POI shift on carbines from prone to positional

[B]

Any shift I have ever seen can be attributed to parallax, keep in mind even "parallax free" optics aren't that when you read the manual. If it weren't that I wouldn't get shifts unsupported and I wouldn't have the same problem R/L. If I am L/R/U/D of target I need to compensate if I want to hit exactly. The shift is so small as to be mostly inconsequential for almost all the shooting I do. That is not a problem I have with irons, which I spent most of my life using over optics of any kind.

 

[beltfed]

Sure, we can agree to disagree but you're also disagreeing with a large body of testing stateside, including from some guys in the USAMU. The reality is that flat top receivers have a certain amount of flex (which has been demonstrated on high speed video) and that a handguard that is attached to a barrel nut imparts a certain amount of force on said barrel nut when a bipod is attached towards the end of the handguard. That same force isn't applied when the handguard is rested on a bag or attached to a tripod back at the magwell. You can claim it's shooter error all you like but I can tell you that I don't execute the fundamentals any differently when I'm shooting prone with bipod and rear bag than I do when I put a bag under the handguard at the magwell and use a rear bag. It's pretty obvious that the whole main POI shifts noticeably. It's also very repeatable. Here's some reading if you'd like to have a read through. The OP of the thread just retired from the AMU: https://www.snipershide.com/shooting/threads/ar-positional-poi-shift-test.7221976/

What you're talking about with the Swiss Arms bipod is similar but is exacerbated by the non-free float handguard (so is obviously also present in ARs that are non-free float). A free-floating handguard lessens the effect but it is still there, to what degree depends very much on the means of attaching the handguard to either the barrel nut or receiver.

I'm not denying that poi shift is a real thing - it is well established.
Flex (and even breaking) in the upper receiver is also a known issue.

I'm saying that poi shift is on the shooter and not the system. This is supported by the fact in almost all cases, POI shift will change from shooter to shooter.

The whole IUR, MWS, etc. were monolithic designs to overcome this, with the predominant issue first arising, at least in the the military context, of soldiers hanging everything including the kitchen sink off the hand guard rails.
Civilian competitors got into heavier barrels which precipitated machined uppers and then tube guns.

If a competitor is spinning on a massive hunk of barrel into a thin walled aluminum upper that that upper was never designed for like they have done in US High Power shooting for the last ~30-35 years - and that upper cracks and becomes non-serviceable, that's on them.

Likewise, if you spin on a full floating hand guard and then load up a bipod sitting out on the end of that tube or run it and expect it to behave like a chassis'd bolt gun, that too is on the shooter.
Shooting from a bipod, you will undoubtedly see varying results shooting it loaded v. unloaded.
That is my argument - the shooter builds and is responsible for the shooting position they create.

 

[rugbydave]

I'm not denying that poi shift is a real thing - it is well established.
Flex (and even breaking) in the upper receiver is also a known issue.

I'm saying that poi shift is on the shooter and not the system. This is supported by the fact in almost all cases, POI shift will change from shooter to shooter.

The whole IUR, MWS, etc. were monolithic designs to overcome this, with the predominant issue first arising, at least in the the military context, of soldiers hanging everything including the kitchen sink off the hand guard rails.
Civilian competitors got into heavier barrels which precipitated machined uppers and then tube guns.

If a competitor is spinning on a massive hunk of barrel into a thin walled aluminum upper that that upper was never designed for like they have done in US High Power shooting for the last ~30-35 years - and that upper cracks and becomes non-serviceable, that's on them.

Likewise, if you spin on a full floating hand guard and then load up a bipod sitting out on the end of that tube or run it and expect it to behave like a chassis'd bolt gun, that too is on the shooter.
Shooting from a bipod, you will undoubtedly see varying results shooting it loaded v. unloaded.
That is my argument - the shooter builds and is responsible for the shooting position they create.

Gotcha, I wasn't tracking exactly what you meant, when you said "it's shooter error" I interpreted that as "not properly applying the fundamentals" as opposed to your meaning, as I currenlyl understand it of "understand your equipment". Correct me if I'm wrong?

Funny enough, the effect of flexing handguards due to running too much stuff on them has precipitated the development of stiffer handguard systems so that LAMs and such maintain zero/don't have shifting POI. Not intended to help with POI shift with regards to what I'm talking about but helpful nonetheless.

As to shooting loading the bipod vs a more neutral load (just taking the slack out/bridging with rifle pulled back into shoulder), for sure, you'll get different results but the latter is the correct way of shooting and the former is just poor practice. Regardless, in most cases with free-float handguards that attach to the barrel nut, there is still a POI shift down when going from bipod/prone to supported positional that needs to be accounted for even if proper practices are employed with regard to prone shooting technique.

I do 100% agree with you though that the shooter is responsible for the shooting position they creat and they need to understand what, if any, effect their position will have on POI relative to POA.

 

[beltfed]

Gotcha, I wasn't tracking exactly what you meant, when you said "it's shooter error" I interpreted that as "not properly applying the fundamentals" as opposed to your meaning, as I currenlyl understand it of "understand your equipment". Correct me if I'm wrong?

A shooter can and often do employ shooting fundamentals differently in various positions - not necessarily for the worse - this is well established and poi shift can be attributable to it, but again it is my believe that any poi shift that is seen for something like a shooter going from prone to kneeling or prone bagged to prone bipod is sighting and shooter / mechanical interference with the rifle system.

 

[beltfed]

As to shooting loading the bipod vs a more neutral load (just taking the slack out/bridging with rifle pulled back into shoulder), for sure, you'll get different results but the latter is the correct way of shooting and the former is just poor practice.

I'm of the opinion neither one is better than the other. If a shooter does better by pre-loading, all the power to them. However, if pre-loading is causing poi shift, then they are doing something wrong.

 

[rugbydave]

I'm of the opinion neither one is better than the other. If a shooter does better by pre-loading, all the power to them. However, if pre-loading is causing poi shift, then they are doing something wrong.

Different things can work for different rifle systems but the currently accepted orthodoxy is not to heavily load the bipod as it's much harder to do so in a consistent manner. Just enough "load" to take the slack out of the bipod and "bridge" the rifle to shooter so it can basically stay on target without rear support (ie before the rear bag is brought under the stock). I'll grant that this is mostly derived from shooting bolt guns but it also applies to gas guns (barring the idiosyncracies of certain systems that aren't free floated).

 

[rugbydave]

A shooter can and often do employ shooting fundamentals differently in various positions - not necessarily for the worse - this is well established and poi shift can be attributable to it, but again it is my believe that any poi shift that is seen for something like a shooter going from prone to kneeling or prone bagged to prone bipod is sighting and shooter / mechanical interference with the rifle system.

Ideally the shooter shouldn't employ the fundamentals differently based on position. Obviously if a super jacked up position is required in order to orient the rifle on target and get a sight picture, then it is what it is but outside mechanical poi shifts (as with a handguard attached to the barrel nut) a shooter should be able to shoot to the same POI when shooting supported positional regardless of position (standing, kneeling, seated). It's something that most high level precision rifle/PRS shooters have mostly mastered (or constantly work on). It's obviously easier with a heavy PRS gun but the principles are the same with a gas gun, the execution just has to be that much better.