Upper Assembly Questions

[keystone183]

Working on getting a couple of new builds together and was thinking about the process. One thing that bugs me sometimes, is getting the gas block/tube aligned just right through the upper, especially with a clamp-on block. Anybody have any tricks to getting this just perfect? I assume that this would be an area that could affect accuracy if not just right. Maybe i'm going a bit overboard?

The idea i was just thinking about was boring out the opening the tube passes through juuuust a hair, giving me a bit more clearance and wiggle room. I always feel like my tube is resting against one of those prongs, no matter how i align it, or even try and bend it a bit.

Any suggestions?

[montana]

I assume your talking about the prongs in the upper receiver?. Don't do it, it is not necessary as the prongs help center the tube. If you get your gas block aligned properly on the barrel your gas tube should fit the carrier key correctly. After assembly I will take my bolt out of the carrier and run it through my upper to see if there is any friction with the gas tube. Getting the gas tube correctly aligned will stop unnecessary wear on the gas tube button which could cause a gas seal problem. It will have no ill effect on accuracy. I will tweak the gas tube with a screw driver if it is needed.

[A5BLASTER]

I just finished my upper build and here is what i did to get proper gas block aliment.

I backed the adjusment screw out of the block and then closed the chamber then stock a small air line from my compresser in the muzzle and turned it on not much pressure mabye 10 pounds, you could also do this with computer duster I think, when I moved the block around and found where I was getting the most air flow coming out the block I made a pencil mark on barrel and bolt.

That mark gives you top dead center, I then removed the block and put blue locktite on the gas tube where it comes out the block to seal it up and then put a small ring of red locktite around the port hole in the barrel ( not to close that way it wouldnt go down port are up into gas block).

I then replaced gas block and set it on the marks and tighted it down.

Almost forgot Im using the JP split yoke .750 adjustable low profle gas block.

Hope this helps I learned to do it like that from more experenced members of the horde.

[ricsmall]

+1 on montanas comments. I take a precision square and mark a line from gas block shoulder out past where end of gas block will be. Then mark center of gas hole in the block, on block so the marks are visible and can be lined up. After assembly but before installing handguard, remove bolt from carrier and run carrier in and out of upper to detect any interference between the two. Turning upper upside down will enable you to observe. The reason for leaving handguard off is in case you need to tweak barrel nut. That should get you pretty good. If is centered in opening in nut and the opening in upper, like Montana said, tweak with a flat head screwdriver.


Edit: +1 on blasters loc tite. I built one upper that wouldn't shoot until I loctited gas block with 242 and barrel extension with the 680 bearing mount.
Richard

[keystone183]

Thanks for the advice guys! This is exactly what i was looking for!

[Klem]

+1 on Montana's advice...don't touch the prongs.

With clamping gas blocks this is what I do;

1. Attach the gas tube to the block and slide this onto the barrel, up against the shoulder.
2. Insert the bolt carrier into battery so the end of the tube is now in the carrier key.
3. Twist/rotate the block clockwise and anti-clockwise so you can feel where it cant go any further in each direction. This then gives a pretty good indication of where the exact middle is, which is where the gas tube is squarest with the carrier key for the best seal and least wear.
4. With the block in the middle of the two extremes, tighten.

I figure there's enough gas in this calibre that you can give priority to squaring the tube with the carrier key. Squaring the tube/carrier is more important than aligning the gas holes exactly. Once the tube/carrier is square, then whatever alignment the gas holes end up in should be pretty close to aligned anyway. If however, after squaring the carrier/tube the holes are not perfectly aligned it's not an issue because there will always be more than enough gas to cycle.