AR Sponsor
Posted: 12/8/2012 6:30:38 AM EDT
|
Hello everybody
I'm having a problem aquiring the proper IBZ zero for my current rifle. I updated my carbine lenght S&W mp15I with Bushmaster made 20" HBAR assembly with non-F marked FSB. The problems aquiring IBZ started since installing the new barrel assembly. No problems wih earlier S&W carbine with F-marked FSB and IBZ. The stuff: - AR15 20" rifle with S&W upper + lower and Bushmaster 20" HBAR 5.56 assembly - Non-F FSB on the barrel - A3 DCH with "Z" setting on the elevation wheel, commercial height - AR15 20" rifle modified 25m zeroing target, modified to 50/200m zero / IBZ by the "thecolter383" - S&B 55gr .223rem ammunition (M193 clone) 1. I put the proper 25m zeroing target to 25 meters 2. I set the rear sight elevation wheel to "Z" marking as the instructions in the zeroing target suggest to get the proper 300m battle zero (+2 clicks to 6/3 setting) 3. I shoot the strings and set the rifle to standard 300m battle zero. POI = POA from 25 meters. 4. After setting he 300m battle zero, I set the elevation wheel to 6/3 setting 5. I take the Allen wrench and make the -4 IBZ adjustements to the elevation wheel 6. I re-tighten the Allen screw 7. I set the elevation wheel to -4 clicks from the 6/3 setting (which is by the way -6 clicks from the "z" zeroing setting of the A3 DCH...) Now when I verify the IBZ zero from 25 meters, everything seems to be fine. The rifle shoots about 3cm or 1.2" low from the POA as it should. POA is in the COM of the 25m zeroing target silhouette and POI is in the modified circle of the 50/200m target, at the bottom line of the same silhouette. But when I start to shoot targets farther away, in 100 meters / 110yards and 150m / 165yds, the rifle shoots way too low. From 150 meters / 165 yards the POI is about 6 to 8" low from the POA. According to the IBZ ballistic charts, it should be about 2" high. Am I doing something completely wrong or is the problem elsewhere? I have a feeling that the problem is somehow related to the combination 20" sight radius, A3 DCH "z" setting and non-F marked FSB? Is this combination incombatible with IBZ setting? I'm pretty sure that the problem and the solution are very clear & simple, just in front of my eyes, but I'm unable to see them at the moment. All the help and advices are more than welcome. I'm a guy who loves shooting irons and IBZ and A3 sights are my favourite. And very special thanks to the member "thecolter383" for the fantastic modified 25m zeroing target. 
-wee |
AR Sponsor