6mm ARC
- Thread starter MoDiver90
- Start date
No. Also I do not recommend light bolt carriers.
No...absolutely not. Do not even attempt to try. I have 2 AR-15 6 mm ARCs with adjustable gas blocks and load to the gas gun pressure. It's the weak bolt THAT cannot handle high pressure ! ...LOOK HOW THIN THE MATERIAL IS THAT IS LEFT IN THE ARC/ GRENDEL BOLT!!! Ya don't want pieces bolt lugs stuck in your skull, or eyeballs. I can't believe it does as well as it does with the gas gun pressures...this is definitely the maximum head dia of a cartridge that one should use in the normal AR platform...I actually can't believe gun designers thought it was a good idea! You'd need an AR10 with an adjustable gas block to run higher pressures of the bolt 6 ARC ...or a bolt gun that has sufficient material to support higher pressures. Do not push the 6 mm ARC gas gun in this instance Max is definitely Max...besides it will work well at those lower gas gun velocities. Want bolt gun velocities get a bolt gun....I like the 6 mm ARC in the gas gun, I have 2 of em, but went to the 6 dasher in the bolt gun because it's a much better option for me...I'll probably never own an ARC bolt gun...Seriously bottom line...if ya want bolt gun velocities get a bolt gun.
If you are concerned with the bolt the look into https://www.sixfiveoutfitters.com/product/ultrabolt-6-5-grendel-6mm-arc-ar15-type-2-bolt-mk136/. John has found a way to increase the thickness of the bolt face wall, .035 to .052 (by my measurements). That is significant and makes for a much stronger bolt.
JP bolt vs UltrBolt
Cheers
Philip
I noticed on your link the manufacturer does not mention using high pressures. Or did I miss something?
Thanks for the post...I did go measure the thickness of my 2 6mm ARC bolts and they are .043" amd .044" thick...not .035" ... but at .053" thickness any improvement in that area would be a bit of insurance and peace of mind, just for the ARC gas gun pressures...and I'd consider them if needed in the future...but I also didn't see any data that would suggest that one could proceed into bolt gun pressures...
I reme
Also, take diameter of bolt face od minus bolt face id. Grendel od .530 minus id .453 = .077 divide by 2 = .0385. Based on published data I found. 223/556 measures .0735 wall thickness. id .383 od .530
Regardless it is still improvement and better safely margin.
Cheers
I remeasured the JP bolt again. .035 with Nitutoyo digital and .037 with 30+ year old old Moore & Wright analog. I have not had them calibrated.
Also, take diameter of bolt face od minus bolt face id. Grendel od .530 minus id .453 = .077 divide by 2 = .0385. Based on published data I found. 223/556 measures .0735 wall thickness. id .383 od .530
Regardless it is still improvement and better safely margin.
Cheers
I believe the discrepancy is the bolt face ID, .445" is normal some go to .447"....but .453" on your JP is quite large...so. .530" - .445"= .085" ÷2 =.0425"
For nominal size thickness ...but I suspect most would run between .040" to .043" thickness so as to have plenty of clearence for the brass head with a few minor dings, dirt, powder residue, etc... cause ya want it to function. But I agree that any additional metal in that area is beneficial....but there are not many areas to improve the .136 deep recess diameter or make slightly smaller the recess and still be reliable within the constraints of the AR bolt and barrel extension relationship.
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. Just received the SixFive AR15 UltraBolt 6.5 Grendel, great improvement over standard.
My idea is to add back the lost thickness of the bolt face wall to the OD of the bolt face and to the OD of the lugs? Looks like there is enough room in the extension to accommodate change of adding .063 to ID of lug and bolt diameter. (.0315 to radius) 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.
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.
Measurement taken with Mitutoyo calipers and barrel extension and bolt drawing spec sheet.
My idea is to add back the lost thickness of the bolt face wall to the OD of the bolt face and to the OD of the lugs? Looks like there is enough room in the extension to accommodate change of adding .063 to ID of lug and bolt diameter. (.0315 to radius) 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.
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.
Measurement taken with Mitutoyo calipers and barrel extension and bolt drawing spec sheet.
I measure the bolt face again. JP .4535, 223/556 .381, Ultra Grendel/ARC .4445.
Maybe the JP is larger to accommodate 7.62x39.
If my JP bolt really is .0085 larger than your grendel bolt then maybe the JP isn't what it's cracked up to be. if so then I'm glad I got the Ultra bolt from SixFive.
Maybe I'm over thinking this.
Maybe the JP is larger to accommodate 7.62x39.
If my JP bolt really is .0085 larger than your grendel bolt then maybe the JP isn't what it's cracked up to be. if so then I'm glad I got the Ultra bolt from SixFive.
Maybe I'm over thinking this.
Last edited:
the bolt rim looks thicker. Do you need a different bolt extension?
No, everything fits perfectly. Well worth the price.
Similar threads
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.