I have handled, but did not fire, a NULA chambered in 300 Weatherby. I bet it was a bit sporty.
The first NULA (actually ULA) I fooled with was one of Melvin's "loaner" rifles, one of several he sent to gun writers for testing, in .300 Winchester Magnum. It had a 24" No. 2 Douglas barrel, and was a bit sporty. But I was young and pretty recoil-tolerant, so worked up some loads, eventually ending up with three that shot well under an inch, using the 165 Hornady Spire Point at around 3140 fps, the 180 Speer Grand Slam at around 3025, and the 200 Nosler Partition at 2950. All shot very well, and in fact I shot three, 3-shot groups (one with each bullet) into one 9-shot group of just about an inch (which is what introduced me to the tendency of Melvin rifles to shoot loads with different bullet weights into the same basic place. Took it elk hunting that fall, but the only elk I saw were not legal in that area--though I did take a mule deer doe with it while hiking back to the truck one night
According to my notes I put 135 rounds through that rifle working up loads. Kinda wanted to buy it, but Melvin wouldn't sell the test rifles. Nowadays I wouldn't even want to shoot it much--if at all!
