Fixed: 18" Alexander Arms barrel: 2.5+ MOA

[bbqncigars]

I highly advise the use of a Magpul Bevblock when torquing a barrel nut or such. It's a nice multipurpose tool that mates up to the locking lug recesses to keep stress off of the upper receiver.

[Lastrites]

I highly advise the use of a Magpul Bevblock when torquing a barrel nut or such. It's a nice multipurpose tool that mates up to the locking lug recesses to keep stress off of the upper receiver.

I've used a Bevblock many times and it works well but note that I would never use it for muzzle devices. Barrel blocks for muzzle work are the way to go.

[A5BLASTER]

I've used a Bevblock many times and it works well but note that I would never use it for muzzle devices. Barrel blocks for muzzle work are the way to go.

The bevblock is designed for muzzle device work as well as thighting barrel nuts.

It's all I use but I also use the no torque technique when installing muzzle devices so basicly I don't need anything to hold my upper/barrel to do muzzle device work.

[Lastrites]

A5 I understand what they say and using it for your no torque technique would be no problem at all but when you run up against a crushwasher cranked on md, I'd prefer not. Swear I could see the barrel twist on one I disassembled while using the BB many moons ago. Isolating the clamping force as close to what's being torqued I feel is the ideal way to roll, especially on an overly torqued md. I like my BB and it has a permanent place on my work bench, use it all the time.

[c3k]

I highly advise the use of a Magpul Bevblock when torquing a barrel nut or such. It's a nice multipurpose tool that mates up to the locking lug recesses to keep stress off of the upper receiver.

I have one.

Without typing a book (and remembering that a picture is worth a thousand words), I did not want to use the locking lugs to torque against. Alexander Arms said I needed to tighten the barrel to the extension with 120 lb ft of torque. I REALLY, REALLY, REALLY don't think it would've been a good idea to use the lugs to resist that force. (Lugs are part of the extension: the barrel had to be tightened onto the extension.)

I cannot emphasize how easily the barrel came out of the extension.

When I put this together, I used the same techniques I've used on my other AR builds.

I'm happy to take the blame for any and all "oddities". But, the fact remains, rounds were hard-stuck in the chamber, repeatedly. This did not stop until I polished the chamber. (I did not borescope it.) When I unscrewed the muzzle brake, I was surprised that I had to use the force I did. It took ~20-30 lb ft. BEFORE the muzzle brake loosened, the barrel spun out of the extension.

[c3k]

Piston set-up and an untorqued barrel from the extension are where you need to look before even worrying about accuracy.

Any time you're torquing on a muzzle device, the barrel needs to be isolated, not clamping force on the upper, which is a separate part.

I wouldn't have high expectations from an external op-rod gun in accuracy, unless the gas system was pinned and the barrel bedded really well.

Short story is that there are major issues with a lot of the components and assembly methods you used, before we can even talk about the barrel's accuracy potential.

Another thing with Grendel AR15s is that you have to shoot them differently than .223 ARs in most cases, since the projectile weight and recoil make the gun handle a bit differently as to positional shift.

Thanks for looking at my thread. I'm happy to hear of better assembly methods (but, I didn't really mention mine, did I?), and am a neophyte to the AR build world with only a dozen to 15 builds. Certainly nowhere near your level.

When I UNSCREWED the muzzle device, I used the upper block. Why? Well, I certainly did not expect it to spin the barrel off. I used my magpul bevblock when I tightened it on, back in the spring.

I've built and used 5.56 and .223 Wylde ARs with external op-rods. I certainly did not expect the poor accuracy from my first 6.5G that I saw.

When I get the barrel back or if Alexander Arms replaces it, I'll put it together again (using my assembly methods, as good or bad as they may be ), and report back with some range pix.

Without getting too expensive, which of my components would you change, and why?

Thanks,
Ken

[koden]

I cannot emphasize how easily the barrel came out of the extension.

Barrels can not rotate in the barrel extension after they are assembled. Once they are installed they are pinned to the barrel.



They cant rotate without shearing the steel pin. If your barrel rotated in the extension then it was not assembled correctly by the barrel manufacturer. The pin was probably not pressed in properly or the barrel was not drilled deep enough for the pin. Can you post a pic of the barrel extension and pin? It would be interesting to see how far the pin is protruding from the barrel extension compared to the pic above.

