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  #1  
Old 12-30-2012, 4:50 PM
bitethebullet bitethebullet is offline
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Default Overpressure question

I have been reloading for a while now, but I have a new rifle that is giving me fits...DPMS LR308. I ran 20 cheap Federal factory loads through it and the primers were flattened...I chalked it up to cheap loads...I have since started reloading the .308. I with an average of minimums from Lyman, Hornady,& Hogdons just to be safe. I also used the longest COAL between the three manuals.The primers were again flattened and a few were pierced. I went to 75% of max load on the rather conservative Lyman manual and still blown or flattened primers....I am using IMR4895 with 168gr Hornady Match, OAL=2.80, case trimmed to 2.008. What could it be? I already made sure I wasn't crimping to eliminate variables.I also make sure neck tension/thickness is consistent between batches... I'm at a loss...the only other thing is maybe crap primers? I am using Winchester WLR, but I also pulled from another stash of same make primers....maybe try on with a harder cup?.....could it be the chamber in the gun?....I'm at a loss....I have loaded a ton .223, 270, & 30-06 and have never run into this before....
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Old 12-30-2012, 5:35 PM
Bill Steele Bill Steele is offline
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Is the chamber oil free? Oil in the chamber or on the cases can raise pressures.
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Old 12-30-2012, 5:37 PM
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You "used the the longest COAL between the three manuals". Are you jamming the bullets into the lands? Typically you can't on a factory chambered gun but I've seen stranger things happen.
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Old 12-30-2012, 5:57 PM
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I've seen the same thing on my DPMS 18" SASS LR-308 upper with reloads that I was working up using WC846. I started 10% below max and was blowing primers. I'll be going 20% down next.
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Old 12-30-2012, 5:58 PM
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possible headspace issue?
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  #6  
Old 12-30-2012, 6:03 PM
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Quote:
Originally Posted by Fjold View Post
You "used the the longest COAL between the three manuals". Are you jamming the bullets into the lands? Typically you can't on a factory chambered gun but I've seen stranger things happen.
Quote:
Originally Posted by russt View Post
possible headspace issue?
^^This is where I'd be looking.

You went max COL perhaps out of concern for pressure but could be creating that very problem by stuffing a bullet right up in the throat. Why don't you try black smoking the bullet with no neck pressure at the case mouth and determine your maximum COL potential, then start backing off that. Are you familiar with that process? This will give you a good comparison to determine if there is a headspace issue, too.

Last edited by Grizzled Bastard; 12-30-2012 at 6:05 PM..
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Old 12-30-2012, 6:05 PM
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Quote:
Originally Posted by Fjold View Post
You "used the the longest COAL between the three manuals". Are you jamming the bullets into the lands? Typically you can't on a factory chambered gun but I've seen stranger things happen.
Yep. This was my first thought too. Seat them .050" deeper and shoot them. Then try .100" deeper. Every .0025" deeper will decrease velocity by 1+- fps, with a corresponding decrease in pressure.
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Old 12-30-2012, 6:29 PM
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actually I think you will be going about 25 fps faster for every 0.05" deeper seating and you will raise the peak pressure by about 2,000 psi for each 0.05". If your load is 41.0g IMR 4895, you are at 100% capacity if you seat down to 2.70" and will start compressing if you go shorter.

You're sure you are loading to IMR4895 and not H4895 right? They are slightly different, but still, there is a difference.
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Old 12-30-2012, 6:41 PM
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Quote:
Originally Posted by Ahhnother8 View Post
Yep. This was my first thought too. Seat them .050" deeper and shoot them. Then try .100" deeper. Every .0025" deeper will decrease velocity by 1+- fps, with a corresponding decrease in pressure.
Wrong! Other way around, seat deeper and you INCREASE the pressure, not decrease it. So drop powder charge slightly every time you decrease OAL.
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Old 12-30-2012, 7:13 PM
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Gas guns run different than bolt guns. I've owned and reloaded for a Knight's SR-25 since 1993. I have to use medium burning powders and cannot run it as hot as a bolt gun, usually 3-2 grains less. I tried some CFE 223 recently and blew primers. It does not have an adjustable gas block.

This rifle beats the brass. I've put in a Tubbs buffer spring and a CWS (Carrier Weight System) which has helped. With Federal Brass, I may get only 2 reloadings out of them. I get better results with Remington, Winchester and Hornady brass, but the brass still gets beaten.

You may be experiencing the same thing with your rifle. Try dropping your powders charges a bit and try some different primers, it may help.

Last edited by FLIGHT762; 12-30-2012 at 7:18 PM..
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  #11  
Old 12-30-2012, 7:27 PM
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Quote:
Originally Posted by Bill Steele View Post
Is the chamber oil free? Oil in the chamber or on the cases can raise pressures.

