I've gone through forum after forum with no luck digging through earlier posts, so I am making one. I purchased a Bushmaster upper 2 years ago, PN: F1007682. I know there are concerns with a non-standard barrel nut size with some of their barrels, but I cannot find anything on this one. I am trying to replace the stock guard with another free float that has rails to mount to. The new free float I bought has a barrel nut with it, and I have tried to grind it out to fit over the barrel but its not going well. I am also having issues getting the specs on this barrel to just have a machine shop laithe it out. If there is one that can be bought off the shelf, (or another freefloat kit that will fit out of box), I would love a link. I am sure this question has been posed before, but I cannot seem to find an answer. Any help would be GREATLY appreciated.

Thanks,
Pie

That should be a standard milspec upper.  What rail are you trying to install?  I'm assuming you got the new nut installed and the rail isn't fitting but I'm not 100%  Some rails just have very tight clearances, so folks put the upper in the freezer for a while or heat up the rail to expand it a bit.

The rail fits fine, its the nut that will not get over the step-up after the gas block. Its a bull barrel, caliber .223 wylde.

Also, without the barrel the threads fit fine.

Unless it is some crazy profile, I'm not seeing how that works.  Can you post pics please?

Buying a new barrel will be cheaper than having that one lathed. I had a DPMS profile heavy behind the hand guards and it fit just fine. I cant imagine a barrel be too thick to fit the barrel nut. We are going to need pictures.

I've attached a few photos. Hopefully this will help.

Ooooh okay I see what you mean.  The section ahead of the threads is a smaller ID than the rest of the nut.  I've never seen that before.  A good smith or machine shop should be able to lathe that out to a thousandth or two of the barrels OD to fit fine.  That said, I'm not sure how much it'll effect the strength of the barrel nut, and the last thing you want is the nut coming loose while shooting.  I'd definitely consult a smith first.  I've never seen that before.  Weird.

That said, for the cost of the work I'd just consider getting a different rail system.  There are a ton of them on sale this weekend.  Guaranteed to fit would be any rail that uses a milspec barrel nut, like the Samson, Fortis REV, Troy, and Rainier rails.  I can't imagine other companies wouldn't fit, but with different barrel nuts my knowledge gets iffy.

There's also the EE here.  You can pick up some great deals if you shop around.

Thanks for the input. I know there use to be a difference in barrel nut ID between a standard and bull barrel. Is this no longer the case with anything that is mil-spec? Most of the posts I found on the topic were pretty old and all went back to having the nut machined out. I don't have a problem buying a new rail set as long as it will solve the issue. While I dont have an issue paying to have it opened up, I am not thrilled with the rail. I found out it was chinese after I bought it and the keymod is out of spec and hard to fit.

I was looking up .223 wylde barrels and Wilson stuck out. I believe that was the manufacturer of mine. Here is a link to it and the specs. http://shopwilsoncombat.com/Match-Grade-Barrel-223-Wylde-Super-Sniper-20-1-8-Twist-Stainless/productinfo/TR-223SS20NF-18/

I have a bull barrel and a standard barrel nut fits no problem.
I would think the Chinese rail is the problem.
Try a reputable brand and I think your problems will be solved.

I am not sure what specs you are looking for.  If you are already looking at going to a machine shop, take the barrel and the barrel nut.  Tell them what you need to happen.  They will ask if you want to reduce the barrel or increase the hole in the nut.  Make your decision and let them do their thing.  You don't need specs for anything.

I will say that barrel looks way too huge, almost as if it was not finished properly.  Most bull barrels will still accept any barrel nut, with some needing the barrel nut to be relieved a tiny bit by knocking some finish off the inside diameter.  But that barrel appears to be ridiculously thick past the gas block journal.

Well, I finally got some time to sit down and open up the barrel nut a bit. I started off with a dremel and a sanding ball... after about 2 hours of going no where, I went and bought a carbide bit for the dremel and opened it up to the point where it was just shy of clearing the barrel and finished it with the sanding ball. Now that its all together and I have the new handguard and rails on I ran into a new issue. This one should be simple, but not sure.  My scope rings profile seem to be to small. I have a 40mm objective on the scope, but the bell hits the rails. From everywhere I can find info, low profile should fit the 40mm obj. I know I had put on medium profile when I mounted it originally. The bell on my scope is 49.3mm in diameter. Nikon scope Without the caps on the scope, it sits about 0.2 inches to low so the bell hits on the forward rail.

Obviously this means I need to go to a high mount. Then I found some people suggesting to go to PEPR mounts. Any inputs on this regarding weight, accuracy, reliability? My gun is heavy enough, so I'm trying to save on weight, but if the PEPR style lends itself better to accuracy, we will see. I bench shoot alot but also like to stand and fire. I attached a photo of my gun so far as well.

Let me tell you, you're not going to be shooting THAT rifle configuration while standing...at least not very much.  Just do what you've been suggested and go with a PEPR-type mount.  They're not all that heavy anyways.  If it were me, I'd remove the angled fore grip, move the bipod forward and call it a bench/prone rifle.