I would also try some 165's or 190's.... 6 inches is a lot IMO at 100. get it online if needed.
When I was a young man I shot at awful lot, and some big guns, 458 Lott etc. I developed a pretty bad flinch, and it comes back easily.
Here's what I do.
Number 1 source of flinch for me is the blast. Double up hearing protection and you're half way there. Plugs that are inserted CORRECTLY, and muffs over the top. Safety glasses to shield your eyes from the blast wave and you'll start getting better
Next shoot a minor caliber. .22 is great, but a violent Springer air rifle is better. Lots of noise and motion going with those, those help me a ton.
Weight on the gun. I have a small 7 mag that about kills me. When I shoot it a lay it on bags and sometimes drape a sandbag over the scope on longer sessions.
PAST recoil shield, cheap and will really absorb recoil.
Use some or all of these, flinching can be a real issue, you can train it out but always be wary of it.
One more thing: stop early. I have found that if I'm tightening up before the shot, I'm tense, it's time to stop for the day or switch to rimfire. That's when the flinch starts to happen