Walther GSP mount problem

My nephew recently purchased a new Walther GSP Expert .22 with a Champions Choice mount. He installed an Ultradot with their rings. He is having trouble keeping the mount tight. The set screws were tightened and Loctite applied, and it still loosens after approximately 100 rounds. The mount was initially installed by Champions Choice when it was shipped. Anyone have suggestions? One of our leagues shooters wants to drill and tap the receiver , however I think that is a bad idea as the metal is too thin.

I’ll have to dig mine out, but I believe steel on top of receiver is thicker underneath the sight. That’s where I drilled and tapped mine.
Jon

I drilled and tapped mine for a Weaver base ahead of the rear sight. This allows me to take off the dot and use the irons. 
I hated the base that replaced the rear sight because it set the dot sight so high on the pistol. It worked fine however. I had no problems with it coming loose.
JKR

Which Weaver base did you use?

Like JKR, I drilled & tapped a low Weaver style base 5/8" in front of the rear sight  (an earlier Weigand 10/22 base-could only use 3 screws). can shoot the iron sights over it. Trick is to get the screws the right length. I tapped the holes just to the point where the screws got a little snug as they neared the bottom of the hole-then blue loctite -- I use a Sig Romeo5 red dot sight which had to be filed a little to clear between the base & pistol. So far so good, but I haven't shot the pistol that much.
2¢ - YMMV
Check with your Pistol smith 1st?  - - - Russ

ps: W/ the red dot sight on it, the GSP IS A TANK (heavy) - ppss the pistol has a great trigger.

Lestuck wrote:Which Weaver base did you use?

I’m not sure. Might’ve been for a 336 Marlin rifle. I had to shorten it. I think any base for a flat receiver could be adapted. 
I agree with Russ. It’s a heavy pistol with a scope on it! 
I’ve owned several high end target pistols and I’ll say that this one is the most reliable of any I own. “Tank” is a great description, Russ!
JKR

Biggest weakness of the GSP is no consideration to optics mounting. [2nd is bbl twist / 50 yard limitations.]

Wanted to drill and tap mine since Day 1 but have been living with it.

I had to use retaining compound on the rear sight pins as one kept walking out on me.

Gotta love the Germans.