proper sized slugs in a barrel you would push inth chamber and about 5 to 10 pounds pressure to go threw barrel at choke , those eungin pellets are a bit larger diameter then say jsb I used to use them in my exanix ar6 , back to airforce they have had many different barrels in size try pushing ammo into breech and pushing threw with your cleaning rod like i said 5 to 10 pounds pressure , like my condor i run slug barrels in 22 and 257 , I did cut in breech to allow slugs to chamber , but a normal pellet barrel by a newer airforce may not even have any breech work so if you cant even seat in breech they not for you if you cant even puch them threw barrel , if you have say a vernier caliper or micrometer , dave corbin told me decades ago push 6 pelletsd threw barrel and exit out muzzle and measure all write down add togeather and divide by 6 and ass .005 or 1/2 thousanth this is proper sixe for a slug , however with pellets the head is a whisker smaller then the skirt the head or round part may be larger then your breech let us know LOU ,