Need some help with a 6BRX problem...

C

cginaz

Guest
I set up two rifles in 6BRX last fall. Both for long range BR, one LG and one HG. Bat actions, Kreiger 30” 1-8 barrels…all good components.

The load that has worked best in these guns is 108 Berger BT, 32.4gr Varget, CCI450 primers and Lapua 6BR brass fireformed with 29.5 of same powder. Match load chronographs at just over 3,000fps. Both guns have shot screamer groups, small aggs and high scores at 1K with no problems until the cases have been fired three times. Then…problems. I can’t seem to get more than three firings per case.

The primer pockets start to loosen on the second firing, get looser on the third and on the 4th or 5th firing blow out primers in half the rounds I try to fire. I see no signs of pressure until the primers start blowing. Happens at 80 degrees or like today at 45 degrees with same charge. On Quickload the pressure seems reasonable, 55,980 for this load. I’ve had the same experience with brass from the older type boxes and recently with a batch of the new blue box brass. It doesn’t seem to be unique to any one batch of brass. All charges are carefully weighed, bullets jammed .015, .001 neck tension.

My question is have others shooting 6BRX or Dasher experienced any thing like this? How long should new Lapua cases last in this chambering? Is is unreasonable to expect 3,000 fps from this round with a charge like 32.4 Varget with the 108’s?

I’d appreciate any thoughts and comments on this problem and as to how I might solve it.

Charles
 
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I'd check your chamber body dimensions if the brass is hard to resize.

If your chambers are oversize by 0.003" or more that may at least be part of the problem.
 
Charles
I used 31.5 grains of Varget in a standard 6BR for almost 10 years so your load seems reasonable to myself.
What I have found in the last 5 years is your brass needs to be shot twice with weenie loads before you do any case work at all.
In the good old days of 2002,2003 you could pull the 6BR brass out of the box and fil it with powder.If you try that today you'll lose alot of cases.
I would take 5 brand new cases and without touching the primer pockets or flashholes I would load 30 grains of varget into them and seat a bullet.After doing that twice load those same 5 cases and see how many times they will reload before the primers loosen up.
Lynn
 
First a disclaimer: Odd things happen. I remember when Dave Tooley made up a new set of cases for his 7mm BooBoo, and kept blowing primers. He never could find the reason, and Dave is a very smart, very experienced gunsmith.

Having said that: the web and below portion of a case is not supported by the chamber, it is hanging into space. It is also not resized with normal dies. If the pressure is too high for the brass in that region, it will grow, and part of that growth is primer pockets loosening. When you say "no signs of pressure" I assume you didn't mike the casehead with the virgin case, and after each firing. That is the most reliable indicator of too-high pressure, where "too high" applies to use, not some number.

So again with the disclaimer, I'd say that the pressure with the load you're using, in your rifles, with your brass, approaches too high. Certainly too high for good case life.

It doesn't matter what Quickload predicts, or other people shoot. For some reason, you are getting too high pressure. In passing, you should also be getting a bit higher velocity than what Quickload predicts or people using the same load without pressure get, but that's a *should*, not a guarantee.

OK, Lynn's response will help if the cause is slightly soft brass. The only way most of us have to work harden brass is to fire it. Each firing will harden it some. If the pressure used isn't too great for the case head, it won't expand much as it hardens. As it gets harder, it will accept more pressure without as much growth.

You could also try forming cases from the older Remington 7mm BR brass. I would doubt it would help, but it is an option.

You could try changing powder. As a gross generalization, Varget shoots best at high pressures. Rel-15 might be more forgiving, e.g., very good accuracy at slightly lower pressures. The same for H4895.

Good luck
 
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Thanks for the feedback guys. I'm going to try the test Lynn suggests tomorrow measuring the web and checking the primer pockets after each firing until they start blowing. It should give me a better idea of exactly what's happening.

Charles
 
Charles G
When you do your testing use 3 pieces of fully prepped brass with your regular load as your baseline.

On your other brass DON'T touch anything on your primer pockets at all.
I will e-mail you a link to a Lapua article on there brass.
Lynn
 
Charles,

I have been shooting two different BRXs. They both have .272 no turn necks and use Lapua brass. It would seem that you either have a small chamber or a fast bbl. I use a grain more powder than you to get similiar velocities with a 107 SMK.

Have you looked at the throat with a borescope? Might you have a carbon ring formed up there that is driving your pressures up?

Is you neck thickness still at new specs?

I am on at least 10 firings with my Lapua brass and no problems with either primer pockets or case life. My cases are annealed after four to five firings to keep neck tension in check.

