AR Positional POI Shift Test

[Veracity]

Edit **I’ve had a few people ask. Here is the link to my test target if anyone is wanting to use it. https://veracitysolutionsllc.com/resources/ **

Finally got a chance to get out and test a few different uppers for POI shift and get pictures.

These are NOT to bash any company but to make aware an issue that could be affecting your shots when changing positions or bipod locations. The point is to test and know if your shift is consistent and repeatable and then accounting for it if the style of shooting and targets you engage warrant it. I have used several methods depending on what I am using the rifle for to work through this. *I understand this isn't super scientific and the data is limited, feel free to test for yourself. More rigid receivers, semi-monolithic and monolithic receivers help mitigate this issue.

1. Zero normally from bipod, and add the shift to my data when in other positions that would have a shift. (Ex. .3 MIL shift, Normal data when using bipod, add .3 MIL to positional data)
2. Zero inbetween the shift as the targets may be tall enough it is in the noise. (Ex. .3 MIL shift, zero from bipod .15'ish high and bagged position is .15ish low)

These were shot from a bench modified prone as neutral as possible to do my best of not affecting results from inconsistent pressure. The bagged shots were taken from kneeling using the same bench.

Harris BRM-S 6-9 Bipod was placed at 12.5” from the front edge of the magazine well, then at 3.5” away, then fired kneeling from an Armageddon Gamechanger shmedium w/ heavy fill. This was done to keep things consistent across each upper.

Uppers:
Semi-monolithic:
Ridgeline Defense RD-15 LPR 16” Proof Research (KGM R30) (Thermal fit and bedded)
Mega MML 18” Noveske Barrel (no suppressor) (Unsure of assembly)
Standard Barrel nut design:
SOLGW Broadsword M76 18” Proof Research (OCL Hydrogen) (Thermal fit and bedded)
Hodge Defense Pinchlock 18” Krieger (OCL OCM-5) (Thermal fit and bedded)

Ammunition:
Black Hills Mk262 Mod 1-C 77gr SMK

Distance:
106.2 Yards (Vortex Fury 5000AB)

Weather:
96° F
29.59 inHg
40% Humidity
3029 DA

 

[PBWalsh]

Nice to see the poat here from IG. Here is anofher data poinf. Vltor MUR/WOA TR handguard with a .4mil shift low. Note: the bottom group was centered due to holding .4mils in the reticle. Top group is bipod/rear bag. Middle is tripod standing/kneeling/sitting off a table/bag. Bottom is the adjusted group.

 

[bfoosh006]

Good to know info. Thank you for sharing !

Having that much possible POI shift, shows that you have to test your rifles setup's. In other words don't assume anything.

Kinda makes me want to check the differences on a few of my rifles.

 

[Veracity]

Nice to see the poat here from IG. Here is anofher data poinf. Vltor MUR/WOA TR handguard with a .4mil shift low. Note: the bottom group was centered due to holding .4mils in the reticle. Top group is bipod/rear bag. Middle is tripod standing/kneeling/sitting off a table/bag. Bottom is the adjusted group.


View attachment 8439938

Thanks for sharing that extra data point. Always loved those VLTOR MUR receivers

 

[msgriff]

In the HK .308/7.62 precision shooting thread here, one of our members from Germany recently acquired a G28. It was asked why HK doesn't extend the bottom Picatinny rail all the way to the front of the handguard, it stops short so that the bipod is about centered underneath the gas drive. It was mentioned that HK determined an unacceptable POI shift if the bipod was mounted forward of that position during testing. I thought it was an interesting design consideration.

 

[Ledzep]

Seekins upper with a 24" bull bartlein 6 ARC barrel. .2 mil hash marks. Windage was on purpose to separate the groups.

I've not been made aware of an aluminum tube receiver style rifle that doesn't do this to some degree. Some are better than others.

 

[Veracity]

In the HK .308/7.62 precision shooting thread here, one of our members from Germany recently acquired a G28. It was asked why HK doesn't extend the bottom Picatinny rail all the way to the front of the handguard, it stops short so that the bipod is about centered underneath the gas drive. It was mentioned that HK determined an unacceptable POI shift if the bipod was mounted forward of that position during testing. I thought it was an interesting design consideration.

I wasn't aware of that. I will have to search for it and check it out. That is interesting info.