However, he did reply that the barrel should be torqued to 120 lb ft into the extension and to use green loctite

I cant believe Alexander Arms would give you this advice. It needs to be headspaced, timed and pinned.

[c3k]

Barrels can not rotate in the barrel extension after they are assembled. Once they are installed they are pinned to the barrel.



They cant rotate without shearing the steel pin. If your barrel rotated in the extension then it was not assembled correctly by the barrel manufacturer. The pin was probably not pressed in properly or the barrel was not drilled deep enough for the pin. Can you post a pic of the barrel extension and pin? It would be interesting to see how far the pin is protruding from the barrel extension compared to the pic above.



I cant believe Alexander Arms would give you this advice. It needs to be headspaced, timed and pinned.

Yeah...all this.

I sent it in, so no pix. The extension pin only flattened the threads on the barrel. The pin did not protrude any more or less than other barrel extension pins I've seen. It certainly did not interfere with the barrel nut being spun on.

There was NO drilling. The pin looked like it had been tapped into place and it flattened a few threads. It may have been pressed, or it may have been lightly hammered. Regardless, it obviously was not securing the extension to the barrel.

[Kswhitetails]

Love it when the answers are easy. Hard to imagine AA let this one through, but if they're standing behind it, I'm positive they're not the first to deal with one or more instances of this particular issue. A buddy of mine took his BCM apart, and said that the pin would come out of the extension when the barrel was rolled over. It happens, somehow.

Glad to see you've got some resolution.

[c3k]

Love it when the answers are easy. Hard to imagine AA let this one through, but if they're standing behind it, I'm positive they're not the first to deal with one or more instances of this particular issue. A buddy of mine took his BCM apart, and said that the pin would come out of the extension when the barrel was rolled over. It happens, somehow.

Glad to see you've got some resolution.

No resolution...YET.

I've sent it in, after trying to tighten it down per their instructions. (Shipping at my cost.) UPS received it on December 19th. With Christmas and New Year's, I know there'll be delays. I'm not sure what priority, if any, my issue will garner. I assume I'll at least get some confirmation email from them at some point.

As of now, after the initial RMA offer, I've heard nothing.

[Kswhitetails]

They're usually very good on this end, I'd be surprised to hear differently. Keep us enlightened.

[LRRPF52]

Thanks for looking at my thread. I'm happy to hear of better assembly methods (but, I didn't really mention mine, did I?), and am a neophyte to the AR build world with only a dozen to 15 builds. Certainly nowhere near your level.

When I UNSCREWED the muzzle device, I used the upper block. Why? Well, I certainly did not expect it to spin the barrel off. I used my magpul bevblock when I tightened it on, back in the spring.

I've built and used 5.56 and .223 Wylde ARs with external op-rods. I certainly did not expect the poor accuracy from my first 6.5G that I saw.

When I get the barrel back or if Alexander Arms replaces it, I'll put it together again (using my assembly methods, as good or bad as they may be ), and report back with some range pix.

Without getting too expensive, which of my components would you change, and why?

Thanks,
Ken

If you use a piston system, the gas block really needs to be securely mounted to the journal, as in pinned with no gas leakage around the seal of the ID of the block and the OD of the barrel.

The barrel needs to be bedded into the upper, either using thermo-fit, compound, or shim stock with compound.

The upper receiver face needs to be square, which is often out of square after anodizing inconsistencies in surface thickness.

With the combined effects of a larger projectile and the asymmetric forces imparted on the rifle from the external piston operation, we normally see measurable and predictable accuracy loss on piston guns.

Some of the more dedicated companies who invested a lot into making their piston guns as accurate as possible had to do a lot of tweaks across the rifle to get them reasonably accurate, the main 2 off the tip of my head being Hk and PWS.

DNS has had good accuracy reports from his piston set-up, not sure what he's using exactly, but he's also shooting suppressed.

I always use the Stoner Internal Expansion gas system, as it is inherently more accurate with minimal asymmetric forces exerted on the barrel.

I check/square my uppers and bed my barrels, bed the gas blocks, balance the torque on the muzzle device, balance the torque on the barrel nut, use equal torque on all my rings, correct torque on the scope base fasteners, I like tight-fitting receivers personally, a great trigger, a bunch of little tweaks with the bolt, ejector, extractor, barrel extension, and certain shooting techniques that I don't need to do with the .223 AR.

