Some said earlier in the thread "heavy " was harder on a springer. I have no clue.
You can use those if you want. It will shorten the spring life. Which is pretty short to begin with. There's dozens of threads about ideal weight for a springer. The R9 of which I own two and tuned several others usually make between 14 and 15 fpe in 177 if it's running right. You're getting about 14 which is more than I'd expect for that rifle with that pellet.I didn't know that regarding a pellet being too heavy. I know very light alloy pellets could damage springers and gas ram because of the piston head slamming the breech with too little air cushion but too heavy is an issue? I shoot 16.2gr JSB Beast's in my R9 and get 624fps. Those are the heaviest 0.177 pellets I can find. Are those too heavy for a springer?
Did you clean your barrel before trying the slugs?I tried jsb 10.3 knockouts in my vortec tuned Diana 48. The velocity started out at around 770-760 but every shot after kept dropping. Can't remember the spread now (sometimes) but after doing the Chrono string they just sit on the shelf until I get either a .177 pcp or a sizing bushing to get the diameters consistent.
OK, that's good to know. I've shot only a few of the JSB Monsters and Beasts. Got a tin of each out of curiosity. I stay in the 7-10 grain range with the R9.James Macarri of Air Rifle Headquarters (ARH) told me a few years ago, anything over 9 grains in .177 caliber was detrimental to longevity of coiled springs. I don't know of anyone in the world who has more knowledge about airgun springs than Jim.
I found the KO work really good in my hatsan 125 sniper but when I tried some 12 grain nsa slugs it just didn't work.I tried jsb 10.3 knockouts in my vortec tuned Diana 48. The velocity started out at around 770-760 but every shot after kept dropping. Can't remember the spread now (sometimes) but after doing the Chrono string they just sit on the shelf until I get either a .177 pcp or a sizing bushing to get the diameters consistent.