Its a good idea which I doubt can harm the seized pistons ?
I've been warned that a solidly stuck set of pistons that refuse to budge could cause the barrel to crack.
It would have to be an EXTREME case. And in retrospect, if it was seized that badly, then the barrel was most likely junk anyway.
No hammer and drift marks all over the piston tops!
No rod damage or bushing damage.
Just one big mess...wish I had a parts washer at home.