[LRRPF52]

Yeah...all this.

I sent it in, so no pix. The extension pin only flattened the threads on the barrel. The pin did not protrude any more or less than other barrel extension pins I've seen. It certainly did not interfere with the barrel nut being spun on.

There was NO drilling. The pin looked like it had been tapped into place and it flattened a few threads. It may have been pressed, or it may have been lightly hammered. Regardless, it obviously was not securing the extension to the barrel.

The torque value and assembly method of the barrel extension is enough to keep it in place if done to 120ft-lbs. The M4 Technical Data Package calls for the indexing pin to be installed with a press fit, no drilling into the threads.

Some AR15 barrel makers in the after-market choose to drill and pin into the barrel tennon threads, but this is nowhere in the TDP. There is no reason to rely on pinning into the threads if the extension is torqued on heavily.

We've seen problems with some manufacturers who drill and pin, where the chamber will expand into that thin area created by even shallow drilling into the barrel tennon, which is probably why the TDP doesn't call for it after extensive testing by the US Army Small Arms Research Lab.

If someone is telling you that it is standard or mandatory to drill and pin into the barrel tennon, they are simply incorrect.

If I remember right, we had this problem a few years back with some initial group buys with one of the vendors.

A few guys had brass coming out with this strange circle mark on the side of the cases. Looking inside the chambers, you could see a little circle indentation where the chamber pressure pushed the wall out in that area that had been drilled above with the indexing pin.

It can be done if the drill is really shallow, but isn't necessary or called for.

[c3k]

If you use a piston system, the gas block really needs to be securely mounted to the journal, as in pinned with no gas leakage around the seal of the ID of the block and the OD of the barrel.

The barrel needs to be bedded into the upper, either using thermo-fit, compound, or shim stock with compound.

The upper receiver face needs to be square, which is often out of square after anodizing inconsistencies in surface thickness.

With the combined effects of a larger projectile and the asymmetric forces imparted on the rifle from the external piston operation, we normally see measurable and predictable accuracy loss on piston guns.

Some of the more dedicated companies who invested a lot into making their piston guns as accurate as possible had to do a lot of tweaks across the rifle to get them reasonably accurate, the main 2 off the tip of my head being Hk and PWS.

DNS has had good accuracy reports from his piston set-up, not sure what he's using exactly, but he's also shooting suppressed.

I always use the Stoner Internal Expansion gas system, as it is inherently more accurate with minimal asymmetric forces exerted on the barrel.

I check/square my uppers and bed my barrels, bed the gas blocks, balance the torque on the muzzle device, balance the torque on the barrel nut, use equal torque on all my rings, correct torque on the scope base fasteners, I like tight-fitting receivers personally, a great trigger, a bunch of little tweaks with the bolt, ejector, extractor, barrel extension, and certain shooting techniques that I don't need to do with the .223 AR.

@LRRPF52,

Thanks. I did a LOT of that. I'll make a new build thread, with pix, when I get a barrel back from Alexander Arms.

Ken

[c3k]

I have an update. Alexander Arms has notified me that they're trying to find an extension that will keep everything lined up. So, perhaps my existing extension was bad? Or the required torque didn't line up the gas port?

I'll post more as I hear it.

Ken

Edited to add: It sounds to me like they're reaching into the parts bin, grabbing an existing extension, spinning it on to the right torque value and then seeing if the extension lines up. Obviously, the parts on the extension (upper index pin (or just the hole?? not sure if they press the pin in AFTER they spin it on) and extension M4 cuts need to line up with the barrel's chamber and gas port.

It's interesting that they're not lining up. If they aren't lining up now (with the proper torque), how did they line up BEFORE?

Also, if all the barrels and extensions are milled identically, the threads would all be timed the same. I have NO idea how they manufacture the barrel threads or the extension threads, but the process of just grabbing extensions and seeing where they end up after spinning them on seems...sub optimal.

Regardless, I have total confidence Alexander Arms will make this right. Either by finally (randomly?) finding an extension that will time correctly with the specified torque, or by replacing the barrel. For that, I'm glad I went with a reputable manufacturer.

End edit.