I have a Browning 300 win mag with a 24" barrel also. I have shot about 1,060 180 grain ballistic tips through it and recently about 250 180 grain Accubonds. All were propelled by 75.5 grains of RL22, Fed 215 primer, and a Frontier (hornady) case. I have tested them on everything from prairie dogs to big horns to elk. I have also religiously practiced with it on the old gong at 1000 yards plus with great precision. Out of all those rounds, I have bought about 8 different lots of RL22, and have chronoed each one. My gun always liked the 75.5 grain load the best, but velocity varied greatly from lot to lot. One lot sent that 180 out at 3245 with 1/2" accuracy at 100 yards. My current lot shot at 3047 average last Friday. Standard deviation on all lots never went more than 15 with sd's of 6 or 7 being more normal. I would suspect that your load is probably well above 3200 with 3300 not being out of the question. Watch those pressures carefully!! It sounds like your on the ragged edge of max.
You asked if that load would be good at 1000 yards. The only way to have a consistent 1000 yard shooter is to get that standard deviation down to at least 10, and have groups like yours. So, you are half way there. But without a chrono, you are just going to have to go try groups at 1000 on a calm day so you can get a good reading of the load. Sometimes, I have had bullets shoot great out to 300 yards, and then go to hell at 1000. I have also had bullets shoot so so at 300, and then lay 'em all into the same divet at 1000. You never can tell until you put them to the test.
As for your velocity being adequate, you bet it will work! That same bullet launched out of a gun with 400 fps less velocity will do it.
My advice is to enjoy that beauty while she's still young. After 1300 rounds through mine, a new barrel will probably be on the way next year!
--good shooting! --goodgrouper
