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Posted: 9/8/2004 9:05:49 AM EST
I was out with my DPMS LR308 this weekend and was shooting some BHA 175 BTHP Match ammo. I was still in the break in prorcess so things were going alittle slow. I got through the first box fine then when got to the second box of ammo I had 4 of the 20 rounds loose their primer upon ejection. I would not expect this with this quality of ammo. Can any one shed some light on this.

Matt Carper
Link Posted: 9/8/2004 9:12:43 AM EST
IIRC, I seem to remember hearing that the 168 grn. SMKs were preferred over the 175s for AR10s and the newer DPMS semi-auto rifles.

BTW the primers aren't being ripped out, their being blown out by excess pressure or loose primer pockets, (not something I'd expect from BH ammo)

Mike.
Link Posted: 9/8/2004 2:51:10 PM EST
Greetings,
My AR10 does the same thing with Federal Gold Match 168 gr. ammo.
But BlackHills 175 gr. doesn't blow primers.
Any chance that you're not completely drying out the chamber after you clean the gun?

Corvette
Link Posted: 9/9/2004 7:06:24 AM EST
Blown primers are a BIG issue. Upon firing the primer typically backs out of the pocket a fraction of an inch. The subsequent pressures developed as the powder burns typically drives the case back 're-seating" the primer.

Primers can be left protruding for a number of reasons. For example, exceedingly light loads may not have sufficient power to reseat the primer. This is not likely or probable with a 7.62. Some case design issues can also result in protruding primers (ie the use of the tapered bottleneck 256 Winchester in some revolvers developed a reputation for protruding primers and 'locked up' revolvers).

Was your Black Hills remanufactured?

The most likely cause for lost primers is oversized, out of spec primer pockets. Black Hills has excellent quality control, but they do use fired cases for their remanufactured ammo. If the previous load was a bit too warm, primer pockets can be expanded, leaving the primer/pocket fit too loose. This is likely the most logical explanation for your primer loss issue. If the case was a once fired military case, the remanufacturing process requires removal of the previous primer stake or crimp. Improper primer pocket swaging can result in oversize pockets as well.

I have previously encountered new cases (winchester in this case) were teh brand new cases had out-of-spec primer pocket dimensions.

Frozenny

Link Posted: 9/9/2004 8:05:53 AM EST
I don't know what chamber reamer DPMS is using, but if the bullet ogive of the 175 SMKs are being shoved into the chamber leade, you could be getting high pressure. Are the primers flattened or blown? Is there gas leakage around the primer? First thing I would do is pick up the phone to BHA and see what they say. They are good folks and will help you out.
Link Posted: 9/9/2004 11:48:21 AM EST
I have contacted Black Hills and DPMS.

What is this about drying out a chamber. I was braking my rifle in and was cleaning ALOT. Need alittle more info.

Matt Carper
Link Posted: 9/9/2004 5:34:31 PM EST
Black hills does not offer or even make remanufactured .308 ammo so the problem isn't because of over reamed primer pockets ( still could be too big right from the start but not because of remaunfacturing process ) and he shot an entire box with out blown primers so my thinking is that over pressure because of the bullet touching the lands is out too.
my thinking is bad box with poorly seated primers.
Link Posted: 9/10/2004 1:38:58 AM EST

Originally Posted By Matth3wdean:
What is this about drying out a chamber. I was braking my rifle in and was cleaning ALOT. Need alittle more info.



What Corvette is referring to is that "tight-chambered" rifles can create overpressure IF the chamber has been well/over lubricated (note: more than likely from cleaning/lubrication of the bore and that lube being present on the walls of the chamber as a result).

As ignition of the round occurs, the walls of the brass expand to limits of the chamber, should the chamber have an overabundance of lubrication present this "could" possibly limit the complete expansion of the brass and as a result create over-pressure, popping the primer.

FWIW, as alot of our custom rifles have extremely tight chambers, this is not something I've ever experienced, but it could happen, especially if the chamber or headspace on your rifle happens to be out of spec, which is more likely IMO.

I'd do what it appears you have done and contact DPMS, let them check it out, as these are a relatively new products and there's always the possibilty the headspacing or chamber is too tight.

Mike
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