Blowing primers problem...

C

cginaz

Guest
This year I built two 6BRX rifles for 1K and 600yd competition. One LG and one HG. Both the same reamer, caliber and chamber. Both have around 400 rounds through them. All with Varget powder and CCI450 primers. I've used various 105-108gr bullets. Until recently I've had no particular problems.

One day recently while the weather was still hot I blew several primers shooting 108BT over 33.2 gr of Varget. Primer pockets had been a bit loose when I loaded the batch. I thought perhaps that pressure had increased due to the heat, tossed the cases and reduced the load to 32.6. All good for a couple of weeks.

Last week I fireformed 100 new Lapua cases...50 in each rifle. Mild load of 30.5 varget. Primers seated normally for new cases...but....in the HG one round of the 50 blew a primer. I tossed the case.

At Saturday's 1K match during a match string in the HG (once fired cases) another case blew a primer. And doing some final load testing this week two rounds in the LG batch (fired twice) blew primers.

I can't figure out what's going on here. There are no signs of excessive pressure. No ejector marks, bolt lifts easily. The loads are moderate (32.6 Varget), the weather mild, the primer pockets are tight, all cases are properly prepped but from time to time a primer blows out. And when this happens the case won't fit into a caseholder on my press indicating I guess some expansion just above the head of the case.

Any thoughts on what could be causing this? Could I have a batch of defective cases? I'm mystified.

Chuck in Tucson
 
Nope and nope...Squeaky clean and using the last lb in and 8lb jug.
 
Nope on the flame cut...I haven't had any pierced...These are blowing all the way out of the case and ending up after I eject the case in the area between the action and the barrel where the lugs fit. When I'm running a string I don't notice the missing primer until I'm finished. I'm not really sure how the blown primers are getting up near the chamber. I'm guessing they fall in front of the bolt when I eject the case and then are pushed forward when I chamber the next round.
 
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Are you F/L resizing? If you push the shoulder back too far and create excessive headspace, this can happen. Took me a while to figure it out.
 
cginaz said:
This year I built two 6BRX rifles for 1K and 600yd competition. One LG and one HG. Both the same reamer, caliber and chamber. Both have around 400 rounds through them. All with Varget powder and CCI450 primers. I've used various 105-108gr bullets. Until recently I've had no particular problems.

One day recently while the weather was still hot I blew several primers shooting 108BT over 33.2 gr of Varget.
Any thoughts on what could be causing this? Could I have a batch of defective cases? I'm mystified.

Chuck in Tucson
Click to expand...

Are you using like actions and have headspace close enough on both guns to allow swapping bolts? My first guess and a very common problem is the iring pin fit on the bolt that is blowing primers. If so you will have to rebush the firing pin hole in that bolt.
 
These chambers both have a .272 No Turn neck...loaded round measures .270

I am full length resizing each firing as my reamer cuts a rather tight chamber. Since it's a BRX I prep the cases in three steps...1st FL resizing with a .308 die, then bumping the shoulder back .001 with a 6BR body die, then depriming and sizing the neck with a .268 bushing in a Redding neck die.

I did start a new 1K case of 450 primers lately...a more recent batch than the ones I was using. I just noticed today that the batch was different. I'm loading the rounds I'm taking to the NBRSA 1K Nationals next week with primers from the old batch in case the new primers are the problem. Not going to have time to do any more testing before I leave.

I've got a BAT action on the LG and a Stiller P1000 on the HG. Both were bought new this Spring. I've been shooting both for several months and it seems like the firing pins have been OK. The primer blowing problem just started to happen during the last few weeks. The only thing that's changed at all is the batch of CCI450 primers I'm using and the new Lapua cases.

I'm hoping that switching back to the older batch of primers may resolve the problem. That and being careful not to load any cases with even slightly loose pockets for the rounds I'm taking to the Nationals. Should be interesting.

Thanks for the comments and suggestions.
 
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what

is the case length do you need to trim your cases mebe??
 
I use a Lyman dispenser and weigh all my charges. Used to check it with a balance scale but never found any variations. It could be I guess that I got an extra grain or so in the cases that blew primers. It happened once on several different days with different batches. Usually one out of 50 rounds. Always a different case since I'd toss each one that blew.

And, I do measure case length and trim to a uniform length each time I load for matches...currently 1.56.

I'm hoping that the problem will just go away.
 
Now that's interesting. All the occasions of blown primers were when I was shooting Berger 108BT. The first time this happened I had planned to shoot 3 10 shot strings to compare bullets in my HG...one with 105VLD's, one with 107 SMK and one with 108BT. All the same load otherwise. I was using 33.2 Varget. The first two strings were fine but the first three rounds of the string with 108's all blew primers. I figured the charge was just too high for that hot day and didn't shoot any more. I later determined that the 108BT's shot best in both rifles and have just been using these with a lighter charge of 32.6since. The LG shot a 4.69" three target agg at last Saturday's Sahuaro 1K match with one screamer group so I don't want to change much. They're only going out at just over 3,000fps but maybe that charge is still a little much for these particular bullets. Seems there is always something.
 
Do you clean with a vibrator or tumbler? Could it be one or two cases have some corn cob left in them?!! This would increase your pressures. The 108 I would guess also has a longer bearing surface and the pressure you are hitting with that combo is higher, but a 4.69 3 match agg, I would not be changing anything at this point!

Only other thought, if you anneal, could you have heated up the head of the case too much and soften them? This too could account for the primers slipping out and deforming the pockets. I anneal, tumble and re-weight sort 'em to the tenth of a grain after 4-6 firings and you would be surprised at how much corn cob I get out of cases I thought were empty using a nylon brush for the necks.

Best of luck to you at the 1K Nats. and if you find your problem, fill us in on the fix.
 
I would check those cases again for length. Maybe you have to start all over on a new load. Primers backing out are caused by pressure or too much headspace. Neck clearance also could be part of the problem.
With the 6mm widcats we are shooting sometimes we are on the fringe of the pressure max.
I'm playing with a dasher from time to time and i have ruined at least 20 cases developing loads.
Each barrel chamber combination is unique. What may be a posted load mat not be the one for your rifle .
You have high quality actions and you should not be having firing pin problems , Jerry is right though Remingtons do need extra work along with a few others. Chrono those loads and see what your getting.
I was using a standard load on my dasher but seating the bullet out way to far. I hope this helps somewhat.
Just what happened to me.
 
Thanks for all the comments and suggestions. I think I understand what the problem is now. And, as usual, it's my own fault.

I prepped 40 cases yesterday that had been fireformed and then fired one more time with the load I'm been using. The primer pockets in several of the cases were so loose that they would not hold a primer, another 8 were really loose and the rest sure were not snug. It's got to be a pressure problem. I must have been just on the upper edge of the pressure maximum shooting 105VLD's and when I switched to 108BT it went over the edge. I somehow got in my mind that some guys loaded up to 34.5 Varget in the BRX and that charges in the low 33gr area would have to be all right. Apparently not with 108BT bullets. I then thought dropping to 32.6 would really be moderate but I guess not. It sure does shoot good though. But, I'm cutting back a little more on the rounds I'm loading for the Nationals and when I get back will do some more testing. This is a new caliber for me this year and I'm still getting used to it.

Thanks again for the help.

Chuck
 
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