My shooting is NRA prone at 600 and 1L yds.

Bob
 
bob3700..

Glad to hear someone is getting 10 firings. Gives me hope. My guns are both .272 necks also and I do check the throat with a borescope at each cleaning.

I'm going to give Lynn's suggestion a try and see what happens to some new cases each time I fire them.

Charles
 
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Charles........I am also shoot a BRX using 33 gr. Varget with a 108 Berger out of a 28" Brux with Fed. 205M primers and getting 2910 fps. I am on my 9th. reload and have no pressure signs or blown primers. I have three friends whose barrels I chambered with the same reamer (.272 no turn). Two of them have no problem what so ever but one has had nothing but problems with blowing primers. Even on lighter fireforming loads? We have done everything from rechambering to getting a new barrel and yet, he is the only one having a problem?
Rich De
 
Rich, the "other" Charles said

32.4gr Varget, CCI450 primers and Lapua 6BR brass fireformed with 29.5 of same powder. Match load chronographs at just over 3,000fps.
Click to expand...

So he's using .6 grains less powder, but getting about 100 fps more velocity. The pressure in his rifle is up there. Any number of reasons .236 lands vs 237 lands?

Whatever the reason, suppose he backs the load off to the 2,900 region. If it's accurate, problem solved. If not quite as accurate, you have a choice: shoot it, and trash cases after 2-3 firings, try a different powder, or accept the accuracy of the load that is within the safe pressure region.

Also worth trying is Lynn's suggestion of work hardening the cases with a couple firings using a bit milder load

(but not what edlongrange mentioned -- it isn't a sizing issue. And when you anneal, brass doesn't change until you're over 670 degrees F or so. At that point the brass turns a silver hue, and you an see it quite plainly. Possible, but I'd strongly doubt it).
 
Rich De said:
Charles........I am also shoot a BRX using 33 gr. Varget with a 108 Berger out of a 28" Brux with Fed. 205M primers and getting 2910 fps. I am on my 9th. reload and have no pressure signs or blown primers. I have three friends whose barrels I chambered with the same reamer (.272 no turn). Two of them have no problem what so ever but one has had nothing but problems with blowing primers. Even on lighter fireforming loads? We have done everything from rechambering to getting a new barrel and yet, he is the only one having a problem?
Rich De
Click to expand...

Hey Rich Old Man, how about the firing pin. I had one Panda that would not hold primers like the rest. Got Terry Leonard to look at it (he can see) and he said the pin hole was oblonged. Sent it to Greg Tannel and problem solved. That Panda at the time had probably 30-40k hot 6-40 Dune loads through it though.
 
Good input. Thanks to all.

I'm going to do a few tests tomorrow. Start some new cases and try some older ones with different powders. There's gotta be a solution.

Charles
 
Jerry..........the hole actually looked OK and I did fit one of Hollands new oversize firing pins. Plus, we used a bot from another Remington with the same results.
Rich De
 
For those interested I did some testing today starting with 5 new cases in my LG. I fired each case five times with no sizing at all. There was just enough tension to hold the bullets after the first firing. I fired 2 at 30gr Varget/CCI450 2,885 fps and three at 32.4gr averaging 3,021fps. Temperature went from 45 to 55 degrees while I was testing.

Measurements at the web started at .4675 for new cases and increased to 4.685, .469, .470, 4.705 and 4.705 on each firing. Primer pockets were very snug when new, stayed snug for the two low charge firings then loosened more on each subsquent firing until after the fifth firing they were looser than I would feel comfortable using. The cases REALLY needed FL sizing after the third firing but I was unable to do this at the range so jammed them in and shot them anyway.

Conclusion so far is that with this load I can’t count on more than three full load firings after fire forming. Not good. A lot of trouble for 150fps more than I got easily from 6BR. I’m also starting to see heat cracking on one BRX barrel after only 750 rounds.

Tomorrow the HG which seems to have a somewhat larger diameter chamber in spite of being chambered with the same reamer. I have a feeling it’s going to be even worse.

More to follow…

Charles
 
Charles,
this is a very good thread=
enjoying it very much=
I have several 6BR's and several 6BR improved's=
It is very surprising how much difference in throat erosion
can be observed between say: a 6BR and a 6BRX or 6 Dasher=
those approx. 3 grains of powder make a very big difference
in barrel life = all others variables being the same=
Pleas post your other observations=
thanks much
Doc Stone
 
"Other Charles"

Couple of things to think about:

(1) A number of rifles shoot best at pressures which quickly destroy cases. Jeff Rogers in Australia shoots a .30 on an RWS 8x68 case very similar to one I use. RWS brass is as tough as it comes. But his cases need the head resized (primer pockets tightened) after three or so firings, he shoots that hot. He also holds most of the Australian 1K benchrest records. I've noticed that when the rifle starts to give more of a crack when fired, accuracy is a bit better. And primer pocked loosen. I'm not alone in noticing this.

