Arca Rail placement on fiberglass stock

[RJ]

Has anyone experimented with the Forward / Aft placement of the Arca mount on the stock in relation to vertical dispersion at extended ranges ?

 

[RegionRat]

Shooting off a tripod with a gun clamped into a ball mount is a very good technique for minimizing your movement during coyote stands. You will certainly need to practice and the "it depends" answers will come rolling in... because "it depends".

The good news is you don't need to waste too many shots for early adjustments. If your crosshair wobble isn't good, there isn't any point to wasting ammo.

When you do settle the crosshairs, the "it depends" physics kicks in since pure recoil and barrel time will play a role. Not every mount can hold a heavy torque offset, but near the balance point they are worth a try.

You could hardly ever get two people on the forum to agree on topics like these cause one shooter is talking about prairie dogs, and the other is talking about hitting a 5 gallon bucket. Not every hunter/shooter should be taking tripod shots at "extended ranges", but it is easy enough to test yourself against a shot-clock and see if you are kidding yourself.

 

[WSnyder]

Just in front of the magwell/bottom metal seems to be the best compromise. Sometimes a bit further out is better but that’s determined more by how long of a rail you’ve installed. If you put a long rail on you can slide and alter the balance for differing shot angles. If you want a short light rail then IMO in front of bottom metal works better than out front near the end of the fore end. Oh and that’s not just vertical, overall dispersion is better IMO with the rail further back.

 

[RJ]

Thanks for the input, I have tried forward on the two swivel studs. The stability was the best there. Mounted back toward the front Receiver screw ,Stability was kind of drifting around. Yet the vertical on target was the worse on the forward mount. I did observe some stock flex while in the ball mount when lifting the rear of the rifle. The Stock is a McMillan A-5. Before I started testing I was almost sure the forward position would have shown smaller groups. Apparently, stock flex may be playing a part in the vertical issue.

 

[drop_point]

Balance, balance, balance!

 

[RegionRat]

Thanks for the input, I have tried forward on the two swivel studs. The stability was the best there. Mounted back toward the front Receiver screw ,Stability was kind of drifting around. Yet the vertical on target was the worse on the forward mount. I did observe some stock flex while in the ball mount when lifting the rear of the rifle. The Stock is a McMillan A-5. Before I started testing I was almost sure the forward position would have shown smaller groups. Apparently, stock flex may be playing a part in the vertical issue.

Are we using an ARCA to clamp onto a bipod? Or, are we discussing a tripod set-up?

When you support toward the front, then the way you support at the rear becomes very important, just like when shooting from the ground or bench. If you are moving around at the back, then it will translate straight into the results.

If you are only using the ARCA as a front connection to a bipod, then the rear rest becomes half the story.

ARCA can be used in several different rest methods. I assumed you were discussing ones where the ARCA is near the balance point or slightly forward of it such that the clamp is the majority of the support.

 

[RJ]

RegionRat, Yes, The Arca is on a tripod. The rear of the Rifle is being supported with my elbow on a sand bag resting on my thigh. I sit in a portable chair. This is a very stable position for me. I'm trying to duplicate the way I'll be shooting while hunting. I lean on the Rifle pretty hard to minimize movement during recoil.

I get less reticle drift with the forward Arca plate position but more vertical on paper. In front of the receiver screw mount, I get more reticle drift and less vertical on paper. The rifle was tested on three different days, the results were the same everyday .

 

[RegionRat]

Sounds to me like you have done your homework and are ready to go.
Good Luck and in for the range reports!