I shot the Viper pellet out of a FWB R1. I have had the rifle for at least 25 yrs. maybe longer. I don't know the twist. The pellet takes some effort to go in the last bit. I tried to shoot a informal group just now, I put a large white card board box liner out at 25 yds. and shot 5 rds. that I sprayed with silicone spray. I put a one inch red sticker dot on for sighting. This wasn't bench rest, I shot off hand with one hand resting on a vertical pole. The first one went in about one inch low at six o'clock. The next four were low and right. The bad news is they all key holed. Some more than others, but there wasn't any round holes. Maybe if I play with some different lubes they will straighten out. It doesn't look good right now for my rifle. Maybe it doesn't make enough velocity for this pellet. I'm open for any suggestions. Regards Rich.

It sound like you need more power like 900fts or more in a gun with 1200fts it may do well.