maddening 6br issues

[jonbearman]

You may have to have the firing pin hole bushed and I would suggest gre-tan rifles in colorado do the work.This will make a marked difference with the way the primer acts with hotter loads.

 

[kelbro]

That's a pretty hot load.

 

[mattlewis]

thanks for all the replies and suggestions. i'm going to proceed investigating a carbon ring, first and firing pin cleaning issues second.

just so we're all clear, i'm now getting pressure at 29.2 with bullet touching lands, when i was previously able to fire the higher charges without pressure.

i'm going to triple check all measurements first, but i'm betting on the carbon issues. i'll report back if i figure anything out.

thanks again to all who offered solutions. i appreciate it.

 

[littlebuddybr]

Its been said several times...Its a pretty hot load. I would start by backing off the powder!!

 

[mattri]

29.2gr of Varget is too hot a load with 108s? Our home page lists higher loads than that:

http://www.accurateshooter.com/cartridge-guides/6mmbr/

Maybe I missed it but did you happen to change powder lots?

 

[1KBR]

Everyone I know with a 6BR runs hotter than 29.2gns, even those jamming the 108s into the lands.

I went up close to 31gns, blew some primers which burnt a chisel shape into my firing pin. This chisel shaped firing pin pierced primers with low pressure.
I would think a good Iosso or JB session for the first 6 inches, especially with Varget which creates carbon in my 6BR. I give my 6mms a good de-carbon every 150 rounds or so when my bore scope shows regular cleaning is still leaving a lot of black in my bores.
Last of all, many barrels get a velocity and pressure increase after a few hundred shots or so.
Could it be that you have one of the infamous fast lots of varget with a tight, high pressure barrel, with a short throat, relatively long/heavy 108s and hot primers, hot summer weather, all working together with an erosion sharpened firing pin?

 

[mattlewis]

Same 1lb keg of powder.

I had to order a couple things to do it with, but I feel certain it's carbon. I'll report back.

 

[Forum Boss]

Same 1lb keg of powder. I had to order a couple things to do it with, but I feel certain it's carbon. I'll report back.

There are many other suggestions here that may be part of the explanation. But I would certainly question the OP's weighing or the accuracy of the scale. He says he was running (initially) 31.7-32 grains varget jammed .010 with 105s. I've been running this site since 2004 and I have never, ever heard of anybody that could run 32.0 Varget in a standard 6mm BR with 105s. Not even close.

Now he says 29.2 is blowing primers. When we've seen this kind of weird result before we usually traced it back to major errors -- such as wrong powder in the powder measure, totally out-of-whack scales, other major reloading errors. I'm not accusing the OP, only saying that 31.7 to 32 grains of Varget doesn't seem a do-able load in this cartridge with this bullet at all, which causes me to wonder about everything.

With .250 of shank in the neck, default case capacity, and bullets seated in the lands, QuickLoad is suggesting a 32.0 grain load would be running 74600 psi and 3158 fps in a 27" barrel. This is with the "adjusted" 6000 psi start pressure I normally use for in-the-lands seating with 6BRs (well below the recommended in-the-lands start pressure). It also shows a 32.0 grain load being at 104.1% fill capacity -- hard to achieve. Sorry, NONE of this makes any sense to me. I can't comprehend the first load numbers, therefore I don't know how to evaluate the claim of blown primers at 29.2 grains. I wouldn't be surprised if the charges are not being weighed correctly or the scale itself is inaccurate.

 

[savageshooter86]

sounds to me like the scale is off. If you cant even run 29 without pressure issues then something is wrong. Just curious what your OAL is when you say you are jamming 0.010"? You sure you measured this accurately?

 

[timeout]

Lots of good advice for the OP to sort through. I have only had one 6 BR. I pierced some primers below 29.0 Varget with 105's. Everything was in order, so I shipped the bolt to GreTan. .062" firing pin and bush the bolt. I have never pierced one since. I only shoot mine to 300 - so far- and am shooting 28.8 Varget with the VLD's .120" off the lands. This is the best shooting rifle I have owned to date. I can only imagine what a good shooter could do with this rifle. I would imagine that were I shooting out to say 600, I would search for a higher node.

 

[mattlewis]

I was not running that amount of powder. I said that was the area that I ran into visible unsafe pressure.

I was running 30.1 gr touching the lands.

NOW, I am getting unsafe pressure signs even at 29.2 gr (that happened to be the lowest in a string of 4 charges I was going to test with)


I have never loaded for groups over 30.3 gr. I have tested for pressure with individual rounds over that, seated to different depths.

 

[Webster]

The Berger manual list 29.2 grains of Varget for the 108 gr Berger Bullet as max load.

 

[tenring]

IMO, max loads in the new Berger manual are on the conservative side.

 

[mattlewis]

Range report -

After using some JB, brushes, and elbow grease, I went back to the range. I fired 3ea at 29.2 29.5, 29.8, and 30.1 with no pressure signs. The 29.8 group was my personal best even.

I did still get dimpled primers (not flattened, not cratered, no extractor marks or sticky bolt), so I think I will go ahead and disassembly the bolt and replace the spring. I think there may be a fragment of primer in there or something from before. If that doesn't work I'll send I to Gre-tan to be bushed.

Thanks again for all the help.

 

[mattri]

Glad it worked out.