see sawing the rifle

[Steve Ladino]

I have a question about the effect on target groups when we see saw the rifle. By see saw I mean that when a rifle is fired while being supported at the forend by a joy stick rest and supported at the butt by a conventional lets say leather bag the rifle butt rides up upon fireing and in order to again be on target the joy stick is raised. Question is that when this takes place what effect does it have on the group size/shape ? I cant get my mind around it so I would appreciate any opinions or a mathematically correct comment. Thanks

 

[ballisticdaddy]

If you are using a flat top rear bag the rifle should be able to return on target once pushed back up against the stop of the front rest. If the rifle is see-sawing then the setup needs to be reworked. As always a photo is worth a thousand words.

 

[dcali]

Something similar happens with my TR setup if my position is off. The answer here is that it doesn't impact the group size at all (well, maybe it does for short range benchrest), but it does mess with your timing and NPA, which is undesirable. The correction is to continue to experiment with your setup until this doesn't happen. The stock shape (no cast-off), bag positioning, rifle support, bag fill and probably a couple other things all go into it. If you get it right, the "seesawing" won't happen.

 

[Eric Leonard]

are the tension screws on your rest tight ,,sounds like your rest may be moving down when you shoot ??

 

[Ned Ludd]

For the type of setup you describe, you typically want a rifle stock that has only a very small angle to the toe, just enough to allow some minimal elevation adjustment. If you use a stock with a highly angled toe, such as a McMillan A5, your muzzle will pointing 30 feet above the target at the end of the recoil impulse, which will require pushing the rifle all the way back forward to the rest stop to bring the muzzle back down. With a front benchrest, you'd normally do that anyhow. But with a bipod in front, it makes life much more difficult.

If you're altering the adjustment of the rifle too much with each shot, eventually the "see-sawing" will make it so the necessary point of aim outside of the adjustment range of the joystick and you'll have to re-adjust and re-center the entire setup. However, as long as: 1) the rifle setup remains within the adjustment range of the joystick AND 2) its alignment hasn't changed so much that it actually alters the tracking of the rifle during the recoil impulse, it shouldn't affect size/shape of the group. Whether both those conditions will continue to hold true over time is another story. That will depend largely on tracking of the rifle. If you've see-sawed it so much while firing that the tracking has changed, it may well cause a change in the group size/shape, even if the intended POA is still [barely] within the adjustment range of the joystick.

 

[Steve Ladino]

I have a question about the effect on target groups when we see saw the rifle. By see saw I mean that when a rifle is fired while being supported at the forend by a joy stick rest and supported at the butt by a conventional lets say leather bag the rifle butt rides up upon fireing and in order to again be on target the joy stick is raised. Question is that when this takes place what effect does it have on the group size/shape ? I cant get my mind around it so I would appreciate any opinions or a mathematically correct comment. Thanks

Thank you all for your input which has helped me to think it through. What I think now and am asking for any comment on is that if a true vertical angle is formed by a point on the axis of a chamber and a point on the axis of the scope and a point on the axis of the bore at the muzzle and this angles inclination to horizontal doesn't change then there is no noticeable difference on the target from shot to shot while its at the same distance and the bullet velocity is consistent. So as the rifle butt elevation is corrected by the front rest elevation stick the bullet approaches the x ring at slightly different angles to vertical. ?