6mm bores, .237 or .236 in 7.5 and 8 Twists

[AckleymanII]

I just went through hell trying to tune a .236 Bore in an 8 Twist, bore was uniform from end to end of the barrel at .236.

I have been a short range benchrest shooter and varmint hunter all my life, these new fast twists are very new to me.

It can be understood that the tighter bore will create more resistance and perhaps spike pressures, but is the .236 bore a deal killer for 7.5 and 8 Twist 6mm barrels?

Thanks in advance for all comments

 

[Pyscodog]

I'm in the same boat as Ackleyman. I built a 6 CM using a 7.5 twist with a .236 bore and my accuracy really sucks. Its bad enough the instead of Creedmoor, I call it Crymoor.

 

[swd]

I’ve run both sizes in F Open and don’t see any difference. If your accuracy sucks you’d better be looking at other things, it ain’t the bore size..

 

[Judd]

Brux has won a lot of stuff with a .236 and I shoot their barrels more than anyone else's. I haven't had that issue but I also feel most folks are over twisting now and I'm on the other end of the spectrum. Not sure if that has anything to do with it but thought it was worth mentioning....an 8 you shouldn't have problem with.

Sorry not much help but maybe we'll get a bump up and someone smarter than me will chime in.

 

[TAJ45]

Following.....

 

[LA50SHOOTER]

I just went through hell trying to tune a .236 Bore in an 8 Twist, bore was uniform from end to end of the barrel at .236.

I have been a short range benchrest shooter and varmint hunter all my life, these new fast twists are very new to me.

It can be understood that the tighter bore will create more resistance and perhaps spike pressures, but is the .236 bore a deal killer for 7.5 and 8 Twist 6mm barrels?

Thanks in advance for all comments

I've read where there isn't a nickel's worth of difference between either size in threads on here and common sense would dictate this to be true. One size may favor a certain bullet but that is not uncommon with any barrel(s). - I've also read on here in past threads that a 0.236 bore favors slower twists (i.e. 1-13.5" & 1-14") and lighter flat based bullets. - And the 0.237 is very compatible with the faster twists (1-8, 1-7.5) and the heavier bullets.
I wouldn't think a 0.236 should be a "deal killer" for the quicker twists. What bullets have you tried ?
@BartsBullets would be a good source of solid information I believe as he shoots both short range BR and 600 yd. with a 6mm and does it very well. And the fact that he also makes a wide weight range of 6mm bullets for both disciplines can't hurt either.
If it were myself, I'd try several different bullets as a first step and hopefully some of the real experienced guys will chime in. - I've shot a 6mm Norma BR for a few years (1.7.5 & 1-8 twist 5R barrels) and have had decent luck but I'm running a 0.237 on both and my experience is limited.

Good Luck

- Ron -

 

[HTSmith]

As far as I know Brux only makes .236 and I have one in 6BR, 7.5 twist. It shoots Berger hybrids good and it was easy to work up a load. (Course I used a top secret load--30 Gr. Varget) I don't think the bore size is the issue.

 

[TAJ45]

I'm really interested as to what the real culprit is. Knowing the OP and his shooting and chambering abilities, his tenacity for methodically running down variables ...... It will be interesting, yup.

 

[Rdlningcltchdmpr]

Food for thought., Sometimes you might have to try 7-8 different powders just to find the one ! I have seen this many times. Even when many powders make about the same speed , one of them will be great ! The others not so much !

 

[swd]

I'm really interested as to what the real culprit is. Knowing the OP and his shooting and chambering abilities, his tenacity for methodically running down variables ...... It will be interesting, yup.

Every great now and then a bad barrel makes it out into the real world..

My last .236” 8” Krieger was a hummer.

 

[TAJ45]

I had a top Quality bbl once and it looked like they tried to rifle it from both ends.....almost. A definite mfrg "OOPS". It was made good however.

 

[Pyscodog]

My barrel is a Bartlien, 6mm, 5R, with a .236 bore. Its chambered in 6 Creedmoor with a minimum spec reamer. Basically a no turn neck but tighter than SAMMI. I have tried everything from 68 grain Bergers to 107 ELD-M with no less than 7 or 8 powders. From kissing the lands to .140 off. I'm not a BR shooter but I can shoot groups. The rifle was a NIB 700 Remington 243, stock was a NIB Stocky's Long Range Composite and a NIB Bushnell Forge. Ackleyman checked my barrel and couldn't find anything wrong with it but I'll be damned if I figure out why it won't shoot. I have 289 rounds through it and one group that was a half inch and it wouldn't repeat itself the very next day with the exact same load. One 5 shot group out of 289 rounds is depressing.

 

[TAJ45]

Arrrggghhhh for sure. :-/

 

[Dusty Stevens]

Youll never know the difference in reality.

 

[Pyscodog]

Its bad when the factory sporter barrel shot better than one I have so much money in.Maybe I should put the sporter back on and use the Bartlien for a tomato stake. LOL

 

[Roeder]

Its bad when the factory sporter barrel shot better than one I have so much money in.Maybe I should put the sporter back on and use the Bartlien for a tomato stake. LOL

For as bad a result as that, there is likely something else contributing to the issue. It could be a lot of things. I have a BAT B that wouldn't shoot with a Bartlein 8 tw .237 bore. The action was a multi flat and the scope rail had a bit of clearance so that it didn't lock up on the adjacent flats. The large, heavy scope (NXS 12-42) was enough that the rail shifted position from recoil. Once I bedded the scope rail, things improved dramatically. I had fitted a second barrel by the time I discovered the problem, so I now have 2 excellent barrels. Obviously not your issue, but it can be necessary to look at everything; bedding, ignition, action, barrel, and certainly scope and mounting. If the action threads are out of parallel and the new barrel is fitted tight, there could be a problem with the joint that the factory barrel wouldn't have exhibited.

 

[swd]

Its bad when the factory sporter barrel shot better than one I have so much money in.Maybe I should put the sporter back on and use the Bartlien for a tomato stake. LOL

Send it back to Bartlein and have it checked out. If they built a bad one they want to know about it and will replace it.

 

[Terry]

How fast are you pushing the bullets? There are many nodes from 2800 to 3000 fps.
More than once has slowing down produced better results.

 

[Pyscodog]

I called Bartlein, I asked if I could send them my barreled action to check out. They said they didn't do that. They recommended having it setback and a new chamber cut. Thats another $300. I didn't like that idea to much. Ackleyman gave me some tips to try, checking max load and velocity was one of them.

 

[AckleymanII]

I did not chamber Psycodog's 6 Creed barrel, just trying to help the guy out.

The particular barrel that I was working with exhibited premature pressure signs in a six Dasher compared to what most people shoot. I backed the loads off around two grains, and found nodes. Nodes seemed to be very touchy from day to day...my first Dasher eight twist with .236 bore.