Weight in the rifle butt

adamsgt

adamsgt

Jerry Adams
I have four benchrest rifles and they were all purchased used. Last year I bought a 2014 Nightforce completion scope at a good price. Unfortunately it's been sitting around while I try to figure out what gun to put it on. I have a LV gun that weighs about 10.377 pounds with a Leupold competition on it. The Nightforce is about 7.4 ounces heavier than the Leupold. The Nightforce would put the gun about 5.4 ounces overweight. On a hunch, I unscrewed the cap on the butt of the rifle and discovered a steel rod that weighed 6.3 ozs. So, if I mounted the Nightforce and removed the butt weight, the gun would make weight. What kind of trouble might I be buying if I do this? What might I expect to see in the guns performance that I could tag to the weight removal? I'd like to get some replies before I do this.
 
adamsgt said:
I have four benchrest rifles and they were all purchased used. Last year I bought a 2014 Nightforce completion scope at a good price. Unfortunately it's been sitting around while I try to figure out what gun to put it on. I have a LV gun that weighs about 10.377 pounds with a Leupold competition on it. The Nightforce is about 7.4 ounces heavier than the Leupold. The Nightforce would put the gun about 5.4 ounces overweight. On a hunch, I unscrewed the cap on the butt of the rifle and discovered a steel rod that weighed 6.3 ozs. So, if I mounted the Nightforce and removed the butt weight, the gun would make weight. What kind of trouble might I be buying if I do this? What might I expect to see in the guns performance that I could tag to the weight removal? I'd like to get some replies before I do this.
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Jerry,
Moving that much weight above the bore will reduce positive compensation (a bad thing), but likely make the gun less jumpy in the bags (a good thing). For short range, positive compensation doesn't make a big difference if muzzle velocity has low standard deviation, so give it a try. You can always put the rod back in and put the Leupold back on. To get a frame of reference, you could test the height of the center of gravity before and after the modifications.

Hope this helps,
Keith
 
mks said:
Jerry,
Moving that much weight above the bore will reduce positive compensation (a bad thing), but likely make the gun less jumpy in the bags (a good thing). For short range, positive compensation doesn't make a big difference if muzzle velocity has low standard deviation, so give it a try. You can always put the rod back in and put the Leupold back on. To get a frame of reference, you could test the height of the center of gravity before and after the modifications.

Hope this helps,
Keith
Click to expand...

MKS,

Could you please explain what you mean by "you could test the height of the center of gravity"

Thanx
 
shinny said:
MKS,

Could you please explain what you mean by "you could test the height of the center of gravity"

Thanx
Click to expand...

The center of gravity is the point at which the rifle balances. It has a front-to-back location, a left-to-right location, and a height. The front-to-back location is probably the most commonly discussed. It can be found by resting the stock of the rifle in its normal orientation on a dowel aligned 90 degrees to the bore, and adjusting the location of the dowel until the rifle balances. The balance point will likely be somewhere between the front of the action and a couple inches forward of the action. The left-to-right location should be directly under the bore, otherwise recoil causes the barrel to whip horizontally. Turn the dowel 90 degrees and align it with the bore. Adjust its location until the rifle balances left and right to find this component of the CG. The third component (the height) can be a bit harder to test. If the stock has vertical sides, it's easy. Just turn the rifle on its side and balance it on a dowel aligned with the bore. If the stock has slanted sides, you can use some double sticky tape (if you trust your paint job) on the dowel to keep the stock from sliding off the dowel. The CG is directly above the contact point on the dowel when the rifle is balanced. The lower the CG is below the bore, the more vertical whip of the barrel is caused by recoil, and the more positive is the compensation. You can have too much compensation, too.

You can find the CG by hanging the rifle from a string, as well. When the rifle is balanced, the string points through the CG.

Hope this helps,
Keith
 
I would add one more thing. Proceeding on the basis of assumptions can lead you astray. For example. A friend likes offset rings on his 10.5# 6PPC, and has not noticed any negative effects on his rifles' accuracy. I think that we are all familiar with stocks that have their forends offset to one side to help counteract torque. I don't remember anything about rifles with those stocks shooting any better or worse. Some time ago, I put a tuner on a rifle, and was concerned about the way that it would change the rifle's balance, because less weight would be on the rear bag. As it turned out, there wasn't a problem. My working hypothesis is that the increase in polar momentum stabilized the rifle during recoil, compensating for the change in balance. One thing that I believe is that there is a relationship between static and dynamic balance, they are not identical. What happens during recoil may be significantly different than what happens when the rifle is at rest or slid by hand on its rests. IMO this is an area where there is a lot of assuming, theorizing, and guessing going on, and I include myself in this.
 
I'd say try it and see. You'll either like it or you won't. Since you have the scope and can make weight with it, go for it. Walt Berger was shooting a NF competition scope on his 10.5 rifle last year when he won a yardage at the nationals at Holton with a .17 agg. It didn't seem to hurt him.
 
Mike Bryant said:
I'd say try it and see. You'll either like it or you won't. Since you have the scope and can make weight with it, go for it. Walt Berger was shooting a NF competition scope on his 10.5 rifle last year when he won a yardage at the nationals at Holton with a .17 agg. It didn't seem to hurt him.
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Thank you Mike. I guess I've got enough time before the Cactus to give it a go. Of course, Walt could out shoot me with his eyes closed.
 
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Offset stocks are an example of solving one problem and creating another. They counter torque better, but cause more horizontal barrel motion, theoretically speaking. Whether the net result is better or worse in practice is of course the most relevant question. For two counterbalancing effects such as these, the difference may be difficult to extract. If the difference is, say, 0.010" or even 0.030" in average group size, how many of us use the statistical tools necessary to find this difference and prove that it is statistically significant?

Looking at what the best shooters use is only a partial answer. New bullets and powder seem to be adopted on an almost match-by-match basis if they shoot better, with barrels and scopes not far behind. Stocks seem to evolve more slowly. Is this because there is nothing to be gained by improving stock design, or is this a neglected area by comparison? I don't know the answer, but I do know that I have observed big differences in handling characteristics of different stocks.
 
I think I'm there

Decided to mount the Nightforce scope after returning from the range this morning. The gun weighed 11.12 lbs after mounting the scope. I then removed the weight from the butt stock and the scope covers and the gun came in at 10.562 lbs. The scale I have seems to weigh a bit high. I placed a set of NRA trigger weights on the scale and it showed 4.23 lbs for 4 lb weight. So that should cancel out the .062 that the gun showed over weight. I'll try and find some other calibration weight to verify the scale.

Followed Boyd's suggestion of determining the weight at the butt of the stock in different configurations. I used six reams of paper to construct a platform for the Farley rest that would match the height of the scale. I used a 2X4 plastic table to hold all this for the measurements. I picked three points of forward, mid and rear to measure for each, the stock stop on the rest and the rear bag. That gave me a nine data point matrix to compare the gun in two configurations. The first gun configuration was the gun as it was with the Leupold scope and weight in the butt. The most weight on the rear bag was 3.827 lbs with the stock stop to the rear and the rear bag forward. The second gun configuration was with the Nightforce scope and the weight removed from the butt stock. In the same test configuration as the first, the weight on the rear bag was 3.622 lbs. The difference being .205 lbs or 3.28 oz. Not too bad. However, I've been shooting the gun with the stock stop in the mid position and the rear bag likewise. In this setup the rear bag had 3.15 lbs versus 3.73 for the original configuration.

Well, this exercise has given me more insight into the effects of moving the gun over the two contact points, the front and rear bags. Next step is to go to the range and see what works best when I yank on the trigger.

Again, thank you Boyd for your suggestion.
 
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