 

[rothgyr]

I see about .4 between a bag and bipod. I just got a thermofit upper receiver and was hoping it might reduce the shift. This makes me think it's not going to be promising...

 

[308pirate]

I'm not surprised by any of this.

While it's a completely different game, NRA/CMP service rifle shooters have known for decades that a POI shift exists when shooting from different sling supported positions and from bags.

That POI shift is present not only on non-free floated rifles used in that sport (M1, M14) but also in free-floated AR-15s

 

[Ledzep]

*cough*
Someone should make a lower receiver with an ARCA+M-Lok fore-end that extends in front of the magazine well and a stainless upper and handguard that fits but never touches said lower.
*cough*

The Springfield thing was close but left a lot of opportunity on the table (ARCA/M-lok). The stainless upper isn't absolutely necessary with said lower but I don't think many people would care about the weight and the Young's modulus benefits are probably worth it just for the upper as a standalone.

The thicker uppers and various handguard mounting options are bandaids for a lightweight battle bullet hose and don't really properly address the problem just make it incrementally better. There's a reason you don't see this in most bolt actions... and a reason why you do see it in some bolt actions for that matter...

 

[Paris_Bulks]

Seekins upper with a 24" bull bartlein 6 ARC barrel. .2 mil hash marks. Windage was on purpose to separate the groups.

View attachment 8440133

I've not been made aware of an aluminum tube receiver style rifle that doesn't do this to some degree. Some are better than others.

Is this the IRMT-3 V3 upper with the triangular handguard and do you call that a .2 mil or .4 mil shift?

 

[Paris_Bulks]

Finally got a chance to get out and test a few different uppers for POI shift and get pictures.

These are NOT to bash any company but to make aware an issue that could be affecting your shots when changing positions or bipod locations. The point is to test and know if your shift is consistent and repeatable and then accounting for it if the style of shooting and targets you engage warrant it. I have used several methods depending on what I am using the rifle for to work through this. *I understand this isn't super scientific and the data is limited, feel free to test for yourself. More rigid receivers, semi-monolithic and monolithic receivers help mitigate this issue.

1. Zero normally from bipod, and add the shift to my data when in other positions that would have a shift. (Ex. .3 MIL shift, Normal data when using bipod, add .3 MIL to positional data)
2. Zero inbetween the shift as the targets may be tall enough it is in the noise. (Ex. .3 MIL shift, zero from bipod .15'ish high and bagged position is .15ish low)

These were shot from a bench modified prone as neutral as possible to do my best of not affecting results from inconsistent pressure. The bagged shots were taken from kneeling using the same bench.

Harris BRM-S 6-9 Bipod was placed at 12.5” from the front edge of the magazine well, then at 3.5” away, then fired kneeling from an Armageddon Gamechanger shmedium w/ heavy fill. This was done to keep things consistent across each upper.

Uppers:
Semi-monolithic:
Ridgeline Defense RD-15 LPR 16” Proof Research (KGM R30) (Thermal fit and bedded)
Mega MML 18” Noveske Barrel (no suppressor) (Unsure of assembly)
Standard Barrel nut design:
SOLGW Broadsword M76 18” Proof Research (OCL Hydrogen) (Thermal fit and bedded)
Hodge Defense Pinchlock 18” Krieger (OCL OCM-5) (Thermal fit and bedded)

Ammunition:
Black Hills Mk262 Mod 1-C 77gr SMK

Distance:
106.2 Yards (Vortex Fury 5000AB)

Weather:
96° F
29.59 inHg
40% Humidity
3029 DA

View attachment 8439911View attachment 8439912View attachment 8439913View attachment 8439914

Can you speak on the Ridgeline design and why you believe it has less shift? Also, what amount of shift in mils do you consider it to be?

 

[Veracity]

Can you speak on the Ridgeline design and why you believe it has less shift? Also, what amount of shift in mils do you consider it to be?

The Ridgeline is a thicker receiver and semi-monolithic where the barrel nut is thread into the receiver and the forend makes no contact with it.

After a few hundred rounds of testing I’ve seen no perceivable POI shift with the Ridgeline. My Seekins IMRT-3/SP-10 and Aero Enhanced w/ Sgt of Arms forend would have up to .1 MIL shift but have always been solid for my use. The Ridgeline is just on another level.