So, you have to decide whether or not that slight improvement in accuracy is worth it to you. There are ways to resize the case head (tighten the primer pockets) of cases. Someone will have to make you dies if that is the route you want to go.

(2) It is a bit quick to say the BRX destroys cases at 150 fps over 6BR velocities. What barrels are involved? Particularly their diameters. And barrels just differ. But if so, so what? There should be several accuracy "nodes" in a 150 fps spread. How do the rifles shoot one node down from 32.4 grains of Varget in your rifle? How does it shoot with Rel-15?

alinwa, who posts here a lot, is convinced, with evidence, that he can shoot hot and get a lot of firings on a case. His method is to use a lot of clearance in the chamber, and season the cases along the lines Lynn suggested. I've never tried it, and don't know of anyone who has, but he's a reputable source with a range at his home, which allows for a lot of testing. Search the archives for his views.

And finally, all this stuff is compromise. You can push a 6mm bullet far faster than 150 fps over a 6BR. It's called a 6mm/06 Or a 6mm/284, full length. Or a 6mm Ackley (7x57 case improved). Yup, barrel life goes way down. What's important, barrel life, or winning? I'm getting old enough that winning may not be first on my list, hard as that is to say. How about you? Cost of cases and prep time versus cost of barrels -- always assuming you need that speed to win.

Or, maybe the big 6mms respond just the same -- more accuracy when pushed to case-destroying pressures. Ask Lynn about the accuracy of his 6/06 sometime. If it was anything like the Cass brothers (now retired), they shot real small around 3,600 fps. And cases didn't last.

etc.
 
cginaz said:
Measurements at the web started at .4675 for new cases and increased to .4685, .469, .470, .4705 and .4705 on each firing. Primer pockets were very snug when new, stayed snug for the two low charge firings then loosened more on each subsquent firing until after the fifth firing they were looser than I would feel comfortable using. The cases REALLY needed FL sizing after the third firing but I was unable to do this at the range so jammed them in and shot them anyway.



Charles
Click to expand...
Still sounds to me like the chamber body may be oversize. Take a new 6BR brass and insert it, primer end first, into the chamber. If it goes in over just barely starting, the chamber may be too large. If that is OK, obtain a lead slug and slug the barrel bore. Your bore may possibly undersize also.
 
Lynn…Thanks for the offer of a reamer. I think I’m going to stick with the BRX until after the April Nationals. Then we’ll see.

Charles E….Thanks for your comments. My LG barrel is a Krieger 5R 30” HV and my HG is the same but straight 1.25. They’re both .237/.243. I did try a couple of groups with 32gr RL15 this week. I got very good groups with 108’s (around .40 at 200yd) at an average of 3018fps E.S.16 SD 6. According to Quickload this load should have been generating about 3,000psi less pressure than my Varget load. I’m going to pursue the RL15 load a bit further and may switch.

You’re right about it all being compromise. At this point I’m more interested in winning than saving money so will just fire form the BRX brass once and then toss it after three more firings. Seems I can count on it holding up that long. I’ve got a fireforming barrel that makes the process somewhat less painful.

As a final follow-up today I did the same test as yesterday with my HG. Results were just the same as the LG. Two light charges left the pockets tight and then over the next three with full loads they loosened to the point that I would not try a 6th firing at a match. They only real difference I noticed is that 5X brass from my HG measured .473 at the web vs. .4705 from the LG. Same reamer. Who knows why? 5X fired unsized brass chambers and extracts better from the larger chamber.

My conclusion is that if I want to get 150-200 more fps than from 6BR with the same bullet I’ll just have to be satisfied with much less brass life and also less barrel life, at least in the rifles I have chambered with my reamer.

It’s been interesting to explore this and I’ve got a lot better understanding than I did of whats really happening in my chambers. Thanks again for all the comments.

Charles
 
brass

I had a Krieger on my first Dasher and you could only get a little more then 2900 with 32 grains of Varget. Right at max for pressure but gun shot really good. Now i have a Broughton 34.1 grains of varget at 3075 and no pressure. A lot of variation between barrels and brands. Case life is good with both barrels. I think you need to look at accuracy nodes for each barrel. Both guns shot equally well within their nodes. Matt Kline
 
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