Did I miss something? If the gun is shooting low and POI does not change when you adjust the elevation, I would say the scope is not working. It should move the POI somewhere.

Thanks! I'll change the mount to make it align with the handle.

XM855 Green Tip.

Yes, I'll definitely recess the mount, per "Grizzman's" suggestion. (Sorry... can't figure out how to stop the icons.....) :D

How hard is it to replace the charging handle with a BCM? I've not yet delved into any mods to the upper or lower itself.

Is there a favorite way you use to test/calibrate the scope "standalone" (i.e. not mounted on the gun)? I can see the reticle move relative to the target's bullseye when I make adjustments, but no matter what I do, the placements are still just south of the bullseye.

I'll start over again and get the scope reset to factory specs. Then I'll change the mount to ensure the eyepiece is flush to the charging handle.

Thanks all!

Google search "scope box test" and you can probably do the test with the scope in a vice or something similar.

Edit.... This explains the box test well.
http://www.rimfirecentral.com/forums...d.php?t=512751

Here is my last DMR poodle shooter with a P.E.R.P mount and SWFA SS 10X scope. MOA all day long with match ammo.

Funny milkman

I had a scope do this drove me crazy . Thru it away .

Try this. ..fire a 3 shot group. If low, aim at the exact same point you aimed when firing, then, holding your rifle steady, adjust the crosshairs down to meet the center of the group. That should zero it at that range. If the next group is low, the scope is suspect imho

Well, first I'll do the "scope box test" per caleb's suggestion. If it comes down to being a "bad scope," then I'll probably just replace it with a BUIS and use that instead. I think Pig may be right... Why put a scope on an AR /M4 variant if you don't need to shoot it at those distances? Better served on more of a "long distance" type rifle.

Bingo, easy peasy....

Fair enough!

Thanks! :)

The charging handle is very easy to replace, and might as well be removed for cleaning/lube any time the BCG is removed for cleaning/lube. Simply place some downward pressure (with the upper upright) on the handle as it's pulled to the rear. The handle should readily slip through the dismount notch.

I wasn't sure what was meant by your "slightly low, no matter what adjustments" statement. I presumed you were surprised at how the POI is with it zeroed at 100 yards.


FYI, the SS109 bullet has a ballistic coefficient very close to the 69 grain SMK, so that's what I used in Sierra Infinity. At 2900 fps with the scope (in P.E.P.R mount) zeroed at 25 yards, the impact is 1.3" high at 50, 3" high at 100, 3.5" high at 150, 2.6" high at 200, zeroed again at 250 yards, and 4.4" low at 300 yards. This allows for hits within + or - 4.5" from POA from the muzzle out to 300 yards.

With a couple exceptions, I run either irons or Aimpoints on all semi-auto rifles....especially carbines. Magnified scopes are only used when developing handloads for them.

Excellent! Thanks! I'll check that out.

They were placing 1-2 rings below the bullseye center dot on a standard AP-1 tombstone target at 100 yds. But, due to my total "noviceness" about sighting in, I'm not ready to declare it's a malfunction of the scope. It's more likely something I'm doing wrong... be it not keeping the rifle level/steady when adjusting, or ensure the scope is mounted properly, or anchoring the front bag directly on the barrel (thanks Pig), or something of that nature. I will figure it out, and I'll get assistance when I run into a brick wall.

I forgot to mention that my XM855 is the standard 62grain green tip variety (Muzzle velocity: 3104 fps Muzzle energy: 1326 ft/lbs). Now, I'll be trying to figure out the exact same graph for the XM855. Again, more of my "noviceness" in re: ballistics, etc. I hope to learn a lot here. :)

I'm beginning to think that's what I should have done on this. Just install and sight in a good BUIS. Which I might eventually do, but I'd like to figure this out (with the scope) and learn from it. After that, maybe I will switch to the BUIS an preserve the scope for a longer range rifle.

Thanks very much! Happy 4th!

Slip back to 50 or, if necessary, 25 yards. If you get consistent but low groups there, there is something wrong with the sights or the nut behind the rifle. :)

OK, thanks!