 

[Ledzep]

Is this the IRMT-3 V3 upper with the triangular handguard and do you call that a .2 mil or .4 mil shift?

Yes, IRMT-3 and I'd say .2-.3 was typical through various positions. .4 in an extreme case.

 

[Veracity]

Yes, IRMT-3 and I'd say .2-.3 was typical through various positions. .4 in an extreme case.

That’s interesting you were seeing a shift with the semi-monolithic Seekins. I’ve shot over a dozen of them and only got up to .1 MIL with loading the bipod fairly hard.

Is this shooting all at distance or at 100y on paper?

 

[Paris_Bulks]

The Ridgeline is a thicker receiver and semi-monolithic where the barrel nut is thread into the receiver and the forend makes no contact with it.

After a few hundred rounds of testing I’ve seen no perceivable POI shift with the Ridgeline. My Seekins IMRT-3/SP-10 and Aero Enhanced w/ Sgt of Arms forend would have up to .1 MIL shift but have always been solid for my use. The Ridgeline is just on another level.

So you are saying that on the Ridgeline positional pressure on the rail is not transmitted to the barrel nut? If that is the case that is outstanding.

Do you have time to mount and zero a LAM, and check the visible laser at dusk through your day optic on an object at 100 or 200 yards when on bipod vs. bag to see if the rail is still flexing independent of the nut? I usually see a .4 mil shift down in the laser when going from the bipod to a bag near the magwell on my traditional forged upper. I am curious of the Ridgeline design fixes this or if there is still shift in the rail itself despite it being thicker.

 

[Paris_Bulks]

Yes, IRMT-3 and I'd say .2-.3 was typical through various positions. .4 in an extreme case.

Thank you

 

[Ledzep]

100-1200yd. Pretty consistent zero shift. I ran 2 different profiles on 4DoF for PRS and would pull from the corresponding profile depending on what position I would shoot.

Bipod along the ARCA rail didn't change a ton until I got the bipod ALL the way to the rear of the rail, but for whatever reason shooting off a bag on a barricade was a surefire .2-.3 low hit from my "bipod" profile.

 

[rothgyr]

100-1200yd. Pretty consistent zero shift. I ran 2 different profiles on 4DoF for PRS and would pull from the corresponding profile depending on what position I would shoot.

Bipod along the ARCA rail didn't change a ton until I got the bipod ALL the way to the rear of the rail, but for whatever reason shooting off a bag on a barricade was a surefire .2-.3 low hit from my "bipod" profile.

"rear" of the rail - are you saying close to the receiver, you were seeing more shift?

 

[Veracity]

So you are saying that on the Ridgeline positional pressure on the rail is not transmitted to the barrel nut? If that is the case that is outstanding.

Do you have time to mount and zero a LAM, and check the visible laser at dusk through your day optic on an object at 100 or 200 yards when on bipod vs. bag to see if the rail is still flexing independent of the nut? I usually see a .4 mil shift down in the laser when going from the bipod to a bag near the magwell on my traditional forged upper. I am curious of the Ridgeline design fixes this or if there is still shift in the rail itself despite it being thicker.

Yes. That’s how semi-monolithic are designed. LaRue, Aero Enhanced, Seekins, Ridgeline, Mega all have models with similar setups. The added receiver thickness helps as well.

I’ll try and mount an LA5 this week and see what I can do for rail deflection. I’ve never seen a rail that did not have some movement so I doubt we will ever get to 0, but some have flexed less than others. The most rigid I’ve seen so far is the SOLGW M89/L89 rails.

 

[Veracity]

100-1200yd. Pretty consistent zero shift. I ran 2 different profiles on 4DoF for PRS and would pull from the corresponding profile depending on what position I would shoot.

Bipod along the ARCA rail didn't change a ton until I got the bipod ALL the way to the rear of the rail, but for whatever reason shooting off a bag on a barricade was a surefire .2-.3 low hit from my "bipod" profile.

Dang. You’re the first person I’ve heard who has had shift like that from a Seekins. I plan to run an SP-10 (6 Creed) and IMRT (6ARC) in PRS next year, mine have been essentially 0 shift.

