Is bolts beaking still a big concern now days with the 6.5 grendel?

[mdewitt71]

Had a guy bring up about how there is alot of the bolts breaking on Grendel ARs.... talked about it happens all the time and often.

I read about the older Grendel bolts breaking but, now days does it happen as much?

Does most Grendel owners buy and carry extra bolts with em?

[LRRPF52]

Breaking bolts is an issue with any cartridge in the AR15 if the following apply:

* Manufacturer used lesser alloy
* Bad heat treatment
* Not shot peened
* No substantive QC process

* Shooter loads well beyond safety margins of the cartridge according to SAAMI
* MLGS 18" suppressed with a large gas port, even on 5.56 guns
* CLGS large port, especially 5.56
* Compressed high volume in short window time durations will reduce bolt life, certain units often see bolt failure with 5.56 before 5,000 rounds even.

Military units with good armorers will replace 5.56 bolts every 5000rds as a general rule so that bolt failure doesn't stall high volume range training, where guns will shoot anywhere from 500-1000rds per day. I've done CQM ranges where I put 1,100rds through my M4 in about 4 hours. Some of the other guys there had put 10,000 rounds through their M4s the day before, and had brand new complete uppers on their guns as a result.

For the civilian who likes to shoot 100-200rds a day through their 6.5 Grendel, I have yet to see one fail subjected to that kind of range session in my DM courses and others dating back to 2009 now. I've seen guys occasionally in this forum who had bolts of questionable origin break them back in the day, but not many.

I personally have only broken 5.56 bolts after 10,000 rounds of tortuous range session use.

I have spares for everything if/when it happens, but as of yet, even with all the pressure ladders I have done since 2009, I have not broken anything 6.5 Grendel. All my bolts are either AA or PF. My diet mainly consists of 123gr Hornady factory ammo, 123gr AMAX/SST on 31.2gr of CFE223, AA 123gr Scenar, PF 123gr Scenar/SMK, NCC.

I'm thousands of rounds into my 2 main Grendels, and have shot a lot of others, while observing them in my courses as well. I've heard of some extractors breaking recently, but am still tracking down the origins of those.

[mdewitt71]

I work for the DOD in the Small Arms development and modernization..... In fact I have some of the highest round count M9 pistols and M4s in the Army inventory right down the road on the wait list for swapping out.

I know the 5.56 bolt breakage numbers are vastly lesser than other caliber ARs... but, again I am new to the 6.5 Grendel arena.
I guess I was just looking for reassurance that 6.5 Grendel bolts now days are built to better specs than years past.
Thanks for the reply... good to know.

[NugginFutz]

Just bear in mind that there is no shortage of recycled information that may or may not have been accurate at one time or another.

That's the problem with the internet, in general. I can't tell you how many times I've seen the same email every year informing me that Mars will be at its closest approach in our lifetimes, or how telemarketers will be allowed to call our cell phones, etc.

Just last week, a poster on another forum was certain that Grendel bolts were nothing but hogged out 5.56 bolts and could not possibly be as reliable the mighty 5.56 / 300BLK bolt. (He'd apparently once read that rumor on the interwebs, and re-inserted the misinformation into the continuum).

That's one of the things I miss about paper magazines and books. You could often tell when they were old by how yellowed the pages were. On the internet, outdated information often looks just as fresh and clean as the newest posts.

[Texas]

The SAAMI spec on 6.5 Grendel is 52,000 PSI and the SAAMI MAP spec on 5.56X45 is 60,000 PSI with the M855A1 running as high as 64,800 PSI.
Given the same care and material in a bolt, the 6.5 Grendel should not be as likely to fail as a 5.56 bolt. As LR55 stated, it is always a good idea to keep a spare bolt and to buy quality.

[ahillock]

0.136 vs. 0.125
Proper vs. improper heat treatment
Proper vs. improper raw material
6.5 Grendel specific bolt vs. 5.56 bolt that is modified for Grendel or a 7.62x39.

I have had good luck with 0.136 specific bolts made from 9130. Just get it from one of the manufacturers that has a good history with making them.

[SHORT-N-SASSY]

What ever happened to the Faxon Firearms ARAK-21 6.5mm Grendel, with beefy radius-lug Bolt, promised a couple years ago ---

(http://www.65grendel.com/forum/showt...l=1#post108197)

[BluntForceTrauma]

My take on the bolt issue:

(1) Alexander Arms bolts have always been good to go. Bill A. is a talented engineer who did his homework for .50 Beowulf/6.5 Grendel bolts. I'm sure some of his have broken over the 14 years of the 65G's existence — either under questionable circumstances or because everyone turns out a lemon now and then — but very damn few.

(2) Other companies that used lesser engineering, essentially making knock-off bolts, have had more failures. Now there are reputable companies that have followed AA's lead and make quality bolts, as well.

