What Breaks?

[Jaywalker]

I'm considering a 6.5 Grendel and am walking around it kicking its tires. One thing that concerns me is parts breakage from a firearm that was designed around a lighter-kicking cartridge.

So, what breaks on the Grendel more than on the 5.56?

[LRRPF52]

The only things I've really seen break on M4's & AR's as far as operating parts go is bolts, and that is on guns run through extreme schedules. While I've heard of Grendel bolts breaking, I haven't seen it yet. I have broken non-MPI bolts on AR's after over 10,000 rounds through the gun within a year. I cracked the handguards on my M16A2 when Clinton got re-elected in 1996 while I was in the field on the DMZ in Korea, but I don't think you're talking about that...

It's always good to have spare bolts on hand, that have the exact same bolt face depth. You should also change your ejector and extractor springs every 2000-4000 rounds, and look at the bolt gas rings around then as well. After about 5k of high volume, gas rings can erode, and cause you to lose your gas seal, leading to short-stroking. Recoil springs are also supposed to be changed at somewhere between 5000 & 7000 rounds, depending on how they measure in length, or if they become weak. Most soldiers don't realize what parts are periodically changed in their weapons because it is armorer-level maintenance. As a civilian, one needs to assume these armorer-level duties oneself. The AR is probably the easiest service rifle to maintain, without any real gun-smithing skills, so only a few basic tools are necessary.

[Jaywalker]

Thanks, I was thinking somewhere along the lines of broken bolts or some such, or possibly odd breaks that don't normally show up in the 5.56.

[TritonArms]

The Grendel pressure levels are just fine for the platform, and do not really have any sort of 'problem' areas any more than a 5.56, expcept for little tweaks such as extractors and magazines. Grendel reigns supreme.

[LRRPF52]

For any rifle, it's a good idea to have as many spare parts on-hand as possible. For AR's in general, that means at least an extra bolt, gas rings, all your springs, pins, and small parts. There are several kits available through Brownell's and Midway to address these demands. Buy a parts box with all the segments in it, and stock it well. Extractor, extractor spring, extractor buffer, extractor pin, ejector, ejector spring, ejector roll pin, firing pin, firing pin retaining pin are the main spares I have always kept on-hand. You can even stow many of them in a Magpul grip on the rifle/carbine.

[QuadCam]

You can even stow many of them in a Magpul grip on the rifle/carbine.

your grip must sound like a bag of marbles. :-)

[warped]

your grip must sound like a bag of marbles. :-)

Nope you wrap them in a piece of closed cell foam.

Heck we carried spares in a regular A2 grip like that, it does not fall out.

Is the bag is water tight it does not even rust when submerged.

Anyone who did winter warfare, jungle school or riverine ops can appreciate that.

[QuadCam]

Nope you wrap them in a piece of closed cell foam.

Heck we carried spares in a regular A2 grip like that, it does not fall out.

Is the bag is water tight it does not even rust when submerged.

Anyone who did winter warfare, jungle school or riverine ops can appreciate that.

I was just messing around, but that is great advice.

[LRRPF52]

Magpul's grip core inserts actually are designed to hold these different parts in an elastomer plug that keeps them from rattling at all. The have one that holds a spare bolt and firing pin, one that holds batteries, etc. Also, the VLTOR, LMT SOPMOD, and Magpul ACS stocks have storage tubes within them that are good for certain small parts.

[Jaywalker]

For posterity - From other threads I learned of broken extractors and sheared bolt lugs, but no real indication of frequency.

[Nimrod]

I just broke an exctracter the other day, my rifle has probably 1200 rounds through it. I don't know if that is commonly broke part though as this is my first AR-15.

[Mutt]

Most broken lugs I've heard about were typically from people reloading thier own. Some like to push the limits a little farther that others. I'm positive you can shoot Wolf Gold all day and never have a bolt lug (that isn't flawed) break on you.

[warped]

Hey last weekend we had an extractor quit working on a 5.56mm so it is not exactly something that only pertains to the Grendel.

I need to test it but it looks like it developed a burr in the groove.

