View Full Version : Question for those with Magpul MBUS
I recently put a MBUS on my flat top AR. It came with the removable cary handle/rear sight.
I went to the range this past weekend, and with the MBUS my POI was about 2.5" to 3" above my POA and only 25 yards. I knew that I would have to rezo the rifle for the MBUS but that seems like its off by "miles" I don't even think the front sight can be raised that much to adjust for it. Can it?
This looks like 10-12MOA off...
At the same time I got the MBUS I also installed a Troy MRF-CX rail. I thought maybe I messed somethink up on the rifle and that is why it was so off. So I put the carry handle back on and shot 5 rounds again. This time it was back to shooting like it did before so it has to be the MBUS no?
My questions are
1. Is it normal for an MBUS to be that far off or do I simply have a defective one?
2. Can the front right adjust for such a huge difference? [If what I am seeing is normal for an MBUS]
Thanks guy!
SWATcop556
10-15-09, 16:55
Are you using the MBUS sight set or just the rear MBUS?
What make/model is your AR?
I'm having some of the same problem. I have an MBUS rear sight on a 16" BCM M4 upper. Shooting it for the first time at 50 yds, POI was high and right and off the paper. I was definitely expecting a much more accurate shooting session. Ammo was Federal 55gr 223. This was the first time shooting my rifle with the BCM upper. I was wondering the same thing as far as a possible defective MBUS sight or the MBUS being the wrong rear sight for my upper. I ran out of time trying to zero the iron sights and am going to shoot again tomorrow. Any thoughts as far as the MBUS being at the wrong height for the BCM upper? I have also had to crank quite a bit of windage to the left to get it on the paper. Wasn't expecting to have to adjust the sights so much especially at 50 yards.
i just sighted in my new spikes upper, MBUS, and RDS. the MBUS was 6in low and left @50yrds.
so my guess is
1. yes
2. yes
Are you using the MBUS sight set or just the rear MBUS?
No just the rear MBUS, Rifle has a FSB
What make/model is your AR?
Its a BM AR [I know I know... I got it before I knew better lol] its an M4 A3, 14.5" pinned brake, pinned stock... the usual NJ AR rifle bull-poop
i just sighted in my new spikes upper, MBUS, and RDS. the MBUS was 6in low and left @50yrds.
so my guess is
1. yes
2. yes.
It required no windage adjustment from what I could tell. I was using 3" Shoot-N-C target stickers attached to a paper silhouette and the POI was almost directly above the bullseye but like I said 2.5" to 3" high at 25 yards.
At first I thought it was me, have not shot in a month or two, maybe my arm was moving a lot. I have a Bipod that I purchased for my GF when she is using the rifle since she has a hard time shooting it w/o one. Attached it to the Troy rail, same result.
Took the MBUS off, put the handle/sight back on, right back to being on target.
Just trying to see if all I should do is crank the front sight post up, but I am just worried that it can not be adjusted for that much. Maybe Im wrong, thats why I am asking.
Thank you so much for your time guys.
IrishDevil
10-15-09, 22:36
You need a taller front sight post as the BM most likely doesn't have a compatible FSB. Although you can probably get the adjustment needed out of the current post with a 50 yard zero. At least in my experience.
You need a taller front sight post as the BM most likely doesn't have a compatible FSB. Although you can probably get the adjustment needed out of the current post with a 50 yard zero. At least in my experience.
Agree. get the taller post from Bushmaster and zero at 50.
The reason the carry handle that comes with the gun works is that it too is lower height to match the lower front sight. If you put that carry handle on a Colt or other gun with an "F-height" front sight base you would potentially have the opposite problem.
You need a taller front sight post as the BM most likely doesn't have a compatible FSB. Although you can probably get the adjustment needed out of the current post with a 50 yard zero. At least in my experience.
Agree. get the taller post from Bushmaster and zero at 50.
The reason the carry handle that comes with the gun works is that it too is lower height to match the lower front sight. If you put that carry handle on a Colt or other gun with an "F-height" front sight base you would potentially have the opposite problem.
AHHHHH
But from what I gather on BM's website, my rifle should have already come with a sight post that is .040" taller... since its an removable carry handle model... And they only offer 2 posts on their website... It meantions Colt carry handle sights, is the BM carry handle sight shorter thus having the rifle come with the standard post?
Bushmaster part #9349056-M. $5.50.
no one is mentioning this but it is also possible that you use the different sights differently. you do know that the MBUS has two apertures, right?
how do you take a sight picture? do you use a consistent cheekweld? do you shoot nose-to-the-charging handle, or do you let your face rest further back?
it's entirely possible that the different sights are causing you to "line-up" on them differently and this all can have a pretty significant affect to the POI at even 25 yards.
good luck...
no one is mentioning this but it is also possible that you use the different sights differently. you do know that the MBUS has two apertures, right?
how do you take a sight picture? do you use a consistent cheekweld? do you shoot nose-to-the-charging handle, or do you let your face rest further back?
it's entirely possible that the different sights are causing you to "line-up" on them differently and this all can have a pretty significant affect to the POI at even 25 yards.
good luck...
Those are all valid points.
I am not experienced enough to answer them definitively, but from what I find myself doing I believe that I have a consistant cheekweld. I do not go nose to charging handle, I like to be further back. I have no problems seeing both front and rear sight. I use the smaller aperture on both the MBUS and the carry handle sight. From what I understand I should use the larger one at close distances such as 25 yards, but I think I am more accurate with the smaller aperture.
I sent this question to BM Tech Support as well and was told the fallowing;
"When Colt came out with the A3 design with the detachable carry handle they made the front and rear sights .040" higher than the sights used on A1 and A2 rifles. The front sight forging is the same but the front sight post when set for mechanical zero is even with the top of the sight ears instead of below them as the plane for the sight post is milled higher. You will notice on 20" A3 barrels there are two raised bands on the barrel under the handguards. This designates that the barrel has the front sight base with the front sight that is milled high for the front sight post. Colt parts lists have a different part number for the higher front sight base barrels and sight bases for A3 and M4 barrels.
We decided when we began to build the A3 models with detachable carry handles that we would keep the sight heights the same for all models so all our barrels would interchange. Our A3 handle, Flat-top Rear Sight and Rear Flip Up Sight has the same rear sight aperture height as on the A1 and A2 receivers so that all barrels with standard height front sight bases will interchange. The Mark Brown Flat Top Mount also uses this same rear sight height.
They also offered to mail me the .040" taller post free of charge.
Say what you will about BM rifle quality, but their customer service is A+
Hopefuly this will solve the problem while I continue to save up for that Aimpoint lol
Thank you so much guys!
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