I had a Battlecomp 2.0 installed a little while back on one of my BCM upper ARs. (Defensive Edge lower)
When I took it out to confirm zero, windage was significantly displaced (IIRC, it was somewhere around 18 clicks) compared to the A2 FH that it came with. My rear sight was pretty much centered with the FH but with the BC, I have just a little bit of space left before it bumps against the left limit. The T-1 needed significant adjustment as well.
It’s zeroed now, and seems to be shooting ok but I’m curious why the big difference. Is it due to the shimming that the 2.0 uses vs the crush washer that the 1.0 uses? For reference, I’ve installed a BC 1.0 and BABC on my SCARs, and neither required more than a few clicks to get back to zero. All installation was done by one of the mods here who is an accomplished armorer.
Something went wacko. There’s a lot of info that’s missing here. If nothing obvious looks wrong though, I’d take off the MD and shoot it plain and see where the zero is then. If it’s good and close to center again, then it’s either alignment or parts issues. If it’s the same, it was probably damaged/torqued from lack of correct tools or installer issues. No matter what, it’s hard to tell what’s going on without some more info and parts in front of me.
I agree, but if the change goes from close to mid adjust to close to the limit, something is going on.
I worked under the direction of a person who would go through a lengthy process of timing the MD in 90 degree increments, and looked to see if the grouping followed after the initial the initial instal was verified and everything else seemed ok. If it followed rotation, look at the MD. If it stayed the same, it was the barrel in some manner.
There’s more to it than this, but it’s really hard to say without having the stuff in front of you. Generally, a FH will be more forgiving of a bad barrel or shoulder etc than a comp.
Another possible variable is that I had the guys at WAR Rifles in Manassass pin the lo pro gas block on this BCM upper before the muzzle device swap (if memory serves).
Maybe I should have checked zero before changing muzzle devices, but they pinned another lo pro gas block at the same time on another upper that retained the same zero before and after pinning the gas block. (Though that upper retained the same FH).
So the barrel’s been ‘messed with’ twice now and your zero has changed? Seems as if that would be understandable. I would inspect the barrel for any protrusion from the pinning and the comp for strikes. Other than that, I’d just accept the new zero and shoot on.
I think Jack’s got it pretty much nailed. By swapping the muzzle devices, you are throwing a whole new variable into the harmonics of the barrel. I swapped an A2 off my 12.5" gun for a Surefire MB556K and had a 3.5 to 4" POI shift to the left at 50 yards. As long as the gun continues to print well after you adjust, rock on.
Some other time I’ll make a long post that includes probability and why. I’m not discounting other posts. I think they have great merit and adds to the discussion. I just simply don’t have the time needed now. When I can do it, I’ll try to do it in a way that’s easy to understand. I’m just too busy now to do it right now.
Exactly, since what I plan to type up is rather long winded and takes some time. Not 30 seconds and a few sentences.
BTW, your last post is very informative and related to the subject. Why jab people?
And yes I’m short on time, I’m still at work now 18+ hours today. If I get 3 hours of sleep tonight, I’ll be lucky.
Ok, cool, whatever. I’m just glad that I got a cab driver that is American and speaks English. If what you posted wasn’t a jab, I don’t care really in the mess of things I’m that I have to deal with, I feel like a zombie now. I’m checking out for a few hours till there is some dead time when I wake up at 03:00.
Weird, I’m getting a 6" shift at 100yds on my SCAR with a BABC and the groups are huge (4 -5"). Without a device on the end I get 2" groups with the same ammo and I’ve got to adjust 6" in the opposite direction. This is my second BABC. The first one gave me just about the same big groups but not as much zero shift. I looked very closely at the opening but didn’t see any strikes. None of the carbon was disturbed nor were there any scoring or witness marks underneath the carbon.
At this point I tend to believe it’s harmonics and/ or torque. The only other brake I have to try on hand is a Griffin. Failing that, I’m going with a flash hider.
I’m going to go out on a limb here and assume that some handguard rail was removed to pin the lo-pro gas block, then replaced. This makes for three variables/changes to the barrel system: installation of the muzzle device, pinning the block, and removal/replacement of the rail (which is connected to the barrel nut?).
Also, the OP refers to adjusting the ‘rear sight,’ so this is not an optic. Since he has a gas block, I am assuming that his front sight is attached to the rail that was removed and replaced. Even if the rail was correctly indexed, there will be variances in the placement of the front sight that alone can cause many clicks to adjust.
Thus, I count four changes the the system. No way he was going to retain zero.
Not slamming anyone, especially considering the likelihood of who did the work, but a windage change like that from a muzzle device change sounds to me like the barrel got torqued either in removing the prior muzzle device or installing the new one.
I would agree with Amicus and others too many changes to expect no change to zero. A thought of the “boss” comp on bolt action rifles came to mind, adjustable to tune for ammo weather ect. There is the main change barrel harmonics and disrupted gas jet at muzzle as bullet leaves comp. That’ll change any rifles zero/ group.
I have not read the whole thread just to be clear, but this is why I clamp the barrel right under the muzzle device if I can or close to it. Giessile extraction rod works just as well, but I still perfer clamping at the MD.
I was going to ask if anyone remembers the Browning BOSS comp?? Group size was changed by screwing the device in or out. Moving it changed the harmonics and affected the accuracy but it was a move and shoot process until you found the sweet spot. GH