Weihrauch barrel attachments

I am wondering if anyone has successfully attached a 15mm to 1/2unf adapter or any type of "aftermarket" adapter to a Weihrauch 15mm barrel? The OEM 15mm Weihrauch mod with the front sight cut out slides on perfectly. I just purchased one of Donny's 15mm to 1/2unf adapter and it will not go over the cut outs on the barrel for the sight. Yes, I have reached out to Donny to see if this is an issue he has experienced, but I wanted to check here too.
 
The sight grooves stand proud of the barrel, since they are formed or pressed instead of cut. This, obviously, makes the OD of the barrel larger than 15mm. You will have to file the raised portion of the grooves off to get a 15mm adapter to fit. 

In other words, the adapter is made to fit on a barrel that's round, and with the raised sight grooves yours isn't round. That's not DonnyFLs fault. 

Personally the slip-on adapters are too flimsy and sketchy for me. I either turn the barrel down round in a lathe, or cut and thread the barrel. I wouldn't fool with it otherwise, since there isn't a huge reduction in noise anyway. 

The Weihrauch setup is really going to be your best bet, and their moderators are the quietest you'll find anyway. Quieter and lighter than the DonnyFLs I've used on PCPs.