Barrel/Gas Block Install

Slug870

Slug870

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Ok, so I am about to begin my first "from scratch" upper build and I have a few questions I would like to ask those with experience. Bear with me as I am new to this and a little OCD as well...

Here's what I am working with;

Vltor Upper
Daniel Defense 12.5" Barrel
Carbine Length Gas Tube
AGW Low Profile Gas Block
Noveske KX-3

And now the questions...

1. Barrel Nut a) I am seeing varying torque specs on the various web sites, youtube etc. What is the recommended range of torque for the barrel nut?
b) What lube etc should I be applying to the threads of the upper prior to barrel/barrel nut installation?

2. Gas Block - Ok, this is the biggie. The AGW gas block is a set screw type. The DD barrel is NOT dimpled for the set screws, which would also facilitate easy gas port alignment. When "dry-fitting" the block on the barrel, my OCD is going ballistic while I am trying to figure out exactly how I am going to ensure proper gas port alignment!
a) Are there any "tricks" to doing this right?
b) Is there a method of somehow marking the barrel for indexing the gas ports?
c) Should I be looking at purchasing one of the jigs for dimpling a barrel?

3. KX-3 a) Is there a range of torque when installing?
b) What, if any, lube/anti seize/etc should be applied?

I know we have some very talented builders on here, and I'd like to here some thoughts on these questions. I am not interested in having someone do this for me, as I plan on doing many more after this one and I need to learn the "ins and outs" so to speak. I would very much appreciate all contributions to this thread; difference of opinion and constructive criticism welcomed.....
 
1 - milspec standard for the barrel nut is 30 ft/lbs minimum and not to exceed 80 ft/lbs - use no lube.

2 - draw a mark on the rear of the gas block and draw a line on the barrel to the barrel shelf from the gas tube hole. Align. - FYI - Gas block holes are large allow for a significant variance - a little off will not make much of a difference.

3 - the KX3 has a crush washer - you shouldn't have to use lube/anti-seize etc - go for 30 ft/lb for torque.
 
"Milspec" torque for the barrel nut only applies to the standard "milspec" barrel nut. As he hasn't stated what barrel nut he is using, it is a little difficult to give values, as different manufacturers give different recommended torque values for their proprietary barrel nuts, and as he is installing a low profile gas block, I would assume he is not installing the standard barrel nut/delta ring assembly. He should follow whatever instructions came with the handguard/barrel nut he is installing.

For example, Daniel Defense specifies that the barrel nut for the M4 RIS II, M4A1 FSP RIS II, and Mk18 RIS II be torqued to 50ft-lb. As those particular barrel nuts do not have the assembly serrations, they do not need to be torqued beyond 50ft-lb in order to align it for gas tube clearance.

If installing a standard "milspec" barrel nut, it is only required to be torqued to 30ft-lb, but this can be exceeded, to an absolute maximum of 80ft-lb, in order to align the assembly serrations for gas tube clearance. always torque upwards to provide clearance, and never loosen the barrel nut to achieve this.

Additionally, the "milspec" for installing the barrel nut calls for the application of molybdenum disulfide grease to the threads of the upper receiver before installation of the barrel according to the following technical manuals:
Army TM 9-1005-249-23&P
Army TM 9-1005-319-23&P
Air Force TO 11W3-5-5-24
Air Force TO 11W3-5-5-42
Coast Guard CONDTINST M8370.9
USMC TM 05538C-23&p/2

When installing the gas block so that it is properly aligned with the gas port in the barrel, it is also prudent to ensure that the receiver end of the gas tube is aligned in such a way that it properly engages with the bolt carrier key, and does not bind or cause undue wear. This can be dealt with by bending the gas tube carefully as required.

Regards.

Mark
 
MWL nailed it. Now to simplify:

I aimed for 50ft-lb's and made it to 65 by the time the nut was clocked for the gas tube to line up. This will differ depending on the nut you need for your rail.

To line up my ports, I used calipers to measure out the gas ports on the block and barrel then I used masking tape to "draw" my center line for the port on the barrel. Seemed to work just fine.

A crush washer makes mounting a muzzle device too easy! If you end up hand tight with about 30 degrees left until you are centered, you're good to go, crush it! If you are more than about 30 degrees you can either pre crush the washer with a smooth vise or you can tighten and loosen the washer until you get to about 15 degrees then proceed to centered.

For a type of thread lube, I like the nickel anti-seize compounds. I've used the Lubriplate and Jet-Lube varieties at work for over 10 years and haven't had a thread gall or loosen with it on. Be careful not to hit top end torque specs with a lube though, you can stretch threads
 
Great information, thank you gentlemen for posting.

I notice that nobody has commented on the "dimpling" of the barrel for the gas block set screws; am I to understand that this procedure is unnecessary?
 
I am not going to comment on the necessity of dimpling the barrel for the setscrews, because I do not know if it is necessary.
However if I wanted to dimple, I would install the gas block, and get it properly positioned. I would lock it in place, then remove one setscrew, and use a drill bit that is a clean fit in the hole to lightly dimple the barrel. Replace that setscrew, and repeat for the others. This way, the dimples will be in exactly the right spots.
 
Good advice on the dimpling. If you feel it is necessary, then go ahead and do it. If the low profile gas block is under the handguard, it should be fairly well protected. It is more for peace of mind.

Just a note on the barrel nut. The "milspec" calls for moly, and the torque values are for use with that. Using different, or no lube, will change the torque value requirements. Probably not enough to make any real difference though.

Just remember, you are fitting a steel barrel, and a steel barrel nut, to an aluminum upper receiver. Although they are all either anodized or parkerized, the moly is there to stop any reaction between the different metals, and make barrel removal easier.

Completely unrelated, the torque value normally given in older military manuals in respect of lower receiver extensions is incorrectly printed, which has led to a lot of internet error. The correct torque values are as follows:
Rifle Length Receiver Extension: 35-39 ft/lbs
Carbine Length Receiver Extension Castle Nut: 38-42 ft/lbs

Regards.

Mark
 
tiriaq said:
I am not going to comment on the necessity of dimpling the barrel for the setscrews, because I do not know if it is necessary.
However if I wanted to dimple, I would install the gas block, and get it properly positioned. I would lock it in place, then remove one setscrew, and use a drill bit that is a clean fit in the hole to lightly dimple the barrel. Replace that setscrew, and repeat for the others. This way, the dimples will be in exactly the right spots.
Click to expand...

That is exactly how I did it Sunday night to a buddy's rifle. Easy peasy.

The gas block was under a FF handguard. Things come loose. Be sure to Loc-tite or stake the gas block screws.
 
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