Mk II Upper & Lower Fit

I have a couple of complete "uppers" and want to use them off a single "lower". One is an adjustable sighted slim barrel and the other a fixed with a 2 to 8X Weaver handgun scope mounted. There's a bit of back & forth movement and I'm wondering what one does to eliminate it. Also, if it can be eliminated should it be snugged up forward upper against lower or rearward?

The wiggle is slight, doesn't affect function nor, do I think, safety. But I figure having even a bit of slop gives the parts a head start to strike each other and that will only worsen over time.

I'd like to function off one lower, having set it up with a nice trigger and other personal touches.

Make a shim from an aluminum beverage can. Cut a square hole in the middle to fit over the hook on the lower, cut the sides so they don't stick out. Works good, I've done this on a couple lowers.

recumbent said:

Make a shim from an aluminum beverage can. Cut a square hole in the middle to fit over the hook on the lower, cut the sides so they don't stick out. Works good, I've done this on a couple lowers.

Click to expand...

I think I've got it - the hook faces forward, adding the shim snugs the front edge of the hook up against the vertical rear of the receiver or barrel tenon. Thanks. :!:

over the years some folks even simply used a piece of business card or a matchbook cover ( remember those?) cram it in, and it snug things up till the next time you take it apart................ 8) :wink:

( yes, the thin aluminum piece works too,but watch you DON'T slice your fingers, blood is NOT good on gun finishes... :roll:

dfletcher said:

I have a couple of complete "uppers" and want to use them off a single "lower". One is an adjustable sighted slim barrel and the other a fixed with a 2 to 8X Weaver handgun scope mounted. There's a bit of back & forth movement and I'm wondering what one does to eliminate it. Also, if it can be eliminated should it be snugged up forward upper against lower or rearward?

The wiggle is slight, doesn't affect function nor, do I think, safety. But I figure having even a bit of slop gives the parts a head start to strike each other and that will only worsen over time.

I'd like to function off one lower, having set it up with a nice trigger and other personal touches.

Click to expand...

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If either upper is from a 22/45 Mark III style, it's quite a chore to fit those to a "steel grip frame". The upper was "smash fit to the Zytel grip frame" and that will need some relieving of metal to get even a sorta nice fit. If both uppers are being fit to a metal grip frame, the shim may work for one but require a different thickness for the other.
I prefer to remove any looseness in the manner that Ruger does it:



Pinch the grip frame edges back to shape in a vise with a one-inch diameter cold-rolled steel bar to control how far the pinching can go.

The movement is front and back. Using shims worked fine. I used scope base shim material (from Brownells) I had laying around and fitted it over the leading edge of the lower's front edge of that hook. Put a dab of red Loctite on it.

The AMT "upper" has a cavity, a little extra space, in that area and I've considered dropping in some steel bedding material. Slather release agent on that hook then reassemble. That would eliminate it all. But, most likely the upper would fit only that lower and this is more or less permanent. I'd kind of like to keep the interchangeability with other lowers. For now anyway.