6mm bra

[Adrain]

Hey guys , anyone noticed donuts in their 6mm bra brass. I'm getting them after as few as 3 reloads. New Lapua brass , Fire formed ,105 Berger Target vld, 31.5 gn Varget , crono at 2817, brux 30in 8 twist Jamed 9 thou in. Will this condition hurt performance.

 

[ngb1787]

Yes and turned necks fixed issue,

 

[Fire Dog]

I only neck size and shoulder bump, clean and anneal {AMP} @ time.
I run the neck bushing down as far as possible and still allow enough movement to allow the case neck to centre.
A very small and slight doughnut is present but since it is just at the start of the neck it fits right into the chamber and if anything it is an aid to centering the round in the chamber..
A NO neck turn chamber and a 1:7 twist Hardy barrel running Berger 108's that are hBN coated and just touching, 5jump, 17-20jump.
30.2gr of 2206H {H4895} & CCI-450
No problem so far on about 6 loading's, primer pockets tight and brass chambers fine.
Sold off my 21st Century neck turning setup as I just cannot be bothered and the NO TURN neck chamber shoots as good or better than the original "tight" one in the last barrel.
Cheers,
Fire Dog

 

[Adrain]

Yeah I have a 272 no turn neck chamber, donut is inside the case, but bullet is seated out away from the donut , just didn't know if it would cause a pressure spike , still trying to get a handle on the 6mm bra , my 6mm br will shoot 1.2 in at 600 if I do my part , 6mm bra can't get below 3.5 , should do better with 33lb gun

 

[Jeffrey Tooker]

Yeah I have a 272 no turn neck chamber, donut is inside the case, but bullet is seated out away from the donut , just didn't know if it would cause a pressure spike , still trying to get a handle on the 6mm bra , my 6mm br will shoot 1.2 in at 600 if I do my part , 6mm bra can't get below 3.5 , should do better with 33lb gun

There are many on this list who are better qualified than I to answer this problem. Adrain is correct the donut is on the inside. There are arguments fore and against removing donuts. When one is using a bullet where the shank of the bullet is either close to the donut, or passed the donut and or the neck shoulder junction, removal of the donut is essential to avoid pressure problems.

However what I was taught about removing doughnuts was this:

Run a 6 mm M die into the neck, passed the donut. This should put the donut on the outside of the case. Now turn the neck to remove the
donut. Remove the donut only. Be careful not to cut into the neck shoulder junction as this will weaken the case. Whether you turn down the
actual neck is a matter of choice. Please correct me if I am wrong.

Jeffrey

 

[Adrain]

Thanks for that reply, thats something I have done on this cleanup we were both thinking along the same lines . Going to a heavier bullet and could have been a burr under my saddle. Brass has been annealed really didn't want to break out a new box of brass after only three firings, and i am not hot rodding load.

 

[Jeffrey Tooker]

Thanks for that reply, thats something I have done on this cleanup we were both thinking along the same lines . Going to a heavier bullet and could have been a burr under my saddle. Brass has been annealed really didn't want to break out a new box of brass after only three firings, and i am not hot rodding load.

Quote from post one:
Hey guys , anyone noticed donuts in their 6mm bra brass. I'm getting them after as few as 3 reloads. New Lapua brass , Fire formed ,105 Berger Target vld, 31.5 gn Varget , crono at 2817, brux 30in 8 twist Jamed 9 thou in. Will this condition hurt performance.

Adrain:
In post #4: "my 6mm br will shoot 1.2 in at 600 if I do my part , 6mm bra can't get below 3.5 , should do better with 33lb gun", You say your
6 BR is shooting well. Check for donuts on your several times fired 6 BR brass. Are the donuts in the 6 BR the same as, more than, or less than the donuts on the 6 BRA brass? Since the 6 BR shoots well this should tell you whether the 6 BRA donuts are a problem.

The accepted premise is that 40* shoulders (6 BRA) allow less brass flow than 30* shoulders (6 BR). Therefore under the same conditions donuts in 6 BRA should be less than in 6 BR. Since the loads in the first post above seem to be fairly normal loads, it may be that the supposed donut
problem is un related to the 3.5" grouping problem in post #4 quoted above. Has the "33lb gun" been shot before with a different barrel and shot well, or is the whole "33lb gun" new?

Jeffrey

 

[Adrain]

Checked out 6br brass no donuts , and yes had a barrel that wouldn't shoot anything, put new barrel on , most problems went away , the first barrel had issue in mgf. And I started over with fresh brass , out of that lot , 50 went to 6br , 50 went to 6bra out of that 50 , 32 have donuts , 18 have no issue , and 1 , well some times you just muck 1 up . Looks like I just need to break out a new box of brass , still less than 275 round down tube, tested some of the good and bad today and there was a major poi difference between the two at 100 yds good brass stayed bunched up bad brass threw flier's.

 

[Jeffrey Tooker]

Watch your new brass very closely. First what will you be using for fire form loads? Someone on this thread should have a fire form load.
The load will be a light load even for a 6 BR case. I was cautioned by a very good 6 BRA shooter to make sure that FF loads are light. I am using IMR 4064 for FF and he said 29 gr or less. IMR 4064 speed is between Varget and H 4895. Your 31.5 gr of Varget (in post #1) is is a fairly normal load for 6 BRA with bullets in the 105 gr range. However I think is is a bit hot for FF. Check your FF cases for donuts from the very first case. I have formed other cases but no 6 BRA yet. BRA barrel is supposed to arrive from Kelbys tomorrow. I believe your donuts may be appearing during FF as this when the brass moves the most.

You might try try removing the donuts in some of your bad brass (see post #5) and see if you quit throwing flyers.

Jeffrey

 

[Adrain]

Will be using 107gn smk mixed leftovers, 28gn Varget load Jamed 10 thou , I tried running a .241 mandrel in bad brass to push donuts to outside of brass , then lightly trimmed the offensive area down, it helped but I decided to quit chasing that dog , still had flier's , I shoot in IBS 600 comp so need to step up and run good brass . Thanks for your help Plan to run ,105 Berger VLDs , with 30.6 H4895 , cronos average 2922fps.

 

[JMayo]

See ya at Piedmont !

 

[Jeffrey Tooker]

Will be using 107gn smk mixed leftovers, 28gn Varget load Jamed 10 thou , I tried running a .241 mandrel in bad brass to push donuts to outside of brass , then lightly trimmed the offensive area down, it helped but I decided to quit chasing that dog , still had flier's , I shoot in IBS 600 comp so need to step up and run good brass . Thanks for your help Plan to run ,105 Berger VLDs , with 30.6 H4895 , cronos average 2922fps.

Sounds like you are in the right place. Best of luck.

Jeffrey