6BR pressure signs low loads

[Northridge]

have you tried any other bullets ? some times weather it be a tight bore or a bullet that simply buildss pressure at a quicker rate than other offerings can result in a situation as this. was this new brass when you started or brass from another chamber?

Shawn Williams

 

[Tokay444]

Just an observation and a pointer, use the upper portion of the your caliper jaws. Not the points.

 

[Murray Brook]

@1sickPuppy I have a Forster FL die and it sizes the 200 line to .4694. Also have a Redding body die and it sizes the case to .4704. So far no clickers.

 

[Dolomite]

My new rebarrel in 6br resulted in a tight bolt the first 3 rds. I used 30 gr Varget which was the only load I used for 4000 rds in the previous barrel (of the same specs). I dropped two grains to finish break in the ladder test from 28 gr upwards still had hard lift most the time and hard extraction. I had mostly “clickers” with most of the twenty ladder loads. The chamber was tighter than my other 6br and my small base harrel full length die, still resulted in clickers. So I lightly lapped the body of the chamber with a fired brass with the shoulder removed and now everything is fine, no clickers and 30 grain or higher loads don’t show the pressure signs.

that is interesting info, I'll try bump the loads like the others stated and see what happens.

 

[Dolomite]

Possible problems:

Lube in the chamber will cause extremes in bolt thrust.

Bolt face may not be square.

Light loads can be problematic, not enough pressure to seal the case against the chamber wall, brass is slammed back against the bolt face.

Round primer indicates that there is no high pressure....look elsewhere

I cleaned out the chamber with some alcohol.

I'm assuming the bolt face is square since its a custom action from terminus.

I'll try bumping up the load some and see what happens.

 

[Dolomite]

excessive over sizing can have this affect also, have you actually verified sizing with proper tools? assuming based off die directions on how to set up a die can be trouble some.

Shawn Williams

Yes followed die instructions, Based is sized .0005 smaller, CSJ is .0015-.002 smaller.

I'm using the Whidden head space gauge to verify I'm bumping .002.

 

[Dolomite]

@1sickPuppy I have a Forster FL die and it sizes the 200 line to .4694. Also have a Redding body die and it sizes the case to .4704. So far no clickers.

That is great info, I was wondering about the Forster FL die as I have one coming in the mail.

 

[Dolomite]

After reading all posts, I have to say this is an excellent discussion and curious given that pressure and velocity aren't interacting as expected.

6BR brass expansion at the case web is well documented and there are several die manufactures offering small base versions. I have found that the clearance is beneficial so I do what I can to avoid clicky bolts.

As already suggested in a previous post, consider trying some small base resized brass and observe those fired cases. If the expanded brass from your Redding dies is contributing to ejector wipe, it would be interesting to see if the wipe marks are reduced with slightly smaller case web diameter from a SB die.

That is interesting info or a good test.

I do have a RCBS small base die that I might me able to use on the BR brass. Not sure if its going to size the body down too much along with the base.

For my 308 it sized the body and the base down quite a bit, have you tried using a small base die? Did it size the body down too much?

 

[Dolomite]

have you tried any other bullets ? some times weather it be a tight bore or a bullet that simply buildss pressure at a quicker rate than other offerings can result in a situation as this. was this new brass when you started or brass from another chamber?

Shawn Williams

Started with all new brass since this is my first 6BR. I just shot 105 Bergers and 95 Bergers, which I'll post the results shortly.

 

[Bill Norris]

My 6BRX Wilson F/L bushing die sizes the 200 line @ .4695 with no clickers. I'm bumping the shoulders back @ .002 with ease and no shell holder mods.

 

[Whisky Tahoe Foxtrot]

That is interesting info or a good test.

I do have a RCBS small base die that I might me able to use on the BR brass. Not sure if its going to size the body down too much along with the base.

For my 308 it sized the body and the base down quite a bit, have you tried using a small base die? Did it size the body down too much?

SB dies should always be the SAAMI minimum chamber spec.
They are handy for fixing brass fired in another chamber.

 

[Dolomite]

My 6BRX Wilson F/L bushing die sizes the 200 line @ .4695 with no clickers. I'm bumping the shoulders back @ .002 with ease and no shell holder mods.

would you happen to know the base size of your chamber? I'm trying to figure out how much spring back is normal for a sized .4695 base.

