I saw ARMS #40 on bushmaster website and it said that because #40 is bit higher than normal, they suggested that I buy taller front sights to accomodate it. When I called my gun dealer about it, he said that he sells ARMS #40 and was not aware that taller front sight was needed with it. So, I'm asking you guys... does ARMS #40 requires it?

I plan to use it with OKO 4W reflex sight on flattop to cowitness the sights. (if that'll help you guys to answer my questions)

-ChaZ

ARMS #40 was designed to be used on military Colt M4's. Not everyone was aware of the fact that Colt was using higher front sight posts on their military M4s than any other front sight ever made. So if you mount the #40 to a carbine that does not have the taller front sight, you may need to buy one. Bushmaster has started to sell them once they were aware of this difference. My suggestion is to try the #40 with what you have. If it works, you are in there. If not, you will know why and you can get the taller post.

The reason that Colt put a taller front sight housing on the M4 is that an M16A2 is at the rifle length ht. Since the carbine, (all carbines) require a higher housing, do to sight plain, the Colt model M4 one is to the mil spec ht.  The #40 works with both carbine and rifle lengths just like mil spec sights have to. The Bushmaster weapons do not have to meet mil spec requirerments as the Gov't doesn't buy them. After market makers reverse engineer what se and then copy. Obviously didn't notice that there is a small dif. in ht's. from an M16A2 to an M4.  It is also cheaper to try and keep making one ht.even after they know it, and try to have one Ht. to fit both, hence they have a problem that they pass onto the civ. customers. The Gov't doesn't stand for that.
Good shootin, Jack

No, the ARMS #40 doesn't require a taller sight post, IMHO.  This is my experience since I've used a ARMS #40 with an OKO optic on my RRA LEGP 16".

The front sight post is somewhat higher than my other AR's but it isn't a problem on my gun.

Good Luck!

Spambo

I personally have replaced my front sights on my pre and post ban bushys with the .040 front sight post part#9349056-M that bushmaster sells. The preban has a SIR #50, post ban has a SIR #46 both with ARMS #40's. I found the stock sight posts were to short and I had them all the way out when zeroed.  Being that far out I found the sight post very wobbley. There only around $5 each anyway, Just don't make that the only item you order or the shipping will get you.

I purchased a #38 Swan sleeve and put it on my RRA 16". I went to the range and expected to have to resight, but at 100yds. it was dead nuts on. The gun came with that lousy "flat top carry handle". Does the RRA A4 have the taller post or am I just lucky?

I had to get a taller front sight post on my Bushmaster when I put the ARMS #40 on it.

With either an HBAR carbine or Dissy carbine, I didn't; with an M4 barrel on the same upper as the dissy, I did (need a taller front sight post).

I bought the BM site post for my BM M4/#40 combo, but didn't end up needing it. Although I did replace the #40 aperature with an A1 aperature.

Nah.
I did have to crank my front site post up a little farther than I'm used to, but it works fine. It's not at the point of falling out or anything. Zeroing at 50 yds. only made the sight base stick up maybe a 1 or 2 mm.