Aero M4e1 Upper POI Shift

[PBWalsh]

Hi,

Wanting to hear input on folks who have an Aero M4e1 upper with the built in barrel nut and enhanced handguard.

Specifically wanting to know if there is any POI shift when in positions other than prone. My current Vltor MUR upper/WOA handguard exhibits a .3mil low shift and .2mil right when shooting off a tripod/barricade and am considering the Aero enhanced or LMT MRP upper to solve this shift.

Thanks!

 

[Clint H]

Are you talking about for NV or thermal use? Or just regular optics?

If for just plain old optics, I have a Mega MML set (similar concept as the M4e1s), and I have still seen a slight poi shift doing positional stuff.

My personal opinion is that parallax from head position and recoil management are often the cause for POI shift moreso than rail flex.

Don't get me wrong, isolating the barrel nut and adding material around the front of the receiver solves one of the main shortcomings of the AR platform, but if you already have a thick-walled upper like the MUR, the benefit in switching to a semi-monolithic style may be marginal.

Now NV/thermal stuff is different. Or if you're running a long, heavy-profile barrel. Then you might see the benefit in reducing rail flex to an absolute minimum.

 

[Rudy Gonsior]

My personal opinion is that parallax from head position and recoil management are often the cause for POI shift moreso than rail flex.

I agree, positional shift is often a mix of mechanical influence of the hand guard along with subtle changes to the attitude of the body in relation to the rifle, and which obviously any error of parallax would be exaggerated. This last part about parallax creeps in a lot when concerning LPVOs.

The mechanical POI shift aspects can vary from design to design, even the particular tolerances with rifles utilizing the same model of hand guards. But mechanical POI is almost always lower (going from prone to alternate position) while lateral shifts are almost always an effect of retarding the head/body position behind the rifle.

A good rifle design fix’s the first half of the equation , while proper fundamentals and well fitted rifles solves the other.

 

[PBWalsh]

@Clint H Yeah this is just for regular optics, I do not currently have NV or thermal equipment.

@Rudy Gonsior My horizontal shift could be a head position issue. I am not the best driver of a gas gun and the consistency on paper shows that, particularly when it comes to tripods. The vertical shift is more of my curiosity.

Rudy, if you or your students are seeing a consistent shift, are you simply accounting for that in your elevation adjustments or zeroing on the positional average (splitting the difference in prone and positional zeros).

 

[Rudy Gonsior]

Rudy, if you or your students are seeing a consistent shift, are you simply accounting for that in your elevation adjustments or zeroing on the positional average (splitting the difference in prone and positional zeros).

So what I’d recommend is mapping out any mechanical POI shift and document the correct in angular units. I like to then, using a paint pen, write that correction directly on the buttstock as a reminder.

You can then dial or hold that correction (in addition to your normal elevation) as need as the situations present. I feel this is better than compromising a solid 100y zero with the “averaging” technique.

Baring the mapping, it’s all proper execution of the fundamentals. But don’t feel bad, that’s a lot easier said than done. I still get caught by sloppy NPA with gas-guns from time to time if I haven’t been disciplined! It’s humbling but damn when it all comes together you remember what gas-gunning is all about!

 

[Clint H]

So what I’d recommend is mapping out any mechanical POI shift and document the correct in angular units. I like to then, using a paint pen, write that correction directly on the buttstock as a reminder.
View attachment 8413902

I'm kinda surprised you're seeing a 0.3 shift out of that LaRue. That's a pretty rigid handgaurd/upper interface from what I've heard.

Slick trick with the paint pen, though.

 

[Rudy Gonsior]

I'm kinda surprised you're seeing a 0.3 shift out of that LaRue. That's a pretty rigid handgaurd/upper interface from what I've heard.

Slick trick with the paint pen, though.

@bigjake83 actually did a really in-depth review on “fixing” some of the OBR shortcomings https://www.snipershide.com/shootin...larues-large-frame-review-part-1-obr.7213077/ I believe my particular OBR might have suffered from this problem he mentioned where the hand guard ever so slightly touches the barrel nut.

Honestly the rifle has been in need of a re-barreling (interestingly due to some seemingly heavy pitting that look identical to some of the bore scope pictures Bigjake83 shared) and has been dormant in the back of my gun safe for several years so I am kinda fuzzy on the details.

I will also say in spite of shooting the OBR since 2013, it’s actually took me a good while to learn how to shoot positional/tripods well enough to actually catch this. This is a problem I think a lot of folks don’t even realize is happening because the shift is getting some what lost in the background noise of sloppy positional work. There was a time in my early years when 2 MOA off of a tripod or barricade would have be acceptable but with the current equipment and techniques 2 MOA is laughable and the “resolution” of precision has advanced quite a bit.

As an example: these days I am typically as good off a bag or tripod as I am prone off of a bipod (or better ).

