I was upgrading my M16 from an A2 to a flatop. I bought a LWRCI upper for this project. It is marked 6.8 which LWRCI said is the exact same upper as their 5.56 models. I noticed my 10.5 inch HBAR (unfortunately it's a M1S...it came with it) fits quite loose as it wobbles significantly more than in my A2 upper. Will this problem be remedied once I put my Larue 9.0 rail on or is this something that should concern me? Thanks.

I don't like upper receiver wobble.

Technically the relation between the bbl and the sights/optics isn't changing when the receiver wobbles, but it bothers me. The fewer distractions you have, the more you can concentrate on keeping the sight picture you want and trigger control.

quote:

Originally posted by LDD:
I don't like upper receiver wobble.

Technically the relation between the bbl and the sights/optics isn't changing when the receiver wobbles, but it bothers me. The fewer distractions you have, the more you can concentrate on keeping the sight picture you want and trigger control.

Oh no, I'm not talking about receiver wobble. When I insert the barrel into the upper receiver (before I install the hand guards), there is more play in the LWRC upper than my unknown A2 upper.

I think I understand now. You are concerned with the bbl to receiver fit?

It's not a good sign, but have you tried locking the bbl down with a bbl nut?

Some barrels fit looser than other barrels. Once you install the barrel nut it should be tight and locked into place. You could always bed the barrel. I've never done that. I would lap the upper receiver before installing the barrel.

If a barrel is moving with respect to the upper receiver and the sights, how in the ever-lovin’, blue-eyed world can the gun possibly be accurate? I’ve only seen that once in my instructor and armorer career, and after it started the previously-zeroed gun produced 6-inch patterns 11 inches left of the point of aim at 25 yards. Someone recently posted here that he had a gun with a barrel that wobbled around freely, and it was supposedly his most accurate AR. I just assumed that I completely misunderstood what he was claiming, that he was incredibly lucky, or that all his other rifles must be really horrible.

Or are we just talking about how loose the barrel is before the barrel nut is installed?

[QUOTE]Originally posted by sigfreund:


Or are we just talking about how loose the barrel is before the barrel nut is installed?[/QUOTE

I don't think I'm doing a good job of explaining myself. The loose barrel issue is without barrel but.

You need to shim it.


You could also use Loctite #609 which is for press-fit bushings. But if the barrel is as sloppy in the upper as you say, I would get some shim stock and get it tight first, then use the shims and the loctite once you know how thick of a shim you need.

Had no idea shimming a barrel was even a thing! This barrel will be used for f/a fire so I don't really need a tack driver. But I believe M1 Sales barrels like the one I have is bottom of the barrel (no pun intended). Maybe I should get a Faxon or Ballistic Advantage barrel as a replacement?

quote:

Originally posted by alou:
I don't think I'm doing a good job of explaining myself. The loose barrel issue is without barrel but.

Not uncommon. Once tightened with the barrel nut, it will be locked in place.

This message has been edited. Last edited by: ed308,

quote:

Originally posted by alou:
Had no idea shimming a barrel was even a thing! This barrel will be used for f/a fire so I don't really need a tack driver. But I believe M1 Sales barrels like the one I have is bottom of the barrel (no pun intended). Maybe I should get a Faxon or Ballistic Advantage barrel as a replacement?

Some companies use barrels that require heat for an interference fit.

For full auto? Screw the barrel nut on and go to work.

Ok as long as it's not unusual or harmful to me/gun I'll just install the rail and chive on.

quote:

Originally posted by alou:
Ok as long as it's not unusual or harmful to me/gun I'll just install the rail and chive on.

You should be fine. There is a little looseness in my target upper, but once I torque down the barrel nut it's a tack driver.

quote:

Originally posted by alou:
Had no idea shimming a barrel was even a thing! This barrel will be used for f/a fire so I don't really need a tack driver. But I believe M1 Sales barrels like the one I have is bottom of the barrel (no pun intended). Maybe I should get a Faxon or Ballistic Advantage barrel as a replacement?

Please dont use that barrel. Ditch it and get a half decent barrel for a few bucks more. Think how close your face is to the chamber, is it worth it?

I dont know what retail is on ballistic advantage is. But i know dealer cost they can be had for around 95 bucks for a M4. So they cant be that expensive.

The problem may not be the barrel, it may be the upper receiver. I prefer shopping for uppers at gun shows specifically so I can test fit a previously purchased barrel to a variety of uppers to get an ideal fit as possible. IMO a loose barrel to receiver fit will NOT produce optimum accuracy no matter how tight the barrel nut is torqued down.

Since you already have both I would suggest that you do what I did with my 300 Blackout where I learned the importance of trial fitting while shopping. With that rifle I purchased everything off the net and like you had a sloppy fit between barrel and receiver. My solution to correct this was to wrap the barrel extension with a single layer of 0.0015 stainless steel shim stock. In the hopes of allowing a barrel change in the future I also locktited that shim to the extension but in spite of trying to keep the locktite from migrating to the shim/receiver side of the fit some loctite bled through the gap. As a result it will require using heat and a bit of hammering with a dowel to separate the two but as the complete rifle shoots a bit under 3/4 MOA I won't complain about that.

Bottomline, Shim your fit till it's perfect. BTW for me a perfect fit is one that will go about 3/4 of the way home if you "lean on it" and requires the use of a 6-8 ounce nylon hammer to get the barrel fully seated. Locktite with a fit like this is optional and may be considered a touch OCD by some. And yeah I am a touch OCD, it runs in the family.