Building for accuracy

[nboost]

Hi everybody,
I'm in the process of getting my upper parts together to build a Grendel. Does anyone want share any tips to help make the gun more accurate. I heard to use locktite when mating the barrel in the upper receiver. Does this sound right? Anything else I need to do to help with accuracy.

Thanks,

[bwaites]

LRRPF52 is one of the board gurus when it comes to building AR's, and hopefully he will chime in. I believe the loctite would be used for the gas block, not the barrel into the upper receiver, though!

[Grendel-Gene]

When you say locktite on the gas block.... do you mean on the set screws or bolts that secure it or on the block itself to the barrel???? Thanks.

[terrywick4]

You don't want to use loc-tite on the barrel nut. The gas tube goes thru the barrel nut. This would prevent the barrel nut from ever backing off. When you put the barrel nut on apply a small amount of grease (I use bearing grease). This keeps the threads from balling up. Torque the nut to 60lbs, loosen up and torque it again. Then tighten it up till the gas tube goes in.

[BenchRider]

Get a lapping tool and lap the upper to square the face where the barrel extension goes with the axis of the bolt carrier bore. Lap until all the black is gone and there's a light, dull-grey surface (aluminum) for the barrel extension to bear against.

Follow terrywick4's advise and torque it twice with some kind of lube to prevent galling the threads (I use anti-seize).

On final installation of the barrel (second torque), goop some loc-tite on the barrel extension to fill in any voids or gaps between it and the upper. I like the blue (removable) stuff.

I'd look up what people are using for torque spec's on the barrel nut. Seems some folks are backing away from the "go to 60 lb-ft and then go till you align the next hole for the gas tube" - particularly with the precision uppers. That said, I think I remember torquing my last .223 build to 60 lb-ft and then lining up the next hole. It shot well, but it didn't meet my 0.5 MOA standards. Barrel wasn't "match grade" anyway.
I wish I could remember what torque we used to install the White Oak 24 in Match barrel in a friend's upper -- that shoots one-hole at 100 yds with 60gr Vmax's.

Lapping is messy. Make sure you clean every last bit of grit or it will affect your torque readings.

After barrel assembly, the next trick is to use a clamp-on gas block. After that, it is aligning the gas tube with the bolt carrier key. After that, well, everybody has tricks they prefer but I can't prove any of mine make a significant difference on the target.

Hope this helps.

[nboost]

After barrel assembly, the next trick is to use a clamp-on gas block.

Do you recommend one.

[Mutt]

Just install the barrel and use the proper torque. Lock tight or bedding the barrel is a waste of time and only makes it that much harder to break the upper apart when you need to change the barrel. If your barrel and upper reciever are both within spec, they should fight snuggly together when you slide them together.

[stokesrj]

Hi everybody,
I'm in the process of getting my upper parts together to build a Grendel. Does anyone want share any tips to help make the gun more accurate. I heard to use locktite when mating the barrel in the upper receiver. Does this sound right? Anything else I need to do to help with accuracy.

Thanks,

Hi,
I've built a few Grendels now, but before I did, I took a class at the NRA school of Gunsmithing at Trinidad from John Hollinger who builds more match winning AR's than anyone. I went to the class to learn all the secrets of building accurate AR's.

What I learned was to start with top quality components and don't worry about it. Since then I've built quite a few sub .5MOA rigs. The most critical component is the barrel, by far the most critical. Use anti-seize on the treads for the barrel nut and green (wicking) locktite on the gas block after it is mounted in place. The wicking locktite will fill any voids in the barrel to gas block interface and dampen any vibrations.

The torque used to tighten the barrel nut in not critical, I've used from 25 to 120 ft lbs with the same results. It is a good idea as stated before to tighten, back off, and retighten once or twice to compress the threads and align the gas tube. Another important point is that the gas tube should align with the center of pass though the receiver. To check this, install the gas block and tube, swing it from side to side and insure the movement is equal on either side of the centerline of the barrel. If not, reposition the gas block until it is.

I've had great results using cut rifle barrels from Kreiger and Satern and button rifled barrels from Wilson and Pac-Nor. I've seen no chrome lined barrels that shot worth having.

Hope this helps,
Bob

[LRRPF52]

You have to be pretty screwed-up to look bad behind a Kreiger, Satern, Bartlein, Pac-Nor, Lilja, Obermeyer, Shilen, etc. For precision guns, I like to have the gas blocks bedded with loc-tite as well. I'll have to look into the wicking loc-tite. I also get a warm & fuzzy when a barrel extension takes significant effort to force into the upper receiver, but I haven't seen any testing to indicate that it matters.

With AR's, a match barrel and nice trigger are usually all that are needed. Some would add tight-fitting receivers, which I like, but that's a two-sided debate as well.

[jwilson1985]

90% parts maybe more. then the rest is installation. its hard to get bad results when you use good parts.

[BenchRider]

Do you recommend one.

I've used the EGW gas block and like it.

I've also heard folks talk of preferring a steel clamp-on gas block because it has similar thermal expansion to the barrel.

I think it's like the rest of the Horde has said -- "Use good parts and it's harder to get it wrong."

[rasp65]

Here is something Bill Alexander said about using Loctite to bed the barrel from the old forum. "It has been found that the harmonics of the Grendel can cause vertical stringing. So to lock this down without LockTite you are talking over 70foot-pounds of torque on the barrel nut. That can be hard on the receivers. As a solution that seems to work quite well was to bed the barrel and gas block in the LockTite 2440 (replaced with 243) and torque to normal specs."

[Variable]

Here is something Bill Alexander said about using Loctite to bed the barrel from the old forum. "It has been found that the harmonics of the Grendel can cause vertical stringing. So to lock this down without LockTite you are talking over 70foot-pounds of torque on the barrel nut. That can be hard on the receivers. As a solution that seems to work quite well was to bed the barrel and gas block in the LockTite 2440 (replaced with 243) and torque to normal specs."

I thought Bill A. was on crack when he first said that, but when I pulled my gas block to install a free float it happened to me just like he said it would. I can personally testify to vertical stringing in my 19.5" upper until I bedded it. At 600 yards it looked like a ladder. Bedded it with blue loctite and it disappeared. After that I listened closely to anything Bill had to say!!!

[LRRPF52]

Yes. Bill A. said that they noticed that about half of the Grendels they were putting out did this, and half didn't. After trying different things on larger batch populations of rifles, the bedding of the gas blocks and barrel nuts shrunk the stringing so that groups printed normally. I also suspect a tighter upper receiver extension channel for the barrel extension would help, as would a 7075 T6 Type III Anodized (harder) billet upper. The AR15 receivers were designed around the .222 Remington cartridge, which was later lengthened to create the .222 Special, or .223 Remington. The impulse characteristics of the Grendel are probably better dealt with using more mass in the receiver junction with the barrel extension, when seeking extreme accuracy.

[Bill Alexander]

Remember when I deal with a rifle it is rarely a specific case but more often a generalized case for production run numbers.

We have a few advantages in building such that we can change the tolerance of the extension to reciever fit. LRRPF52 suggest a tight fit and we typically have a press fit in this area, but in the shop we can push these together when it is not practical or easy for a home builder. The loctite follows the same rational. We cannot afford to have a sample of rifles shoot badly so everything gets loctite. This is not to say it needs it, or that different parts will demand the same solution, it is generally the observation based upon production.

However the advantages also have a down side. Rifles become generalities not specifics. Variation can provide problems which the home builder will easily solve but which we cannot tolerate.