Experiments with Brian's Stock Adapters

[Jim in Texas]

I have been experimenting with one of Brian’s picatinny stock adapters on a MK760 and thought I would start sharing the results of my experiments with the group.

Let’s start with some basics.  I am not an engineer or a professional gunsmith.  Additionally, there are a lot of variations in the world of 76/760s.  These ideas may need to be modified, or they may not work at all with your particular firearm.  

One thing I observed early on is that the stock adapter has only relatively short, cantilevered support in the vertical axis.  I decided to try to lengthen the support areas with a couple of shims.  

One shim goes between the top of the stock adapter and the bottom of the grip block.  

The second shim goes between the bottom of the stock adapter and the top of the grip.  

I think this will give some added support to the stock adapter without requiring any modification to the firearm itself.  Thoughts?  Suggestions?

[Rekraps]

Hey and great post. I am a bit confused however as i have two of his mounts and both of them had to be carefully filed down, not shimmed, to mate with the receiver. Clearly the 760 is a tad off with respect to OEM measurements. That being said, your shim seems (looks) great with the fit and finish. Great job!

The adapter is super strong and makes the gun a worthy and wonderful shooter.  I mated my adapter with SIG Minimalists, looks good and has the perfect shoulder relief.

[Jim in Texas]

Like you, I had to file the two pads to get a good fit between the stock adapter and the grip mount.  

I made these shims because I was concerned about: (1) the relatively short engagement between the stock adapter and the grip mount; and (2) relying solely on that short, cantilevered fit to keep the stock rigidly attached for years to come.   The red double-ended arrows in the first photo show just how short that engagement surface is.

By adding additional support behind that cantilevered interface, I hope to keep the stock stable for the long term.  The red arrow in the third photo show how much longer the top engagement surface becomes with just the addition of the small square shim.  The red arrows in the last photo show how much longer both the top and bottom engagement surfaces become when both shims are used.  

Does this help to clear up the confusion or have I managed to muddy the waters even more?

Jim

[Rekraps]

11 hours ago, Jim in Texas said:

 

Like you, I had to file the two pads to get a good fit between the stock adapter and the grip mount.  

I made these shims because I was concerned about: (1) the relatively short engagement between the stock adapter and the grip mount; and (2) relying solely on that short, cantilevered fit to keep the stock rigidly attached for years to come.   The red double-ended arrows in the first photo show just how short that engagement surface is.

By adding additional support behind that cantilevered interface, I hope to keep the stock stable for the long term.  The red arrow in the third photo show how much longer the top engagement surface becomes with just the addition of the small square shim.  The red arrows in the last photo show how much longer both the top and bottom engagement surfaces become when both shims are used.  

Does this help to clear up the confusion or have I managed to muddy the waters even more?

Jim

Quite clear now. I really like your thinking, obviously you are an engineer or metal worker of some experience. That being said, I went down and examined the two M76's I have with the original Brian adapters and IMO, there is not sufficient weight or potential stress on the fit (without shims) to concern me. I can easily pick up the gun using the new SIG Minimalist stocks, and they are rock solid, very tight and seem adequate. I tend to  move on the "over" engineering side of the house, but in this case, and probably because it would be such a huge pain the ass to remove them, will leave them as is. 

But.... again, your work is really nice, and clearly thought out.