Another approach to rear bag to stock fit....?

B

Boyd Allen

Active member
Bags are important. They can be too hard, and if you are shooting free recoil, too soft, and fit is important. In order to arrive at the best possible fit, it seems to be common to have tried several different bags, and fills. If it has not, perhaps it should have. It is probable that in many cases, the search may have ended too soon. Bags can get expensive, and if one is just pretty good, it may be hard convince oneself that one's bag is a problem. In any case, the typical route is to buy a rifle and then go looking for a bag to fit.

What if there was another way? What about designing the stock around the bag? They could be marketed as a matched pair. I know....dream on, but bear with me for a minute. There may be a third alternative that we can easily do, modify the bottom of the butt stock to fit the bag by attaching a "keel" that is specifically designed for optimized fit in a particular bag. What would be wrong with that?

Of course you can take the early Libby approach. I remember, years ago. I had stopped by at a match at Visalia. There were one less than every type of commercially available rear bag, all filled, and only slightly used, for sale. Tom had bought one of everything, filled them, tried them out, and kept the one that he liked, selling the rest. I have always admired that sort of thoroughness :)

Anyway, not being willing to buy one of each bag, or perhaps one of each stock, and have it fitted to a barreled action, I am left with choice number three, tape different "keels" to the stock that I have. Thank goodness that I have what it takes to do that. (a table saw, wood, and some tape) Soooo...what do you think? My first experiment will involve a standard Edgewood medium Cordura rear bag....triple stitch, over filled in the base, and then adjusted, with tightly filled ears, that require working the stock between them. Sitting next to it, looking surprisingly functional on first try, is one of those tri-lobed architect's scales, that is soon to be taped to my stock. Boy! is it going to look funny. I like that. I can put my stepped fire forming barrel back on, with Jackie's tuner (pre cuttless beariing) and the prototype Sims deresonator right behind it, and it should be worth at least a couple of questions from fellow shooters the next time that I am at the range. OK I was kidding about the fire forming barrel; the taped on scale should be sufficient.

All kidding aside...what do you think that the ideal butt stock to bag configuration should be? Pretend that you wouldn't have to do any work, and that it was free.
 
maybe, just maybe the JTR was designed with that in mind, we made sure the rear matched the bag angle,

someone with access to a bunch of different stocks could take some pictures and overlay them to show how they fit in certain bags, (some issue though with the different ways of completely filling the rear ears and "adjusting" the ears to fit the stock). and others think the stock either fits the bottom or trough of the ear set up or partially up the sides of the ears.

the J in JTR Jefferson

(hidden tip= think about the reverse taper edgewood and how the ears are constructed underneath mmmmmmm maybe a base to help if the body of the bag is not filled properly or happens to settle when driving to a match. less drop if the ears have a good double base, or maybe edgewood does it for hidden fashion only)
 
Boyd dont forget at some point to consider rules and regulations.
Being taped to the stock means it would have to be part of the weight of the rifle. not to mention other aspects of regulations.
Neat idea just dont forget the other considerations.
Kind of like the guy I saw velcro a box to the bottom of his stock to catch brass from a drop port. Some how didnt think the box needed to be taken into consideration as part of the weight of his rifle. Found out he was wrong the hard way.
 
There may be a third alternative that we can easily do, modify the bottom of the butt stock to fit the bag by attaching a "keel"

When I started IBS, shooting 600 at Oak Ridge, I made such a modification because the rear bag ears seemed to induce torquing when moving from sighter target to record target in my setup (I can't squeeze rear bag). I needed weight at the rear anyway, so made a 1-1/2" wide monorail of babbit metal and attached to bottom of buttstock, giving me substantial wide platforms at front and back of rifle.

Next I removed ears from Predator rear bag. I glued 2 thick strips of leather to the bag, spaced 1/8" wider than the monorail. This solved my torquing problem. Proly not ideal for a fast shooter at the bench since it takes a little longer to re-center crosshairs, but has served me extremely well in F Class where we have plenty of time to adjust for recoil.

Also made monorail of light wood for second rifle that did not need the weight. FWIW.....model airplane hobby shops have some pretty dense and strong balsa that weighs practically nothing.

For my next new stock, will have bottom of stock left at 1-1/2".

