First Upper Rebarrel, & Questions

AR/M4 AR Technical Discussion
1

For those who may have happened on my various “help me” questions, including my gas tube removal problem, I finally rebarreled the RRA upper with the cursed barrel. I took my time, used most of the right tools, and I don’t think I messed up (except for losing a gas tube roll pin).

For what I spent, not including tools, I could have purchased 3/4ths of a new BCM midlength upper, but I wanted to learn how to do this. Now I have a midlength M4 cut bbl on a non-M4 cut upper (shouldn’t be a problem); glad I got the stripped BCM bbl. I really want this as a test bed for equipment I am thinking about using on other uppers (sights, brakes, mounts, etc.) Due to Massachusetts’ continuation of the old federal “AW” ban and other insane anti-gun laws, I have to test certain items on preban configurations before deciding to put them on postban rifles (e.g., muzzle brakes must be permanently affixed to a barrel).

Anyway, a few questions:

(1) I snugged the bbl at about 30 ft. lbs. (maybe slightly less), which lined up with a gas tube slot in the bbl nut, and then tried for the next slot. I gave up when the torque wrench read 75 ft. lbs and I had 3/4ths of a slot to go, returning to the previous slot. Although I tried this twice, the result was the same. I did use wheel bearing grease on the threads. Is this going to be a problem?

(2) I did not want to use the regular FSB as a gas block, so I used the YHM folding sight. It hand fit quite well (before actual installation), but when it came to pushing the gas tube through the receiver and into the gas block, the tube would not go all the way in, despite quite a bit of pushing. After accidentally knocking over everything on the bench trying to get the tube out, I fit the tube into the sight, then placed the sight on the bbl, passing the tube into through the nut, delta pack, and into the receiver. Everything appears good. Any problems here?

(3) Short of actually firing the carbine, is there any way to test to see whether I aligned the gas block properly?

(4) Although the tube appears to fit the bolt carrier key, is there anything I should do to check proper alignment?

Thanks for any help.

2

(1)
where did you leave it? are you using an OEM sprocket-type bbl nut? if you took it up to 75, then backed it down to the previous slot/hole, that’s probably not ok. i would be OK with 30ft/lbs, but the first hole is probably less than that, now… maybe substantially less. the best way to install a bbl nut is to tighten it down 3 times, to work the threads, and then roll back to the next hole. i suggest wiping off all the grease you have on there (but not stripping it off- ie, still slightly lubricated), and giving it another 3, 4 tries. i’ve gone to 80ft/lbs… but dont go higher than that. if you’re using the sprocket-type, you can cut the interfering spike off, if you just simply cannot get it in under 80ft/lbs. just grind it off with a dremel. this’ll be harder if you’re using a proprietary bbl nut.

(2)
doesn’t sound like it… your second attempt was the correct way- affix tube to block, slide block on and fasten.

(3)
nope… the hole in the block is about twice the size of the gas port, so you’ve got some room for error. if you’re restricting gas flow, you should notice the block is visibly canted. likewise, if it’s restricting front or back, the gap between the shoulder on the barrel and the gas block will be all big and obvious… should be about 1/32nd to 1/16th away from the shoulder- but i suppose this can depend a bit on the block… i have no experience with the YHMs.

(4)
just pull the charging handle, field strip the carrier, and slide the carrier into the upper… if the tube is out of alignment, you’ll feel it strike the gas key.

hope that helps- definitely double check your bbl nut. that’'s the most important thing out of your concerns.

3

bkb:

Thanks for the suggestions. After cleaning (not stripping) and working the threads several times, I have addressed the bbl nut problem (it was an OEM-type). Higher torque would only start to strip the nut (DPMS) as the wrench began to slip. Perhaps I need a better wrench. I satisfied myself that the I could get about 50 ft. lbs. of torque in a mid-slot position, removed the nut, dremeled the offending spike, torqued to 50 ft. lbs., then called it a day.

After removing and replacing the torx screws on the gas block so many times, they have begun to strip (and I am using the correct torx head). Why are supplied mounting screws so soft? Grr.

I’ll try the rest of your suggestions tomorrow. Thanks again for the help.

4

You have 2 choices on the stripping screws on the YH. Either contact them and have some sent out or go to your local bolt and screw place. I’ve had to get replacements for many over the years when my “friends” bring their stuff to me to put together for them after they mauled the parts!

As an FYI for the future, this sounds stupid but works well. For checking the alignment of the gas port to gas block when you don’t use a spacer, stuff an ear plug into the chamber and blow on the muzzle end. You can move it around and hear when it in the proper position. When I was told this I laughed but it works.

I feel your pain on the tools. Over the years I could probably purchase a new Noveske for what I’ve spent on tools and doodads for firearms. They are worth it. I’ve got a $200.00 torque wrench that I never use anymore! Once I put a few together I stopped using it except for showing friends how to assemble properly. Good luck, when are you going to start gathering up parts for your next build? Because you will…

5

Yeah, won’t be the first time I’ve had to replace OEM mounting screws with something from the store, sometimes because I am a klutz, sometimes because the screws just aren’t up to the task.

