I have been out of shooting for about ten years and am just getting back into it.  Currently I own two pre-ban 20" colt A2's.  One is an H-bar, the other just say's Gov't model.  

I want to change the gov't model to a carbine/ m-4 type rifle. My question is what is my best route to go on an upper?  It seems the easiest is to buy a bushmaster m-4 upper but i'm not sure I want to mix manufacturers. Will colt sell just uppers in preban configuration?  I didnt see any on the their website.

Next question is the colapsable stock.  How easy is it to put on a rifle? does it require gunsmithing or is it something I could do myself.

Thanks

It's cheaper to just change out the barrel, hand guards, and gas tube.

As for  the how to, here is the manual:
[url]http://old.ar15.com/books/TM9-1005-319-23.pdf[/url]

How easy is it to change out a barrel if one has never done it?

Once you understand how the barrel is attached to the upper rec'r, it's a fairly simple process.  BUT, you must have the right tools: a barrel wrench, a vise, and either a barrel vise or an action block.

What about the removal of the Gas tube/front sight assembly?

Read the fucking manual!

Oh, you want a quick answer.

Pop the retaining pin out of the front sight base, twist the gas tube back into the upper reciever, then pull forward when it clears the delta rings.

You have to remove the handguards, bolt, carrier and it's a good idea to demate the upper from the lower.

Keep your current upper together as it will give you the versatility to switch back at some point if you want--or to build another [:D] Removing the buttstock is a piece of cake. Installing the collapsible buttstock is even easier but you will need a wrench for the task(under $10-I know Bushmaster has them for sure, so do others).

I'd highly recommend the USMC M16 Manual. Lots of info on assembly and disassembly as well as troubleshooting($6).

You can get Colt uppers in preban config from several internet suppliers. One is KY Imports and I think Hoplite has also. RGUNS has what you are looking for but they are a total roll of the dice and if you have any problems you are just plain screwed. I'd avoid them like the plague. All have restocking fees which are a total ripoff.

My 2 cents.

[b]Check your IM[/b]

One more thing. Your lower is probably grey. All the new uppers are black. Just so you know.

If you want a grey upper you will have to find one pre-owned. Try sturmgewehr.com, subguns.com, etc. They are a little steep and go very fast. Some may be 14.5 in barreled but this is easily remedied by having someone permanently affix a FS. If you do so consider a vortec or phantom as they work best to supress flash.