I have a Colt Spoter 20" HBAR A2 with the fixed carry handle.  I am interested in changing the gun from the A2 Upper to a Colt 20" A3 upper.

My question is, do I have to buy an entire new upper for the weapon, Or can I buy a new receiver and just use everything else from the old upper?

I don't know what I'm doing, so any help would be appreciated.  

You can just change your receiver.  All you need is a few tools, a bit of moly disulfide grease (sans graphite), and a good vice.

I did mine earlier this year (A2 type to flattop).  First one is a learning experience and its best to have someone who's done it looking over your shoulder (especially if you are not mechanically inclined).  Otherwise take it slow and easy.  Just follow the -23&P [Maintenace Manual - you can find it on the home page in the books section] and you should be good to go.

If you don't have the tools (barrel wrench, torque wrench, barrel or reciever blocks, pin punch) then you could send the upper off to a gunsmith to swap the receivers.  (since you're sending an upper its not as bad as shipping a firearm - unless CA has some strange laws).

You can buy the reciever and swap everything over providing you have the right tools and know how. I personally think its easier to just buy the complete upper. Or here is a better idea, just go over to the equipment exchange and see if you can get someone to swap ya.

Just buy a flattop reciever from Model 1, Bushmaster, etc. and and put your old barrel assembly on it. No need to headspace it if you are using the same bolt. Slap it on a lower and shoot away.

I did this recently and it is not hard.  I got the RRA upper complete with dust cover and F/A installed for $90 + $4 s&h.

I also got the ARMS #40 BUIS from them for another $100 or so(they are $95 now!)  These are about the best prices I could find, ordered on tues. morn, had em by friday.

http://www.adcofirearms.com/


Make sure the viseblock you get has the cut-outs for flattop uppers.  Had an OLD one that gave MUCHO problems, till I borrowed the correct one.  Only other difficulty was removing the gas tube from the FS.  I had shot this upper alot, and it was a PITA, but we managed to get it out by using very mean looking pliers.  If your gun is new or hasn't been shot much, then this wont be hard.

Tex78

It amazing simple once you get the hang of it. The last one I barrelled all I needed was a hammer and a $12 GI barrel nut tool.

Start the nut by hand, place upper and barrel on a carpeted floor using your foot to hold it down, and tighten down by tapping the nut wrench with a hammer until the proper hole lines up in the barrel nut then insert the gas tube. There's no guess work involved. Only one notch will line up anywhere close the proper torque value.

Sorta the Mujahadeen (sp?) of AR building.

Say, do you actually know Krav Maga? Last I heard, that form of fighting was very effective.

If by A3 you mean flattop you're not going to be able to use the barrel that was on your fixed handle upper. Colt barrels intended for use on flattop uppers have an "F" stamped on the front sight bases (FSB). They are a different height than standard FSBs.
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Subject over covered [url=http://ar15.com/forums/announcement.html?b=3&f=66&id=185]here[/url]

I am thinking about switching my upper as well.
who sells this "F" sight post?

It's not the post that is a different height, it's the base. I don't know if Colt sells them independant of the barrel.

Thanks Tweak, I meant the whole assembly, not the post.

I think I may call Colt to find out. I'll post results.

Tweak is correct about the sight base heights, but I have not found it to make any actual difference [;)].  

I built my M16A4 clone with a 20" barrel from a Blue Label Sporter and an Armalite flat top.  No problems sighting in with an ARMS #40 or a GG&G MAD.

Please let me know if Colt will sell a FSB seperately? I here is does not make a differance on 20 inch barrels, but does on the shorter ones. Thanks

If you want a big hole upper a3 call Daniel Defense they have them for sale for $225 but the will fit with out a adaptor pin