Bolt or complete BCG

[Huntchic]

Im considering replacing my bolts in 2 Grendel's. considering Nickle boron. should i just get bolt or complete BCG. Also considering Cryptic manufacturing brand. noticed that Brownells has a house brand also but dont know if they are any good.

[Eggman2.0]

My rexus ultra BCG has served well for me, the overall quality and finish is top notch and the extractor the best out there IMHO.
I just got a nickle boron bolt for my .300 Blk but have yet to shoot it so, I do like how it looks and feels...time will tell.

[Huntchic]

I should have stated this earlier. I have used and do have Nickle boron bolts in nearly all my AR's Why i asked about just switching out the bolt vs an entire BCG is because i have a couple new Nickle boron BCG's in 5.56 i have never even taken out of the package. thought was to just get 6.5 Grendel bolts and swap out vs buying an entire BCG. Any reason this would be a problem?

[LRRPF52]

Bolt carriers are the same for 6.5 Grendel, as long as the Bolt Carrier meets the TDP dimensions and material qualities.

If the carrier bore inner diameters are not correct, it can lead to gas system problems with a leaky set-up (too loose IDs).

Notice the 3 inner diameters of the bore where the bolt cylces inside, starting with the orifice, then the compression ring section, then the tail.

One common problem with most of the special coatings carriers is they end up being too loose, because they use the same machining dimensions for a Mil-Std carrier, but don’t then apply the hard chrome inside this area that is part of the TDP. Most of the coatings are a lot thinner than hard chrome, so the finished product is not in-spec.

Actual TDP-compliant bolt carriers are the safest bet, and only a few companies are known for consistently cranking them out, some of those companies experiencing degradation of standards compliance in the last few years due to the new wave of young employees who have never been held to any standard before entering the work place.


As to bolts, Nickel Boron typically causes hydrogen embrittlement like Hard Chrome does, so I avoid it in AR-15 bolts even in 5.56.

I went through the phase in the 2000s through early 2010s experimenting with the different coated BCGs, like Titanium Nitride (TiN), and Nickel Boron (NiB), and after long-term testing of them in the Arctic, we didn’t see any real benefits over a real Mil-Spec BCG. (Most BCGs are nowhere near Mil-Spec)

For Grendel, my go-to bolts are the Rexus in a Bootleg Adjustable Gas Carrier.

[grayfox]

You can get any bolt carrier you want and use the grendel bolts in them. I typically get the PSA nickel boron bcg and then just swap in my grendel bolt already on hand. So yes, that will work fine for you.
The only thing different in the BCG for a 556 or related cartridge is the bolt itself.
300 hamr, 300 blk (both which use 556 bolts), 6.5 grendel. 6 ARC, 22 Arc (all 3 of which use the 6.5 grendel). Only thing to watch out for is some, some earlier grendel bolts has only a .125 depth bolt face; these are pretty much all gone but just be aware.

[Huntchic]

LOL. Thanks gentlemen. Well understand LRRPF52 checking dimensions. gray fox, I laugh because The Nickle Boron bolts i have are PSA 5.56 and im looking at putting Tool craft bolts in them.

[Huntchic]

Ive used Faxon, PSA, Tool craft and JP mostly over the years. Heard cryptic was good have never used anything from Stoner.
My only reason for Nickle Boron is because it cleans so easy.

[montana]

The fit between the bolt and carrier can change when switching bolts..Unless you have pin and ring gauges to measure, it can be a guessing game...

Fortunately military test have found .0004 to .0005 under the minimum tolerance between the bolt tail and carrier bolt tail bore does not effect performance..
.0075 to .010 below specification will effect reliable performance..

The powder, barrel port and other factors will also play a part when searching for the best accuracy and reliability .

The bolt support shoulder O.D. can effect accuracy as can the play in the carrier to upper.

Firing pin protrusion can change when switching a bolt as can head space..

I recommend checking head space when switching bolts and make sure the back of the carrier pushes the buffer back when closing the upper to the lower..There should be very little wiggle between the cam pin and bolt and if possible I would check the firing pin protrusion..I agree with 52 and would stick to a Mil-spec phosphate bolt..I will never use any Nickle Boron carrier or bolt in my rifles..

[imaguy3]

I have a cryptic bolt in mine now... so far no problems
they have a lifetime warranty

[LRRPF52]

This is the best break-down on the different AR-15 BCGs I have ever seen, though it is specific to 5.56 mainly.

[Huntchic]

Thanks for the input gentlemen. I've put in and run a bunch of nickel boron psa bolts and no complaints with any. I know ive got over 1-2 k on some of them. Im not sure where i got this from but i was told that the PSA bolts were actually made by Tool craft but that could be incorrect, just wat i was told a couple times.

[Huntchic]

WOW, That was a very informative video. Just proves your never to old to learn something. Some of the things discussed i was aware of but it brought many things to light i didnt realize. Thank you LRRPF52. excellent education.

[LRRPF52]

WOW, That was a very informative video. Just proves your never to old to learn something. Some of the things discussed i was aware of but it brought many things to light i didnt realize. Thank you LRRPF52. excellent education.

About 24 years ago, I thought I knew pretty much all there was to know about the AR-15 just because I had read The Black Rifle Vol I, The Great Rifle Controversy, Ichord Subcommittee Hearings, all the TMs and TCs/-1s, all the gun rag articles, ARDEC Reports, ballistics studies, critiques, Colt brochures, schematics, memorized the entire parts count and identifications for the M16/M16A1/M16A2/M4A1/M4, etc.

Turns out I had just barely climbed the 1st hill, which I thought was the mountain. Once I crested the hill, saw the valley and another giant mountain range, I realized I didn’t know much really, but had put in the legwork for the next part of the journey for sure. I didn’t know all the metallurgy, processes, critical dimensions, peculiarities of the gas system dynamics, didn’t know the full detail of the 601, 602, 603 parts and dimensional changes, gauging, pressure containment requirements, and things of that nature.

Getting more into the Retro stuff and 6.5 Grendel has been an experience for certain. I credit Bill Alexander as a refreshing resource in that regard, since he was trained by Stoner and worked in the UK MoD on small arms repair and depot-level services.

I’m still always trying to learn something more.

The most recent thing I learned was how terrible 5.56 is at converting propellent, and lets a lot of unburnt powder exit the muzzle as waste.

Would love to see some 6.5 Grendel slow-motion/high-speed photography at the muzzle, because 6.5 Creedmoor was extremely clean with very minimal particulates on-camera.

6.5 Grendel is a more efficient case design than 6.5 Creedmoor since the propellant column is shorter, and it shares the 30 degree shoulder. Same with 6.5x47, which is probably the best 6.5-08 variant of them all I think.

[Huntchic]

One thing I’ve learned in my job and life is the more you know the more you find out you don’t know and have to learn.

[SDW]

That video makes me want to buy their gauge kit. I have enough BCGs to justify it. Plus I might pick up one or two BCGs for spares:

https://schooloftheamericanrifle.com/shop/gauges/41501/