Sheared bolt lugs

[noone]

That is the same lug that broken on the 3 bolts I had. After having the front face of the receivers were trued up, I haven't had any more broken bolts. Keep in mind that even with the AR15 in 5.56mm, it is recommended that the bolts be replaced every so often. With the thinner metal around the base of the Grendel/7.62x39 cartridge family, it only stands to reason that those bolts would benefit from replacement more frequently.

[glane5910]

I've used the lapping tool from Brownell's(still use it) but I really haven't found an upper that was so obviously out that its done anything. I've broken one bolt a couple of years ago in my 6.5 CSS build on an AA billet upper. The bolt was a Model 1 bolt I had for a spare. I had been running a DPMS bolt and never had an issue. The Model 1 bolt broke the lug in less than 10 rounds. That rifle now runs a LMT Enhanced bolt. I have the DPMS for a spare. Model 1 sent me a new bolt and its just sitting on the shelf.

[LRRPF52]

Gents,

This is the one area where we really need a dedicated bolt and barrel extension for the Grendel, with increased mass around the bolt lugs to support the cartridge head, as well as balance out the load on the lugs.

glane, did you have the LMT enhanced bolt face opened for the .444 Grendel, or is it a 7.62x39 version? Any pics? Does it offer more beef to the lug roots? It would be nice to see a line-up of a 5.56 bolt, Grendel bolt, and your enhanced LMT bolt.

LRRPF52

[glane5910]

The LMT Enhanced is the 7.62x39 bolt. They didn't have it listed so I had to call and order it. here is a link to pics of bolts at ARFCOM http://www.ar15.com/archive/topic.html?b...1&t=473085

[LRRPF52]

glane,

That link indicates that the LMT 7.62x39 bolts are no longer made. Do you know if that's true? Looking at that pic (I've seen it before), I still don't get a warm and fuzzy about how thin the walls are around the bolt face and lug root area. I want something more like my AR10 bolts, where there is way more mass compared to the bolt face.

I like the direction AR Performance went by increasing the mass around the lugs, as well as around the cam pin hole. I've broken and seen bolts broken at the cam pin hole, in addition to shorn lugs on 5.56 guns that are shot in abusive high-volume sessions.

LRRPF52

[glane5910]

They had stopped making them but had some left in stock. IIRC, they are made 9310 carpenter steel that is nitride/chrome plated of some sort. The lugs are radiused for stress relief. I run pretty hot loads out of my rifle and it just keeps on ticking. A beefier set up would be the ticket. Something like Oly Arms uses on their WSSM AR-15 uppers that looks like a modified AR-10 but then you start looking at high costs to change things around. I wonder what the % of grendel shooters vs the number of bolt failures is? I'm guessing it's pretty insignificant.

[glane5910]

IIRC, AR -Perf had to get new modified, bbl extensions to go with those bolts didn't they?

[LRRPF52]

AR Performance makes a special 6mm BR bolt and barrel extension, but I think their improved bolt designs for 5.56 and 6.8 slip into standard extensions. Harrison seems pretty committed to the 6.8 SPC, and has been considered one of the go-to guys all along for doing the 6.8 SPC chamber right, while certain makers jumped the gun and screwed the pooch royally with an 80 degree hand-off from the leade to the rifling, resulting in some serious kaboom. I'm not really interested in investing in the 6.8, and I wish ARP would offer conversions to 6.5 Grendel with his bolt geometry, even if it meant doing an AR10 style bolt face/lug and matching extension like Oly and the WSSM's.

Can you compare an AA Grendel bolt face recess dimension to the LMT enhanced 7.62x39 bolt face recess? Do you use the LMT 7.62x39 as a drop-in with AA or other Grendel barrels?

LRRPF52

[glane5910]

The AA actual grendel bolt face is 0.011" deeper than the standard 7.62x39's bolt face. When I bought my bbl from CSS/LW a few years ago, they were only chambering their bbls to use the standard depth bolt face of the 7.62x39. You wouldn't be able to chamber a round in a Grendel spec'd bbl using a 7.62x39 bolt. If I tried to use a Grendel spec'd bolt in my CSS, I'd have extremely excessive headspace.

[noone]

I really wish AR performance would have the "Big Bolts" available. They look like a great idea as not only is the bolt beefed up, but the system includes a specially made barrel extension to accommodate the beefed up bolt. I really doubt that anyone who is even close to the listed max loads would blow bolt lugs off the "Big Bolt" system.

[LRRPF52]

Harrison might have told me that he has done them for custom requests, so I imagine he could use his 6BR bolt/extension combo and just machine the bolt face for a .444" cartridge versus the .473" one. The bolt face depth and extractor notch location also have to be worked out, but I just wish he would offer a production run of these for Grendels. The 6.5BR takes up a ton of magazine capacity, although it does hold a lot more powder. He claims an average of over 150 fps over the Grendel with the 6.5BR.