Blowing primers at MINIMUM load?

1

19dsniper

Sergeant
Full Member
Minuteman
May 25, 2010
316
71
Fort Hood Texas
#1
Need a little help here. I have been reloading for over 10 years and have never had this happen before, so now i am stumped.

Rifle: DPMS LR 308 24" barrel

Brass: LC 11 Match prep (FL resize with Redding competition die, swage primer pocket, trim to 2.010", debur flash hole, chamfer case mouth inside and out.)
Powder: Hodgdon Varget starting at 42.0 grains-45.0 grains in 0.2 grain increments. All weighed out on an RCBS Chargemaster combo and every 5th powder charge double checked on a beam scale.
Primer: Winchester Large Rifle
Bullet: 175 grain SMK separated by weight (0.2 grain extreme spread)
COAL: 2.80"

Temp: 55 degrees
Elevation ASL: 850 ft.
Humidity: 22%

I loaded these up starting at 42.0 grains based off of Hodgdons reloading information, and information i gathered from other reloading manuals.
At 42.0 grains of Varget i noticed my primers are not flat but i did have SLIGHT cratering, and i don't have any other pressure indicators except that on one of them i had a small pinhole pierce on the far side of the primer body where it meets the primer pocket. I figured this to be a fluke or that the case wasn't swaged correctly as the other 4 cases fired at 42.0 grains did not show any pressure signs. So i continued to the 42.2 grains.
At 42.2 grains the first 4 shot a good group of less than 0.75 moa, and then i had something happen i have only seen and never experienced. The 5th round fired at 42.2 grains had a blown primer where there would normally be the dimple from the firing pin. Not the entire primer, just the round hole where the dimple would be, and flattened primers. I know this all points to being over pressure, but how or why? I guess i will load Lower and see what happens, i just don't want to go too low.

Needless to say i stopped right there and came to you guys after racking my brain for a while on what could cause blown primers and high pressure at such a low powder charge. I tried setting up my chrono this morning to gather data on my firing strings but i kept getting an error and finally put it away, so i don't have any Velocities for either the 42.0 or the 42.2.

Measured case before and after firing:
Before: length 2.010", just above rim 0.468
after: length 2.010", just above rim 0.469

Any and all help would be greatly appreciated.

BTW: According to Hodgdon the Minimum is 42.0 grains at 2,583 with a Maximum charge of 25.0C (compressed) at 2,690.
I know this load data is for a bolt gun and should be reduced for a gas rifle, But pierced primers at a minimum charge weight? I have seen guys loading up to 24.5 grains or even higher in their LR-308 rifles. I know every rifle is different, but this has me stumped. I need your help.
 
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#4
42grs sounds a bit high for a 175MK and LC brass, that load with a 168AMAX would be perfect in my bolt gun. Drop your charge is all I can think of, if it were me, I'd load em up with 2000MR.
 
#5
Read this from the Sierra manual.

primersa-1_zps144ecb5f.jpg


Check how much your bumping the shoulder back, if you over resize the case this creates excess "head clearance".

HEADCLEARANCE-a_zps1a9a1011.jpg


When you pull the trigger the firing pin pushes the case forward until the shoulder of the cartridge case contacts the shoulder of the chamber and then the cartridge goes bang. As the pressure builds the primer is forced out of the primer pocket back over the firing pin. If you bump the shoulder back too far this creates excess "head clearance" and how far to the rear the primer can move. Basically the firing pin hits the primer and then the primer is forced "back over" the firing pin which then acts like a cookie cutter and punches the center out of the primer that it just hit.

HeadClearance_zpsf30a3af1.gif


The problem is exacerbated by over gassed semi autos that sill have pressure in the barrel as the bolt unlocks and starts moving to the rear allowing the primer to back out of the primer pocket even further. And this is why the military crimps their primers, military type rifles have longer headspace settings than their civilian counterparts so proper shoulder bump with your reloads is very important. A adjustable gas block helps with this problem and lighter bullets and faster burning powders to lower port pressure.


Excessive shoulder bump/head clearance in a over gassed AR15 caused the problem below and the primer anvil did its best to block the gas "leak".

piercedprimer-2_zps2d386fad.jpg


The Hornady cartridge case headspace gauge is a must have to solve a problem like this, you measure the fired case and then only bump the shoulder back .002 to .004. You will also need to make sure you have tight primer pockets, I use pin gauges to check the primer pockets for being over sized.

