In the mid 80's, I shot ground squirrels with a guy that shot a 22 Cheetah that had UBR brass with the small primer, 7 1/2's with a 52g Sierra at 4500 fps. On cold S. Ca. mornings, his gun was not reliable at all. He finally went to making cases out of 243 brass with the large rifle primers...end of problems.
I shoot a 6 PPC Panda with large rifle primers the brass made from 7.62x39 brass and agging in the 2's is no problem and groups in the 1's are shot also. I gave up making bullets and shooting BR some years ago and had rather eat a rat than shoot another BR match.
I talked to Pindell some years back when I bought a couple of his FDC actions concerning the choice of large and small primer pockets. He related to me that in their initial testing of the 6 ppc there was very little difference between the large and small primer performance but the edge was to the small rifle primer, but everyone thinks that there is a huge difference, at least in the 6 PPC. A well perceived lie is better than an unpopular truth.
The whole issue on large vs small primer pockets has gotten blown way out of proportion, and the entire concept of the small rifle primer is only applicable to the person that is wanting to shave .035 off his group size and is willing to go to the expense and trouble for the extra .035.
I have had a lot of wild cat reamers, and the standard 6/250 and the 6/250 AI being one of them. I believe that you are cutting your own hamstring by going to the small rifle primer on a case of this size, leading to ignition issues that vary considerably more from day to day as the temps and humidity changes. Powders very greatly in their types of coatings, and some powders need a very hot primer,especially the very slow burning powders when you are shooting heavy bullets.
When shooting BR, we usually load at the bench on the day of the shoot. There is a great advantage in loading on the day of the match at the range, early in the morning, the gun may like an additional .5g more powder. During the heat of the day, you may need to back off .5g. The whole issue of a small primer igniting 40g of powder, magnifies this whole issue of the powder column being sensitive to the heat/humidity of the day when you are looking for the "bug hole" accuracy.
An example of this ignition issue is a cartridge that I chambered 20 years ago called the 6 BR Long. The 6 BR long was made using a 243 AI reamer ran in 0.100 longer than a 6BR go Gage, very similar to the 6 Dasher. I shot more zero's with this cartridge than I ever did with the many, many custom 6 PPC's that I owned. I was shooting 38.0g of powder shooting the 60's at 3850 and 35.5g of powder shooting the 70's at 3550. On colder mornings, I noticed that I really had to add more powder. So, I put the cases in a lathe and bored out the primer pockets to a large rifle primer and CCI-200's fixed that problem! Group size did not change, but my velocity went up 65 fps and extreme spread was down to next to single digits.
I contemplated shooting the 6 BR long in the Cactus Classic, but jeez how I do hate the madness of a Registered BR Match.
I hate to see guys going through the madness of the small rifle primer on a large case...it may take a guy 5 years to figure out all of the problems associated with the small primer, because one day the gun will shoot like a World Record Gun and two weeks later, the whole rig has gone to heck leaving the shooter scratching his head wondering what kind of brain fart he had while he was loading his ammo or who knows what else.
I normally don't stick my neck out, but I hope that you don't have to go through the expense and frustration that I went through.
