Recoil & Stock Design

Get or give advice on equipment, reloading and other technical issues.

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AlanF
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Re: Recoil & Stock Design

#91 Postby AlanF » Fri Feb 12, 2016 6:48 pm

Some recent posts relating to a US stock maker have been moved to a more appropriate forum : http://ozfclass.com/phpbb/viewtopic.php?f=25&t=7594.

DenisA
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Re: Recoil & Stock Design

#92 Postby DenisA » Fri Mar 18, 2016 10:52 am

I've been thinking about the behaviour of a couple of different hypothetical stock design's. Thought I'd throw them out there to prove how silly I can be.

Ignoring that barrels aren't perfectly straight for the moment. The first is based on a thought that:
The only reason we're so hell bent on 3" fore-ends is because the rules are based around traditional rifle designs and traditional ideas of trying to control stability, recoil and torque, using traditional techniques. The game has changed so much though and maybe some traditional views might not be so relevant.
The stock uses the centre bore line as its axis for rotation. The fore-end is round and sits in a round front bag. The radius of the fore-end is worked off the barrel centre bore line. The butt section rides in a high rear bag (with round inner ear profile), is round and its radius is based off the centre boreline. The stock could have a handle only used for setup, re-levelling after the shot and counter balancing the scope and any other weight above the barrel centre bore line. The technique would specifically be no hand grip and complete free recoil.
The idea is that the complete rifle would torque as it wanted to and the centre of the muzzle should stay in the same position (bore straightness aside). As usual no shoulder contact means no fulcrum or muzzle lift.

The idea is based on accepting and working with torque and trying to allow the barrel to rotate on its centre bore line rather than trying to control it in a traditional style stock and having the muzzle follow an arc as the rifle torques.

The second idea is a little more traditional. And is based on centring the rifle barrel with the bottom of the fore-ends bag riders. The front sand bag would have to have a gap in the middle too allow the barrel to stay clear. So basically, imagine the last half of a traditional 3" fore-end was rotated around 180 degrees so that it was bridged above the barrel. The scope may have to be mounted a little higher depending on materials and construction. I'm sure people have pondered on this one before.

RMc
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Re: Recoil & Stock Design

#93 Postby RMc » Fri Mar 18, 2016 6:26 pm

Denis here is the basis of a rilfe I have been shooting since the Canberra Queens Last year, I have the center of the bore in the center of the bag riders.

We have filmed it during recoil and it shows no sign of torque and is very easy to shoot.
Unfortunately I have not been able to teach it to read the wind flags.

The stock was originally built to conserve weight and I was able to get it down to 1.1kg. But since I am using a palmer barrel I have added weight and shoot it at 2kg.

It uses a barrel clamp and is designed to accept a heavy barrel in the future.

Image

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DenisA
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Re: Recoil & Stock Design

#94 Postby DenisA » Fri Mar 18, 2016 7:48 pm

Hi RMc,

That's a great accomplishment designing that, putting it together and getting the results. Any photos.

Your barrel in relation to the bag riders is very close to AlanF's design. Not that it would make much of a difference, but what I'm pondering is bring the barrel down further so the centre of the bore is inline with the bottom of the bag riders. Hence the need to introduce a gap in the centre of the front bag..

Thanks for the diagrams. That's an awesome rifle. How does it feel different in behaviour to conventional rifles you've shot?

RMc
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Re: Recoil & Stock Design

#95 Postby RMc » Fri Mar 18, 2016 8:30 pm

Denis my bag riders are higher than Alans, With a heavy barrel in his he can still get away with a flat surface on top of his rest. With mine the barrel will be below the bag riders thus I have a recess in my rest.
I designed around the fact that I wanted the bore to be center of the allowable 25mm high riders, I use solid guides on my rest with a thin carpet type material. Doing this the bag riders bear on the whole 25mm of vertical and thus the torque is evenly dispersed on both sides and the rifle stays in the same plane.

I shoot in F standard with a 308 and basically no shoulder or cheek pressure, the rifle simply moves back lightly. The difference between the original stock and this one is pretty different.

I do not feel that when I make my next version that I will change the geometry that I have, just the way that I manufactured it.

Richard

RMc
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Re: Recoil & Stock Design

#96 Postby RMc » Fri Mar 18, 2016 8:31 pm

Denis I forgot to say that I do not have any photos, but I will be at the range tomorrow and will get some

Richard

williada
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Re: Recoil & Stock Design

#97 Postby williada » Sat Mar 19, 2016 8:40 am

Very good work Richard. Its great to see the Mann bobsled taken further along the development path as did Gene Beggs. I refer to photos page 5. Have you considered the anchor points could be located on nodal points or make them length adjustable to tune? Why I say this, on a machine rest I designed years ago I found I had to tune the rest before barrel evaluation was effective. In that case, I altered the lift with vertically adjustable weights. No reason the mass could be moved fore and aft to control lift instead of vertically as yours could do. If your neat design was braced between, it may also add to barrel rigidity and complement the barrel block. Lots of possibilities here in relation to the degree of stiffening for desired lift or recoil in a straight line. Also lots of possibilities to dampen reflected vibrations on the anchor points. Thanks for sharing Richard. Denis, I can here your mind ticking from here. David.

RDavies
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Re: Recoil & Stock Design

#98 Postby RDavies » Sat Mar 19, 2016 10:06 am

williada wrote:Very good work Richard. Its great to see the Mann bobsled taken further along the development path as did Gene Beggs. I refer to photos page 5. Have you considered the anchor points could be located on nodal points or make them length adjustable to tune? Why I say this, on a machine rest I designed years ago I found I had to tune the rest before barrel evaluation was effective. In that case, I altered the lift with vertically adjustable weights. No reason the mass could be moved fore and aft to control lift instead of vertically as yours could do. If your neat design was braced between, it may also add to barrel rigidity and complement the barrel block. Lots of possibilities here in relation to the degree of stiffening for desired lift or recoil in a straight line. Also lots of possibilities to dampen reflected vibrations on the anchor points. Thanks for sharing Richard. Denis, I can here your mind ticking from here. David.


