6BR chamber print

[krxm21]

anyone have a 6br chamber print that shows headspace dimensions with datum line? I'm trying to compare 6br and 6mm Creedmoor headspace

 

[AlNyhus]

The SAMMI website will show you the difference in case head-to-datum. -Al

https://saami.org/wp-content/uploads/2025/04/SAAMI-Z299.4-CFR-2025-Centerfire-Rifle-Approved-2-10-2025.pdf

 

[krxm21]

am i missing something? I don't see 6br on their website and the attached drawings don't give the datum dimension or headspace.

 

[Just Say Moe]

am i missing something? I don't see 6br on their website and the attached drawings don't give the datum dimension or headspace.

PM sent

 

[DaveTooley]

CIP specs

 

[Hengehold]

am i missing something? I don't see 6br on their website and the attached drawings don't give the datum dimension or headspace.

Same here. I don’t see 6BR listed in the link provided.

 

[AlNyhus]

I stubbed my toe on this one...it's a CIP spec'd cartridge, not SAMMI. Thanks to Dave for the link to the CIP pdf. -Al

 

[SKWERLZ]

anyone have a 6br chamber print that shows headspace dimensions with datum line? I'm trying to compare 6br and 6mm Creedmoor headspace

Datum for headspace or throat?
JGS prints have a very useful throat datum.

 

[Ray Gross]

It requires a little math to compare them. The 6 BR has a headspace dimension of 1.167 to the .350 shoulder datum. The 6 Creedmoor headspace is 1.541 to the .400 datum.

They are comparable because they both have a 30 degree shoulder. The datum can be converted to anything you want. For these two, you can split the difference and recalculate the headspace length to a .375 shoulder datum.

For the 6 BR it is 1.145349
For the 6 CM it is 1.562651

For those who want the math-

(original datum-new datum)/2 * cotangent(30) + original headspace = new headspace

 

[SKWERLZ]

Why would you put up a Print for the 6BRA

Because it’s the only print I had showing the throat datum and headspace datum from JGS.

 

[krxm21]

Thanks Ray, I'm trying get a little more performance out of a single shot that has been sitting around unused for quite awhile. Doing it on a budget - so I thought we could grind a spacer and attach it to my 6BR go gage with a small neodymium magnet. If it shoots as well after the conversion I'll shoot it at Perry for long range. Kent