As an FYI for the future, this sounds stupid but works well. For checking the alignment of the gas port to gas block when you don’t use a spacer, stuff an ear plug into the chamber and blow on the muzzle end. You can move it around and hear when it in the proper position. When I was told this I laughed but it works.

I am definitely going to have to try this. :stuck_out_tongue:

I feel your pain on the tools. Over the years I could probably purchase a new Noveske for what I’ve spent on tools and doodads for firearms. They are worth it. I’ve got a $200.00 torque wrench that I never use anymore! Once I put a few together I stopped using it except for showing friends how to assemble properly. Good luck, when are you going to start gathering up parts for your next build? Because you will…

Well, I don’t know where I went wrong on this, or even if I did. I do wish I had been able to follow the instructions I found on various websites (TOS “build it yourself,” Brownells, you-name-it), which made the process sound so easy. Perhaps I need a better bbl wrench. Perhaps my torque wrench was messed up. (I tend to think it was the bbl wrench.)

I know what you mean though. I haven’t even finished this one and I have plans for two more: a SPR and Mass-legal build with nothing flashy.

6

First off you need to know the torque limits. 30 ft./lbs is the minimum and 80 ft./lbs is the max. So when you stopped at 30 and everything was lined up you were good to go.

The best method is to torque to threads 2 times, apply some grease or anti-seize and then make the 3rd time the final time. This will allow you to work the threads and get a better seat.

Not a big fan of gas blocks that aren’t pinned. The better option would be to use the original FSB and have someone cut and shave it down.

7

Thanks for your response. I was concerned that the torque when everything was lined up was slightly under 30 ft. lbs. Hey, do I sound like I know what I’m doing? :smiley:

Maybe I should have stopped there. I do know that trying to go to the next alignment hole was a mistake, but that’s what most (more like all) of the instructions stated.

Well, the next time I do this (and there will be a next time), I will have a bit more confidence that what I think is right will actually be right. If I had to do it all again, I would seriously consider stopping rather than trying for that next alignment slot. I also think that a better, dedicated barrel wrench like this:

http://www.brownells.com/.aspx/pid=27412/Product/AR_15_M16_AR_10_reg__BARREL_NUT_WRENCH

Or this:

http://www.brownells.com/.aspx/sid=1992/pid=468/sku/AR_15_M16_Combination_Wrench?review=1

Would be vastly superior to one of those “all in one” type I was using.

As for pinned versus bolted gas blocks, I tend to agree, especially now. But, I wanted a lightweight flip up sight and, considering my lack of experience here, did not want to tackle the pinned gas block/FSB problem immediately. The bbl I installed was not set up for it (it only had the dimple) and I thought, if my info is correct, that I would have to drill pin grooves in the barrel. Or, is my ignorance showing again?

Speaking of that, can anyone refer me to some information about setting up a pinned gas block/front sight base?

8

Pinned low-pro gasblock setup: https://www.m4carbine.net/showthread.php?p=317054

9

that’s the low-pro block… these are for FSBs https://www.m4carbine.net/showthread.php?t=26630

these are the only commercially available FSB jigs i’m aware of… before them, you had to come up with your own clamping system or make your own jigs. i made my own, but it took a lot of trial and error over the years to get a good system down. while i havent had a chance to try one of comp1911’s jigs (the money and the market ran out about the time they FINALLY got up on the site, but i fully intent to secure one in the near future), but i’m sure it’s a substantial improvement over any method i’ve used.

this is something even most armorers wont do… it’s not that it’s hard, it’s just really easy to fuck up. and since you only really get one shot at it, that’s gay. don’t do it without the proper tools- it wont come out right.

you’re gonna need a mill or really good press and a steady arm, center drill, GOOD cobalt drill, machinists vise, and a basic understanding of machining hard metals- low RPM, plenty of loob, store bites, etc… you’ll also need, if you’re going to taper (and you should taper), a 2/0 reamer… with a good mill, you can mechanically ream, but i usually hand-ream- i’ve got a good press ('50s or so Craftsman), but there’s still just enough leadout that i won’t ream with it.

10

My error, fixed.
Thanks bkb0000.

11

Folks,

Thanks for all the advice. Not being satisfied with the results of the bbl install, I decided to start over. I pulled everything apart, checked for wear and damage, pulled together a few new parts and tools (especially a new bbl nut), and started over.

Instead of worrying about the precise torque, I just tried to snug the b-tard up three times and go from there. To my immense relief, when snugged, the torque measured about 42 ft. lbs. (the only time I measured it) and had about 1 arc mm. to go to clear the gas tube. Another snugging push and … done.

Of course, after all was fixed in place, when I decided to loosen my vise to rotate it slightly on the horizontal axis for another job, I accidentally loosened the locking screws too far and dropped the retaining plate into the vise. Today’s job? Repair the vise. :frowning:

Really, thanks for all the help. There ain’t no substitute for experience.