Originally Posted by westcliffe01
Where the rings attach to the scope base, they are much closer together than the rail overall length, so the total dimensional change is less. Consequently, even though the scope tube is aluminum, with the rings being close together less deflection will be taking place and at some point a change in impact would not be measurable.
My comments were with regard to this "quote" from your first Post. You state that where the rings attach to the scope base, they are much closer together than the rail overall length. Well the distance between the rings is the same on the scope base as it is on the scope tube. So the differential expansion or contraction will be identical over an identical distance between materials with different rates of thermal expansion and contraction. The length that the scope base rail protrudes past the scope rings in both directions is inconsequential. Same with any of the scope tube that extends outside of the scope rings.
Further, the differential expansion or contraction between the receiver and the one-piece scope rail is only effective
across the distance of the fasteners - the scope base screws. Any extension of the rails past the scope base screws will simply result in those portions of the scope rail shifting position differentially with respect to the surface of the rifle's receiver. No differential movement forces can be generated where the two surfaces are no longer connected or restrained beyond the scope base screws.
So I may have misunderstood your communication. And I must still misunderstand.
These facts are true. The differential movement between two dissimilar metals is a function of their coefficients of expansion, the span or distance between fastening points, and the total change in temperature. If the temperature doesn't change - no differential movement occurs. If the distance between fastening points is very small, very little differential movement occurs. Further, differential movement can only create undesirable forces between the two dissimilar metals between points where the dissimilar metals are fastened or connected together. For example, the scope rail could be extended to the same length as the barrel forward of the receiver, and as long as it's not connected to the barrel at any location forward of the forward-most scope base screw on the rifle's receiver, there will be no flexing compression or tensile forces generated between the two dissimilar metals forward of the forward-most scope base screw.
The biggest reason I use aluminum bases and rings rather than steel, is to reduce weight. My hunting is almost all backpack hunting in the mountains of Alaska. The 7075 grade aluminum is more than adequate strength-wise, and weighs much less than any grade of steel.
One of my points earlier was that even if you place a steel scope rail on a steel receiver, and mount steel scope bases on that steel one-piece scope rail base, these are all still fastened to an aluminum
scope tube. There's no way to keep everything steel unless you purchase and use steel scope tubes, which virtually nobody does. The fact that the scope rail and the scope tube is separated by about 0.75" will allow for some flexing of the scope rings - more so than between the rifle receiver and a scope rail that are mounted flush together. But there is still going to be some forces imposed due to the differing thermal coefficients of expansion between all of these steel components, and the aluminum scope tube. So we can spend a bunch of time worrying about a problem for which there is no solution, or only worry about it when it becomes a demonstrated problem with its effect on accuracy. And I've not seen any demonstrated negative effects on accuracy that are large enough to stand out amongst all the other accuracy impacting variables. Simply the fact that the temperature changes can have affects on accuracy due to barrel bore expansion and constriction, differing rates of powder combustion resulting in differing muzzle velocity, mirage in elevated temperatures compromising the ability to target the crosshairs, etc.
Until proven to be a significant factor, I'm not going to begin worrying about transitioning from steel to aluminum. If it was a terrible problem, scope manufacturers would be manufacturing 4 lb rifle scopes out of steel tubing, rather than aluminum, and then convincing us that if we continue to use aluminum scope tubes, we'll never obtain reliable, repetitive, consistent accuracy.
Another point of fact and consideration, which demonstrates the relative insignificance of dissimilar metals between receivers, scope rails, scope rings, and scope tubes:
Using a one-piece scope rail creates undesirable forces between the rifle receiver and the scope rail between the scope base fastening screws - and because the scope rail screws are separated by approximately 5 inches on a one-piece scope base, the differential expansion is 5 to 10 times greater than what would exist between the two base screws on a single, two-piece
scope base. So there's differential movement generating potentially detrimental forces created over this 5-inch distance as temperatures change. A quick way to reduce these differential forces is to switch out and use a two-piece scope base setup. Then the scope base screws are only separated by 1/2 to 5/8". Do I use two-piece scope bases or recommend two piece scope bases? No way. A one-piece scope rail fastened to a solid one-piece steel receiver with four fasteners is a much more rigid setup. More resistant to lumps and bumps that could cause point of impact changes and loss of the rifle's zero. I only use one-piece bases, and don't worry about the differential expansion and contraction between my aluminum one-piece bases on steel receivers, because differential expansion is a minor issue compared to having the rifle lose its zero due to a light thump or bump while out hunting in the wilds of Alaska.
Further, my range of temperature shifts in Alaska are relatively minor. I worried about this subject once many years ago. After consideration of the above 'facts', I've never worried about it again for purposes of mounting scopes on my long range hunting rifles.
If anyone has an article which reports on experiments that have quantified the negative affects to accuracy consistency caused by the use of aluminum scope rails and aluminum rings on steel rifle receivers - please post the links. There's theoretical problems, and there are real problems. It's doesn't hurt to be aware of the theoretical ones. But it's not paying attention to, and avoiding, the real problems that will bite you in the butt.