I just had my Bushmaster Dissapator(16")barrel replaced with a new Bushmaster M-4 barrel with AK brake. I went to rezero the rifle yesterday, but it was shooting very high and to the left. I was able to adjust for the windage problem, but to try to compensate for elevation required me to turn the front sight almost past the ears.I had the barrel installed by one of my units armorers so it was done correctly and to mil-spec. Any ideas??

Sounds like you need to send that puppy back to BM and get it re-indexed. It's a problem...there's a lot of threads about the same thing.

I had the barrel installed by our armorer, watched the whole thing. This guy has done about 200 conversion kits, I am certain it was done right. I watched the torque wrench it hit 45 lbs which is way under the 80 max. I think the sight radius has changed by the new profile of the M-4 barrel.

The two problems that may are occurring are that,

1. The bullet is hitting the new brake on the way out.  Check the brake for signs of copper fouling/rubbing.

2. As for shooting High, the new barrel may have a A-1 sight tower or sight pin.  The a-1 tower and pin are lower/shorter than the a-2 and will cause the shot to be high.  As far as the shot going to the left, the barrel may have twisted during install, casing the front sight to be canted.  Did the armorer use a sighting bar to confirm that the front sight was indexed with the carry handle?????  Did the armorer use a upper vice block or a barrel vise block?


Im off to go shoot, so get back to use with more details, and we can help you trouble shoot the rifle this evening.

Dano

A barrel vise block was used to install the new barrel. No alignment tool though. The weapon is still within spec as far as windage, less than 12 clicks I believe is the spec. My duty weapon is set to the right as well (not as  much). My big concern is the front sight. I qualify with this type of weapon twice a year, I know the course of fire and how to zero. It was very windy yesterday (right-left) that may have affected windage, but the elevation is not right. I have never had to make such a drastic adjustment to a front sight, ever.Thought about the brake too, looked it over carefully as I cleaned last night no marks or scratches in the phosphate.

Your sight pin/front sight tower is a too short.

The easy fix is to install a longer front sight pin.  This will allow you to zero the front sight, without having the base of the pin above the top shelf of the base tower plain.

As for the windage, if you can live with it great.  Myself, I would strip the barrel and re-index the barrel to dead center.  But then again, I strip rifles apart for any reason given, and some time, just because I am bored. It keeps me from having to watch TV to pass the time.

DPMS sells what you need:
www.shooterstore.com/acb/showdetl.cfm?&DID=90&Product_ID=11538&CATID=494

P.S. Shooting was fun, just a little colder that I would like. Figured that I would get back to you before I bury myself in the gun room cleaning weapons.

I could change the front sight, adding a longer one. I shouldn't have to though. The standard A2 sight should work, without being modified. If I do add an extended post more than likely it will protrude beyond the ears.

If you manage to zero the rifle with the standard sight, then the new front post will be no higher that your current sight, just the base will be lower. This will allow the detent pin to retain the pin better that having the pin base rim wandering above the top of the base.

If you saying that with the rear sight cranked all the way down, the front sight pin will need to higher than the ears, you have barrel problems.  The barrel is either not set correct in the upper(canted), the barrel is bent or your detachable handle is sitting way to high to zero out the rifle.  

Your armour should have caught this at install, but may need to take a look at the rifle a second time to catch the error.