Tried the 12.5 & 15’s in the .177 Avenger. The 12.5 required reg to be cranked up and the fill pressure maintained above 3Kpsi. Accuracy was inconsistent. The 15’s would not leave the barrel of the rifle. Used a rod & drove a stuck slug back out the breach. Measured the slug (.173). The unsized slugs just weren’t a good choice for the avenger. A year passed. I purchased a NOE sizing die kit and saw they offered a .173 bushing. I thought this could be the fix that the Avenger needed to run NSA slugs. Purchased the required kit and resized some of the 12.5s. WOW! Just what the Avenger needed!! The gun will shot the 12.5s with the reg @ 2K and the rifle will continue to sling them when fill pressure even drops to or slightly below Reg setting. With the reg cranked up I’m pushing the 12.5 to 975 fps and it’s grouping under 3” at 100 yds. Honestly, near golfball accuracy. Here are 100 yd groups. 100 Yard .177 Avenger W/Slugs - 975 fps & 26 FPE https://youtu.be/4Sm9aW7g8xU So, dang good slug for a dang good entry-level air rifle, as long as you’re willing to resize them to .173. Hey Nick, feel free to save me some time and offer them at .173? Anyway, I like them and the performance & accuracy is worth my time to resize them!!! 4 stars cause I have to resize them. After sized, 5 star performance! Good stuff! Hope this helps someone with the little avenger.