Yes, the chamber is oil free and clean...thanks
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Old 12-30-2012, 7:46 PM
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Quote:
Originally Posted by GeoffLinder View Post
Wrong! Other way around, seat deeper and you INCREASE the pressure, not decrease it. So drop powder charge slightly every time you decrease OAL.
Have you tried it? I did the testing for the CA Service Rifle Team. What I said is true. How/why, I don't know. But I have fired thousands and thousands of rounds over a chronograph. It kind of makes sense though. When a bullet is jammed, pressures go up. As you seat the bullet deeper, pressures go down. Is there a limit to this rule? I don't know, but up to .250+" of bullet jump and pressures don't go up. Sometime I will post some targets with the load data on them. Some of the charge weights might give some here a heart attack.
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  #13  
Old 12-30-2012, 7:52 PM
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Quote:
Originally Posted by Fjold View Post
You "used the the longest COAL between the three manuals". Are you jamming the bullets into the lands? Typically you can't on a factory chambered gun but I've seen stranger things happen.
I am using 2.80" COAL, which is the longest length I saw in the manuals. I used the old dummy round and magic marker trick and didn't see any marks on the bullet from hitting the lands...I read somewhere that jumping can cause pressure spikes also...
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Old 12-30-2012, 7:57 PM
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Quote:
Originally Posted by russt View Post
possible headspace issue?
I will need to check....That will be one more thing to take off the list...Thanks!
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Old 12-30-2012, 8:03 PM
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Quote:
Originally Posted by rsrocket1 View Post
actually I think you will be going about 25 fps faster for every 0.05" deeper seating and you will raise the peak pressure by about 2,000 psi for each 0.05". If your load is 41.0g IMR 4895, you are at 100% capacity if you seat down to 2.70" and will start compressing if you go shorter.

You're sure you are loading to IMR4895 and not H4895 right? They are slightly different, but still, there is a difference.
Your right...Last think I want to do is create more pressure....some cases also had smear marks where the brass flowed into the bolt face....not good

Black bottle, purple label: IMR 4895...You are correct, H4895 is a slightly faster powder
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Old 12-30-2012, 8:10 PM
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If you are too close to the lands then seating the bullets deeper will lower pressure. Roy Weatherby proved that with his proprietary cartridges. He stuffed more powder into bigger cases and then lengthened the throats on his rifle so that the long jump to the lands before the bullet meets the lands lowered the peak pressure of the cartridge.

That's the same reason that the 5.56 can run hotter than the 223, the 5.56 has a long throat which lowers the peak pressure. The combustion chamber is larger because the bullet has a lot of room to move forward before it is forced into the rifling.

The peak pressure isn't reached in the cartridge case. And the variations in the size of the pressure chamber due to the seting depth of of the bullet is minor. It takes very little pressure to push the bullet out of the case (a primer alone can do that). The maximum pressure of 50,000 - 60,000 PSI peaks after the bullet hits the rifling as it requires more pressure to engrave the bullet and force it down the barrel.
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Last edited by Fjold; 12-30-2012 at 8:18 PM..
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Old 12-30-2012, 8:23 PM
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Are you loading from the Magazine or one at a time?
If loading semi auto from a mag could the bullet be getting bumped deeper when chambering from the mag? (not enough crimp)
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Old 12-30-2012, 8:25 PM
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Quote:
Originally Posted by FLIGHT762 View Post
Gas guns run different than bolt guns. I've owned and reloaded for a Knight's SR-25 since 1993. I have to use medium burning powders and cannot run it as hot as a bolt gun, usually 3-2 grains less. I tried some CFE 223 recently and blew primers. It does not have an adjustable gas block.

This rifle beats the brass. I've put in a Tubbs buffer spring and a CWS (Carrier Weight System) which has helped. With Federal Brass, I may get only 2 reloadings out of them. I get better results with Remington, Winchester and Hornady brass, but the brass still gets beaten.

You may be experiencing the same thing with your rifle. Try dropping your powders charges a bit and try some different primers, it may help.
Seems like the guns are pretty similar on how finicky they are to charge weight. What kind of receipe have you been using? I don't know how much further I can go under minimum charge weight with IMR4895? I am at 41gr (typical minimum) with a 2.80 COAL.

I also tried 10 rounds with CFE223 that I use for the smaller rounds. I went a full 1.6gr under Hogdon's minimum fearing that it would produce similar results as the IMR4895 at minimum charge and it did the same thing as you stated...pierced a primer and some were cratered....
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Old 12-30-2012, 9:15 PM
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A few of my loads I've shot recently.

Loads with not too much trouble are:
43.0 RE-15 W/ 168 A-MAX in R/P cases without much galling.
40.0 AR-COMP W/ 168 A-MAX is pretty accurate.
43.0 AR-COMP W/ 155 Nosler OTM
42.0 Radway Green 4895 W/168 Nosler OTM
43.0 XMR 4064 W/ 168 A MAX
42.0 H-335 W/ Hornady 168 OTM

Loads that stretched primer pockets:
42.0 AR-COMP W/168 A MAX
43.0 8208 XBR W/168 Hornady OTM
42.0 8208 XBR W/ 178 A MAX
46.0 CFE 223 W/175 Nosler OTM

If I keep the loads down 2-3 grains less than I use in my bolt guns, the SR-25 shoots fairly well. This rifle has a tight match chamber. When It was new, it blew primers with Federal 168 GMM. It got a little better over time, but stills beats the brass with the GMM.

