change scope, change vibrational characteristic?

[lrgoodger]

I posted this over on benchrest central and have no replies yet.

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?

 

[necchi]

That means re-tuning the load. Correct?

Well??
Maybe not, it could be that the change is minor enough to simply equate to a different point of impact.
Most finely tuned loads fit within a "window" of harmonic vibration. How narrow that "node" is,, is a variable with each gun and shooter. Just like a change in hold or rest/pressure point could change the vibration.
And whether that node is changed significantly by the addition of a different scope/balance point/vibration is something each gun and shooter will have to determine,, :-\

It's kinda simple, if the group opens then re-tune the load. But a scope change won't automatically change the vibration,, again it could,, but not always.

 

[Shynloco]

I think necchi gave the best answer to the question posed. Now I'm no engineer, but I too have read Tony Boyer's book as well as that written by Mike Ratigan (Extreme Rifle Accuracy), both of which I keep handy when issues arise. And since I'm an accuracy freak and load and shoot several calibers for that purpose in mind, in consideration of the question posed, it strikes me that in any discussion of "barrel harmonics," we're talking about the barrel itself and not the receiver, the stock or any other component you might find on a particular rifle that the owner has "messed with", changed or alterered to his or her liking. And it also strikes me, that if the theory of changing a scope somehow alters the "barrel harmonics", then changing any other parts of the rifle would alter the harmonics as well, which is REALLY a stretch. In my life long experiences, I have only found a limited number of changes to a rifle actually alter the accuracy (both good and bad) and mounting a specific scope versus another scope isn't amoungst those factors. Scopes may help the shooter see the target better, but I seriously doubt it'll make a bad load suudenly better, or a good/tuned load worse. Just my thoughts.

 

[Shootinstick]

As stated by others, a change in a receiver mounted scope will mst likely have negligent effect, other than an increase or decrease in sighting capability (higher or lower magnification). With a barrel mounted scope like a Unertl, it can very much effect the barrel vibrations. On my Anshutz 1813, I went round and round with this. I switched from a 1 1/4" Unertl 14X with a 30% increasing eyepiece added (approximately 18x overall) to a 2" 20 power Unertl. While I could see better, the rifle just would not shoot as accurately and my x counts dropped. I swapped between 3 different scopes to verify, but the much heavier 2" scope upset the vibes. Possible that changing to different ammo may have cured the problem, but I simply chose to keep the ammo and went back to the boosted 1 1/4" at the time.

 

[FroggyOne2]

I change from iron sights to scope regularly, can't see any difference in accuracy with my rifles.

 

[lrgoodger]

What prompted this question was my friend's 6BR. I built the gun for him last summer and tuned the load for it using my Scmidt and Bender PMII. It was averaging groups in the low 4s at 100 yards. He finally bought a nightforce 12-42x56 benchrest scope to put on it. I sighted that scope in for him with the load I developed, but I didn't shoot groups with it to make sure the load was still tuned. He brought it over yesterday so I could check out a problem with his front rest and I checked the sight in for him (he had not sighted it in since I gave it to him last summer, but had it on two PD hunts since then). It would not group worth a flip. Everything was about an inch at 100 yards. I took the nightforce off and put on my weaver fixed 36X target scope and it wouldn't group either. I ran a dollar bill underneath the barrel to check stock clearance and it was tight right at the fore-end. I pulled the stock off and could see where the barrel had been bouncing off the stock. I quickly dremeled out the excess and put the weaver back on. The first group was back in the 4s where it had been averaging when I built it. I can only assume that the wood had moved over the year since I gave it to my friend. I put the nightforce back on and the groups were better, but not near what they were with the weaver. There is a comparatively large weight difference between the weaver and the nightforce, not to mention a significant difference in tube and bell size. That HAS to affect vibration on the rifle as a whole. My friend left the gun here and I am going to do some further testing on it with different scopes this week, including the S&B that was used to develop the load. It could simply be that the nightforce has gone bad. I will post results to enhance the general knowledge base here.

 

[fm1947]

in short if you tune a load to a $1500 or $2000 dollar scope then you buy a $125 BSA do you think its going to group the same with any load, I have 3 leupold scopes all over $1000 I switch them around all the time my groups are consistant, load to scope has nothing to do with anything its load to gun, you put a cheap scope on a good gun you got nothing and no load is going to change that