I am considering buying a set of the ARMS 30mm quick-detachable steel scope rings that you offer under the AR-15 Accessories section on your website. Offered in three sizes, I am unsure which to purchase and was hoping you'd help. I am mounting a Tasco Super Sniper 30mm 10x42 scope and would like to keep it low enough so a cheek rest isn't necessary on the stock, but high enough so it doesn't touch the handguard. I was thinking the mediums would probably be best, but would like your opinion. Thank you.
As you might imagine, I have absolutely no idea, as it's impossible to have every scope on hand to measure, particularly since we don't deal in scopes! However, I've worked up a procedure that will let you figure out what rings you need.
OK, here goes:
I've done some measurements and calculations on the ARMS QD rings, and have a specific example. First, here are the ring "heights" from the bottom of the inside of the ring, where the scope seats, to the top of the dovetail cut in the bottom of the ring (all measures are approximate):
RING HEIGHT
Low: 7,8mm
Medium: 14,2mm
High: 20,5mm
As the ARMS rings are 30mm each ring height will give a measure from the top of the dovetail to the scope centerline (this the same for 1" scopes, as the 30mm to 1" reducing spacers center the scope in the rings) of:
SCOPE CENTERLINE HEIGHT
Low: 22,8mm
Medium: 29,2mm
High: 35,5mm
Lay a steel rule on the top of the dovetail, keeping it parallel, out to where the objective lens will be. Measure the minimum clearance between the bottom of the straightedge (i.e., the top of the dovetail) and the rifle below. Note that individual rifles will vary, so measurements of my rifle might not be the same as the same measurements on another rifle.
An example:
Let's say that the "clearance" from the top of the dovetail out where the objective lens would be, to the rifle below, is 10mm. The total clearance would then be:
TOTAL CLEARANCE
Low: 32,8mm
Medium: 39,2mm
High: 45,5mm
Measure your scope. In this example, the objective OD is 50,0mm. Half that is 25,0mm, giving 7,8mm of clearance between the objective bell and the rifle. Thus, the low rings would seem to suffice.
However, in this example, the governing dimension is *not* the objective, but the eyepiece. One must repeat these calculations for the other end of the scope, the eyepiece end! In this example, while Low rings would allow the objective bell to clear, one must use the Medium rings to allow the eyepiece to clear the ARMS Detachable Flip-Up Rear Sight. The Medium rings give 14,2mm clearance at the objective bell.
If you're interposing the ARMS QD Base or ARMS Multibase you will be raising the scope further. The QD base adds 11,3mm to the total clearance, for example.
I hope this helps.
Thanks for your very kind business!
Best regards,
Walt Kuleck
Fulton Armory webmaster