My very first rifle was a Mosin M91/30
I made the very horrible mistake of snuggling up all nice and cozy onto the rifle while shooting off the bench.
I'll tell you, I never did that again.
I've had no real trouble with it since, though I tend to shoot my AR more simply because I want to develop my skills before trying to tackle it again. Don't want to get the flinches because of it.
Only thing I can recommend is to let your body "give" as you fire, don't stay rigid, because that makes it worse.