AR Sponsor
Posted: 6/16/2009 8:46:24 PM EDT
|
Can a standard .223/5.56 bolt be opened up to work with a Grendel?
Would the extractor have to be modified, and if so, how would this be done? |
|
Quoted:
It takes what, a year now, to get anything from AA? From what I've read here, its not QUITE that bad but its not a one week delay either. That said, post on the grendel forum, I am sure someone would part with one for the right price. I guess it just depends how badly you need one right now, next week etc. |
|
Quoted:
Quoted:
It takes what, a year now, to get anything from AA? From what I've read here, its not QUITE that bad but its not a one week delay either. That said, post on the grendel forum, I am sure someone would part with one for the right price. I guess it just depends how badly you need one right now, next week etc. Is the bolt the same size as the 762x39? If so, you can order one from LMT. I checked Ammo Guide, and it lists .441" as the size (vs .447" for the 762x39). |
| Is it an AA barrel? Their bolt face has a deeper depth and a regular bolt wouldn't headspace correctly. However the 7.62x39 bolt has the correct diameter. Standard bolts can be machined to work, just don't have them EDM'ed. That is what was causing some of them to break from what I recall. |
|
You have to call LMT. They have 7.62X39 bolts but dont advertise them.
What barrel do you have, and how did you manage to get it without a bolt? The 7.62x39 boltface is shallower than an AA 6.5G bolt. The LMT bolt will not chamber a round on an AA barrel. You'll need to deepen one or the other. Best to fix the headspace by recutting the chamber on the barrel rather than @#$! with the bolt. Expect clocking problems if your gas port is already drilled. |
|
Quoted:
You have to call LMT. They have 7.62X39 bolts but dont advertise them. What barrel do you have, and how did you manage to get it without a bolt? The 7.62x39 boltface is shallower than an AA 6.5G bolt. The LMT bolt will not chamber a round on an AA barrel. You'll need to deepen one or the other. Best to fix the headspace by recutting the chamber on the barrel rather than @#$! with the bolt. Expect clocking problems if your gas port is already drilled. All way thought it best to modify the least expensive part? What if a AA 6.5G bolt becomes available? The mention of problems with the gas port/cycling would be another reason not to mess with the barrel. |
|
All way thought it best to modify the least expensive part?
I prefer to modify the part that is least likely to fail from the modification, and that is easier to modify. What if a AA 6.5G bolt becomes available?
Changing to 7.62x39 headspace is essentially a one way mod. The mention of problems with the gas port/cycling would be another reason not to mess with the barrel.
I didnt mention any problems with the gas port/cycling. I said that you may have problems with the clocking of the gas port - when headspaced the port may not line up with the gas block. That is true whenever you alter headspace on an AR barrel that already has the gas port drilled. It is probably easier to avoid that problem when carefully reaming the chamber rather than when recutting the bolt face. |
|
Most aftermarket 7.62x39 bolts are 8620, which is not the TDP material for AR-15 bolts to begin with. AA uses the official TDP material of Carpenter 158 which should serve better (proper heat treat can still mess things up). The AA bolts are 0.010 deeper - why you ask? Look at a .223 AR15 bolt, notice the recess on the outer edge of the bolt face? If you take a .223 bolt and open it up on a lathe to the depth of the bolt face, you will be left with a small circular depression in the bolt face. To make that disappear, you remove the top surface of the bolt face. AA will tell you it was done to "strengthen the bolt lugs" Whatever... you cannot strengthen something by removing more material, it simply serves to hide the fact that modified .223 bolts were originally used. It also causes the firing pin to protrude more, which may help with ComBloc milsurp primers, but could lead to pierced primers in commercial loads.
Best solution, get a TDP 7.62x39 bolt (Colt, LMT) made of Carpenter. Find a 6.5 reamer and ream the chamber 0.010 deeper. A competent AR smith can do this without causing "clocking issues" as it is done all the time. Careful reaming after setting up on the lathe with proper instrumentation can do it very easily - we modified a bunch of AA Genghis barrels to accept TDP depth bolts without issue. There will also not be an issue with the location of the port, as the location relative to the extension has not been altered so it is not like you will have your gas tube sticking further into the carrier... |
|
Quoted:
Thanks Marty. That's the kind of response I was really looking for. The firing pin protrusion issue hadn't crossed my mind yet. That's an incredibly good point. I did order an LMT bolt, but damn those suckers are expensive. They are worth it...no denying that! |
|
Quoted:
Most aftermarket 7.62x39 bolts are 8620, which is not the TDP material for AR-15 bolts to begin with. AA uses the official TDP material of Carpenter 158 which should serve better (proper heat treat can still mess things up). AA will tell you it was done to "strengthen the bolt lugs" Whatever... you cannot strengthen something by removing more material, it simply serves to hide the fact that modified .223 bolts were originally used. AA does not use Carpenter 158 for 6.5G bolts. AA uses something akin to Latrobe CBS-223 VIM-VAR or SAE 9310 for the 6.5G bolts. The strengthen the bolt lugs comparison is a comparison between the 5.56mm bolt dimensions in Carpenter 158 vs. the 6.5G bolt dimensions in CBS-223 / 9310. Note: The alloy product CBS-223 has nothing to do with the 223 Rem cartridge. |
|
I have used a carbide boring bar to increase the diameter of a standard 223 bolt for many years with no problems. For a Grendel application you will also have to recut the boltface approx. .010-.013 inch deeper. You will also have to massage the extractor several ways if you want it to function correctly. It is easier to purchase a 7.62x39 extractor. Just got a complete bolt from Model 1 sales, took 3 days.
Good luck "FINDING" a reamer. They are proprietary and only available through a licensing agreement with Bill Alexander. FYI––if you want 6.5 Grendel ballistics without the Grendel hassel, get a 6.5 BPC reamer from Dave Kiff at Pacific Tool and Gage. Only difference is .007 headspace. Grind .007 off of your Grendel resizing die and it will work correctly. No mods needed for bullet seating dies. Neck down Winchester 7.62x39 brass(cheap), load and shoot. Yes, it works very well. |
|
Quoted:
Quoted:
Most aftermarket 7.62x39 bolts are 8620, which is not the TDP material for AR-15 bolts to begin with. AA uses the official TDP material of Carpenter 158 which should serve better (proper heat treat can still mess things up). AA will tell you it was done to "strengthen the bolt lugs" Whatever... you cannot strengthen something by removing more material, it simply serves to hide the fact that modified .223 bolts were originally used. AA does not use Carpenter 158 for 6.5G bolts. AA uses something akin to Latrobe CBS-223 VIM-VAR or SAE 9310 for the 6.5G bolts. The strengthen the bolt lugs comparison is a comparison between the 5.56mm bolt dimensions in Carpenter 158 vs. the 6.5G bolt dimensions in CBS-223 / 9310. Note: The alloy product CBS-223 has nothing to do with the 223 Rem cartridge. I stand corrected. One of the articles about their offerings stated that they bolts were Carpenter, but this might have been their .221 Genghis. However, the "strengthen the bolt lugs" statement is in reference to comments to industry personnel by folks from AA, not some magazine article. And it goes back to the days of Anglo American... |
|
Quoted:FYI––if you want 6.5 Grendel ballistics without the Grendel hassel, get a 6.5 BPC reamer from Dave Kiff at Pacific Tool and Gage. Only difference is .007 headspace. Grind .007 off of your Grendel resizing die and it will work correctly. No mods needed for bullet seating dies. Neck down Winchester 7.62x39 brass(cheap), load and shoot. Yes, it works very well.
Couldn't one feed the reamer in an extra .007? |
|
I stand corrected, as well.
I did not know there was a history to these claims, where the argument is based upon geometry alone. Quoted:
However, the "strengthen the bolt lugs" statement is in reference to comments to industry personnel by folks from AA, not some magazine article. And it goes back to the days of Anglo American... |
AR Sponsor
Win a FREE Membership!
Sign up for the ARFCOM weekly newsletter and be entered to win a free ARFCOM membership. One new winner* is announced every week!
You will receive an email every Friday morning featuring the latest chatter from the hottest topics, breaking news surrounding legislation, as well as exclusive deals only available to ARFCOM email subscribers.