 

[pdhntr]

I have chambered half a dozen barrels for myself in the last 10 years or so. .236 and .237 Krieger and Bartlein. Shot Varget in all of them. I know this is only a test example of one, but I think, using a load of 28.5 with a 105 gr. bullet, I could neck size only for two or three loadings. In my light rifle I am at 29.7 and can close the bolt on a once fired case with slight pressure.

Your case expanding (at .200) to cause problems at 28.5 grains of Varget just doesn't make sense to me. However, I could be totally wrong.

Is it possible who ever chambered this used a 6Br Remington reamer? Not sure if this could cause the problem but just trying to help. Again, good luck.

6BR Remington discussion

Jim

 

[Dolomite]

I have chambered half a dozen barrels for myself in the last 10 years or so. .236 and .237 Krieger and Bartlein. Shot Varget in all of them. I know this is only a test example of one, but I think, using a load of 28.5 with a 105 gr. bullet, I could neck size only for two or three loadings. In my light rifle I am at 29.7 and can close the bolt on a once fired case with slight pressure.

Your case expanding (at .200) to cause problems at 28.5 grains of Varget just doesn't make sense to me. However, I could be totally wrong.

Is it possible who ever chambered this used a 6Br Remington reamer? Not sure if this could cause the problem but just trying to help. Again, good luck.

6BR Remington discussion

Jim

thanks I confirmed it’s a 6BR Norma used in PRS style shooting. I verified with a borescope using a fired case OAL 1.553 and there is lots of clearance for growth.

 

[Dolomite]

Shot a few test rounds today different bullets and weights. 105 Hornady BT, 105 Berger Target and 95 Berger Classic.

Some notes from todays sample.

105 gr bullets - 27.3 grains varget 2530 FPS avg (28.5 grains carget 2575 FPS) Maybe barrel not broken in yet?
95 grain - 29 grains varget 2750 FPS avg

Clean Barrel
Lock Ease
Clean and dry chamber
Neck Tension .001 (plan on increasing this to .002-.003)
Didn't anneal the case - (different from previous fired case)
Lapua 3x fired - Bullet now drops freely into neck
Horrible SD and ES
Tested BR4 and CCI400 - BR4 about 15-20 FPS slower than the CCI400
Bolt lift slightly less but a tad heavy - Ejector taken out for testing
Case OAL shrank .001
Neck OD fired case .271
CSJ OD fired case .461
Base .4695 at .200 line
Group were decent avg .3

Based on the advice someone mentioned about marking up a fired case, chamber it and look for contact points to narrow down where on the brass may have an issue.

Chambered the fired case (firing pin removed from bolt) and no evidence of clicker just heavy bolt lift.

I have marks on the brass below the shoulder body junction, one side of the neck and none on the base.

Anyone know what does that mean? Is my die over sizing or under sizing the shoulder area?

.461 CSJ fired
.459 CSJ sized

Any comments or suggestions will be greatly appreciated.

 

[boltfluter]

Bolt face has no burrs I double checked. I’ll try another lot of varget.

I’m not sure why I get heavy pressure and low velocity. is that from the powder being too fast?

I wonder if I could color up a piece of fired brass insert it into the chamber and look for any rub marks? If not I’ll try and find a way to cut up the brass as you mentioned.

I do have a 308 small base die which I could try. Would it be sizing the upper body of the brass too small? The 308 small base die really squeezes the upper portion of the brass down a lot.


I believe the blown out shoulder is causing by the heavy pressure which is causing the heavy bolt lift.

Yes, to a fast lot of Varget. A buddy has an 8 pounder that is unusable in his 6 Dasher. A standard .308 die is what I meant to say. Just sizes the base and nothing else. I honestly believe you have two problems going on here.

Paul

 

[Bill Norris]

would you happen to know the base size of your chamber? I'm trying to figure out how much spring back is normal for a sized .4695 base.

Will check my print

 

[Bill Norris]

Will check my print

My reamer print is showing .470 @ the 200 line.

 

[RustyInBend]

One way to eliminate "powder" and/or "primers" is to load a few at an obviously low charge ... for several hundred fps lower ... and shoot them. If you still see the same pressure signs, then something about the case and/or sizing is the issue. Just a thought ... probably not very helpful.

 

[Tokay444]

He’s already too low in charge weight and that could be part of the issue.