Okay, here is what I see in the Trailhand and Trailhand Pro. I measured and this ridge is maybe a couple mm past the 3.5" mark (both guns). You can see for yourself this is a SERIOUS ridge, not some tiny bump. I tried putting in the X-caliber insert and yeah if I push on it I can feel it kind of maybe slipping in, but there is zero chance I would ever mallet this into one of my guns, lol. If it doesnt fit freely, its not to spec, in my opinion, and I doubt the problem is the adapter. My longest shooters box adapters are all only 3", so they fit no problem. Of course they won't be nearly as accurate, but they work, and as long as its not a rimfire cartridge it won't keyhole at 20 yards. 
