In have 2 Huben K1 .25 calibers. One of them is a 2023 model and the other is a 2024 Model. They both are the K1 lights with the carbon fiber stocks. I spent some time finding the perfect slug for this set up both of them. I am shooting NSA’s 38.5 grain.254. One of them I am currently using as my night hunting rig and the other I don’t really use much. With that said, I have been thinking about selling one of them. they both shoot very accurate with the 38.5 green slugs. One is tuned to shoot just shy of 1000 ft./s and the other one is about 980 if I remember correctly.. you do have to be careful with the diameter of the slug. If it’s too small, it will definitely jam the rifle. The older models I know had different magazine and or diameters. I believe they were a bit tighter so you were able to shoot the smaller diameter slugs. Let me know if you have any other questions or if you’re interested in possibly buying one of mine. I can send you pictures and exact speed if you are interested. I do a lot of work with The Pellet Shop and they can verify who I am And that if you purchase something for me, it’s going to be exactly what I’m telling you you’re going to get as far as condition and accuracy.