Posted: 11/14/2024 12:54:33 PM EDT
[Last Edit: billclo][Edited]
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I've got an issue that I'd like help with. I am shooting an LMT 16" M4 type rifle, with an Aimpoint Comp ML2 on it. The gun is zeroed on the bench, impacting dead on at 50 yards, and typically 3-4" high at 100 yards. I wear prescription glasses (tri-focals). I decided to practice position shooting (prone, kneeling, standing). In all positions, the shots are going way low, like 4 - 6" at 100 yards. Even standing at 50 yards, shots are way low. For standing, I was thinking that I wasn't supporting the rifle well enough (I'm pushing 60 years old, and I'm not as strong as I used to be), so I was trying to pull my left arm in to rest against my chest to give more solid support. Not much change. Shooting prone headshots on an 100 yard torso target was yielding a lot of stringing (10 oclock to say 4'oclock), with the groups being a little low. I could see the sights wiggling lefft to right. But aiming at the upper chest, 4 - 6" low, not much left and right stringing. Kneeling about the same result. A fellow shooter I was talking to, when I said that I have a hard time getting my left arm into good position under the gun to support it in prone, he said try resting the gun on the end of the magazine (monopod). To my pleasant surprise, it really tightened up my groups, but the shooting low is still present. Here is a picture of today's 100 yard target. Prone, using the mag as an mono-pod, XM193 ammo. Aim point is the neck. I dialed the dot brightness down a little to get a more precise dot.  I don't have anyone around here that I can ask about correcting my technique; the club doesn't run high power/competitions, etc. I'm expect its me and not the gun. I did some browsing online, and it appears that a) I should rezero the gun for prone, as I won't be lugging a bench around, but b) that while a shift in point of impact between bench and prone is expected, its usually nowhere near as big as I am seeing. I wanted to ask around for ideas first, before changing the zero. Thoughts/suggestions? |
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You're 60, wearing glasses, and prone/standing... I'd click the aimpoint up 2 clicks, and call it a day. If you're dead on at 50, you should only be 2 up at 100. Given the evidence, do the clicks, and call it. ETA: stick a piece of printer paper up, and take some shots. Hit it, and you're good. Is it at 100? Is it at 200? Good hits are good hits. |
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WTB: Glock 17 gen 2. SN CAF 895
Win if you can, lose if you must, but always look good for the crowd.
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Originally Posted By Mindless: When you zeroed on the bench, did you support the front of the rifle on the barrel opn the hand guard or bottom of the magazine? If supported by the barrel, you can expect a significant drop in the point of impact when firing from other positions. Originally Posted By Mindless: When you zeroed on the bench, did you support the front of the rifle on the barrel opn the hand guard or bottom of the magazine? If supported by the barrel, you can expect a significant drop in the point of impact when firing from other positions. I supported the rifle on the bottom of the handguard. I wasn't using the monopod concept at that point. Originally Posted By MisterPX: You're 60, wearing glasses, and prone/standing... I'd click the aimpoint up 2 clicks, and call it a day. If you're dead on at 50, you should only be 2 up at 100. Given the evidence, do the clicks, and call it. ETA: stick a piece of printer paper up, and take some shots. Hit it, and you're good. Is it at 100? Is it at 200? Good hits are good hits. I haven't checked the 200 yard zero in years, so I should get my butt out there and check it. I haven't shot 200 yards in quite a while. I think it'd be prudent to confirm point of impact at 200 first, before fooling with the zero. As a check, I think I'll also try my other 16" carbine to see if I see the same thing. Its zeroed the same way, 50/200 rested on the handguard, different optic (but that probably won't make any difference). If I see it with that gun too, that'll let me know for sure its me and not something weird with the first gun (which I doubt). |
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Originally Posted By JoeDevola: And what are you supporting the handguard on when shooting from the bench? If it's something hard, and you're bearing down on it, "locking down" the gun, so to speak, it can affect barrel harmonics, which will change POI. The "rest" is a wood box, with a doubled-up towel on top of it. I don't believe I was bearing down on it, but I can't rule out that possibility either. Normally I let the foreend sit there, with my support hand under the butt of the gun locked up against my chest. |
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Originally Posted By billclo: Nope. Magpul MOE handguard. Originally Posted By billclo: Originally Posted By JoeDevola: Is the gun free-floated? Nope. Magpul MOE handguard. That’s your issue. Non-free floated hand guards will apply pressure to the barrel. If you are not applying pressure the exact same pressure in the exact same place it will change your zero. Free float it and you should see that problem go away. |
Did you just assume my anatomy? - Cowbell
No Tyrant has ever found itself guilty of tyranny in its own court. - ohland
Weapons of war are our birthright - Dark_zero_x
The dildo of consequences rarely arrives lubed - Lube
No Tyrant has ever found itself guilty of tyranny in its own court. - ohland
Weapons of war are our birthright - Dark_zero_x
The dildo of consequences rarely arrives lubed - Lube
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I did take the rifle back out to ensure that the 50/200 yard zero was still there. I had to adjust point of impact by 2" elevation at 200 yards, but otherwise it was good. I had intended to re-shoot prone to see if the issue was still there (I expected it would be), but instead checked the zero of a second rifle and ran out of time. Maybe next week... |
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Originally Posted By motoguzzi: Could you be "chicken winging"? If you are right handed that can move your groups. I used to do it all the time. I've been working on not doing it. I do tend to use it on the bench, as I don't have a proper rest (wooden box with towel on it, left hand tucked under the butt to support it and press against shoulder, right elbow on the table). |
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Originally Posted By bluedog82: If the rifle is still zeroed when shooting from the bench, then you know it’s not an issue with your optic or ammo. As mentioned, a non free-float rail can include a POI shift when pressure is applied (or not applied in this case). I have seen the same issue irregardless of whether I am using a classic prone position (L hand holding the forend) or recently mono-poding it. Nonetheless, I strongly suspect its me. I'm going to re-shoot hopefully next week and I am reading up on how to improve my prone position. May affect it, may not. I am strongly tempted to just zero the gun in the prone position to remove a variable, but haven't yet done that. |
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Originally Posted By billclo: I have seen the same issue irregardless of whether I am using a classic prone position (L hand holding the forend) or recently mono-poding it. Nonetheless, I strongly suspect its me. I'm going to re-shoot hopefully next week and I am reading up on how to improve my prone position. May affect it, may not. I am strongly tempted to just zero the gun in the prone position to remove a variable, but haven't yet done that. It's not a zero until you shoot it at true range and verify and record it. |
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Since my eyes are getting older, I added a magnifier and picked up a pair of M-Frame eyewear that eliminate optical distortion. That helps. Also consider collecting some ballistic data. I don't consider myself zeroed anymore until I've got the data:  What Distance Should you Zero your AR 15? |
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