The Wilson type case gauges are setup for civilian chambers and your cases may end up over resized, with the Hornady gauge you just measure a fired case and adjust your dies for less shoulder bump.

gauge002_zpsd2792ffa.jpg


Shoulder bump is the distance below from the red dotted line to the green dotted line and you want to keep this between .003 to .004.


shouldersetback_zps59bf1b04.jpg
 
#8
HodgdonExtreme said:
No.



No.
Click to expand...

Actually George from Gap recommends just a hair over 42 grains of Varget for a gas gun. Part of the issue is the firing pin hole on a DPMS bolt is larger than that of an Armalite causing the cratering. The issue with the small pinhole, almost looks like a hairline crack on the primer near the outside edge of the primer is a common problem with Winchester primers. I had the same issue with my AI shooting 44 grains of Varget over a 155 scenar causing pitting on my bolt face. Winchester wanted my rifle, 600 rounds that I had loaded up along with the remaining primers in that lot so I just figure I will worry about it when it gets worse.
 
#9
Bradu said:
Actually George from Gap recommends just a hair over 42 grains of Varget for a gas gun. Part of the issue is the firing pin hole on a DPMS bolt is larger than that of an Armalite causing the cratering. The issue with the small pinhole, almost looks like a hairline crack on the primer near the outside edge of the primer is a common problem with Winchester primers. I had the same issue with my AI shooting 44 grains of Varget over a 155 scenar causing pitting on my bolt face. Winchester wanted my rifle, 600 rounds that I had loaded up along with the remaining primers in that lot so I just figure I will worry about it when it gets worse.
Click to expand...

I agree WLR primers are apt to rupture, indeed at considerably less pressure than most reloaders very often (safely) run.

I agree an oversize firing pin hole increases the likelihood of a "blanked" primer, as the primer cup thins as it stretches into the clearance between pin and bolt.

Disagree wholeheartedly that 42gr Varget is a heavy load in a DPMS 308. I have had direct experience with at least 5 of them.
 
#11
Let everyone know the lot # of those primers if you would. I have had problems with WLRM primers recently as well, & after calling Winchester, sending some of the suspect primers back, waiting over a month, & finally calling them back myself they told me there was nothing wrong with them. I switched lots, & problem solved. Pi$$ed me off as they had flame cut my boltface. Winchesters CS sux to say the least.
Several threads on these from last year to read about. I'm going to switch primers as soon as I can FIND SOME!!!
 
#12
I have just ordered the Hornady cartridge case headspace gauges so that i can measure shoulder bump, but i have never had this problem before. But then again, this is my first time to sit down and work up a load for this gas gun. Also, seeing as George recommends around the 42 grain mark, what kind of velocity are people getting from a 24" gas gun on such a light load? I am going to try again in a few days with a different BCG to see if maybe something just isn't right with that particular BCG. I have had a chance to read up on some of the issues very similar to mine with guys having the same problems. Unfortunately, there were a number of suggestions made to those people, with no follow up with what finally resolved their problems. So all i can do is read about their problem, but am no where closer to fixing my own. I guess the best thing right now will be to pull all the bullets and start over. I just don't know weather to start over with lower powder charges and just accept it for what it is, a slow load. Or to instead start over with new primers and the same powder charges to see if that helps. I normally run CCI BR primers, but i have over 5,000 WLR primers and figured, what the hell!
Keep the info coming guys, I'm trying all i can think of, just not sure what my next step should be.

ETA: None of the primers were loose when i loaded them. I use a hand primer and all were tight.

The lot # on the primers is: CFL487G
 
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#13
I would try again with another primer first. In my case I had a load for my 300WM that I fired over 1000rnds with no problems. Then after running out of the lot I was using I went to the new lot, & suddenly started to blow primers. Ended up going to another lot, & viola no more problems.
And Winchester said they tested the ones I sent in, & they "are within spec". They wouldn't tell me any specifics on the tests or what pressure they tested to. Nor would they accept another sample for testing. They basically told me, bummer about your boltface don't call again.
 
#15
givey said:
Sierra has a publised max for this of 41.7 When in doubt alwasy refer to the bullet man. View attachment 35635View attachment 35635
Click to expand...

And Hodgdon calls for a max of 45.5gr.

Who's right, the "powder man" or the "bullet man"? I wonder what the "primer man" would have to say about it? The "brass man"?

Neither are exactly right, which is why you work up your own loads.

