change scope, change vibrational characteristic?

L

lrgoodger

Guest
I've done a ton of reading over the last two years (including precision shooting's "The Benchrest Shooting Primer" and Tony Boyer's "The Book of Rifle Accuracy") and I've never seen this question addressed. My common sense as an engineer tells me that if you tune a load for a rifle with one scope on it and then put a different type of scope on (not replace with an identical scope, which would give you a pretty good chance of not changing vibrations significantly), you have changed the vibrational characteristic of the rifle. That means re-tuning the load. Correct?
 
I have no clue if it would require retuning the load (My instinct is that it would not.), but the only fellow that I have ever seen with an oscilloscope on a shooting bench, and some sort of transducer taped to the muzzle, told me that changing ring or scope position change barrel vibrations. At the time, I didn't have the presence of mind to ask him if the difference was large enough to require load changes. It looks to me like you need to do a little informal testing. Perhaps you could report back on what you find?
 
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I'm not the brightest guy in the world but maybe tune your load with the other scope to begin with, however the basic answer is no.
 
Testing is on the agenda for this week. I will indeed report back. An initial scope change on the rifle in question showed significant differences. After solving the basic issue, which turned out to be not enough clearance between the barrel and the stock fore-end (there were marks on the stock where the barrel had been bouncing off it), I took off the nightforce BR scope and replaced it with a fixed 36X Weaver. The Weaver grouped well but the nightforce would not. I have further testing to do to find out if the nightforce has gone bad. There is a significant difference in weight, tube and bell size between the two scopes. That HAS to affect overall system vibrations.
 
Don't know about barrel vibrations, but if you change from say a Leupold (LCS) to something like a Nightforce, you have significantly changed the balance of the rifle & the way it rides the bags. And, of course, if the rifle was optimized for weight before, the change to a much heavier scope (approx 1 lb.) would require a complete rebalancing of the rifle & consequent effects.
 
I was quite surprised once to see how little it takes to make an action flex. This of course changes bedding. The transition from
a weaver to a nightforce would require ring changes and possible alignment issues. So not only might the balance be altered, but
stress induced. The nightforce would be much less forgiving than a thin walled weaver.
 
Your engineering intuition is good. If you decrease the weight of an 11.5 or 13.5 lb gun by about 1 lb and lower its center of gravity by doing so, how could it not change the vibration of the rifle? The dynamic characteristics of the barrel and stock are still the same, but the bolt thrust now has a longer moment arm around the center of gravity, which increases the amplitude of the response. In addition, the different scope has different stiffness, which is imparted to the action, and different vibration response of its own. There is a video somewhere of a scope vibrating during recoil. Very interesting. Looking forward to reading about your tests.

Cheers,
Keith
 
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