Need help from SEB Joypod users on mysterious problem

[jlow]

Using two of my rifles with this bipod and getting a lowering of point of aim after a few shots.

So let me back up first give some detail the conditions:

Two chassis rifles, an AI AT and a Tikka T3X Varminth in an MPA chassis. Both solid rifles, hits what I aim at with sub MOA precision despite the above problem. Both have a pic rail that the Joypod is attached solidly to, and both rifles have a bag rider on the stock.

Shooting from a solid, flat, level concrete surface with a Midway USA shooting mat. Joypod is sitting on the front non-padded single layer canvas surface, and rear is on a SEB “Bigfoot” rear bag correctly loaded with sand.

I tap the rifle bag rider down on the rear bag to properly settle it before I start, and I adjust the joystick so that it is in the middle position in terms of height adjustment. Adjust both legs so that the scope reticle is pointing at the target. Lock both legs and can lever down.

I take a few shots and I find that my scope is now pointing low and eventually so low that I cannot compensate with the joystick with a 32x NF scope at 200 yards or 55x NF scope at 600 yards.

Now I realize that since the rear bag is sitting on the shooting mat (and not on the ground), it is not ideal since it is padded and can settle, BUT if either the bag settles on the mat or the bag rider settle on the bag, I would think the stock will sit lower and reticle would be pointing higher and not lower on the target?

This is what I have not been able to figure out.

 

[jlow]

I did a Google search for "FTR rear bag settling" and found a thread on this board in 2017 started by CharlieNC. Now he had the opposite problem but one comment by Johara1 caught my eye, he said:

"If the muzzles is going down the butt is going up... too much sand in the bag. If the muzzles is going up the butt is going down..... I never saw a hard bag work yet...... Jim "

So perhaps I have too much sand in my bag and the sand in the ears are settling under the stock and pushing my stock up?

 

[CADDIE5]

Is the stock placed at the same position within the Bigfoot ears after each shot? Concrete pad maybe sloped and shouldering rifle could be pushing it forward and down. Our 30 position 300yd line has 6" wide concrete pad with firing positions paint stenciled on it. Some positions are flat others have slight slope. Does rifle with JoyPod jump left or right depending on barrel twist and caliber when firing? Have you tried a 24" wide x12" deep carpeted board under the JoyPod?

 

[jlow]

Thanks for your reply!

I cannot say the stock is at the same position after each shot. There is of course recoil which moves the rifle back and I do shoulder the rifle and is likely not pushed back at least with one of the rifles which is only a .223, but I will check next time.

In terms of whether the pad is level, I don't know but will check.

One thing I should add is the change in POI is pretty big. This last week shooting the .223 at 200 yards with a 32x scope, the drop was more than 3-4' at the target and not just a few MOA which I normally can easily adjust with the joystick.

I have not tried the carpeted board but would be interested in understanding the rationale. The Joypod has "ski" that it rides on and my understanding is it is made to allow straight movement backwards in respond to the recoil?

 

[CADDIE5]

Rear bag has to be square to target- natural point of aim. While in position push rifle forward and back to original position on ears. If not aiming through scope at same point on target you are not aligned or canted. Also is your cheek pressure the same everytime on the stock? I set JoyPod so I have equal joystick movement L and R on target as well as waterline, ie centered. I use the carpeted board when shooting LR matches on stone or gravel.

 

[Lbart]

Jlow,
While I shoot F-Open with a Neo; not F/TR, I find I run out of joystick elevation unless I do this…pound the rifle into the rear bag, then set rifle up on X with stick centered. Next move the stick all the way down. At 1k the cross-hairs should be below the target frame. If not, use leg adjustment to get there. How much below is a judgment call. Then check that stick can still move cross-hairs to frame top. Done this way as the rear bag settles I never run out of elevation movement. In effect I have built in for bag settlement. Works for me.

 

[kzin]

I tap the rifle bag rider down on the rear bag to properly settle it .

One logical possibility is that you're overdoing this so the leather or sand expands or rises as you shoot.
Try just setting the rider gently on the bag and see if the problem goes away or reverses.
Seems especially possible if the rider is a shape that could 'dent' the bag rather than a largish flat surface.

Beyond that, mark the mat, bag and rider so you can verify everything is in the EXACT position and relationship as the good initial setup.

 

[jlow]

Caddies – I understand the importance of the bag being square to the target, but I think this and the carpeted board affects lateral position of the gun after recoil and not the up and down position. All this info is helpful but I think at this point, it is important to focus on one which is why my POI drops when I fire.

Lbart – I basically do the same thing.

Kzin – sorry but this goes 100% against what is recommended by SEB.

I come back to the comment by Johara1 which I think is correct. One thing I should mention is I walk to the 600 yard line with the rifle in a drag bag on my back and the SEB rear bag in my other hand. Those who use the SEB bag knows that it comes with a carry handle at the front – it is very convenient for travelling as mine weights in at around 15 pounds.

One problem I think is as you walk, this cause the sand in the bag redistributes in a manner which is different than say if I could carry it horizontally i.e. like how it sits when I shoots. Obviously, it is difficult to carry the rear bag this way by hand, but because it was carried in an un-natural orientation prior to use, I think the sand re-distribute itself when it is put down just before I shoot, and especially when the gun fires. So if some sand which found itself jammed in the back of the ears now distribute down between the ears, this will of course as Johara1 predicted elevate the stock which will result in exactly the condition I find…

I will try to redistribute the sand before I shoot or failing that, carry the rear bag in a cart in the “normal” configuration to see if that helps.

 

[gunsandgunsmithing]

Let someone else shoot your setup. I'm guess the gun is nose heavy and/or the rear bag is too hard but this is one of those things that an experienced shooter will likely pinpoint right away but it's difficult to diagnose without seeing it in person

 

[jlow]

I went out and shot using the rear bag yesterday, but this time taking care to not take it out of horizontal – absolutely no more problem – mystery solved.

 

[seb]

Jlow, I am glad to know the mystery has been solved.
All the best,
seb.