Bill you must have some time on your hands...good work!
I’m glad someone took the time to do this test.
One thing though…….applying a 5lbf at the muzzle will not neutralize the weight at the front receiver ring. It minimizes and pretty much eliminates the bending stresses associated with the cantilevering barrel and I think that’s what you mean. There is still a 5lb force at the front receiver ring as well.
Prior to placing the weight on the barrel, did you try eliminating the induced deflection in the receiver due to the weight of the original 26" barrel? I suspect you already had some preload in the receiver from the original barrel weight when the dial indicator was zeroed to measure the impact of the 12lb weight. Granted it probably wasn't much, but sure there was some movement..... I see everyone now doing this test at home.....kidding of course but it would be interesting to see what happens with all the different actions.
With the generous clearance of most actions, I didn't think there would be an issue w.r.t. bolt contact or binding, but when you start approaching .001" clearance at both rings, it could start to play a role.
Some interesting points. The retaining points (threaded screws into the receiver) are not actually good examples of true pin connections since they do not allow the action to deflect freely. The recoil lug fully seated against the stock lug also tends to help resist the bending or complex convex shape the receiver takes on from bending. Obviously the longer the lug and thicker the lug, the more it would help prevent this bending as long as it is held tight against the stock recoil lug. If you put a dial axially at the end of tang, a person may be able to see how much the barrelled action moves forward...
What also happens and to a much lesser degree is the tang flexes as well, since on the Remington and some others, the tang cantilevers off the rear receiver bridge. One of the actions made in Finland, modelled after the Tikka M65/55 actions moves the rear tang screw directly under the rear receiver ring. This increases the force in the rear screw due to the reduced torque arm, but it also minimizes additional dreaded receiver flex at the rear. Does this deflection mean anything.....in the real world....probably not, but if your making something from scratch, why not try to eliminate as many variables as long as it doesn't add to much to the cost or sacrifice some other feature.
A stiff stock, I.E. aluminum or Steel frame would help isolate the receiver movement, but since you don't shoot from something like this it is really irrelevant.
Once you start using a barrel 30”+ range, especially on a magnum caliber, the dynamics really kick in when the barrel starts whipping. As you know, the barrel block is intended to do at least two things: one is eliminate stress on the receiver (helping maintain perfect alignment) due to the barrel weight and two, to allow you to reduce barrel whip and enabling you to use a heavier diameter and longer barrel…..
I believe Dan Lilja has posted some calculated static deflections of a sample barrel as you increase its length....the results are surprising.
Thanks for taking the time to post the results of your test....good show.
joe
