AR15: Bipod loading and POI shift Testing

[Cactus kid]

A topic that currently has my attention and thought you guys might be interested.

Reloading Allday tested quite a few AR15 platforms and how much bipod position and bipod pressures changes POI on different platforms. The testing method seems solid, a laser mounted on the barrel, and later confirmed with live fire.

Summary of results: Seems that monolithic and semi monolithics fared the best, with about .4 mil shift. The only AR system that has ZERO shift with the Springfield EDGE ATC.

A bolt chassis was tested as well and had zero shift.

Would like to pass it along or open it up for critique.

Curious how the MK12 would fair, seems to be a very robust system.

 

[wind gypsy]

A topic that currently has my attention and thought you guys might be interested.

Reloading Allday tested quite a few AR15 platforms and how much bipod position and bipod pressures changes POI on different platforms. The testing method seems solid, a laser mounted on the barrel, and later confirmed with live fire.

Summary of results: Seems that monolithic and semi monolithics fared the best, with about .4 mil shift. The only AR system that has ZERO shift with the Springfield EDGE ATC.

A bolt chassis was tested as well and had zero shift.

Would like to pass it along or open it up for critique.

Curious how the MK12 would fair, seems to be a very robust system.

Great share, thanks. Those are some big shifts!

 

[Wapack]

Thanks for sharing. This saved me some money, was looking at the larue stealth mono upper but it dosent seem like it’s any better than what I have.

 

[alexnelon]

I’d like to actually see the gas block clearance on each of those rails with that fat barrel. I’m very suspicious that there’s contact.

 

[Cactus kid]

I’d like to actually see the gas block clearance on each of those rails with that fat barrel. I’m very suspicious

I don’t know why there would be anymore contact than a thinner barrel, aren’t gas blocks pretty standard? And I think serveral of those have the low profile blocks.

I am ignorant on this subject

 

[alexnelon]

I don’t know why there would be anymore contact than a thinner barrel, aren’t gas blocks pretty standard? And I think serveral of those have the low profile blocks.

I am ignorant on this subject

Gas blocks vary wildly in almost every measurable dimension. Gas block contact is extremely common especially on barrels with a .936 journal (like the one in this video) and the symptoms are exactly what is shown in the video.

The contact is almost always on the shoulder of the block, so the thicker the gas journal, the less clearance you have and the harder it is to avoid contact.

Several of these rails were not originally designed to cover the gas block anyway. The old Larue quad rails barely even clear the gas tube so they eventually designed their own gas block and tube to fit under it.

I obviously can't say this is the whole reason for the results in this video, but to me the method is more important to show than the results. I would much prefer to see proof of clearance and then deflection measurements rather than a green dot on an amazon box for 45 minutes.

 

[Cactus kid]

Gas blocks vary wildly in almost every measurable dimension. Gas block contact is extremely common especially on barrels with a .936 journal (like the one in this video) and the symptoms are exactly what is shown in the video.

The contact is almost always on the shoulder of the block, so the thicker the gas journal, the less clearance you have and the harder it is to avoid contact.

Several of these rails were not originally designed to cover the gas block anyway. The old Larue quad rails barely even clear the gas tube so they eventually designed their own gas block and tube to fit under it.

I obviously can't say this is the whole reason for the results in this video, but to me the method is more important to show than the results. I would much prefer to see proof of clearance and then deflection measurements rather than a green dot on an amazon box for 45 minutes.

Thanks for the info! I have more to learn.

But whether it is the forend adding pressure to the gas block or adding torque to the barrel nut this testing does point to a problem with the overall system.

Interesting that the Springfield had zero deflection, so it seems possible to develop a system that works.

I saw the results of the centurion mk12, but it is not the same system as a mk12 mod 0, that beefy full length pick rail has to be doing something.

 

[wind gypsy]

I’d never even heard of that Springfield model before. Interesting.

 

[flyfisher117]

Interesting. I wish I still had my Aero enhanced receiver set to tinker with.

 

[alexnelon]

But whether it is the forend adding pressure to the gas block or adding torque to the barrel nut this testing does point to a problem with the overall system.

No way to know without controlling for any variables.

 

[alexnelon]

I’d never even heard of that Springfield model before. Interesting.

It's discontinued. They sold like 5 of them.

 

[PathFinder]

I haven't noticed any shift on my Larue upper from bipod->bag->tripod, though it may be worth an in depth check. Lots of 10 round zero checks on that gun with no shifts. Mine is a light profile barrel with a small block, maybe that's the difference.

 

[alexnelon]

I haven't noticed any shift on my Larue upper from bipod->bag->tripod, though it may be worth an in depth check. Lots of 10 round zero checks on that gun with no shifts. Mine is a light profile barrel with a small block, maybe that's the difference.

I watched a little bit more of the video, and it looks like the guy is also putting an exorbitant amount of preload into the bipod too which could also explain some of it.

