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IMR4227 is a moderately fast double base stick powder. It's commonly used for the 223 Rem with light (40 grain) bullets though some more modern powders give higher velocities at the same peak pressures.
Quickload shows me that 9.8 of IMR4227 in a 300/221 would drive a 240 gn SMK at 1010 fps assuming an unlubricated bullet and normal barrel friction with an 85.9% case fill and 2367 psi muzzle pressure. It seems to me that could be a reasonable and stable load for use in a AR-15 for use with a suppressor. The peak pressure however is only 30kpsi so it will probably leave residue. Personally I'd choose a little faster burning but bulkier powder for heavy bullets in my 300/221s. Lighter bullets need even faster powder.
For a 10" 30 Carbine T/C pistol a good subsonic load using a 240 grain SMK seated at 2.28" OAL over 9.1 grains of IMR4227 is a 100% case fill, 1020 fps. 38kpsi peak, 3.7kpsi muzzle.
It's stable with the 10" twist barrel because where I shoot at over a mile elevation.
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