6.5 Grendel Upper Build

[Kansaswoodguy]

I do like to locktite the barrel extension into the upper receiver never trued one so can't speak to that. I do believe a heavy wall upper reciever makes a diffrence I have a Slick side DPMS that is very accurate and I just recieved a couple Mega SBU uppers I ordered for a couple more precision builds

 

[catorres1]

Thanks for the response. One thing I was told by a builder is that while lower to upper fit generally does not make a difference, when we are talking sub .5 MOA, it matters.

I checked the Aero upper to the Aero lower I have. Unfortunately, it's a somewhat sloppy fit in the front, leaving a lot of lateral movement. My Anderson lower is actually about 4 or 5 thousandanths tigher. I checked an HK 416 lower for comparison, and it's probably 16 thousands tighter or so.

So now I am looking at lots of variables. Looks like the front lugs on all the upper receivers I have are about the same, it slop in the lower that is showing up.

Anyway, I am going to research options on how to fix it, looks like a shim can probably do the trick, but I did find a builder that is going to true the upper and be the whole thing for a decent price, so I'm going to do my best to cover all the possible variables.

 

[Rockfish Dave]

For barrel bedding I have had good results with: Bedded with Loctite 234772 Green 620 High Temperature Retaining Compound. It is specifically for filling press fit cylindrical voids.

 

[catorres1]

The builder is going to go ahead and true and bed the upper and barrel. But my lower was a little looser (laterally, in the front), than I was happy with. It was fine for a regular AR, I supposed, but I am trying to get max accuracy. Maybe it matters, maybe it does not. In the end, I looked at a few lowers and found one that was tighter, so I just bought it. Can't hurt to have a few extra lowers laying around, I suppose. I will use the first lower for a run and gun build, or maybe a dedicated 22lr upper.

Or maybe I will just sell it at some point.

 

[Autorotate19]

I have a forged Noveske Lower and Biller Noveske upper and it's so tight I almost have to use a punch to get the rear take down pin out.

 

[catorres1]

I am not so lucky as that, wish it were. I know I could get there, but I blew my cash on other stuff (lilja barrel, HS National Match DMR trigger). If I had known what I know now, however, I could have just bought a better lower in the first place....but what's done is done, so I'll have to make due with what I've got.

Next time, however....

 

[Kansaswoodguy]

I have multiple AR's don't worry about the upper to lower fit it's not worth your time