This was an RD15 LPR I threw over a barricade w/bag…and don’t mind the sloppy zero, I didn’t really bother refining it as I was just looking see what I could do in regards to precision.

 

[PBWalsh]

@Rudy Gonsior

I’d love to have a consistent 3moa tripod group! Have you noticed stock position affecting anything? I run mine a click longer in prone compared to other positions. Or is this more of a head issue and translating to horizontal shift.

You know, you think you’re a decent shooter until a little gas gun draws out your inconsistencies.

 

[Rudy Gonsior]

@Rudy Gonsior

I’d love to have a consistent 3moa tripod group! Have you noticed stock position affecting anything? I run mine a click longer in prone compared to other positions. Or is this more of a head issue and translating to horizontal shift.

Yeah sometimes coming in a notch on the stock help shooters get behind the rifle a little better, as long as it’s not too much of a compromise in the LOP. The lateral POI shifts could be from sloppy NPA (it’s very tempting to muscle the rifle in a tripod/barricade). Could be from over/under driving the face into the stock due to poor fit of the rifle in conjunction with the absence of the rear bag under the stock (if the comb is too high or low, or the optic mount is). Could be incorrect parallax (common struggle with LPVOs).

Hard to say ultimately but this is what I most commonly see with ARs. And again a properly fitted rifle can’t be overstated here. A rifle that fits well is going to be easier to apply the fundamentals to but a rifle that doesn’t fit, is going to take a lot more effort.

 

[PBWalsh]

Thanks @Rudy Gonsior for the information. I know my rifle is probably not optimal for precision but it works well for what it is. I’m seriously considering the next iteration using an adjustable stock like the B5 Precision to make me more comfortable behind the rifle.

 

[JR1200W3]

Hi,

Wanting to hear input on folks who have an Aero M4e1 upper with the built in barrel nut and enhanced handguard.

Specifically wanting to know if there is any POI shift when in positions other than prone. My current Vltor MUR upper/WOA handguard exhibits a .3mil low shift and .2mil right when shooting off a tripod/barricade and am considering the Aero enhanced or LMT MRP upper to solve this shift.

Thanks!

I see the most mechanical shift in ARs when shooting in the prone on a bipod. This comes directly from how much torque you impart on the bipod as a shooter.

Before I even explain that, I'll clarify that I do not hard load bipod legs when shooting groups or zeroing in the prone. I learned that lesson many years ago at a zero event at a military competition. You can't always guarantee in every position that you can drive the gun in the same way that you would in a hard bipod load, solid support bag. It's kind of an artificial position. If you're shooting off a barricade/ bag, tripod, or what have you it's not likely that you can trap the gun in that same "vise" type of hold. Hell, if you shoot off a polished concrete floor you can't load the bipod like you would if you were driving it forward into a half sunken 4x4. So I zero with a neutral load because it's more reproducible from position to position. If anything, I'm not driving my shoulder into the buttstock but pulling back on the pistol grip to pull the buttstock into my shoulder. To be honest, I shoot the best 100yd prone groups with a very light, neutral hold which is still a little bit artificial because you can't manage recoil that way in alternative positions. But all of that is positional shift. Back to mechanical shift.

Even with a neutral bipod load, light shoulder pressure and light or firm shooting hand grip, you can impart flex on the fore end by bearing down with cheek pressure. If the toe of the buttstock is anchored pretty good in a firm bag like a heavy fill game changer and you place a lot of weight or pressure from your head with your cheek(just forward of the rear anchor), that will impart torque on the bipod and cause flex in some fore ends. Especially 16" long handguards with the bipod as far out as possible. I've found that combined with varying amount of shoulder pressure or contact it's a recipe for wierd high and low shots or vertical stringing. In my experience shooting from a bag on a barricade or on a tripod both have the same mechanical influence on the handguard. The forward anchor point is too far back on the handguard to flex it. If there's a shift there it's more than likely positional. If it's vertical shift it's an angle of departure effect caused by differing amounts of recoil management. If it's horizontal or diagonal it's likely head position.

The latter is why I like to use a taller HOB. Having your head in a more vertical, upright posture in the prone is going to transition a more similar eye relief and head position to kneeling or standing. If you're super low in the prone position your neck is elongated in a horizontal attitude and the base of your skull is contorted at a more right angle to your neck line. As you elevate in shooting position your neck and head align more naturally vertical and this undoubtedly has an effect on eye relief and head position. I think if you're shooting with eye pro you're doubling down on this effect by changing the ocular position your eyeball is in. From extreme angle just under your eyebrow and top of your undoubtedly angled eye pro lenses to a more centered in the eye socket, directly straight out, and perpendicular to the flat plane of the lens.

To complete not-answering your question I just bought a M4E1 upper and handguard and installed it on my 22 ARC. So far it seems to be reigning in some oddball flyers. I only have two range sessions with it so haven't really proven anything yet.