Smith Enterprises Scope Mount " Abuse"

[jmoore]

Sometimes things just don't go as expected.

Whilst playing "musical chairs" with scopes and mounts lately due to a swap off of a newer M1a (since swaped back in a completely different format), I found that the mount I THOUGHT (and still can't can't keep thinking) came off the Glenn Nelson built rear lugged M1A apparently didn't! The clip guide interface is so far forward on this rifle that the main screw for the mount would barely enter the hole on the receiver side even with the cam all the way offset.


In actual fact, this photo was taken after the first cut. The cam and screw would not fit at all before cutting!

Plus, the clip guide key slot was so offset as to be useless.

Before cutting.

An early ARMS18 mount was on this rifle previously but presented no mounting problems. However, it became part of a related optics swap. Need to find another scope like the old one, though. Very nice!

Previous set-up as posted elsewhere, including a brief range report. Link here: M16a4 ACOG and Ammo Test. Some M1a/M14 time as well. See post #4 and following.

Another ARMS 18 mount wouldn't work, as the scope and rings chosen won't clear the rear sight. Phooey!

So, off to the mod shop. Set up my angle plate on a Bridgeport mill, trammed everything in, and set the mount at the proper angle by making the face parallel to the cutting plane.

Parallel was held down by finger pressure whilst indicating.

As it's a fairly simple set-up, I did the cutting in two phases after making a SWAG as to the amount to come off. Took 0.025" off to start, checked it on the rifle, went back and whittled off another 0.022". Quite a bit, but it's partly because of the angled nature of the interface between parts.

In process, second go around after trial cut to establish overall fixturing and math soundness.


Reset the mount on the rifle and discovered, to no great surprise, that about 0.025" needed to come off the top of the key. That leaves a little air gap between the key and the mount, less than original, but it's there.


Mount is now well centered over key, but doesn't actually touch it anywhere.

Cam position is OK, everything works well now! Tested it and the scope is reasonably optically centered, but with extra room for long range, probably 25-30 minutes. Maybe 15 minutes off R-L.




Ugly rifle to me, and awkward, except at the range, where it performs well and feels VERY comfy, aside from some buttplate slippage in the prone position. (no sling)

The scope is huge, but it does special things, so it'll stay until way obsolete.



(This thread is a long delayed spin-off of a previous similar issue started by Stevo. Link here: ARMS #18 install problem. )

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