Still, 42gr Varget under a 175 is NOT a heavy load. Period.
 
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#17
I know sierra lists the load lower than Hodgdons recommendations of 42.0-45.0C. I have already ordered the Hornady cartridge case headspace gauges and will measure everything up again as soon as they get in. I have a feeling that its a combination of things and not just one thing in particular. I have a feeling that i may need to use a different primer with a harder cup. I also think its possible that my reloading die is adjusted correctly. I recently cleaned the die and when putting it back together i used a fired case, brought it all the way down to touching the shoulder and then gave it a little nudge more, maybe 1/8 of a turn. Maybe that was too much. I will have to wait to get in the correct tool to truly determine what may be causing this problem. I have also read about DPMS rifles using a larger firing pin of .080 and that it can cause problems of clearance around the firing pin causing primer flow. I have called a few gunsmiths and even though they agree that its possible that it may be the cause, none of them are willing or capable of bushing the firing pin hole. So, as it stands, i know that anything below 42 grains is safe. When the proper tools arrive, and if everything measures out correctly, i may start there and work down just a little bit. I know its backwards and that you always work up, but it sounds as if i now know what my max safe charge is.
 
#20
Quantumkid, that was an interesting read. Thanks for the link. I contacted Forster about my N.M. dies and made sure everything was good. No problems with the dies. They walked me thru resetting them and checking case shoulder set back, i already knew how to do it, but had them walk me thru it incase something changed, or in case i was wrong. Everything checked out. I have pulled all the loaded ammo. I am going to resize the brass and use either CCI BR primers or Federal Match, reload again with Varget, working up from 40.0-42.0 in either 0.2 or 0.3 grain increments, and then go shoot them. I will then be able to check only one variable at a time with the primer being what I'm going for right now. I will continue to check pressure signs as i work up to the 42.0 grain load and then compare the primer and pressure to the exact same load only with the winchester primers. I have a feeling that it may all be the same as far as pressure goes because i am using LC brass with a smaller case volume. I have seen where a lot of guys running LC are reaching max loads at 42.3 grains of Varget. Hopefully i can get my chrono to work and stop giving me Error codes. I will report back with what i find out from starting lower with the loads and working up. Im still confused why some guys are able to load 44.0-45.5 grains of Varget (YES, I KNOW THIS IS ABOVE POSTED MAX LOAD DATA) and get good accuracy, no to little pressure signs, yet i can't get a load 3.5 grains less to not show pressure. Im still stumped. Maybe DPMS is turning out inconsistent chambers and mine and other happen to be a lot tighter than some of the others out there. Hopefully once i find a load within normal pressure it will still have the velocity to get to 1,000 yds. Otherwise I'm chasing a lost cause.
I will keep you guys posted as i continue to work this.
 
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#24
For years the "go to" load for f/tr was 45 gr. varget with the 175 Sie. mk. without any problems. Hundreds of shooters used this load before the advent of Berger technology, etc. So, all I can say is "sumting wong"!
 
#25
In the shotgun sports, we run into problems with certain brands of primers which encounter breaches in the metal work. I blame it on the ductility of the metal. Of course, I don't use those primers in my guns. They have a habit of eroding the firing pins with continued use, causing ignition problems, and requiring servicing and replacement of parts.
 
#26
The bolt on my DTA has been screwed because of Winchester LR primers.

Brand new Lapua brass, minimum loads of Varget (41gr) shooting 185 bergers. I didnt even get from minimum load on my ladder testing before I had sustained 4 blown primers. The gas seems to have escaped from the edge of the primer, so i dont believe it to be a pressure issue and it definitely is not a brass issue. The primer cups just aren't doing their jobs. Good way to ruin a perfectly good bolt.

Never again will i use Win primers.
 
#27
Vman, thats very similar to what i was running into. I backed everything off a little bit and went out and shot again today. At 39.0 grains of Varget i was getting groups in the .4-.6 moa range. Its a pretty accurate load, not hot at all, no pressure signs whatsoever. I will have to load up a few more and give it another go around with my chrono set up this time. My wife wanted to go too so she could shoot her new DDM4V7. So we had to get a baby sitter and be a little quick about it.. I will get everything set up and try again soon to gather chrono data.
 
