Ok, having been in the business for awhile,I have seen this. I am shoot a XXX brand gun with a 1:28 twist ans shooting a 200 grain bullet at anything over a 100 grains of powder I am not getting good groups. You have to match the bullet to the gun. yes you can shoot a 200 grain bullet but adjust your powder charge accordingly at most likely around 75 to 80 grains. shoot the 300 grain 330 grain bullet with 100 grains and I bet it will be very accurate. No you don't need a chronograph to do your testing. find the accurate load then chrono the load.

Now that I have said all this. PR Bullets, and one or two others make some light bullets that should do very well in your rifle due to design, yea there are going to be folks who disagree with what I said, but it is true. if you want to shoot a 200 grain brand X bullet fast, get a gun with the approiate twist.

I have a traditions 45 caliber with the1:20 twist. shooting a 330 gr conical andI forget the sabot bullet weight but it is in the upper end for the rifle. I cannot shoot over 80 grains and get any accuracy. so much for shooting 150 grains, or even a 100 grains. Good luck.