Reloading failure

[Strigidae]

Gentlemen,

At a range session today i had a scary occurrence that id like to share and get some clarification on.

Info:
Reloader for just shy of 9 years with no problems until today.
Remington 700 aac thread protector only on it
40g IMR 4064 hand measured on an RCBS 505 and trickled to final measurement.
Mixed mil brass small base resized trimmed to around 2.010 case lube wiped off
WLR primers
2.810 coal (chamber is close to 2.9-3.0 with crude measurement)
175 SMK firsts
60 degrees
Slight rain

This load was ladder tested and group tested and my most accurate combination I could find so far. 42g was my max according to sierra. I am not a professional but just enjoy the pursuit of precision as best i can.

The situation occurred after 4 shots into a 5
shot string. Noticed no change in felt recoil or report but saw smoke from the chamber and the bolt was slightly sticky. The case came out without the primer. I stopped and cleared the weapon and did a red check and all good. Looks like extractor marks on the head. Lots of soot. No flattening of the letters on the head i can see. No flattening of the primers i can appreciate. The case lengths measure the same as the other cases. The width at the body just after the extractor groove is .475 as the other brass is .470. The extractor lip portion measures .585 compared to .472 of the others. The flash hole empirically looks larger than normal but may be due to expansion. No bore issues noticed. No hole in the primer noticed. No change in POI at 100 yards (solid 1 MOA gun). This was shot number 142 after cleaning. Shot one more round with no issues and then the same smoke etc with the next round. Cleared as before with same results. Changed runs of reloads and continued to shoot 10 shots with no incident.

Gentlemen, I've not had an issue until today and just wanting to know your thoughts. I can handle that i may have screwed up. I pulled that entire run and no over or under charges were measured. Im meticulous about my loading even though i use crappy brass and primers. Any thoughts other than i screwed up and missed 2 over/under charges. Searching here and elsewhere I find info for failure in over/under charge, headspace, case lube, barrel obstruction/constriction, primer failure, etc.

Many thanks gentlemen for any insight or advice.

 

[dauntedfuture]

You poped a few primers. This is the cases way of telling you that the load is too hot or the brass is worn out. The edges of the primers still look round so im more inclined to think that the brass is worn out but its hard to tell. Another possibility is that you got water on your ammunition. That will spike pressure if you get it on the bullet or case or in the bore.

 

[culater]

Thats what happens when you get MIX MIL BRASS WHEN RELOADING IT.To many people go the cheap route and can get hurt, use fresh brass with a bolt gun. yes I use once fired brass for my ar-15 and do fine with it. I keep the charge below max for safety other than that use fresh stuff because you know how the brass started its life.

 

[Strigidae]

Thank you gentlemen.

 

[BC 6.8]

My guess would be the brass is worn out.

 

[BIPMaster]

I would trash the brass that popped primers and carry on with the rest of the brass. For precision though, you may consider sorting the brass by headstamp and year, and working up a load based on one group of matching headstamp/year.

 

[former naval person]

Just for giggles, Put a fired primer in and measure water capacity of the good cases and the ruined cases.

 

[sierracharlie338]

Could have been caused by the rounds getting a little wet from the rain. There was a thread similar to this about a week ago. Same type of primer blowing issues all of a sudden after shooting the same load with no issues a number of times before.

Just a thought

 

[0311@LAR]

Loose primer pockets would be my guess.

 

[Strigidae]

Just for giggles, Put a fired primer in and measure water capacity of the good cases and the ruined cases.

I can plug it with clay but the primers will not stay. They jiggle in there now.

 

[bax]

I can plug it with clay but the primers will not stay. They jiggle in there now.

You blew two primers. There was enough gas pressure to flow around the primer and against the bolt face and smoke came out. You might check your bolt face for a little etching where that gas flowed against the bolt face. In my experience, if the case is a tight fit in the chamber when the round fires, the primer doesn't have enough room to back out of the case. If your full-length sizing die pushes the shoulders back a few thousands then this is more likely. You might verify that your cases are sized JUST enough for the bolt to close freely.

I know of only two ways to get primer pockets that loose: shoot them hot or use a carbide Sinclair primer pocket uniformer to clean the primer pockets. Please don't ask me how I know this.

Your primers don't indicate very high pressures but they could have been shot hot at some earlier time and the primer pockets were already loose.

If you used a primer pocket uniformer to clean pockets and you cut away too much brass, a blown primer is standard stuff. If you didn't, then we have a mystery.

Is there any chance that the primer pockets were loose then you primed them? Primers should require some force to insert into the case ...

 

[Tristian19]

I would dump your fired brass and go with brand new Lapua brass or whatever NEW brass manufacturer you wish and run with it. Not worth possibly hurting yourself or damaging your hardware.

My .308 load is:
175 SMK or 178 AMax
43.0 grains IMR 4064
Lapua Cases @ 2.800 (Magazine fed)
No issues or pressure signs out of my CZ 750 Sniper .308

Just my two cents...

 

[918v]

Your load of 40grs of 4064 under a 175 SMK is light. FGMM 175 uses 41.8grs of 4064 and FC brass is very close in capacity to LC. I doubt it's an excessive pressure issue, but do weigh the two offending cases and see if they are significantly heavier than the rest. They should weigh around 181grs.

How many times have these been reloaded?

 

[Strigidae]

Thank you very much gentlemen.

I believe i have found the issue with your help. I do remember some brass being a little easy to prime. I hit up a friend for some brass to help me get to the required round count for an upcoming class. That lot had his brass in it and he loads hotter than i usually go. I have set aside and pulled bullets on those that have his marks from decrimping. I do believe this is the issue. My brass is sourced from everglades and is fired and processed in lots. This current batch has three firings if i count the bullet in them now. My buddies brass... i assumed too much.

The 40g mark was not by my choice but rather by ladder and group testing. The gun likes that combination.

 

[Strigidae]

You gentlemen are fantastic. Thank you all again.