ARCA rail bipod placement

MarinePMI

Battery Operated Grunt
Belligerents
Jun 3, 2010
4,137
2,931
219
San Diego, Ca
Listened to the latest podcast with Frank and Mark, and the whole "having to adjust the bipod on the ARCA rail" piqued my interest. I never put it together until that, but I also have seen some weird accuracy issues at distant ranges since using an extended aluminum ARCA rail on my AT. Going to have to pull that bipod back a few inches (so it's under the front of the fore end) and see if that resolves the issue. I never really thought about it until Frank mentioned it in the podcast, and then it went "click", followed by a low mumbled "sonnofbitch"....

Thanks for that little nugget Frank; it's things like this that keeps me listening.
 
  • Like
Reactions: Wolfhunter

M113A3

Online Training Member
Online Training Access
Belligerents
Minuteman
Feb 18, 2018
132
32
34
San Francisco
For those of us that have not heard the podcast can you give a recap?
 

MarinePMI

Battery Operated Grunt
Belligerents
Jun 3, 2010
4,137
2,931
219
San Diego, Ca
Essentially, those extended aluminum ARCA/RRS rails tend to flex some. This leads to some vertical stringing at distance, and I'd imagine some horizontal drift if the bipod legs are not equally loaded. At any rate, Frank mentioned seeing it with one of his class students, and the student mentioned just putting the ARCA rail their rifle. Frank and Mark had him move the bipod back, under the fore end, and the vertical dispersion went away. Their anecdotal conclusion was that the rail was flexing ever so slightly, that while not noticeable at closer targets, was clearly demonstrable at the 1000yd target. Makes absolute sense to me...
 

M113A3

Online Training Member
Online Training Access
Belligerents
Minuteman
Feb 18, 2018
132
32
34
San Francisco
Thanks! I am using a spigot mount on a KRG W3 chassis so I think I am ok... I only use the spigot in the prone
.
 

IronOperator87

Online Training Member
Online Training Access
Minuteman
Jul 22, 2018
41
38
24
I am the student from Alaska prc with the rail that was flexing. I was getting really good groups previously with an atlas psr in a spigot Mount and noticed vertical stringing after I put the rrs spec’d Rail on it with a cal. The cal is a great bi pod but I noticed the rail was flexing up and down when the bipod was all the way out front. You could see it when you pushed on the butt pad of the rifle. I ran it by Frank and he agreed then suggested I move it back and that worked. Groups tightened back up to where they where. Another thing to think about is the spigot interface doesn’t allow a rrs/arca rail to be bolted to the chassis until 1.75 inches back from the front of the chassis so that allows more flex. So you basically have 4” of rail that’s not bolted down sticking out the front on an AT. That 2” of over hang might not be an issue on other rifles.
 
Last edited:

Subwrx300

Major Hide Member
Belligerents
Jan 15, 2014
1,287
799
219
Cedar Springs, MI
Found the same issue even on Manners PRS2 that has rail that extends forward of stock. I make sure the front edge of RRS clamp is placed directly under a mounting screw for this reason. Had 1-2" extra vertical that I couldn't explain until move bipod rearward to a better supported area of rail.

Glad a few can confirm it wasn't just me!
 

samb300

Anarchy Outdoors, Accuracy Obsession
Belligerents
Feb 22, 2013
685
751
99
Milwaukee, WI
For you guys running an AT, I can understand the issue that's going on. @IronOperator87 you make a great observation about the amount of rail forward of the attachment screw contributing to the amount of flex.

If you haven't seen it yet, check out the bipod spigots I designed and partnered with Anarchy Outdoors to make. I have a picatinny version and a RRS/Arca version. They replace the entire factory bipod spigot block that is housed inside the forend tube, and are rock solid. The RRS version gets you much closer to the bore axis as well. It is designed and engineered to be stiffer than a factory MPA or KRG spigot mount on those respective chassis systems.

The Anarchy page is HERE

The SH post is HERE

Thanks,

Sam

7094340
 

IronOperator87

Online Training Member
Online Training Access
Minuteman
Jul 22, 2018
41
38
24
@samb300 I like how close the RRS version gets you to the barrel. Looks like it will put the Atlas cal in a position where the apex will be above the barrel. Great stuff
 

samb300

Anarchy Outdoors, Accuracy Obsession
Belligerents
Feb 22, 2013
685
751
99
Milwaukee, WI
@samb300 I like how close the RRS version gets you to the barrel. Looks like it will put the Atlas cal in a position where the apex will be above the barrel. Great stuff
Thanks! Yes, the RRS/Arca version is approximately 1” closer to the bore than the typical forend rail, helping move that apex point up.
 

Steel head

Uncouth heathen
Belligerents
Aug 3, 2014
1,123
525
219
Washington
Essentially, those extended aluminum ARCA/RRS rails tend to flex some. This leads to some vertical stringing at distance, and I'd imagine some horizontal drift if the bipod legs are not equally loaded. At any rate, Frank mentioned seeing it with one of his class students, and the student mentioned just putting the ARCA rail their rifle. Frank and Mark had him move the bipod back, under the fore end, and the vertical dispersion went away. Their anecdotal conclusion was that the rail was flexing ever so slightly, that while not noticeable at closer targets, was clearly demonstrable at the 1000yd target. Makes absolute sense to me...
Interesting subject.
I felt I had more vertical than usual my last two trips to my 1000+ spots.

I had just starting hanging the bipod out past the forend on a ARCA rail.

I’ll pull my bipod a bit back and try it out tomorrow.
 
  • Like
Reactions: MarinePMI

Steel head

Uncouth heathen
Belligerents
Aug 3, 2014
1,123
525
219
Washington
Ok

I’m almost positive I noticed a difference.

Winds were a bit tricky today and lots of mirage yet vertical just wasn’t an issue today as long as I did my part.
 
  • Like
Reactions: MarinePMI

Simia Dei

Boendr
Belligerents
Feb 11, 2017
479
347
69
Found the same issue even on Manners PRS2 that has rail that extends forward of stock. I make sure the front edge of RRS clamp is placed directly under a mounting screw for this reason. Had 1-2" extra vertical that I couldn't explain until move bipod rearward to a better supported area of rail.

Glad a few can confirm it wasn't just me!
I had the same issue, same stock too. Had inconsistent groupings, I may just be shit though. Here's my home bodge solution:

7096430
 
  • Like
Reactions: Subwrx300