#28
Just a follow up on my rifle. I used a friends gauges to check shoulder bump and he explained that he thought his might be giving a false reading. So i finally got my hornady gauges in today and here is what i have.
My fired cases are measuring 1.625" from base to shoulder before resizing. After resizing i am measuring them at 1.624" with some measuring 1.6245"
So I'm only bumping the shoulders back 0.0005" to 0.001" with the .001 being the average. I am using Forster bench rest dies for all my sizing and reloading. So I'm not bumping the shoulders back too far. I haven't tried any other brand of commercial brass yet as i bought 1,000 pieces of LC brass and have already fully match prepped all of it for this rifle. I expected to have more case damage than i am encountering, based off of all the reading i did. A lot of guys were saying that this rifle, DPMS LR 308 24", was notorious for tearing up brass. Thats why i went cheap on the brass. Im still a little hesitant to start running Lapua thru it only bc its not cheap to replace and i don't want to leave it laying all over the range at a match. Hence, the whole reason for buying so much LC brass.

Anyways, the best conclusion that i have been able to come to so far is that with the combination of LC brass having less case volume and and the fact that you normally need to lower your charges for gas guns like this anyways, that i will just be stuck running 39-40 grains of Varget in this rifle if i choose to stick with this brass. I will still load up some more ammo with winchester, Federal, and Lapua brass and at least see what happens when i get closer to the 42.0+ range of charges. I will also set up my chrono to get a good idea of what the current load of 39.0 gr Varget is doing, and to also see if the commercial brass is any better in this application. I still feel as if the brass is the main culprit because there are a lot of other people that are loading hotter, but with different brass.

For now i will leave well enough alone until i have time to load up some more ammo and head back out to the range with the chrono. But i will make sure to follow up on here to let everyone know what i find out. I know there were others on here that have run into similar problems with theirs as well.
 
#29
vman said:
The bolt on my DTA has been screwed because of Winchester LR primers.

Brand new Lapua brass, minimum loads of Varget (41gr) shooting 185 bergers. I didnt even get from minimum load on my ladder testing before I had sustained 4 blown primers. The gas seems to have escaped from the edge of the primer, so i dont believe it to be a pressure issue and it definitely is not a brass issue. The primer cups just aren't doing their jobs. Good way to ruin a perfectly good bolt.

Never again will i use Win primers.
Click to expand...


Once I use up what I have I will be switching manufacturers too. I already plan on sending the bolt off to get the bolt face tig welded and machined.
 
#30
I've also had trouble lately with Winchester LR primers. Utter garbage. I will be keeping my remaining 800 or so for emergency use only. Switched back to CCI primers when they came back in stock locally and haven't had any issues since. Winchesters were loose and inconsistent, had a few pop … and leakage, too. I will never use them again unless there is absolutely nothing else.
 
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#31
I did bother to read the whole thread....

I had an episode similar to OP in which a near MIN load would show excessive pressure signs.
There are a couple of physical things that can happen:

1) If the load is so light that the bullet starts to decelerate while in the bore the supersonic balst wave can reach the back of the bullet, this can setup a shock wave and display excessive pressure. RSI has a graph on their page shoing a large secondary pressure spike late in the firing sequence. The report of the gun will have a shriek rather than a standard bang.

2) The pressure can be so light that the case does not expand down to the bolt face quickly--but the primer does, this makes it look like the primer has no radius on its edge, some cratering (depending on firing pin tolerances) BUT in general if you have sooty necks, the primer pressure signs are to be ignored. You have to get the pressue up to the point where the soot disappears on the necks. The report of this load will be a standard bang.
 
#32
MitchAlsup said:
1) If the load is so light that the bullet starts to decelerate while in the bore the supersonic balst wave can reach the back of the bullet, this can setup a shock wave and display excessive pressure. RSI has a graph on their page shoing a large secondary pressure spike late in the firing sequence. The report of the gun will have a shriek rather than a standard bang.
Click to expand...

I am having trouble making sense of how this would work. Can you post a link, the graph, or at least what RSI is so I can read up on what you are talking about?
 
#33
CMH said:
I am having trouble making sense of how this would work. Can you post a link, the graph, or at least what RSI is so I can read up on what you are talking about?
Click to expand...

Google "RSI secondary pressure" and PRESTO https://www.shootingsoftware.com/pressure.htm

What happens is the expanding blast wave reaches the back of the bullet and reverses coourse. The blast wave detonates the unburned (but still burning) powder on its way back towards the chamber. That is the powder does not burn (conflagrate), but after a point is simply explodes (detonate).
 
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