Good question Richard... I have been reluctantly satisfied with the Rem brass to this point as I was shooting 180 E-Tips to 3400 plus from the Ultra. I have always wanted to try the GS 177's because they have a very good BC for their weight and... their design allows for less pressure and higher velocities going down the tube. In my testing a couple of days ago. I got up to about 3550 (92 gr RL17) with some external pressure signs. 93 gr blew a primer and caused a very stiff bolt.
The 92 gr brass will not hold a primer. The 91 gr brass will, but another firing at 91 grains will likely ruin the pocket with a 2 shot case life. I expected all along to be able to excced 3500 with the 177's and that velocoity improves their ballistics and stability. I should be able to get it. The E-Tips on the other hand are maxed out at about 3400 or so and that's all the farther they can be pushed. They pressure up real quick once they get to their threshold.
Another cartridge? I have also pushed the 180 E-Tips to 3190 in a 300 WSM
using RL17 in a 24 3/8ths barrel. Thats only a little more than 200 fps behind the much larger RUM which takes about 50% more powder for about 8% more velocity. RL17 is the way to get the higher velocities, but it's too fast for most bullets in the RUM unless your shooting something real light. That's where the GS 177's come into the picture and they are maxing right about were I expected, but the brass is not holding up.
I have been considering some other cartridegs and wildcats like the 300-375 Ruger, 300 Dakota (same 404 Jeffery parent case as the RUM), and the 300-338 Ultra (which is Rem brass only deal). These smaller capacity cases would be more friendly to RL17 as a propellant.
That being said, I shot 180 Cutting Edge bullets up to 3450 with Retumbo and they have a little better BC than the E-Tips and they are a lot cheaper than the 177's. Hope to go out again this afternoon and revisit the CE and GS bullets.
If I can get the hoped for performance of the 177's, it will have an effective expanding range to 1500 yds plus which is wayyy farther than any other 300 RUM combo. if the CE 180's shoot well to 3450, they'll get me past 1200 for a more cost effective solution.