the equipment:

Barrett M99 50BMG rifle
Leupold MK4 6.5-20x50 ER/T TMR M5 scope
LaRue LT-107 50BMG QD mount
PMC 660gr ammo


the issue:

we went out to get a basic 100 yard zero with the 50 today and ran into a small problem / issue... it wouldn't zero. after running to elevation all the way down we were still 3 full MILs high. now don't get me wrong, it shoots great but i would really like to be able to get a 100yd zero. more often than not i shoot at the public range that only has 150yds and when i get a chance to walk out further the scope & mount combo should more than allow for enough correction.

the LaRue mount has 30 MOA built in and from what i found on the Barrett site the M99 should have zero.  

this isn't my first time shooting a 50 but it's my first go with the Barrett / Leupold / LaRue combo.

where did i go wrong?
how can i fix this?
am i stuck with the 3 MIL hold under for 100yds?

the low hold didn't keep us from shooting though. we put 20 rounds of the PMC through it today and plan to shoot more tomorrow.  



the wife loves 50BMG

it's a LaRue mount so it's one solid piece. as i understand it there is 30 MOA in the mount and zero in the rail.

Does it bother her to shoot it left handed at all?  I shoot left handed and am interested in getting a 50. but kinda crossed this one off the list because it doesn't look very left handed friendly.

Thanks
JCM

nope, not at all. the safety is similar to that of an AR and she shoots *regular* ARs and M1A1s just fine (although her AR is 100% lefthanded). as for the bolt, it actually works very well for a lefty and with a gun this size it's not like you're taking *off hand* shots.

50BMG is her favorite thing in the world. she's shot this one and the Steyr HS 50 so far and loves them both. the M82A1 is next on her list....



video

This is going to sound odd but I wonder if the scope is messed up somehow.  Have you run elevation adjustment all the way up and down to make sure its getting the full advertised total adjustment?  My brother had a similar issue with a Swift scope.  It functioned fine but he couldn't zero it.  When he checked the elevation adjustment it only got about half of what it was supposed to.  He took it back and got it replaced.  

He also said that the dealer put it up to a mirror and used the elevation to line up the crosshairs in it, the recticle and the reflection on the mirror.  When he couldn't do that it meant something but I don't remember what.

just got a reply from LaRue Tactical....

that particular mount is good for a 500yd bzo. it looks like i've got a bit more MOA built in than i need for the shorter range stuff.




edit:
all of the adjustment was there.

Your scope as 70 MOA of total elevation adjustment with windage centered.  That's 35 MOA up and 35 MOA down.  With a 30 MOA mount like the the LaRue, you should be able to get to a 100 yard zero with your knobs, IF you actually had a flat railed M99.

I pulled up the current spec sheet from Barrett on the M99 and they are indicating that the rail has a 27 MOA slope built in.  With that, things start to make a little more sense.

http://www.barrett.net/pdfs/Model-99-Sales-Sheet.pdf

You state you are running about 3 MILs high at 100 yards with glass bottomed out.  That would be about 10 MOA high.

So.  You've got 57 MOA built in to the rail and the mount.  Your scope has 35 MOA.  That puts you about 22 MOA high.  Figure a couple minutes drop to 100 yards for the bullet, a few minutes for the scope height, plus a handfull of minutes for manufacturing variations and there you are, 10 MOA high at 100 with the scope bottomed out.

I don't like having my scopes bottomed out, EVER.  So my suggestion would be to sell the Larue and get a no-slope set of rings.  27 MOA slope built into the gun is plenty for an M99.  The mount just doesn't work for this application if you want to have a 100 or 200 yard zero.

Reason I keyed up on your post was I've seen this before.  Had a new shooter at an FCSA match last year with an M99 he couldn't get on target with set of Barrett adjustable slope rings.  Had about 30-40 MOA in the rings....thought the rail was flat...and couldn't figure out why he couldn't get on target at 600 yards with the damn thing.  Pretty simple math.  I took all the slope out of the adjustable rings and he was on target in 2 rounds.

-David
Edgewood, NM

thanks for the reply. i couldn't get the M99 specs to load on my phone last evening and the info i could find was showing either so i wasn't sure.

this is definitely a first for me and that much MOA built in is waaaay more than i will ever need with this thing. as an immediate fix and per a short discussion with Mr. LaRue i just turned the mount around. it's not a long term fix but works well under the current circumstance.




just a thought, are there any M99 flat rails to be had? a swap for this 27 MOA rail? would that work or did they change anything?

i'll give Barrett a call tomorrow.

Is your rail bolted on?  I thought it was machined as part of the receiver but then I haven't looked at one in a while.

Curious, though...  Why are you so wedded to the LaRue mount?  Only reason I see for a QD mount like that is if you are going to use a scope on multiple rifles and they all need 30 MOA.  The innovative thing about that mount is that it's 50 BMG-tough AND has 30 MOA for rifles with flat rails.  Badger rings are fine, they're cheaper than that mount, and they're less likely to move than any QD setup, I don't care who makes it.

If you really like a one-piece mount but don't want any slope built in, the Armalite works great and will only set you back about $75.

-David
Edgewood, NM