bybon--
Been there before. Excellent site and I found what I was looking for. It appears that the concern is not 'vibration', it's 'thermal expansion', but, not much of a concern.
I'm sticking with my mounting decisions based on what I read here.
The link to VarmintAl's shooting page is:
varmintal.com/ashot.htmFor those of you that don't go to the link, here's the text:
ONE OR TWO PIECE SCOPE BASE.... The question of one piece or two piece scope base is a tricky question. There are
a number of other factors that need to be considered to optimize the situation. Let's assume that that both bases fit the action
reasonably well. First, the action is usually 4140 steel or equivalent with a Coefficient of Thermal Expansion (CTE) of 6.2E-6
in/(in-°F). One exception I know of is the Stolle Panda action which is aluminum. Aluminum 6061-T6 has a CTE of 13.1E-6 or
more than twice that of steel. The difference in thermal expansion is the major problem with a one piece aluminum base on a
steel action. When the base is screwed onto the action at say 72 °F and assuming it fits well, it is stress free in the axial
direction. If the assembly is then heated to 120 °F (which is possible in full sun), the differential in expansion between the base
and action for a 5" span is:
dL=L * da * dT,
where dL is the length difference (in), L is the span length (5 in), da is the difference in CTE's between steel and aluminum
(6.9E-6 in/(in-°F)), and dT is (48 °F) the temperature change.
Running the numbers, the 5" section of a free base would lengthen about 0.00166" more than the action would. The
cross-section area of the B-Square base on my Savage 12BVSS is approximately 0.12 sq-in and force required to compress
the 5" section of the base 0.00166" is,
Force = K * dL = 398 lb
Where the spring constant, K = Area * Elastic-modulus / Length
Area = .12 sq-in
Elastic-Modulus = 10E6 lb/sq-in
L = 5 in
K = 240,000 lb/in and the force required to shorten the base 0.00166" is 398 lb. This is a lot of force! The stress in the
aluminum base is 3,300 psi which is well below the yield stress.