Your load of 41.0 of IMR 4895 should not be too hot. Give the chamber a good scrubbing for caked up carbon. You can use a 50 cal. bronze brush for a chamber brush with a good carbon cutter.

I seat my bullets to about 2.780"- 2.8" for reliable feeding from the magazine.

You can look into the Tubbs Carrier Weight System, it's not too expensive, it might help. It has two weights. I use the heavy weight.

http://www.davidtubb.com/ar-15-carrier-weight-system

It fits into the open hole in the rear of the carrier. I don't know if it will fit your DPMS, you can give them a call and ask. I'd figure out what you've got going on first.
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Old 12-31-2012, 4:04 AM
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I have seen brass from factory 5.56 with primers that almost flowed out into the entire primer pocket. I never saw this on my Federal, nor my PMC X-TAC, but range pick-ups I have. Even 27.2 grains of Varget with 62 grain projectiles don't seem to make the primer flow like that, if at all or I'd be backing off (I don't know if because I have a 20" barrel, or if that even makes a difference)...

WC846 is what I was thinking about getting for my next powder purchase, and you helped me decide: Yes for sure!
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Last edited by the86d; 12-31-2012 at 4:07 AM..
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Old 12-31-2012, 8:18 AM
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Quote:
Originally Posted by FLIGHT762 View Post
A few of my loads I've shot recently.

Loads with not too much trouble are:
43.0 RE-15 W/ 168 A-MAX in R/P cases without much galling.
40.0 AR-COMP W/ 168 A-MAX is pretty accurate.
43.0 AR-COMP W/ 155 Nosler OTM
42.0 Radway Green 4895 W/168 Nosler OTM
43.0 XMR 4064 W/ 168 A MAX
42.0 H-335 W/ Hornady 168 OTM

Loads that stretched primer pockets:
42.0 AR-COMP W/168 A MAX
43.0 8208 XBR W/168 Hornady OTM
42.0 8208 XBR W/ 178 A MAX
46.0 CFE 223 W/175 Nosler OTM

If I keep the loads down 2-3 grains less than I use in my bolt guns, the SR-25 shoots fairly well. This rifle has a tight match chamber. When It was new, it blew primers with Federal 168 GMM. It got a little better over time, but stills beats the brass with the GMM.

Your load of 41.0 of IMR 4895 should not be too hot. Give the chamber a good scrubbing for caked up carbon. You can use a 50 cal. bronze brush for a chamber brush with a good carbon cutter.

I seat my bullets to about 2.780"- 2.8" for reliable feeding from the magazine.

You can look into the Tubbs Carrier Weight System, it's not too expensive, it might help. It has two weights. I use the heavy weight.

http://www.davidtubb.com/ar-15-carrier-weight-system

It fits into the open hole in the rear of the carrier. I don't know if it will fit your DPMS, you can give them a call and ask. I'd figure out what you've got going on first.

I will look into the carrier weights....in the meantime, I will try lowering the charge weight and get some harder primers
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Old 12-31-2012, 9:57 AM
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Quote:
Originally Posted by bitethebullet View Post
I will look into the carrier weights....in the meantime, I will try lowering the charge weight and get some harder primers
All large rifle primers are .027" cup thickness. Have not heard of any being of a harder or softer material, only larger or smaller in diameter.

Primer piercing or more accurately, blanking, is commonly caused by too large of a firing pin hole in the bolt face. This will also cause cratering, even before excessive pressures are reached. Oh, and those "blanks" are somewhere in the rifle. They will stack up inside the bolt and eventually cause failure to fire and some can get down into the trigger area also.

Rather than carrier weights, many of us in highpower fill the buffer with lead or lead shot. It will not help your problem, but it helps with brass longevity and felt recoil.

Primer info - http://www.jamescalhoon.com/primers_and_pressure.php
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Old 12-31-2012, 12:24 PM
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Quote:
Originally Posted by Ahhnother8 View Post

Primer piercing or more accurately, blanking, is commonly caused by too large of a firing pin hole in the bolt face. This will also cause cratering, even before excessive pressures are reached.

All large rifle primers are .027" cup thickness. Have not heard of any being of a harder or softer material, only larger or smaller in diameter.
This is true. If you're getting "Blanking" (a round cookie cutter hole) the firing pin hole in the bolt may be too large. Usually, a firing pin hole greater than
.065" can cause blanking in .308 AR gas guns.

That can be checked in the O/P's bolt.

CCI does make a L/R and S/R Military spec primer cup for autoloaders a #34 and #41, which they call "Mil Spec sensitivity".
http://www.cci-ammunition.com/produc...ers.aspx?id=30

Wolf/Tula also makes a S/R primer that they say has a harder primer cup. I use them in my .223 gas gun loads.
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