 

[ironpony52]

*cough*
Someone should make a lower receiver with an ARCA+M-Lok fore-end that extends in front of the magazine well and a stainless upper and handguard that fits but never touches said lower.
*cough*

The Springfield thing was close but left a lot of opportunity on the table (ARCA/M-lok). The stainless upper isn't absolutely necessary with said lower but I don't think many people would care about the weight and the Young's modulus benefits are probably worth it just for the upper as a standalone.

The thicker uppers and various handguard mounting options are bandaids for a lightweight battle bullet hose and don't really properly address the problem just make it incrementally better. There's a reason you don't see this in most bolt actions... and a reason why you do see it in some bolt actions for that matter...

When you say Springfield thing are you referring to the Saint Edge ATC Elite chassis?? it is rigid and very accurate with minimal deviation.
A little heavy.

 

[Ledzep]

"rear" of the rail - are you saying close to the receiver, you were seeing more shift?

Yeah if I zeroed for the bipod all the way forward, zero wouldn't noticeably shift until I got ~75% back with the bipod mounting location then it would start hitting low. Shooting off of a bag with the rifle resting on the HG just in front of the mag well was the lowest POI.

Also, if you got the bipod caught on obstacles such that it torqued the rail side-to-side it would cause horizontal POI shift. If you hard locked the HG into a tank trap so it was bound up tight against 2 of the 3 legs of the trap it would shotgun pattern like 4 MOA+.

Not a bag on Seekins I don't think it's limited to anyone of these uppers. Like I said I've even seen the behavior in bolt action rifles configured this way. It's a limitation of aluminum.

 

[Veracity]

Yeah if I zeroed for the bipod all the way forward, zero wouldn't noticeably shift until I got ~75% back with the bipod mounting location then it would start hitting low. Shooting off of a bag with the rifle resting on the HG just in front of the mag well was the lowest POI.

Also, if you got the bipod caught on obstacles such that it torqued the rail side-to-side it would cause horizontal POI shift. If you hard locked the HG into a tank trap so it was bound up tight against 2 of the 3 legs of the trap it would shotgun pattern like 4 MOA+.

Not a bag on Seekins I don't think it's limited to anyone of these uppers. Like I said I've even seen the behavior in bolt action rifles configured this way. It's a limitation of aluminum.

Right on. I’ll try and get out this week and test my Seekins rifles again. I’ve never seen a semi monolithic style have that much of a shift. I was able to get the LaRue to shift as well but that’s loading it abnormally hard. I shoot from a bipod as neutral as I can and don’t load in actual use.

Are you loading the bipod?

 

[Ledzep]

No, nothing aggressive. Same as I shoot a bolt gun. I have heard of up to and over a mil shift while guys are shooting down-hill in steep terrain with their body weight really resting on the bipod, though.

 

[Veracity]

No, nothing aggressive. Same as I shoot a bolt gun. I have heard of up to and over a mil shift while guys are shooting down-hill in steep terrain with their body weight really resting on the bipod, though.

I’ve seen that on traditional receiver designs but not on monolithic type. I’m going to mess around with the Seekins this week and see if I can induce any shift.

 

[Paris_Bulks]

Yes. That’s how semi-monolithic are designed. LaRue, Aero Enhanced, Seekins, Ridgeline, Mega all have models with similar setups. The added receiver thickness helps as well.

I’ll try and mount an LA5 this week and see what I can do for rail deflection. I’ve never seen a rail that did not have some movement so I doubt we will ever get to 0, but some have flexed less than others. The most rigid I’ve seen so far is the SOLGW M89/L89 rails.

Thank you on the LA5 testing. I would appreciate that.

 

[DeathBeforeDismount]

Makes you wonder why no one has made a stainless or steel upper to help with barrel nut deflection.

 

[Veracity]

Makes you wonder why no one has made a stainless or steel upper to help with barrel nut deflection.

DPMS did uppers and lowers years ago.

 

[dms416]

Makes you wonder why no one has made a stainless or steel upper to help with barrel nut deflection.

The krauts at HK did the upper receiver of the G28 in steel because the standard aluminum 417 wasn't cutting the mustard.

In that spirit, the HK 416 could have some gnarly deflection depending on the rail being used. Mounted out at the far end, a 14" Geissele or RAHG loaded decently could shift groups down. Scuttlebutt is they know this and this is why their OEM longer rails won't let you attach anything that far out and they advise not mounting a bipod forward the gas block area of the barrel.

