I just bought a Bushy XM15-E2S. It has the carry handle permanently attached. I would like to replace that reciever with a flat top. Is it a pretty simple swap? Is there anything I need to know? I would also like to switch out the hbar barrel for one with a threaded end so I can install a flash hider. Any recommendations on this swap? Last question guys, is this a decent weapon? Thanks for your patience, I am new to AR's.
John
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Your rifle is sorta like mine before I modified it(mine had a fixed stock).  As far as replacing the upper yourself, I say since you want to replace the barrel also just get a new complete upper.  Although AR's are known for thier simplicity in building, I would recomend you bypass the tooling etc unless you plan on building a few.  If you want to replace the entire upper with a flat top, its as simple as popping out the takedown and pivot pins and replacing the upper(Im sure you can offset some of the price of your new upper by selling the old one here on the EE).  Bushmaster is considered one of the top tier weapons with colt, rock river arms, and others, so rest assured that your weapon should give you years of great service with propper maintenance and cleaning.

I had the same situation and found that I didn't like the scope mounted so high, even with a cheekpiece.  I just sent my upper to Bushmaster and purcased the stripped down A3 frame.  They are switching it out for me.  The frame cost around $140 and the return shipping was $16.50.  So it was cheaper than buying the tools to do the job.

Quoted: I just bought a Bushy XM15-E2S. It has the carry handle permanently attached. I would like to replace that reciever with a flat top. Is it a pretty simple swap? You will need an upper receiver block, barrel wrench, torque wrench, along wih go and NO-go chamber gauges to install the barrel on a new A3 upper. Is there anything I need to know? Get the US Marine Corps M16 manual for all the info you need to know on building an AR15. Check out GI Jane's it's the best $6 you'll ever spend. I would also like to switch out the hbar barrel for one with a threaded end so I can install a flash hider.  Any recommendations on this swap? Last question guys, is this a decent weapon? Heck yea! Tt's an AR15 + it's a Bushmaster you can get much better. Thanks for your patience, I am new to AR's. John

If I was in your position and didn't plan on building more AR15's I'd pick up an A3 upper from carricoz armory for $85 and then send it to an AR Smith like Kurts Kustom Firearms and have him install the new A3 receiver and thread the barrel for a flash hidder.  I had him do  couple of mine after the Ban and his work is first rate + it was only like $36 to have him thread the barrel.  ADCO (go's by the name "BigBore" on this site") can also thread your barrel and get you a pretty good deal on a flat top upper receiver, everyone here says he does good work also.

BTW welcome to the club.

I would like to replace that reciever with a flat top. Is it a pretty simple swap? Is there anything I need to know? I would also like to switch out the hbar barrel for one with a threaded end so I can install a flash hider. Any recommendations on this swap?

You don't need ANY tools if you are swapping out both the upper receiver AND the barrel.  

What I would do is find the upper I like (flattop plus threaded barrel) from J&T without bolt carrier assembly and use the bolt carrier assy you have now.  Or, you can simply sell your whole upper half and buy an upper half.

From J&T there is not much price difference between a whole kit (everything but the lower receiver) and a complete upper half.  

You could buy a carbine kit with flattop and threaded barrel, there's your upper half, keep the lower parts kit for spares, and sell the adjustable stock and upper half at the next gun show.  There are lots of guys wanting to replace fake CAR stocks with real one.