Maybe I have some droop?

The 124 has a very weak breech lockup mechanism, and a long barrel that compounds the problem. If your breech seal is new, or too thick, it can cause lockup issues and make the barrel point downward as well. 

Or you could just have droop. I had one that did. I fixed it by filing the breech until it locked up correctly. You can also bend the barrel a smidge, but it takes a LOT of force and a solid way to hold it while it's removed from the gun. 

But all that crap aside, are you sure it's shooting at the right velocity? It could just be super slow. Especially if the seals are rotted, the breech seal is bad, or the spring is broken. All of which are common 124 issues. 

As for the mounts, I just use BKL mounts. They don't move and don't need a stop pin. If you want to spend money on a band-aid solution, they make a droop compensated mount or an adjustable mount. They are expensive but very well made. 

Personally I'd check velocity first, then remove the breech seal and see if the gap at the top of the breech tightens up. If it does, size your breech seal. And don't sand the face of the seal, you need to take material off the diameter.

Good luck. 

A shim in the rear Will help.

I use a section of credit card type material that I cut to fit and somewhat pre-form (slight bend) after heating it in hot water. 

I'm sure others will chime in,however,this has worked well for me for decades with no adverse side effects. Hope this helps you!

Mike

Then find the cause of the droop, and fix it. One and done, fixed forever.

I'd still check to see if the professional sized the breech seal correctly, and see what kind of power it was putting out. 

Shims and BKL mounts don't mix in my experience, it's a real easy way to get a crimped scope tube if you aren't careful. If you do, I'd suggest two layers of aluminum can. That will give you right around .006" of height, and that's pretty close to the .007" that most drooper mounts have. 

Have used these with success.

https://us.hawkeoptics.com/mount-inserts-30mm.html

JUST BEND YOUR BARREL STRAIGHT UP IF YOU'RE NOT WANTING TO PAY FOR $59 95 BKL 1 PIECE .007 DROOPER MOUNTS.

YOU COULD ACCIDENTALLY FIX IT BY LOANING IT TO SOME IDIOT WHO COCKS IT AND ACCIDENTALLY PRESSES THE TRIGGER WHILE BARREL HANGING OPEN TO SLAM THE BARREL UP. 

Oh! Take the stock off first before loaning it for the ACCIDENT because the stock WILL MOST LIKELY CRACK at the GRIP area when that's done!!! 

Based on real life first hand experience. Shoulda loaned it without its stock but no more barrel droop that's for sure! Glued and peened the stock back and took off the drooper mount and it shot high had to really crank down the elevation to zero but good news it could zero at 100 yards after that.

My son did that to my Beeman R10 when he was 12 years old. He was trying to show off in front of his cousins, as they were using Crosman pump up pellet guns, while he was using an “adult air rifle”



he pulled on the trigger while while it was broke open, and results as what Yo said, “up droop”. Tried fixing it the conventional way, but my OCD just wouldn’t let me remount the barrel. Sourced one thru T Chambers in 177 to replace the other one. If I had to do it again, I should’ve upgraded to a 20 cal instead.