 

[Gentleman4561]

Good info Scott.

I did some test between a ADM upper with a IWI Arca handguard and a Aero Enhanced with a SOA.

I found that the ADM/IWI set up saw a consistent .3-.5 .mil shift at 225 yards while the Aero saw .1 or less. Tough to really make the call on .1, as I can’t shoot .1 groups off a bag with a gas gun.

After that, every AR I have built has gotten some form of a monolithic upper.

Thanks as always, Luke

 

[LRRPF52]

Yeah if I zeroed for the bipod all the way forward, zero wouldn't noticeably shift until I got ~75% back with the bipod mounting location then it would start hitting low. Shooting off of a bag with the rifle resting on the HG just in front of the mag well was the lowest POI.

Also, if you got the bipod caught on obstacles such that it torqued the rail side-to-side it would cause horizontal POI shift. If you hard locked the HG into a tank trap so it was bound up tight against 2 of the 3 legs of the trap it would shotgun pattern like 4 MOA+.

Not a bag on Seekins I don't think it's limited to anyone of these uppers. Like I said I've even seen the behavior in bolt action rifles configured this way. It's a limitation of aluminum.

I remember when we were doing live-fire stalk lanes in Korea with the M24, and after the stalkers were busted, we all had time to burn through some M118. (Shooters didn’t go live until the observers near the targets pulled off/behind berms.) We set up on one of the final firing positions one of the shooters had used on a hill on the edges of the stalk lane boundary, and I wedged the M24 SWS in between 2 thick branches. The forend was touching the tree, but not the barrel and the group opened up quite a bit.

I think it has to do with harmonic resonance in the rifle. If the rifle is wound-up tight and vibrates like a tuning fork, any added or adjusted tensions placed on it will change how the barrel whips.

For the AR-15, I’ve never liked how minimal contact there is with the barrel extension and the upper. This is one of the areas where I think Hk really did it better with the 416 and how long that barrel extension is. I still think you would see POI shift with tension shifts on a free-floated Hk with Stoner internal expansion gas system vs the Tokarev/AR-18 gas.

 

[PBWalsh]

Good info Scott.

I did some test between a ADM upper with a IWI Arca handguard and a Aero Enhanced with a SOA.

I found that the ADM/IWI set up saw a consistent .3-.5 .mil shift at 225 yards while the Aero saw .1 or less. Tough to really make the call on .1, as I can’t shoot .1 groups off a bag with a gas gun.

After that, every AR I have built has gotten some form of a monolithic upper.

Thanks as always, Luke

I was just about to ask if anyone had experience with this on the M4E1 upper. .1 mil shift would probably get lost in the noise of my group size as I'm not shooting .36" groups.

Good to know, definitely considering one of their enhanced uppers.

 

[Gentleman4561]

I was just about to ask if anyone had experience with this on the M4E1 upper. .1 mil shift would probably get lost in the noise of my group size as I'm not shooting .36" groups.

Good to know, definitely considering one of their enhanced uppers.

Yep, I think the M4E1 upper is a great way to go.

 

[yinzer_724]

Glad I found this thread as I am offloading my factory CLE-built rifle as I can't get a replacement tube from them when this one's toast. Essentially, if I comprehend this correctly the way to go with a replacement rig would be Ridgeline, SOLGW, VLTOR, M4E1 Enhanced, or some sort of semi-monolithic if at all possible to minimize shift/deflection?

Who else is in the semi-monolithic game? LMT, Cobalt, Larue?


Thanks for the solid thread and write-up. This is beyond helpful for us new to competing.

 

[Coffee_and_Pipes]

Glad I found this thread as I am offloading my factory CLE-built rifle as I can't get a replacement tube from them when this one's toast. Essentially, if I comprehend this correctly the way to go with a replacement rig would be Ridgeline, SOLGW, VLTOR, M4E1 Enhanced, or some sort of semi-monolithic if at all possible to minimize shift/deflection?

Who else is in the semi-monolithic game? LMT, Cobalt, Larue?


Thanks for the solid thread and write-up. This is beyond helpful for us new to competing.

LMT does some conventional uppers where you attach a handguard to the barrel nut, but their claim to fame is that they make a truly monolithic upper.

