Recoil & Stock Design

[IanP]

[williada]

[IanP]

Williada, Your knowledge in this sport is amazing and like me you have an inquiring mind and want to know the why and how of all things to do with it. Unlike me, you seem to be on top off the issues I'm just starting to explore. I look forward to your continued contributions!

Ian

[DaveMc]

[DaveMc]

[DannyS]

[IanP]

Dave, always grateful to receive your informed input and contribution. I'm sure you have considered recoil in some depth so look forward to reading more from you on this subject.

You ask the question on what am I wanting to achieve and I'll keep it brief and to the point. I am wanting to achieve consistent stability under recoil in two axis and weight my rifle/stock to best achieve it. I am wanting to use any means I can to limit the effects of recoil.

1. Find the best setup to limit fore and aft pivot/lift under recoil.
2. Find the best setup to limit torque effect.

To achieve this I want to evaluate weight distribution over the bags and consider the balance point fore and aft. Also consider if a low c of g will help counter torque reaction. What stock design will provide for balance and counter weight against torque? All this is to have the rifle recoiling back into my shoulder in a single direction without lift or torque. Is it possible under our rules and weight restriction for F-Class rifles? This is what I am wanting to explore. To understand the forces at work that need to be considered and prioritised in order to overcome or limit them.

Ian

[bsouthernau]

My understanding - if you could call it that - is that there is nothing you can do about the actual torque being applied to the rifle. Conservation of angular momentum requires that in the absence of any external torques the rifle will attain an equal but opposite angular momentum to that of the bullet. As what we're seeking to do is minimise the rotational speed the course of action is to maximise the moment of inertia. As a general principle the way to do this is to increase the weight - but we're limited there - and have the weight distribution as far from the axis of rotation as possible.

The alternative is to devise a system of applying a countering torque to the rifle as the bullet passes down the bore. Best of luck!

Barry

[DaveMc]

My understanding is the same as yours Barry (although my terminology is often corrected) - so to slow the speed of torque roll and help gain "control" or lessen speed of impact on bags one way is to apply the weight (we are limited to) as far from the axis as possible but also balanced as much as possible.

Some examples - High scope (e.g. heavy NFBR on ultra high mounts), offset around cg of boreline by low stock weights in butt. Also a large diameter, short but heavy tuner on front. (You may need to look at barrel diameter and stock weight to get under weight)

To decrease muzzle lift (and possibly bounce from torque roll) though I try and build centre of gravity as high as possible and close to in line with bore (this can be done with an adjustable weight system of several holes bored in from buttplate and weight can be moved from one to the other - I use a cleaning rod down bore balanced on table at muzzle to look at cg. I also try and shoulder the recoil contact point up as high as possible and close to centre line for less muzzle lift (it is amazing what this does to front bag bounce). If free recoil then cg is important and also low friction on bags (heavy friction on bags may reduce felt recoil but add more resistance on a low point and create muzzle lift as well). If friction on front bag it will drive butt down into rear bag, if friction on rear bag (or low shoulder) it will cause extra muzzle lift.

I think the balance of weight on front and rear bags is hard to define. With long forends you can get away with less weight on front rest. Typically I start with the old 2/3 - say 6-kg (front) and 3 kg on rear and build up from there. I nearly always end up adding more weight to the rear though I also experiment a little with front and rear rest placement to see which shoots best on a new rifle (video helps here)

With better balance (vertical cg in line with bore) and lessened torque roll effect I believe the exact positioning of bags becomes less critical.

Have a look at Alan Frasers barrel height in his forend. Almost zero. This helps with torque "control" (and defined lightly) as well - so does high vertical sides in the front rest. In FS you can only go 1 inch (and not as heavy a requirement) but I believe higher in F open. My 30 cal rifle stock will have low barrel and high sides (and of course a good "sissy pad").

[Barry Davies]

[johnk]

[DannyS]

[IanP]

[IanP]

[RAVEN]