(3) The competition for the 6.5 Grendel, more specifically the hard-core 6.8 SPC crowd, was more than happy to lump AA bolts in with the knock-offs, in order to taint the whole 6.5 Grendel program since it was/is their biggest threat. Ask any 6.8 guy about the 6.5 Grendel; first thing they'll say is, "everybody knows it breaks bolts right and left." And like Big City voters, they're happy to repeat it "early and often" in every online forum they post. (Same as they like to say the 65G won't work as a belt-fed.)

(4) The 6.5 Grendel is THE absolute best all-around, multi-role cartridge that can be shoehorned into standard AR receivers with a viable double-stack, high-capacity magazine. The 6mmAR wildcats with their wonderful external ballistics are a close second if your game is long-range targets, but they can't use the same bullets used to kill beasts up to and including moose like the 6.5mm can. And don't get me started on the 65G's utility as a tactical round. . . . If I could build a new assault rifle from the ground up for the 65G, would I "strengthen" the bolt? Yes. But even Cris Murray, designer of the 6.8 SPC, and then later changing his mind to create his dream 7mm cartridge which is very much Grendel-like, stated that no assault rifle cartridge should exceed 50,000 psi.

Whew! So where was I? Back to the original question: No, bolt breakage was NEVER a big concern using a purpose-designed bolt under normal conditions. Poor bolts will break, and any bolt will break with abuse.

[sneaky one]

Missed this thread. I ran some really hot loads 4-5 years ago - as an impromptu ladder test, when I met up with mseric at a gravel pit - shooting range in N. MN. My loads were probably at the 56 K range for the Grr case which is designed to take 58 k as a failure point.

I was There Close to the edge- We witnessed my 90 grn. Gmx go thru 8 - 1 gallon H2O jugs,,,,, I have never seen this level of penetration before! From the Grendel.

6" wide each !--- 44" of penetration !!!!!! We looked at each other and said , it's unstoppable! Bullet was out the side of 8th jug. Never found it... 1 petal inisde jug 7

Crazy thing was--- no flattened primers , or other signs of way high pressures. As Joe stated- can't always trust the primers as a sign.


Bolt is still Fine. 800 rounds of Gmx Experimantes later.... AA bolt- 2008

Yes, after chatting with Jasmith, I learned a bit upon Grr pressures- I stay in the 50-52 k range now. Once in a while -- 53K.

[Grendel]

Maxim Firearms, are these bolts good to go?

http://www.maximfirearms.com/online-store/complete-6-5-grendel-bolt/

[BluntForceTrauma]

This is just hearsay, no personal experience, but I seem to remember good things about Maxim. I wouldn't hesitate to buy one, just because I trust my gut that someone I trust must have said something good at some point and that warm feeling is floating around somewhere in my brain.

[mdram]

Maxim Firearms, are these bolts good to go?
http://www.maximfirearms.com/online-...-grendel-bolt/

[hikfromstik]

I will vouch for Maxim bolts . I've put about 500 rds through one ( w/ lilja barrel ). I've never shot bi-metal wolf so I can't speak on that matter ,but Hornady ,AA, and Lapua are gtg. Never had one hiccup with it.

[mdewitt71]

Good info gents.... Thanks.

[LRRPF52]

I was talking with one of the engineers at Colt Canada down at SHOT.

He said when they heard about M4A1 bolts breaking all the time, they wondered what was going on because they never saw it with C7s or C8s.

It all comes down to processes. One of the biggest problems with a US TDP bolt is that the Mil-Std call for High Pressure Testing (non-destructive testing).

They take a proof cartridge and stress the bolt on its first firing, then MPI it later in the process. Many engineers I have spoken with frown on this bigtime, and this is also why SR25 bolts are known for their longevity, whereas M110 bolts have been breaking. They are made by the same company (KAC), and the company would eliminate the HPT test if they could because they know it induces early fatigue to the part.

I just saw POF's Revolution, which is literally an AR15 that fires 7.62x51 NATO. It uses an AR15 carrier no different than their POF P415, the same upper receiver as their new AR15 product line, and an AR15-sized bolt, but with a .473" capable face for the larger .308 Win. I watched numerous videos of them doing mag dumps on full auto, using 25rd PMAGs. They claim they haven't broken a bolt yet, and didn't release the design until they had tested it for more than a year.

I have my reservations about it still, but that bolt design and alloy has been lasting them through some pretty tortuous testing on full auto, so the idea that you can't make a viable AR15 bolt in 6.5 Grendel working much lower pressures can be seen in that light.

I also asked Bill A. and Melissa last year how many bolts they have seen returned for breaking. Melissa got a puzzle look on her face, and said it was so rare that she really can't think of many. I remember a guy here who came on the forum to ask about breaking his bolt, where he had loaded up something 140gr on some powder so fast, we don't even use it in Grendel at all-even with 85gr bullets. Not sure what rifle he had, but he cracked a lug of course and was wondering why.

Knowing what I know about the engineering behind the 6.5 Grendel bolt, I'm not worried about it.