Rifle Scopes YHM riser problem

[Mike_R]

Hello everyone,
I am having an issue with my YHM picatinny scope riser that somebody might have run across before. I added their 1/2 x 5 1/4 extension riser to get adequate eye relief and height on my AR. Both of those goals have been achieved.

The problem is the rail slides on over the rail on the gun and then locks with 2 cross bolts that run between the groves on the a3 receiver. The design is such that no matter how much I tighten the cross bolts the riser does not clamp, it is fairly rigid. The bolts run low (low enough to mark up the bottom of the grooves in my upper) but are smaller than the groove on the upper and allow the scope to slide a bit more than a 16th back and forth. This is distracting and I imagine transmitting more shock to the scope so I want to get the rail mounted firmly.

I tried shimming it with some sheet metal but the shims jumped out. Other solutions I have come up with are maybe hose over the bolts(to increase the diameter) or drilling and installing a set screw at an angle that I tighten to either lock it at the front or rear of the groove.

Any ideas would be appreciated, I haven't been able to find solutions to this problem. Thanks in advance!

 

[LtDan47]

Re: YHM riser problem

Try this, remove the clamp plate and turn it around it might have been assembled wrong. The clamp may have two different levels of beveled ridge.

 

[Mike_R]

Re: YHM riser problem

If there is a clamp plate mine came without it. I don't see where there would be room for one on the yhm design. I guess I should clarify that the riser slides over the rail with very little play side to side even with no bolts. The bolts *should* locate the scope and prevent it from moving front to back, but don't. The threads don't seem strong enough to make the riser (which is 1 piece and relatively thick) clamp.

 

[Mike_R]

Re: YHM riser problem

I called YHM and the gentleman on the phone explained to me it is most likely tolerance stacking. He said if I sent it in they would check to make sure it's in spec and if it wasn't they could send me a new one, or measure a few and send me one of the "tighter" ones.
I am still trying to come up with a solution to this. I don't think that would help me much because the design relies on little threads that are supposed to "bend" the much thicker body into full contact with the rail in order to locate it front to rear.
I am thinking about using an epoxy to make a "recoil lug" in one of the receiver slots, then drilling and tapping it to run a screw through the mount into the lug... or even an aluminum lug. That or a pair of angled set screws... it is only a .223 so recoil forces aren't that great. I just don't want it sliding around.