I have a 6 mm ARC AR15 but using 6.5 Grendel brass necked down. This rifle has 26 Bartlein barrel by Craddock and mainly used for steel out to 1,000yrds (once I get load development done). The dies, FL neck bushing from L E Wilson, were over sizing down by .0075 vs my 223 by .003. So Im having Whitten make me custom dies to be more inline with SAAMI specs and about .0025 down from fired brass (minus spring back of .001+-). This should cut stress on the brass and better fit chamber.
Next inquirer is bolt questions. I have the JP Grendel bolt so I think I have one of the best but still feel the bolt is the weak link for both Grendel and ARC. The Grendel bolt face ID measures .444 and the 223 measures .382 so the the wall thickness has been reduced by about half. What does your bolt face measure out to?
For you engineers and machines out there. Can you add back the lost thickness of the bolt face wall to the OD of the bolt face and to the OD of the lugs? Is there enough room to add those dimensions to the barrel extension? Would this bring the Grendel bolt strength back to a point that it could be considered safe at 60k psi capable platform?
Current OD for lugs is .740 Plus lost wall thickness of .0315 (x2) That would make lug od .803. The current extension id is .830 should make enough clearance.
Current bolt face OD is .530 plus .0315 (x2) is .593. plus needed clearance.
Keeping the lugs and wall thickness to 223 configuration. Wall thickness of .074 vs .0427 and lug hight of .179 vs .1475. I think the barrel extension can handle the change. I guess the question should be is a redesign worth the effort.
I think the extension can handle that change.
Measurement taken with Mitutoyo calipers and barrel extension drawing spec sheet.
What are your thoughts?
YMMV
Cheers
Philip
Next inquirer is bolt questions. I have the JP Grendel bolt so I think I have one of the best but still feel the bolt is the weak link for both Grendel and ARC. The Grendel bolt face ID measures .444 and the 223 measures .382 so the the wall thickness has been reduced by about half. What does your bolt face measure out to?
For you engineers and machines out there. Can you add back the lost thickness of the bolt face wall to the OD of the bolt face and to the OD of the lugs? Is there enough room to add those dimensions to the barrel extension? Would this bring the Grendel bolt strength back to a point that it could be considered safe at 60k psi capable platform?
Current OD for lugs is .740 Plus lost wall thickness of .0315 (x2) That would make lug od .803. The current extension id is .830 should make enough clearance.
Current bolt face OD is .530 plus .0315 (x2) is .593. plus needed clearance.
Keeping the lugs and wall thickness to 223 configuration. Wall thickness of .074 vs .0427 and lug hight of .179 vs .1475. I think the barrel extension can handle the change. I guess the question should be is a redesign worth the effort.
I think the extension can handle that change.
Measurement taken with Mitutoyo calipers and barrel extension drawing spec sheet.
What are your thoughts?
YMMV
Cheers
Philip