Might also consider 2 rails on bottom of monorail to help make it bite and track, such as I have on bottom of my forearms.

Frank B.
 
I just stood the scale on end on a piece of paper, and drew converging lines along the edges of the faces that were making contact with the bag ears. After carefully extending the lines, I measured the angle between them. It was 90 degrees. Imagine an isoceles right triangle with the point formed by the right angle pointing downward, between the ears. On this bag, the configuration seems to be very stable. I cannot push the rule down between the ears, and there is good lateral and roll stability. The point does not touch the body of the bag. As I stated in an earlier post, the ears are very full.

I am aware that by reducing the amount of fill in ears, that a better stock fit can be achieved, BUT if the down force by the butt stock on the ears is reduced, as I believe that it is as the rifle recoils, the pressure that gives the ears their stability of shape is removed, and with that their stability. Because the motion of the stock during recoil is initiated differently than it is when a rifle is slid forward and back by hand, this unloading and momentary lack of down force is easily missed. It seems to me that the only way around this, with cordura ears, is to fill the ears to their maximum, and redesign the surface that rides against them so that the fit is optimized. Of course there are other ways to get around the problem. Leather, and cloth covered leather ears can be wet shaped (to a greater degree with fabric sizing) but for all the existing Cordura eared bags, that have no shape memory potential, I think that what I am proposing may have some merit. Of course none of this is as critical if the shooter holds his rifle. This whole subject is mostly about free, or nearly free recoil.
 
Boyd always has good ideas, as we have discussed several in the past. I guess after reading this what comes to my mind is how do you know what bag fits the best for what ever stock one might have? In my mind the only real way to know is to shoot the rifle and evaluate from there. If ones rifle is agging properly then no more research is needed. If ones rifle isnt shooting properly then i would have to think it would be the tune. After all i have come to the realization that the majority of shooters do NOT know how to properly tune a rifle. Me included for the most part. So this brings me back to the original post. How does one know if he even has an issue with the rear bag?? Maybe we need to talk about identifying that there is in fact an issue with the rear bag before we talk about how to over come the issue? Or maybe, doing what Mr Allen has suggested will help one understand better how the relation ship between the stock and the rear bag needs to be, thus reveling that maybe there is some issues that need addressed??? Boyd is a pretty smart man and i always enjoy his assignments. I learn a little something most every time. thanks Boyd for the interesting topic. Lee
 
Butch it was not his I was referring to.
This incident was at Tomball in 03 or 04. As I remember he ended up being DQ'd for it.
 
No, it won't work, anybody and.......................

everybody knows, if you use Brass, Babbit, or Balsa, it won't make the ears last any longer.
I even talked to a HOF'er, and HE SAID, even wet ears won't make the keel last any longer..............:D:D:D:D

Not to get too far off topic, Boyd, but, isn't Robert Whitley already doing something like this for AR-15s and tube guns??
 
Boyd Allen said:
All kidding aside...what do you think that the ideal butt stock to bag configuration should be? Pretend that you wouldn't have to do any work, and that it was free.
Click to expand...

Boyd,
Here's what I think about bags: If one is after ultimate accuracy, one would not choose sand bags, because the response of sand to dynamic loading is inherently nonlinear and inconsistent. But since they are in the rules, we have to live with them. The objective of the bags is to constrain the motion of the rifle in specific ways. The front bag should constrain the downward but not upward vertical motion of the forend, as well as lateral motion and rotation around the bore axis, and nothing else. The rear bag should constrain vertical and lateral motion and nothing else. The points at which the constraints are applied should not shift during recoil and should be consistent from shot to shot. Ideal bags would have only small areas of contact to keep the constraints from shifting. However, sand deflects over small areas, so we live with larger areas, which imparts extra constraining forces and torques that we would rather not have.
For the rear bag, the ears should only be tall enough to consistently constrain the butt laterally, and should be as short longitudinally as possible to avoid shifting the contact points fore and aft as one shifts POA across and up and down the target. The new Edgewood bag with radiused faces on the ears is interesting, and I think a step in the right direction.

Cheers,
Keith

PS. I think I have seen pictures of a Scoville stock with a replaceable keel, but I couldn't find a link. A sliding dovetail might work well to rigidly connect the keel to the rest of the stock.
 
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