6BR pressure signs low loads

[pdhntr]

It’s the second firing that got the heavy bolt lift and ejector marks.

I agree with boltfluter. Try to find the area in the chamber (on the case) that is giving the issue of hard bolt lift. It can be hard to cut a case with a hack saw, but it doesn't take long to file it down in steps, and as he said, it works very well.

You also mentioned coloring it, that can work also.

Interesting problem, good luck.

Jim

 

[Dolomite]

I agree with boltfluter. Try to find the area in the chamber (on the case) that is giving the issue of hard bolt lift. It can be hard to cut a case with a hack saw, but it doesn't take long to file it down in steps, and as he said, it works very well.

You also mentioned coloring it, that can work also.

Interesting problem, good luck.

Jim

I have a dremel, going to try and make it to the range to get some fired cases...

 

[Dolomite]

Measure before and after sizing at the csj and the .200 line as well as the length to record the amount of sizing your die is capable of.
Below I’m comparing two different dies, the one on the left gives me clickers

Funny thing I did that and the Redding is only getting the base down .0005. I had the same issue with my 308 and ordered a custom die from Whidden. Should be here in a month or 2.

I have a Forster FL non-bushing die on the way and I can check to see how that sizes the brass.

I wonder if I need a custom die from Harrels or Whidden?

Maybe a SAC die would work as it suppose to size the base smaller but $375 all in is hella expensive.

 

[243winxb]

I was trying to avoid neck turning

You measurement seem to point to no neck turning needed? But if the loaded rounds OD is like the drawing, turning is a must do. The
.2717" at the neck shoulder junction looks like a pinch point?

 

[Dolomite]

You measurement seem to point to no neck turning needed? But if the loaded rounds OD is like the drawing, turning is a must do. The
.2717" at the neck shoulder junction looks like a pinch point?

Is there a rule of thumb for enough neck clearance? like .004 would be a minimum clearance before having to neck turn?

 

[Dolomite]

Loaded round




virgin brass



I wonder if a non bushing die would size that part of the neck down better?

 

[Dolomite]

You may have found your problem .0005 is not enough sizing at the base, how about the CSJ measurements ?
Wilson makes dies.. so does Hornday , name on a door doesn’t mean squat only thing that matters is dimensions

Would the base be causing the high pressure or just a clicker?

My 308 would have the heavy bolt lift at the top stroke or clicker. Didn’t have any pressure signs.

 

[holstil]

No sizing lube left on cases right?
you chronographed both virgin and resized firings?

 

[Dolomite]

No sizing lube left on cases right?
you chronographed both virgin and resized firings?

yes I tumbled the cases after sizing. yes chronoed both virgin and resized and its about the same, in fact the speed dropped 20 FPS on the sized brass.

I guess the barrel still needs break in, I'm waiting to see if the barrel speeds up.

 

[holstil]

Try a cpl cases after sizing without tumbling.

 

[Dolomite]

Clickers’ mainly but I think that comes as the case expands under increased pressure
.270 That’s pretty tight for a .272 neck

CSJ is .459 sized and .461 fired.

I'm currently using a redding bushing die, I have a Forster FL die coming to see if that would make a diff.

If I end up with clickers definitely going with another custom die.

 

[Dolomite]

Try a cpl cases after sizing without tumbling.

that would be another good test, I thought the lube on the case affects the ability of the brass to grab the sidewalls of the chamber which causes heavy bolt lift and pressure signs on the brass face?

 

[holstil]

I believe it does.

 

[holstil]

I don’t like shiny chambers or brass.

 

[243winxb]

Loaded round. I wonder if a non bushing die would size that part of the neck down better?

The loaded measurement is taken where the bushing has sized.

Loaded round .270" ? Neck chamber .272" ? The bushing is not an issue, unless its hiding a donut.

A bushing die can NOT be used when neck turning.

 

[holstil]

I used bushing dies and turned necks. Haven’t seen any issues there. Lil more room for brass to flow.

agree about the .002 I’ve run them way tighter without causing pressure signs.

 

[AckleymanII]

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

 

[Northridge]

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

 

[Albany Mountain]

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 breaking the battle in. Later 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.

 

[Whisky Tahoe Foxtrot]

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.