Upper question on Bushmaster?

[nate392]

first post :cool:Hello everyone, ok here is kind of a newbie build question. I bought a brand new bushmaster xm-15 e2s that I bought without a flat top( didn’t know much about the differences with the two when I bought it) but now
I would like to buy a flattop to have installed but I need to know if I can put an m4 upper with extended feed ramps. Can I put on a a3 m4 upper with this model?, I am not sure what sort of feed ramps it has, does it include a m4 barrel extension?, or should I stick to the regular, a2 flat top( i think it is called) without extended feed ramps?.
thanks guys.
-nathan

[Col_Crocs]

Just to be clear, yours doesnt have extended feedramps?
For now let me assume it doesnt.
You have 2 options:
1. Buy an A3 upper. (flattop with no feedramps) thereby not needing any modifications.
2. Buy an A4 upper (flattop with feedramps) and send your barrel and new A4 upper to Adco to have your non-M4 barrel feedramps machined to fit your A4 upper and installed.

[fdxpilot]

Second question. Are you getting a stripped upper receiver or a complete upper?

If stripped, the previous answer is good. If you are getting a complete upper, just slap it on and your GTG.

BTW- If you are getting a stripped upper and using your current barrel, you will need a new front sight or gas block. With a flat-top, you either need an F marked FSB, a new flip up sight, or a railed gas block to mount a sight on. The F marked sights have a slightly higher pedestal for the front sight post to match the rear sight position on the rail. Otherwise, you may not have enough travel on the sight post to properly zero the new setup.

[m4forme]

front sight base... just get a .040 taller front sight post... that will take care of any sighting problems... when you have the work done then you can sell your take off upper to get back some of your money...

[Alex V]

BTW- If you are getting a stripped upper and using your current barrel, you will need a new front sight or gas block. With a flat-top, you either need an F marked FSB, a new flip up sight, or a railed gas block to mount a sight on. The F marked sights have a slightly higher pedestal for the front sight post to match the rear sight position on the rail. Otherwise, you may not have enough travel on the sight post to properly zero the new setup.

I ran into this problem when I put a Magpul MBUS on my Bushmaster M4A3. The FSB was not an F-Marked base and zero was WAY off. The awesome guys on here sugested I get the taller sight post, Bushmaster sent me one and the problem should be resolved [should because I did not go to the range yet]

Here is the thing, Bushmaster makes their removable carry handle sights, such as the one that came on my flat-top, to match their lower FSB's. So if the OP gets a flat top upper receiver, a Bushmaster removable carry handle rear sight and retains his Bushmaster FSB, there is no need for the taller post. However, if the OP gets anyother rear sight, then yes, it will need the .040" taller post as m4forme has already said.

[6933]

I mean this constructively: Do you have the ability to sell it and buy a different gun? Certain brands such as Colt and BCM would be GTG right out of the box for not too much more $$$. Buy once, cry once.

Good luck.

[nate392]

thanks for all the great replies guys, I still have to look and see when I get home again to see if I have extended feed ramps or not, so I guess it will be from there. I plan on buying a complete upper using the existing barrel. Any recommendations on brands of uppers?. I would buy a whole new gun, but money is a bit tight right now due to gradschool loans :rolleyes: which severely sucks when you have such a money draining hobby/ love affair haha.:cool:

[6933]

Nate- We sure did love the loans while in school though, huh?:p Hope it all washes out for you. Lots of good info. on M4C.

[nate392]

I was looking at this upper, any opinions?

http://www.rainierarms.com/?page=shop/detail&product_id=193

I am a bit confused, so if I get a milspec a3 flatop using my barrel and flip rear sight it will be off from the front sight?, the front sigh should be labeled fsb? or can I jus use this milspec with the existing front sight?

[fdxpilot]

I ran into this problem when I put a Magpul MBUS on my Bushmaster M4A3. The FSB was not an F-Marked base and zero was WAY off. The awesome guys on here sugested I get the taller sight post, Bushmaster sent me one and the problem should be resolved [should because I did not go to the range yet]

Here is the thing, Bushmaster makes their removable carry handle sights, such as the one that came on my flat-top, to match their lower FSB's. So if the OP gets a flat top upper receiver, a Bushmaster removable carry handle rear sight and retains his Bushmaster FSB, there is no need for the taller post. However, if the OP gets anyother rear sight, then yes, it will need the .040" taller post as m4forme has already said.

If he sticks with Bushmaster parts, that is an acceptable solution. However, if Bushmaster didn't insist on being non-standard and putting the same sight on all their rifles, it wouldn't be a problem. Milspec for a railed receiver is the higher front sight base.

[Alex V]

If he sticks with Bushmaster parts, that is an acceptable solution. However, if Bushmaster didn't insist on being non-standard and putting the same sight on all their rifles, it wouldn't be a problem. Milspec for a railed receiver is the higher front sight base.

I agree completly. I can not assume for Nate, but I bought my Bushmaster before I knew better [thank you M4c.com] and as I really could not afford to do a redo at this time, I had to find a way to deal with it and thats what I did.

However, I have to hand it to Bushmaster. I e-mailed them about the problem and they mailed me the front sight post free of charge. Sure its only $6, but they could have made me pay for it all the same. Excelent customer service on Bushmaster's part I have to say.