I'm shooting 88 Eldms out of a 22 Creed which is fairly similar to 22.250 Ackley.
Found RL16 favorite powder, followed by 2209 & 4831sc.
RL26 might be another option, and is popular load in the States. I had some great results with it but then had carbon ring issues, probably to do with shorter barrel and suppressed.
You can probably get a wide range of powders to work fine, I use 4064 in my 22.250 with 69's.
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