DeBois,
I had a problem similar to yours with my new pro-hunter 243. I was handloading with various powder\bullet combo's and just could not get anywhere near acceptable 100 yard groups. There were times when 3" groups started looking like a good day.
A muzzle crown may help any barrel, I don't know, but you may want to try some simpler matters first. This is what I did to get sub-MOA groups from my pro-hunter 243:
First I floated my forarm. I didn't do a small float, but I did one that was solid yet got the forarm a good 1\8" away from the barrel. The only "pressure points" or parts that now touch the barrel are the two uncle mikes spacers that are between the forarm and the barrel. (see the picture). Actually, I took an Uncle Mikes Contender spacer, cut it in half and Dremmeled the barrel contour...then gouped\superglued the spacer onto the forarm.
The next thing I did was to make sure the forarm did not touch the frame when I locked up the gun. I made sure upon lockup that I could slide a business card inbetween the forearm and the frame on each side. Also, be careful when you change barrels that your forearm doesn't "shift" and one side is touching. This only takes a second to check, and only a second to fix when you change barrels.
These "little" fixes made my pro-hunter a forever keeper. It pops those 70 and 80 grainer Nosler's down range like they were on a lazer.
Oh, in order for the float to work, I had to get longer screws from Brownells to make it work. I don't remember the screw size....but it's not the "standard" contender size (go figure).
I have some pictures for reference: