I built my gun with an Aero BCG. Had the bolt matched to the barrel when it was chambered. I noticed a headspace change (.0015-.002") when measuring my fired brass. I started looking around and found the lugs on the back side of the bolt are a little worn and very lightly mushroomed.
So I'm going to replace the bolt. Any suggestions. Are JP bolts worth the money? I would try a Monster but can't find one. Maxim?
(01-06-2022, 03:14 AM)popgun Wrote: I built my gun with an Aero BCG. Had the bolt matched to the barrel when it was chambered. I noticed a headspace change (.0015-.002") when measuring my fired brass. I started looking around and found the lugs on the back side of the bolt are a little worn and very lightly mushroomed.
So I'm going to replace the bolt. Any suggestions. Are JP bolts worth the money? I would try a Monster but can't find one. Maxim?
...interesting. How many rounds thru it and hot are your loads?
The Maxim bolt oughta work OK. I think that's the bolt Precision Firearms uses. At $75 it looks like a good bolt for a good price. Alexander Arms (AA) has Grendel bolts but I can't guarantee they'll be in stock. You can't tell by their website. Call 'em & ask. At one time AA had "hard use" Grendel bolts. Not sure the one they have on their site is that bolt or their standard bolt. Fail Zero Grendel bolts are out of stock but you can get on a wait list. Underground Tactical Grendel bolts are out of stock also. They have wish lists if you wanna start one there. I keep hoping the Monster bolts will be released. I wanna a couple of 'em.
The trick is growing up without growing old. -- Casey Stengal
01-06-2022, 01:23 PM (This post was last modified: 01-06-2022, 01:54 PM by popgun.)
I have about 250 rounds through the gun most of them hand loads with 28.7 gr of LVR and 105 BTHP with a velocity of 2685 to 2710 depending on environment. Very light ejector marks on 35% of the brass with no marks on the remaining brass. I've shot some hotter loads during development but very few and not what I would consider excessive. This is a 22" barrel that gave velocities of 2765+ with hornady black ammo.
grayfox. My brass came from factory ammo and once fired measured 1.191"+- with a hornady headspace comparator and settling in at 1.192" after second firing. The same brass now measures 1.1935" and once fired Lapua brass 1.195"
I use a Hornady FL die and bump the shoulder .0025-.003" and trim to 1.483"
Thanks Bob, that's exactly what I was thinking. The Maxim, PF appear to be available and opticsplanet "shows" JP bolts in stock. Now the question is which one of those. I don't have a problem spending a little more on the JP if I'm getting what I pay for and it's actually in stock. I don't like wasting money either.
Several guys have had some trouble with opticsplanet showing stuff in stock but actually it wasn't. If you want to avoid that hassle I'd go with PF, if they say they have it then they do.
Roger on the comparison-delta, now that small amount of difference, could be the brass is a bit more work hardened so is a bit more resistant to the re-sizing, just a thought to consider. So maybe the current bolt isn't too worn, but it's good to have a spare anyway. If you get the new one then this one could go as the spare...
The brass not springing back as much crossed my mind. I need to figure out how to post pictures. I just ordered a bolt from PF. I went with them over Maxim because PF bolts have a nitride finish and the Maxim I'm pretty sure is a phosphate finish, not a big deal. It won't hurt having a spare anyway.
The PF bolt was not a good choice. I had extraction problems. 7 out of 37 rounds fired had extraction issues. I probably should have inspected the bolt more closely when I had a piece of brass that did not extract when initially checking headspace. I just ordered a Maxim bolt.
01-23-2022, 01:11 AM (This post was last modified: 01-23-2022, 01:20 AM by popgun.)
PF bolt I got to replace damaged bolt. Like mentioned before, I had extraction issues with the PF bolt. Aero bolt on top PF on bottom. Notice extractor height in relation to top of bolt. It was the same when I switched extractors.
I never had an ejection/extraction issue with the Aero bolt and about a 4 o'clock ejection pattern. The damage to it was probably my fault, not resizing the brass with sufficient headspace. Trying to extend the life of nearly unattainable brass.
I think the PF bolt has the extractor pivot hole about 10 0r 12 thousandths to far from the bolt face, giving zero tolerance and unreliability.
...just a couple of observations based on the images:
(1) the PF bolt has longer length lugs than the Aero.
(2) Original bolt's lugs peening/mushrooming can be (a) excessive bolt thrust during firing or (b) improper hardening of the metal.
(3) In the side-by-side image, the PF extractor appears to be "shorter", the front edge slightly behind edge of bolt's leading edge, which could impact groove that case rim sits in.
(4) Images measuring pin to bolt face relationship may be misleading, same measurement to rim groove's front/rear edges would provide more pertinent info as to how it affects ejection. The pin hole locations would have more affect on the pivot point and attendant leverage pressure of extractors grip on rim.
I would suggest measuring the bolt face depth cut to ensure what type of bolt it is, Type 1 or Type 2.
popgun, I was thinking the same thing r.t is alluding too. Caveat: beer tonight. 0.12" is a difference between a Type 1 (7 62x39) and type 2. I have both on hand. I'll try to give a measure tomorrow.
01-23-2022, 09:53 AM (This post was last modified: 01-23-2022, 09:56 AM by r.tenorio671.)
...I can't recall the specific difference, but read article claiming there is also a difference in length's for "true" 6.5Grendel bolts versus .223/556 bolts. The Grendel bolt was slightly longer IIRC. The article referenced the difference being the cause of folks experiencing primer piercing and/or light strikes. Additionally, the firing pin length also differed between the Grendel specific versus the 223/556 specific firing pins.
To be honest, I don't have any practical knowledge of the 6.5 Grendel world so I couldn't tell you if there is any truth to what the article claimed, YMMV.
Both bolts are type 2 bolts measuring .136" bolt face depth.
r.tenorio671
The lugs appearing to be different lengths is probably poor photography on my part. The PF lugs measure .275" the Aero .2735+- depending on lug measured, which is understandable considering damage.
Yes the tail of a type 2 bolt is longer to compensate for the deeper boltface and still use a standard AR 556/223 firing pin.
Yes the extractor appears to be shorter on the PF bolt. But as mention before, when I switch extractors the results are the same appearing short on the PF bolt. The extractors are identical on both bolts. It's the pivot pin location that's different between the two bolts.
The damage to the Aero bolt may have been my fault as mentioned before due to not enough headspace and binding the bolt. A soft bolt could be a possibility or contributing factor. I read that nitriding could possibly anneal a bolt because the temperature in the process is close to annealing temperatures. I'm not a metallurgist and don't know if this is true.
Both extractors have the same groove width and fit nicely to brass rims. I suppose I could measure the distance between the boltface and extractor claw, but at this point I would bet the farm that no matter which extractor used the PF bolt will measure .010" to .012" less/tighter than the Aero bolt. Also when inserting a case into the PF bolt by hand it is extremely tight with zero endplay, whereas the Aero bolt you can feel slight movement (my guess would be about .010"