If you go with one of their monolithic uppers, you’re going to have to go with their barrel attachment system. You can buy factory LMT barrels or have someone like D. Wilson ( @unclemoak ) convert a non-LMT barrel for you. There have been some complaints about LMT’s QC as of late, so do a little investigating before you jump in.

Seekins Precision does a semi-monolithic upper where the handguard attaches to the upper receiver not the barrel nut.

I’m sure there are others I haven’t mentioned or don’t know about, but I would start by looking at those two companies along with Ridgeline Precision.

 

[yinzer_724]

LMT does some conventional uppers where you attach a handguard to the barrel nut, but their claim to fame is that they make a truly monolithic upper.

If you go with one of their monolithic uppers, you’re going to have to go with their barrel attachment system. You can buy factory LMT barrels or have someone like D. Wilson ( @unclemoak ) convert a non-LMT barrel for you. There have been some complaints about LMT’s QC as of late, so do a little investigating before you jump in.

Seekins Precision does a semi-monolithic upper where the handguard attaches to the upper receiver not the barrel nut.

I’m sure there are others I haven’t mentioned or don’t know about, but I would start by looking at those two companies along with Ridgeline Precision.

Ya, I have a buddy who sent some LMT work to D.Wilson and it came out fantastic. Buddy of mine has a true lmt mono gun and it's had some QC issues. But, to be my sr15 and a buddies also did. Everything breaks eventually.

Really like the seekins stuff.

 

[Veracity]

Glad I found this thread as I am offloading my factory CLE-built rifle as I can't get a replacement tube from them when this one's toast. Essentially, if I comprehend this correctly the way to go with a replacement rig would be Ridgeline, SOLGW, VLTOR, M4E1 Enhanced, or some sort of semi-monolithic if at all possible to minimize shift/deflection?

Who else is in the semi-monolithic game? LMT, Cobalt, Larue?


Thanks for the solid thread and write-up. This is beyond helpful for us new to competing.

MEGA MML receivers are also semi monolithic as well as those you mentioned. Not all of those companies receivers are so double check.

Fully monolithic like LMT can still shift a small amount, as well as semi mono if loaded hard enough. Hard to get away from completely with aluminum but the Ridgeline has been the best I’ve seen so far.

 

[357Max]

VLTOR Fusion F15 is a monolithic albeit keymod only. I'm hoping to test mine for shift this weekend @500y.

LWRC receiver sets are very nice but not often for sale as just receivers. They don't have the best selection of longer hand-guards.

 

[PBWalsh]

VLTOR Fusion F15 is a monolithic albeit keymod only. I'm hoping to test mine for shift this weekend @500y.

LWRC receiver sets are very nice but not often for sale as just receivers. They don't have the best selection of longer hand-guards.

I am definitely interested in that test result.

 

[yinzer_724]

I am definitely interested in that test result.

Same. Just wish it was updated and not keymod.

 

[45custom]

MEGA MML receivers are also semi monolithic as well as those you mentioned. Not all of those companies receivers are so double check.

Fully monolithic like LMT can still shift a small amount, as well as semi mono if loaded hard enough. Hard to get away from completely with aluminum but the Ridgeline has been the best I’ve seen so far.

Any chance you've tested an LMT MRP to compare yet, or if you're otherwise aware of any testing data on the platform?

 

[Veracity]

Any chance you've tested an LMT MRP to compare yet, or if you're otherwise aware of any testing data on the platform?

The 16”MRP I tested had .2 MIL shift. However sample size of 1 and it was only 2, 5-shot groups.

 

[45custom]

The 16”MRP I tested had .2 MIL shift. However sample size of 1 and it was only 2, 5-shot groups.

Thanks. Could I also assume that was the rifle length MLOK rail?

 

[Veracity]

Thanks. Could I also assume that was the rifle length MLOK rail?

13” or 13.25” whatever the full length MRP is. Wa suppressed with RC2 as well.

 

[357Max]

I've got 40 rounds loaded for the test. 6ARC
Lapua Grendel necked down
108 eldm
29.4 Lever
2.290 oal
should be 2670-2700 This barrel only has about 40 rounds on it. It is the replacement Rainier UM. If head space grows over these 50 rounds they can stick this barrel up their ass.

