Laser boresighting conundrum

[Mord]

First, allow me to introduce myself - my name is Mike, and this is my first post to the firing line. Up until now, I've been content lurking around a myriad of forums in search of the answers I seek, and never felt the need to make a post or register on most of them. I feel I have a slightly better than average understanding of firearms and ballistics as a result of my experience as an armorer. That being said, I've run into an issue for which I can not find a logical explanation. Allow me to elaborate...

I recently built a 10.5" pistol using a radical arms complete upper (minus BCG), an aero-precision lower, and a selection of mid-range parts. For the optic, I decided to throw on an RMR and set of MBUS that I had lying around (not my first choice due to engagement range limitations, but it saved me from buying a new optic until later).

I zeroed the rmr with my aimshot LBS prior to going to the range a couple of weeks ago. Fast forward to range day, I was using bulk federal XM855, and my groups were bad, to say the least. They were about 4 MOA, which I sort of expected due to the cheap ammo and rack grade barrel, but what really troubled me was the group placement. Despite zeroing with the LBS, my groups were consistently landing about 4MOA to the right from the POA (what should have been POI, based upon the boresight). I went ahead adjusted the zero to the right to bring the POI and POA in line, and the groups were hitting (albeit at 4MOA) where I wanted/expected them to hit.

I went back home that night and placed the LBS in the chamber once again out of curiosity. As suspected, the POI according to the LBS was about 4MOA left of the current POA through the RMR.

I successfully ruled out the LBS as the issue - believing it could possibly be ever so slightly angled - I did so by placing the LBS in the chamber at several different orientations, expecting that if the LBS was misaligned, the laser would end up in different spots every time I re-seated it in the chamber.

Assuming that the LBS is not the issue, then, I'm left with two possibilities - some part of the upper (the receiver or the barrel), or the ammo. I'm inclined to believe it is the upper, as I'm not seeing any uneven wear on the BCG, and I would think that if the barrel were bent slightly, the POI from the laser would be where the rounds would actually land.

Has anyone encountered a problem such as this? Were you able to find a solution or cause?

[TXAZ]

Welcome.
4MOA PoI difference is a lot. I would check it again by clamping the firearm down and rotating the LBS through 360 degrees, and marking where it's hitting on a target 5+ yards / as far away as you can reasonable see it.

Or you may have parts that are not mating well, are loose or not traveling smoothly.

Or you could have some really 'craa-pay' ammo that is from different lots / whatever that's causing the error, but that should make the PoIs more like a shotgun.

Good luck.

[imashooter]

Welcome to the forum. I have multiple caliber LBGs. Prefer the cartridge style. I've used them on a few weapons, probably around 10. 1911s and 5.56s. Not bad at all. Very easily got me on paper at ranges from 7 - 15 meters for the pistols and 25 for the ARs though I normally do the LBS at 25 meters. If the hits are grouping well I doubt if it's the ammunition. With the bore sighter, I wouldn't exceed 25 though some say they're good to 100. I don't find them to be very accurate at 50 though I've done one or two at that distance.

Cutting to the chase, I'd take the laser out of the equation and with your optic, see what you zero at using 25 yards / meters and go from there to your final zero. I think (hope) you'll be ok.

[Art Eatman]

Purely personal opinion: Once I'm on paper in my sight-in effort, I have no further interest in "what was". What difference does it make where the laser pointed? All that matters, IMO, is that the sights and the impacts are POA = POI.

[Mord]

Originally Posted by Art Eatman

Purely personal opinion: Once I'm on paper in my sight-in effort, I have no further interest in "what was". What difference does it make where the laser pointed? All that matters, IMO, is that the sights and the impacts are POA = POI.

An absolutely valid point, Art, and one that I agree with entirely. I suppose my frustration and desire to find the cause/solution arises mostly from perfectionism, and the fact that I hate not being able to solve a problem.

TXAZ, mostly out of curiosity, I went ahead and threw the rifle in the vice and did my best to rotate the lbs inside the chamber. I have the external battery pack for the aimshot lbs, so it wasn't the easiest to rotate, but I did it. From what I could tell, there was no variation in point of impact. I marked a piece of paper after each turn, and the resulting ticks were (with extremely minor variation) on top of each other.

imashooter, essentially that is what I've done at this point. I went ahead and adjusted the zero at the range so that POI and POA matched up. What is strange, is that the resulting POA is so far to the right of the barrel, it is obvious that something is off.

I know it's probably an exercise in futility to narrow down the exact cause of this issue but it will probably keep me up at night if I try to let it go lol.

I'm planning to pick up a few different boxes of ammo to see if I get any different results. I find it very strange that a particular load would consistently group to the left or right of center, but then I'm not a ballistics expert.

I don't think there is a bend in the barrel for two reasons: when I visually inspect the barrel interior, there are no visible light distortions - everything is concentric. Second, while not a great way to judge, the lbs dot outside the chamber and inside the chamber look the same - there is no indication of distortion, such as bouncing off the barrel wall or hitting the flash on the way out the muzzle.

I also don't think the issue is inside the upper receiver, as I don't see any prominent uneven wear on the BCG or inside the receiver. There was some play between the upper and lower, which I corrected with an accuwedge - in my experience as an armorer the play was entirely within tolerance.

On another note, TXAS - it is reassuring to know that you aren't a terrorist. lmao

[jmr40]

Bore sight tools only purpose is to get the 1st shot on paper. You have to fine tune after that. Personally I think they are a waste of money. At most they MIGHT save you 1 shot getting a rifle zeroed.

[Mord]

I'm not necessarily relying on the LBS to give me a perfect zero, but at 25 yards, we're talking about a POI that is (visually) about two inches (so I guess more like 8 MOA) to the left of the POA, yet when I'm sending the rounds they're hitting at that POA, or damn close to it. Something seems off about that.

[cecILL]

Hello. Ditch the bore sighter.