I have a post-ban Bushmaster A2 with a Mini-Y comp.  I want to replace the Mini-Y with a shorter flash suppressor.  I have read some posts and seen some pics for removing one, and I think I know how to do it.  So, here are my questions:
1.  When I remove the Mini-Y will I find that the barrel is indeed threaded, and will a different flash hider thread right up without any problems?
2.  Even though the ban has died will a shorter comp make the rifle "evil" or illegal in any way?
3. What is the functional difference between a "birdcage" and a "Phantom" flash suppressor?  
4.  If I choose a Phantom will it have to be installed permanently or can I unscrew it at will?  I would like to be able to interchange a flash suppressor with a sound suppressor depending on when/where I'm shooting.
Thanks in advance.  You guys are the experts.

Do you have a 14.5 or 16 inch barrel?

If you have a 14.5 inch barrel then you have a threaded muzzle under the brake.  You WILL have to permenantly attach a muzzle device to bring the barrel past 16 inches to be legal.  The Phantom does a better job at reducing/eliminating flash.  The A1/A2 'Birdcage' flash hiders are not long enough to bring your barrel out to the legal minimum length of 16 inches.

The bushmasters with the mini-Y are 14.5" threaded barrels. It was their answer to find that nitch in the market to have 16" barrels with compensators.  Another muzzle device should be able to threda right on, though you may need to get another crush washer for correct timing of the device).  If you remove it, it will be an 11.5" barreled rifle.  The good news is, is that the next muzzle device you put on it (as long as it's 1.5" or longer), you can still have a rifle that has a 16" overall length barrel.  The bad news is, is that you have to perm. fix it to the rifle to have a barrel of legal length.  So choose a muzzle devise and fix it on.  If you want to be able to swap muzzle devices, you should get a 16" barrel, or perm fix a threaded muzzle extender.  From what I've seen on the range at night, the Phantom works better than the bird cage.  I have this same dilema as I want to tinker with different muzzle devices (Levang comp, Phantom, 5.5" tupe, etc...).

But one thing I am going to do before I cut my own mini-y off is to try and modify it first.  as I'm going to basically destroy it taking it off, I might as well play with it.  I'm going to try and grind off the ramps that force the blast back toward me.  Then maybe try connecting the 2 holes (to make it like a AK style brake). Then continue the cuts from the holes out to the front (to make a duckbill type front end).  And if I'm then still not satisfied with it, cut the thing off and pin on another device of some sort.

Anyone want to donate to me a removed mini-y to experiment with?  I'll post pics of my progess in modifying it.

Answers:

1.  Yes, the threads located on the barrel, under the Mini-Y-Comp, can be uesd to install a ne suppressor.

2.  The overall barrel length has to be at LEAST 16", which can include a PERMANETLY attached flash suppressor.

3.  The popular opinion seems to be that the Phantom is somewhat more effective at reducing flash.

4.  Since your BM barrle is omly 14.5" long, the Phantom will have to be permanently attached to reach the required length of at least 16".

This "permanetly" attatched thing sucks.hDragonfly, you can have mine once I get everything swapped out.

Quoted: This "permanetly" attatched thing sucks.  Could attatch it myself or will I have to take it to a gunsmith? Dragonfly, you can have mine once I get everything swapped out.

If you don't have the equipment, a pin or weld type attachment would probably better off going to a gunsmith. You could attempt to solder it yourself by ordering some +1100F solder paste and using a MAPP torch.

If you don't have the equipment, a pin or weld type attachment would probably better off going to a gunsmith. You could attempt to solder it yourself by ordering some +1100F solder paste and using a MAPP torch.

No thanks.  I think I'll let a pro do it.  Do you have any idea how much this will cost me?

Quoted: No thanks.  I think I'll let a pro do it.  Do you have any idea how much this will cost me?

Here's a list of Adco's shop services along with prices. It'll be about $85 to do the work, which I believe includes the price of the Phantom. I think you'll find many people that are pleased with the work that Adco does.

quick question: If your barrel is 16" with out the flash hider, is it  now OK to own a treaded barrel without needing to permantly attaching the FH?

I got a  LMT 16" M4 upper and I understand the barrel is 16" without the FH. I just needed to know if my FH needs to be perm. attached or not, before I go to the range.

The mini-Y is better at reducing recoil and muzzle flip and rise than the Phantom.  However, in doing a better job, it blows all the crap back at the shooter, doesn't look as cool, and heavier.  If you change your mini-y to a phantom, you'll notice a definite weight reduction and increase in muzzle flip when shooting (especially while unsupported (standing)).  But all minor when it comes down to getting rid of that mini-Y.

Quoted: quick question: If your barrel is 16" with out the flash hider, is it  now OK to own a treaded barrel without needing to permantly attaching the FH? I got a  LMT 16" M4 upper and I understand the barrel is 16" without the FH. I just needed to know if my FH needs to be perm. attached or not, before I go to the range.

If you have a 16 inch barrel, you will not need to permenantly attach a muzzle device.