There are just too many variables in his testing method to give any credibility to his results.

 

[Formidilosus]

A topic that currently has my attention and thought you guys might be interested.

Reloading Allday tested quite a few AR15 platforms and how much bipod position and bipod pressures changes POI on different platforms. The testing method seems solid, a laser mounted on the barrel, and later confirmed with live fire.

Summary of results: Seems that monolithic and semi monolithics fared the best, with about .4 mil shift. The only AR system that has ZERO shift with the Springfield EDGE ATC.

A bolt chassis was tested as well and had zero shift.

Would like to pass it along or open it up for critique.

Curious how the MK12 would fair, seems to be a very robust system.

There is so much wrong with that video. I know that people all over the internet are loving it…


You have to put a stupid amount of pressure in the bipod on some of those rifles to cause a .4 mil shift.

 

[Formidilosus]

Today I checked a MK12 Mod0 with Harris bipod mounted to the front of the handguard. The gun is zeroed with 77gr TMK, I used ADI 55gr Blitzkings today. Notice the deviation from center of the two groups.

This rifle-



One target is a neutral hold- near free recoil; no pressure forward or back at all, soft on the grip and shoulder. The second dot is with EXTREME forward loading the bipod- my entire body weight, much more and it would have broke something. No one would ever put that much pressure into a gun.

First shot 10 rounds with the neutral hold. Then, shot 10 rounds on a second dot with extreme forward loading the bipod. Then 5 more rounds on the first dot with neutral hold again, then five more rounds in the second dot with extreme forward load. 15 rounds per dot.


Neutral hold is -.33 of an inch from center:




Extreme forward loading of the bipod is -.54 of an inch from center:




For a difference of .21 of an inch. Not even a single click of the scope between a near free recoil, zero input hold- and loading the bipod until it feels like it will break. .21” difference is inside the expected variation of the cone for 15 round groups anyways (though in this case my guess is that a .2 MOA difference between those two extreme hold is probably repeatable).
Now, there certainly are a lot of hand-guards that will show on observable shift between a light hold and extreme loading of a bipod… but the effect is way overblown for functional shooting with good guns. Especially as it relates to bolt guns and “different zeros” from prone, versus barricade, versus tripod. That’s all an excuse because people do not want to admit they suck and need practice. Then they shoot one or two 3-5 shot groups and try to read tea leaves and explain why the two groups don’t look the same…

 

[Cactus kid]

Today I checked a MK12 Mod0 with Harris bipod mounted to the front of the handguard. The gun is zeroed with 77gr TMK, I used ADI 55gr Blitzkings today. Notice the deviation from center of the two groups.

This rifle-
View attachment 1003439


One target is a neutral hold- near free recoil; no pressure forward or back at all, soft on the grip and shoulder. The second dot is with EXTREME forward loading the bipod- my entire body weight, much more and it would have broke something. No one would ever put that much pressure into a gun.

First shot 10 rounds with the neutral hold. Then, shot 10 rounds on a second dot with extreme forward loading the bipod. Then 5 more rounds on the first dot with neutral hold again, then five more rounds in the second dot with extreme forward load. 15 rounds per dot.


Neutral hold is -.33 of an inch from center:
View attachment 1003440



Extreme forward loading of the bipod is -.54 of an inch from center:
View attachment 1003442



For a difference of .21 of an inch. Not even a single click of the scope between a near free recoil, zero input hold- and loading the bipod until it feels like it will break. .21” difference is inside the expected variation of the cone for 15 round groups anyways (though in this case my guess is that a .2 MOA difference between those two extreme hold is probably repeatable).
Now, there certainly are a lot of hand-guards that will show on observable shift between a light hold and extreme loading of a bipod… but the effect is way overblown for functional shooting with good guns. Especially as it relates to bolt guns and “different zeros” from prone, versus barricade, versus tripod. That’s all an excuse because people do not want to admit they suck and need practice. Then they shoot one or two 3-5 shot groups and try to read tea leaves and explain why the two groups don’t look the same…

Thanks for taking the time to test it live fire, those mk12s really are something special

Do you see similar results with the LMT rifles ?

 

[Formidilosus]

Thanks for taking the time to test it live fire, those mk12s really are something special

Do you see similar results with the LMT rifles ?

I’ll check. But I have never seen an observable real shift regardless of position.

 

[RockAndSage]

I’ll check. But I have never seen an observable real shift regardless of position.

Are there any premium, aftermarket barrels for LMTs?

 

[T_Widdy]

Are there any premium, aftermarket barrels for LMTs?

D Wilson will do a conversion on several ar barrels

LMT MRP Barrel Conversion

www.dwilsonmfg.com

 

[Formidilosus]

Are there any premium, aftermarket barrels for LMTs?

As @T_Widdy posted: DWilson.