I thought the front of the stock could be38mm high, not 25mm or has this changed?

RMc
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Re: Recoil & Stock Design

#99 Postby RMc » Sat Mar 19, 2016 7:41 pm

Rod the 25mm limit comes from the allowed bearing area of the front rest in F standard

20.10.1 If the front rest is a pedestal type or a sandbag:-
(a) The shooter may use his hand between the rest and the fore-end.
(b) If the fore-end is in direct contact with the rest, the maximum
bearing surface between the front bag or rest and the fore-end may
be no greater than 76.2mm length, by 76.2mm width, by 25mm high
on each side of the fore-end.

Richard

pjifl
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Re: Recoil & Stock Design

#100 Postby pjifl » Wed Apr 06, 2016 12:29 am

I like to see people experiment with unconventional ideas.
Unfortunately, it can often be difficult because of rules which always enhance the mundane.
90% of rules are to keep the wingers quiet and they really have little effect on an 'even playing field'
In fact, they often impact negatively on an even playing field but they keep non thinking people happy which is probably important.

Some thoughts.

1/ Torque on the rifle does not try to turn it around the bore line. It tries to rotate the whole structure about its centre of mass but parallel to the boreline.
It is the interaction of forces created as the stock rotates that produces a rotation about a vertical and horizontal axis and the interaction of the underside of butt and bag that moves the butt sideways because of a paddle like action of the butt in the bag. And as soon as the rotation moves past the rifle to the stand or bipod the entire centre of mass is now different so rotation occurs about a different axis. Or tries to.

2/ Bringing the centre of mass in line with the forces on the butt by shoulder and bags tends to favor rotation only and minimizes any paddling effect of the butt.

3/ If it is advantageous to raise the centre of mass of the rifle, a high mounted scope is very effective. Many seem to think extra low mounts are better for some reason but a high mounted scope has a place.

4/ Weight distributed far off axis tends to reduce the angular acceleration caused by torque dramatically. There are not many ways to achieve this. Two are a high heavy scope (on good solid mounts) and a large diameter muzzle weight but neither can be taken too far.

Peter Smith.

DenisA
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Re: Recoil & Stock Design

#101 Postby DenisA » Wed Apr 06, 2016 9:14 am

pjifl wrote:
1/ Torque on the rifle does not try to turn it around the bore line. It tries to rotate the whole structure about its centre of mass but parallel to the boreline.
It is the interaction of forces created as the stock rotates that produces a rotation about a vertical and horizontal axis and the interaction of the underside of butt and bag that moves the butt sideways because of a paddle like action of the butt in the bag. And as soon as the rotation moves past the rifle to the stand or bipod the entire centre of mass is now different so rotation occurs about a different axis. Or tries to.

Peter Smith.


Hi Peter.

Thank you. I didn't consider that the rotation uses the centre of mass line over the bore line or that the centre of mass line changes when the energy is passed through to the front rest. I have experienced this but I haven't put it in to words.
My experience with it is simply how much more aggressively my left hand off set fore end stock feels like it torques over my conventional stocks when introducing an early fulcrum point to free recoil. The shot goes high left every time and much more than the conventional stocks. I originally thought that the offset would help to counter the torque, but my experience says it causes a larger muzzle arc. That's why I was toying with the notion of having the forend round and the barrel centred in it.

What if we slightly modify the first hypothetical idea and barrel clamp a barrelled action into the centre of a pipe. The pipe length runs from the front rest to the rear bag. The handle is specifically designed counter the scope weight. Any necessary weight would be balanced out on the opposite side of the bore line. Now the centre of mass would be the centre boreline.

I should add that I'm a left handed shooter so when I contemplate how the complete stock might torque, I'm imagining that the handle would torque away from my left hand and not in to it.

Tim N
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Re: Recoil & Stock Design

#102 Postby Tim N » Wed Apr 06, 2016 12:11 pm

Dennis,
I had thought along the lines of what you are saying with a tube gun and the whole thing is free to twist in the front and rear rest with the recoil pad in line with the bore and the only negative I could see was that me being right handed would send the scope anti clockwise and maybe into my forehead (which some may consider worthwhile :D )
You however being left handed may see the scope twist away from you when free recoiling?
We don't rise to the level of our expectations, we fall to the level of our training. Archilochos 680-645 BC

DenisA
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Re: Recoil & Stock Design

#103 Postby DenisA » Wed Apr 06, 2016 12:50 pm

Tim N wrote:Dennis,
I had thought along the lines of what you are saying with a tube gun and the whole thing is free to twist in the front and rear rest with the recoil pad in line with the bore and the only negative I could see was that me being right handed would send the scope anti clockwise and maybe into my forehead (which some may consider worthwhile :D )
You however being left handed may see the scope twist away from you when free recoiling?


LOL, good point Tim. All you righties will need to start shooting left handed. :lol:

What if 2 spaced apart bearings were pressed onto the barrel forward of the action in place of a barrel block and then the bearings were clamped into the tube. The scope, handle and recoil pad were attached to pipe. The pipe has a cut out in it to allow the trigger to rotate around. A stop could be introduced to limit and/or dampen the torque. Now the stock doesn't rotate externally, but the barrel does.

It's getting crazy now. Probably time to stop.


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