I have a Creedmoor canvas jacket, Hardback heavy, and a Freeland international jacket. If the three I much prefer the Freeland (I have a Monard standard on order). The hardback heavy doesnt allow you to get a position with your hips out. It limits you to a fairly upright position because of how stiff it is.
Also look at the Freeland light coat.
Matt
All right, another "you don't need a Hardback" shooter! That makes my day right there. Thank you sir. (For the record, I have a Freeland heavy-canvas coat, and I started with the light canvas model and shot a few good offhand scores with that one.)
To the OP, to improve your scores, shoot more, and focus on what you are doing harder. It's better to practice making 10 GOOD offhand shots than 20 so-so ones. Remember the only thing that matters is the front sight and trigger squeeze. Don't think, don't over-analyze it (I know, very hard to do), your subconscious knows what needs to be done. Let it work.
I shot smallbore all winter and have noticed a marked improvement in my prone scores, consistently. Unfortunately I slipped backward offhand and sitting so I am still shooting about where I was last season. Smallbore and air rifle are much more demanding than Highpower in my experience. A good Highpower shooter makes a mediocre Smallbore shooter.
Oh, don't dwell on the bad shots and beat yourself up over them. Focus on the good ones and remember what you did to make them. Focus on repeating that procedure. It's as much of a mental game as a physical one many days.
The last thing I will mention is that I do think physical conditioning is important. I don't think it will make or break your game, but late on a long day of sitting in the sun, pulling targets, marching up and down the Viale desert, etc, being conditioned to some kind of exercise won't hurt. I ride bicycles all summer long, maybe more than I shoot, and I am positive it made an improvement in my ability to withstand long days on the range without wilting.
Hope some of this helps and good luck and good shooting!
Nate