I need a more competent gunsmith/armorer’s opinion/advice

[jMarine]

I am working on a large frame AR rifle I’ve had for awhile and swapping out some parts for some better ones. The rifle is an Aero M5 receiver set with a 16” Noveske barrel. One of the things I am switching out is the handguard to a KAC URX 3.1. I am working on trying to get the barre nut wrench and there’s a guy on here that is willing to let me borrow his. This evening I was just dry fitting everything and was going to recheck some tolerances regarding the GB when I determined the barrel nut will not fit over the last inch or so of the barrel. I checked it with my calipers and the ID of the nut measures 1.197 and the OD of the barrel near the extension is 1.198-99.

I’m sure the best fix would be to apply heat to the barrel and nut… will that be enough to give me a few thou more of play so that the nut freely goes of the barrel and can be screwed into place? Should the barrel be turned down? Should the nut be turned? I’m debating sending it off to a KAC armor/smith but I don’t know.

 

[hlee]

JFC. Between this thread and the others you have starred about this build, the universe is telling you not to go forward with this combination. But, I’m not a gun smith…

 

[BangBang77]

Use the very tips of the caliper inside Jaws and re-measure the ID of the barrel nut. They have a tapered edge at the tip that will increase the accuracy. Even them you are using a flat to contact a radius so you can get close but not exact.

Then post up your new dims.

 

[BangBang77]

Adding - if your dimensions are correct as posted, no, that barrel nut will not work with that barrel. One of them needs machine work, and in my opinion the nut is the cheaper component. Any machine shop can handle the needed work.

 

[Evintos]

You need to bore out the ID of the barrel nut.

 

[jMarine]

JFC. Between this thread and the others you have starred about this build, the universe is telling you not to go forward with this combination. But, I’m not a gun smith…

Haha yeah I know right! This rifle was perfectly fine before I had to go and fart with it. I’m just steadfast on the URX rail. I think it’s one of the best looking rails for this platform!

 

[jMarine]

Adding - if your dimensions are correct as posted, no, that barrel nut will not work with that barrel. One of them needs machine work, and in my opinion the nut is the cheaper component. Any machine shop can handle the needed work.

Even though it’s just a few thou, this wouldn’t effect any of the integrity of the nut do you think?

 

[Skunkworx]

Even though it’s just a few thou, this wouldn’t effect any of the integrity of the nut do you think?

Depends how much you take off. If you take 5-10 thosands probably not, 120 different story.

 

[jMarine]

Use the very tips of the caliper inside Jaws and re-measure the ID of the barrel nut. They have a tapered edge at the tip that will increase the accuracy. Even them you are using a flat to contact a radius so you can get close but not exact.

Then post up your new dims.

Yeah I knew better than that. Not sure why I measured it that way. Going back and rechecking though and my measurement I mentioned was accurate. There’s about .0015-.002 difference in the 2

 

[tuckybill]

Could be the paint on the barrel making it not fit. Freeze the barrel and heat the ring. I've built three Aero .308 and I don't see how that barrel nut will do anything there to retain the barrel into the upper. Is that nut just for the handguard not retaining the barrel to the upper? If so just use sandpaper to get it to fit over the barrel.

 

[jMarine]

Could be the paint on the barrel making it not fit. Freeze the barrel and heat the ring. I've built three Aero .308 and I don't see how that barrel nut will do anything there to retain the barrel into the upper. Is that nut just for the handguard not retaining the barrel to the upper? If so just use sandpaper to get it to fit over the barrel.

The URX rail threads onto the receiver extension and the nut threads into the rail until it sandwiches the barrel extension. It’s the same concept as any other just reversed make/female because of the handguns

There’s no paint. It’s just blasted stainless

 

[BangBang77]

Even though it’s just a few thou, this wouldn’t effect any of the integrity of the nut do you think?

Take both the barrel and the nut to the machine shop. I had a URX back in the day but don't remember the nut dimensions. The machine shop should be able to determine if there is enough material in the nut thickness to remove 0.001 or 0.002 of the inner diameter and not compromise structural integrity. As another member stated, they may be able to work some surface magic on the barrel OD and make it all work.

Just an FYI - make sure you have a muzzle device on the barrel or tape it up to protect the crown. You never know how a shop will handle your hard earned money.

 

[357Max]

Open the bore on the nut. It'll be fine.

I had to open one .040 to clear the extension on a large frame Centurion rail. You only need like .005 - .008 if your running the calipers right.