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Posted: 7/8/2006 11:46:54 PM EDT
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i have a bushmaster m4 a2 carbine, and i'm very seriously considering switching my a2 upper receiver for an a3 . i am a diy type person with alot of mechanical ingenuity, but i don't want to jinx my bushy and make it any less reliable than it is in the factory built form ( which is 100%). should i send my barreled upper to bushmaster, and have them do the switch and head spacing? is it a pretty simple operation to do myself, with the proper tools ? would it be more cost effective to buy the upper and tools, headspace guage, or mail it to bushmaster for the gunsmithing. by changing the upper receiver , would i also have to change the fsb? would an a2 co-witness gooseneck mount allow me to see my iron sights well , and cowitness with an EOtech? this gun is absolutely awesome and i don't want to screw it up, so any opinions would be greatly appreciated. e.t.a another Q. |
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It's about $85 for a GOOD multi-purpose wrench and an action block. You probably already have a bench vise, hammer and pin punches right? I charge $40 to tear down and rebuild an upper which covers swapping out ANY component. Going to a flattop and some kind of backup rear sight, you will probably need a taller front sight post (but not the base), but this is only a $5 part and easy to swao yourself while zeroing the rifle with the new rear sight and flattop receiver. As far as cost effective, not really, but if you think you will build more uppers or you just want the tools to do it right, I highly encourage you to buy them. Self gratification is worth something too you know. If it's a one-time deal, then pay someone else to do it.  |
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thanks for the reply. this is a one time deal, and if i decide to build another rifle later, i was planning on buying a complete upper. another question about the front sight, i have a trijicon dot front sight, would i have to ditch it to keep the a2 fsb? thanks again. |
Depends on what rear sight you use. There are some out there which are "commercial spec", which is to say that they are not "mil spec" height. One of these would work fine with your existing front sight post. I can't say which sights are which height as I don't know for sure. Most top quality rear sights are made to "mil spec" height for use with the taller front sight base/post. Maybe the YHM that bushmaster offers would be lower. |
| I am a diy person too. I recently switched uppers on a a bushmaster. just use a small nail small enough to drive out the roll pin on the fsb which holds the gas tube. pull the gas tube back into the receiver and out around the fsb. then I used an old leather boot top to wrap around the barrel. I put barrel in vise very tightly and with the gi barrel wrench loosened the barrel nut and took off upper. replace with new upper and tighten until gas tube hole lines up with barrel nut gap. put tube back in and back into fsb and repin with large punch. I don't bother headspacing. I've never had one of my guns blowup yet. thats the cheap way. I have a very large vise in the garage. |
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imo, i'd save on the shipping and gunsmith fees, and just get a good armor's block, vice, and AR armory wrench and do it myself just follow the insturctions tagged up top--its real easy! if you just switch out to an A3, you should not have to change anything on the FSB/sights--but that will also depend on your replacement sights |
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