get you started. Pushed back primers wouldn't overly concern me, but flatttened primers definitely get my attention, so be careful.

 

[nowler]

sounds to me like you have headspace problems, probably due to oversizing, ie pushing shoulder back too far.....

 

[257speed]

Nowler is correct, if he is getting 3 to 5 thousandths backout, this means there is a gap behind the case and the front of the bolt. This my friends is called EXCESS HEADSPACE! And 3-5 thousandths is not good. It is most likely caused by a sizing die that is not set up properly and is bumping the shoulder back a slight amount. Start over with some new brass and set up your sizing die to fit the fired case, ignoring the manufacturers suggestion of turning it down to the shell holder. Good luck.

 

[playersc]

I had the same problem on my Remington 700 VS 308. After firing 20rds I noticed that the primers were pushed out further than the case head anywhere from .002"-.006" ( .006" is how much the shoulder moves in my chamber from new brass to properly fireformed). I am unsure if my load was too light or if I just have a rough chamber that will not let the brass slide properly. The only way I could get the brass to fireform properly was to lube the outside of the case same as you would to full length resize and fire. I hope this helps Playersc

 

[ricka0]

[ QUOTE ]
<font color="purple"> Nowler is correct, if he is getting 3 to 5 thousandths backout, this means there is a gap behind the case and the front of the bolt. This my friends is called EXCESS HEADSPACE! And 3-5 thousandths is not good. It is most likely caused by a sizing die that is not set up properly and is bumping the shoulder back a slight amount. </font>

[/ QUOTE ]
That would be my guess too. Doesn't the firing pin slam the cartridge forward (or potentially)?

Really good info in this thread.
Playersc writes:[ QUOTE ]
<font color="purple"> The only way I could get the brass to fireform properly was to lube the outside of the case same as you would to full length resize and fire. I hope this helps Playersc </font>

[/ QUOTE ] I thought this was dangerous, especially with excessive headspace as it doesn't allow the brass to *stick* to the chamber but is free to do a CHS (Case Head separation).
Take a look at
Partial Full Length Resizing (PFLR)
Yet another reason not to use reduced loads. I want to use reduced loads so I can easily get BC numbers with the same gun/bullet but at different velocities (without moving the chronys)

 

[257speed]

Bigbore, you are correct on both, in the first, the firing pin knocks the case forward until it finally fires. The sides of the case grip the chamber and it sets the primer back. Worst case scenario is that you get a case head separation, releasing dangerous gases through the action.

[ QUOTE ]
I had the same problem on my Remington 700 VS 308. After firing 20rds I noticed that the primers were pushed out further than the case head anywhere from .002"-.006" ( .006" is how much the shoulder moves in my chamber from new brass to properly fireformed). I am unsure if my load was too light or if I just have a rough chamber that will not let the brass slide properly. The only way I could get the brass to fireform properly was to lube the outside of the case same as you would to full length resize and fire. I hope this helps Playersc

[/ QUOTE ]

Lubing the case is a bad idea. I would love to see a test design on this, as there is no doubt that you are creating an incredible amount of bolt thrust. Meaning the case is not able to grip the walls of the chamber, so the entire case is able to push back against the bolt face with much more thrust than is normal. With a heavy load, this "Has the potential" to be a disaster. It may not ever, but it is certainly not a recommended practice. Headspace problems can only be corrected properly one way, and that is by having CORRECT headspace in the first place, with a properly cut chamber.

 

[Wayfaroff]

I trim all cases to the same length, use an electronic scale to weigh each round, bullets are all seated to 2.80 oal. Use a wilson headspace gauge to set the resizing die, to spec. 41grs -42 grs of H4895 should be fine, not to lite, or to hot. Fired brass fits perfectly in the gauge.

Could be the FC brass is to soft after a couple of firings.
Primer pocker stretched.
Chamber is smooth and clean, bolt face looks fine.
Will try resizing and chambering until the bolt closes per
suggestions.
And will try a different brand of brass and primer.
Thanks to everyone for their ideas and suggestions.

 

[davewilson]

you're using a headspace guage to set your die,that's the problem.the difference between a long chamber(might be a little longer than it should be) and a go guage could be 8-10 thousands or more.set the die until the bolt just closes or a few thousands longer than before.

 

[LB]

I can't be sure what the problem is, perhaps improper resizing? But, for sure, the place to detect loose primer pockets is when seating primers. If they go in too easily, discard them, waste a primer, if you must.

Good hunting. LB