In order for me to install a freefloat handguard on my new Bushmaster 14.5" postban barrel assembly with Y comp I need to remove the barrel extention to get the freefloat barrel nut on.
The reason I feel I need to go this route is that I cannot remove the welded Y comp and get the front site off.

Anyways - it looks like I need to buy a "barrel extension wrench" from Brownells to achieve this task.

Has anyone removed the barrel extension off a Bushmaster barrel assembly? Do you forsee any problems?

Also when I go to put the barrel extension back on what torque setting should I use?

Many Thannks!
PMD

By removing the barrel extension you will void the headspacing set at the factory. Reinstallation of the extension or a new one (which is most likely because of dinged threads or locking lugs) will not guarantee that the head space will be correct. Only if you get luck the first time will it be right. once head space is correct, then the front sight tower and gas ports will have to be checked for proper location and alignment. If the holes are out, weld up the old ones and drill new ones at the proper location......................................

I think you can see where I am going with this. It would be cheaper and easier to buy a new barrel of the desired profile and install the handguards on that one. That way you could get whichever Comp you want and have it drilled, pinned and welded by you local 'smith (maybe $50 max)

A far superior idea:

Take the barrel to a GOOD gunsmith who owns a good lathe and knows how to use it.  And get yourself a comp that you WANT on the gun.

The gunsmith can chuck the barrel up in the lathe, shave the comp off, and leave a nice clean surface to attach the new comp on, this time pinned on so it can be removed if necessary.   And of course, he'd install the freefloat barrel nut before putting the new comp on.

This is by FAR the best solution.

CJ

Sounds like you should give Kurt Wala ([url=http://www.kurtskustomfirearms.citymax.com/page/page/8932.htm]KKF[/url]) a call, that's right up his alley.

I have done exactly what you describe on two rifles.  Contrary to what Tac40 mentions, the headspace was not actually affected after reinstalling the original extention, but what was affected was the "clocking" of the extention lugs to the gas port.  Tac40 is 100% correct if a new or replacement extension is used, then headspace and gasport alignment will be a major issue.  In my case, the change was slight but noticeable when rezeroing the rifles after all the work was completed.

Should you decide to tackle this job, you will need a set of barrel viseblocks to hold the barrel when loosening and retorquing the extension.  The proper torque is 150 ft/lbs.

I, too, encourage you to just buy a new preban barrel and brake to do your floating HG conversion.  Makes the job a whole lot easier and perhaps less expensive in the longrun.

Opps.  Just reread your post.  With a 14.5" barrel you are going to have a real problem.  After sliding on your new hand guard and or locking ring you have little to no barrel ahead of the sight post to grab with the vise blocks.  You may have to clamp around the existing compensator to retorque your extension rather than the barrel itself.

I may be completely missing the boat here, but if you mean torquing the barrel nut, if that is similiar in operation, just use a receiver vise block and clamp the receiver instead of the barrel.  Again, I may be totally on the wrong page here.

Thanks for your input...
I think I will attempt to remove the barrel extension and then after switching the barrel nut re-install the original barrel extension.
If the barrel extension gets dinged or damaged I'll go the rifle smith route. If not, I'll reinstall to the proper torque setting and recheck head spacing.
I'll update you after my barrel extention wrench arrives.

Thanks!
PMD

Hope you have a damn good barrel vise that will handle 150 ft/lbs of torque.

If you're going to go the barrel extension route, grind or file an alignment notch somewhere on the outside of the extension and the barrel.  When reassembling the barrel and extension, ignore torque specs and just reassemble it until the notch is perfectly realigned.

Even a mark made with a pencil might be adequate, but I'd be concerned that it might rub off.

CJ

AK-Mike:  

PMD is talking about the barrel extension not the barrel nut that attaches the barrel to the upper receiver.

Thanks Russ4777.  My ignorance is screeming through again.  I didn't realize the barrel extension was screwin in/on, and didn't know it was that tight.  All I know is I want to avoid all that if I can.  I think I would much rather lathe off the compensator.

BM removed and replaced my barrel extension after the barrel nut was damaged. They have a very experience tech up there that does this at least a couple times a week. He said "No problem" and it wasn't. Everything was lined up perfectly. No change in headspace or alinement. Need HUGH vice, 10 Ft cheater, barrel extension wrench, some luck that everything comes apart easily and a couple of extra hands to do it right, thats what BM said and thats what they did.

PMD,

I strongly recommend against this, it's a hell of an operation even in an equipped shop.

I used to do it 3-4 hours a week while working in barrel assembly and it's more involved than it sounds. It is indeed "no problem" if you've done it often and have the right tools and spares.

When you reinstall the extension it is going to screw on tighter (further) than it did previously. This will affect the alignment between the front sight and the alignment pin.

This leaves several options.

1. Using the same extension and reclocking the barrel as you would do when setting back the barrel on a bolt gun. Except that shortens the distance between the extension and the fsb making the handguards even more difficult to remove and causing the gas tube to stick too far to the rear.

2. Using the same extension and not reclocking the barrel. Except you'll have to shim the extension or not tighten it as much.

3. Try fitting different extensions until one lines up looser when hand tight and lines up properly when torqued. If you swap the extension you'll probably have to modify (deepen usually) the headspace.

Honestly, the Y comp is a nasty thing fobbed off on serious AR owners it's no loss.

To all - Thank you for your input.

fyi - I own a few service rifle uppers built by Frank White and John Hollinger that I use for shooting accross the course.
This rifle project with the "Y" comp was a project for shooting bowling pins at 50yds. This project is only for fun shooting and the "Y comp" was a must have for me.  

Anyway - yesterday prior to reading tha last few posts I did work on this project. My barrel extension wrench arrived from Brownells and I was off.

My biggest challange was to tightly lock the barrel in a vice. Using alum barrel blocks and fortunately having a really large vise (weighs a good 100lbs and is well bolted down) in my machine shop. First couple of tries I needed to tighten the vise a bit more. With the aid of a 6 foot pipe I was able to acheive the needed grip.

Using the barrel extension wrench and a torque wrench the extension came right off (using a little muscle).

Once off I switch the factory barrel nut with the free float  alumn one. The challange now was to properly reinstall the extension.

Prior to removing I mark its location on the barrel. Setting my torque wrench to 170lbs I put the extension back on and after the "click" of the torque wrench I was able to line up the existing barrel extension with the existing barrel.  Tweak was right that I probably could have tightend past the mark but, I opted to stop at the mark since I know it was over 170lbs.

Last night I went out to the range and test fired. The gun cycled great and seemed to perform perfectly. I guess the only thing I need to do now is get used to the wallop of the "Y comp" which by the way worked extremly well.

Again many thanks for all your input.

PMD

For future reference you don't remove fasteners with a torque wrench it's an excellent way to damage them.