[ctrmass]

I've done some research before getting one to assemble.
Seems as though the sheared lugs can be attributed to the front of the upper receiver being slightly off spec on many uppers.
If you have a lathe to check the flatness where the barrel extension mates up to the upper this is a non issue.
Of the sheared lugs I've read about, all can be attributed to the receiver being off spec, thus the bolt does not have adequate/complete contact with the lugs in the bbl extension.
I true all my uppers as a routine. One less possible problem.
You'd be surprised how "off" this surface can be!
JM.02

Edit: I'm sure putting your rifle on a strict maint schedule couldnt hurt. Bolts DO have a service life.

[Mutt]

Most of what you see break or wear out on any AR, M16 or M4 (same parts) is ..... gas tube rubbing, plastic handguards breaking, plastic butts cracking, bolt lugs cracking/breaking (not as comon as you'd think) broken firing pin (usually the tip), extractor and pin. Everything and anything can break, and the thing you'd think would be the least likely is the part that will break first ...... LOL.

But, in general. If you keep a complete lower parts kit, complete bolt (but not bolt carrier group) and spare firing pin on hand, that would pretty much cover you for most of your run of the mill field repairs. I'd also keep a spare gas tube on hand because they tend to rub and wear out on the end where it contacts the bolt carrier group.

You really should get yourself an armors manual. I do believe they list the round counts for each part, when they should be changed and at what intervals they should be serviced. Not a bad piece of information to have on hand.

[Drifter]

Of the sheared lugs I've read about, all can be attributed to the receiver being off spec, thus the bolt does not have adequate/complete contact with the lugs in the bbl extension.

Perhaps my perception is flawed, but it seems the Grendel has more bolt and extractor issues versus other common AR-15 cartridges. While a barrel-upper receiver connection could certainly be a contributing factor, I don't think this issue is any more prevalent among Grendel rifles versus other cartridges. I think there's simply less metal on the bolt surrounding the cartridge head due to the size of the cartridge head itself.

Like someone has mentioned previously, I think many issues are with handloaded ammo that might lean to the hot side. But I still perceive the issue to be more common with the Grendel. I've shot thousands of rounds of 5.56 and 6.8, both factory and hot reloads, and have never broken a bolt or extractor. In just a few months using 3 different Grendel barrels and one 264 LBC stick, I've broken 2 bolts and an extractor on another.

I'm not knocking the 6.5; it's my current favorite. Perhaps like someone else has said, the bolt and extractor act as a pressure gauge. When they break, take a serious look at what you're feeding the weapon.

[ctrmass]

Could be Drifter. Gotta remember, the 6.5 G owned by a civilian is NOT on a strict mait schedule.
I dont own a 6.5 G yet. I'm still assembling one.
This is only info I've gathered through searches.
Using 5.56mm pressure ammo, IMO the M4 platform is operating at close to it's limits.
Throw into the fact that the head needs to be "opened" to accomodate the larger case cant help in the longevity dept.
As a man once said "Man's got to learn his limitations". Dont hotrod it!
Disclaimer: I'm not an schooled engineer, just a casual observer.

[LRRPF52]

I've always felt that the standard AR15 bolt geometry was too wimpy for even 5.56, which is already on the edge of max pressures by design. The original objectives of the Small Caliber, High Velocity Rifle was 3400 fps with light projectiles, but they realized they were pushing way too far with the pressures. They wanted to extend the explosive lead shower effect on tissue that SCHV projectiles exhibit when going over 2600 fps. Even after lowering the pressures to 55,000 psi, the AR15 was and is a very high-pressure system with a low-mass bolt, with wall thicknesses on the sketchy side of logical in my book. The .270 Winchester max's out around 51,000 psi, for comparison.

On the other hand, if you look at an AR10 bolt, it is really well-built, and hefty. I was surprised recently when looking at an FN SCAR 7.62 bolt after breaking it down-It had a wimpy little bolt with thin walls, but was made of some different type of steel alloy, which showed early signs of surface corrosion. I wonder how long it will be before they start letting go, or if the alloy will take a beating of repeated 7.62 in high-volume.