VLTOR Fusion F-15 Face trued & shimmed. The VTOR Fusion extension is just as loose as the MUR's
Steel KRG Arca rail
22" +2" gas barrel
Gun weight with Ckyepod & no mag is 15lbs-6oz.

I'm thinking 5 rounds to get a good zero @100y Bi-pod/rear bag & light preload, 5 more to true dope to waterline at 500y with same bi-pod rear bag. Then build and break position 5 x with 3 shots each from prone bipod/rear bag to kneeling off a barricade with a smedium heavy fill up against the magwell.

Does this sound like a reasonable test?
What is the preferred program you guys would suggest I use to calculate mean radius after this test??

500Y on paper will probably hurt my feelings. Hopefully the load will be at or under 1 moa at 100y

Thanks

 

[PBWalsh]

I've got 40 rounds loaded for the test. 6ARC
Lapua Grendel necked down
108 eldm
29.4 Lever
2.290 oal
should be 2670-2700 This barrel only has about 40 rounds on it. It is the replacement Rainier UM. If head space grows over these 50 rounds they can stick this barrel up their ass.

VLTOR Fusion F-15 Face trued & shimmed. The VTOR Fusion extension is just as loose as the MUR's
Steel KRG Arca rail
22" +2" gas barrel
Gun weight with Ckyepod & no mag is 15lbs-6oz.

I'm thinking 5 rounds to get a good zero @100y Bi-pod/rear bag & light preload, 5 more to true dope to waterline at 500y with same bi-pod rear bag. Then build and break position 5 x with 3 shots each from prone bipod/rear bag to kneeling off a barricade with a smedium heavy fill up against the magwell.

Does this sound like a reasonable test?
What is the preferred program you guys would suggest I use to calculate mean radius after this test??

500Y on paper will probably hurt my feelings. Hopefully the load will be at or under 1 moa at 100y

Thanks

1a. I wonder if the steel KRG rail bolted to the handguard makes for a stiffer upper? Obviously the issue we are all seeing is the area around the barrel nut, but I am curious if a steel ARCA rail aids in less POI shift.

1b. Does anyone have the means to test this? Do a normal test without the rail, then another with the rail on? I assume there would be less shift due to higher rigidity along the length of the rail, but testing alone would show this.

2. Paper groups at 100y seem to show well enough POI shift. At 500, there is a bit more noise from velocity and BC rounding errors and inconsistencies compared to 100y. 100y is just cleaner.

 

[357Max]

1a. I wonder if the steel KRG rail bolted to the handguard makes for a stiffer upper? Obviously the issue we are all seeing is the area around the barrel nut, but I am curious if a steel ARCA rail aids in less POI shift.

1b. Does anyone have the means to test this? Do a normal test without the rail, then another with the rail on? I assume there would be less shift due to higher rigidity along the length of the rail, but testing alone would show this.

2. Paper groups at 100y seem to show well enough POI shift. At 500, there is a bit more noise from velocity and BC rounding errors and inconsistencies compared to 100y. 100y is just cleaner.

The gun still has a gap between the magwell & the rail. For the poi shift flex must be happening across the joint where the extension mates to the upper. Seems like the steel rail may actually aggravate the issue since it's heavy. In addition to the heavy Arca, I've got a few weights out towards the front of the rail.

The range I'll be shooting at for this has 100 & 500 only.
I could just shoot dots @100y, but I'd still want to enter them all into some program to calculate mean radius from dot center for the total group of 15 per position. Not sure what tool/program is best suited to do that?

 

[rothgyr]

I doubt the rail will change the POI shift. I have a KRG rail on my PRI delta forearm, and it's still .4 between bag and bipod.

 

[PBWalsh]

The gun still has a gap between the magwell & the rail. For the poi shift flex must be happening across the joint where the extension mates to the upper. Seems like the steel rail may actually aggravate the issue since it's heavy. In addition to the heavy Arca, I've got a few weights out towards the front of the rail.
View attachment 8442357



The range I'll be shooting at for this has 100 & 500 only.
I could just shoot dots @100y, but I'd still want to enter them all into some program to calculate mean radius from dot center for the total group of 15 per position. Not sure what tool/program is best suited to do that?

Just shoot the dots in prone and off a bag, the impacts will show any shift.