I spent hundreds of hours developing throat designs for the 338-300 RUM and testing it from 1998-2000 and rebarreled numerous rifles for guys during those years. By 2001 when the 338 RUM was introduced I had the 338-300 RUM down pat as a super long range cartridge for large big game that fit on a standard magnum action. Through extensive testing on my range the 338 RUM did everything the 338-300 RUM would do. The velocities were so close the two can not be seperated because the accuracy loads all overlap from 2750-2850 fps with 28-30 inch barrels in both. The 338 RUM fits better on a standard mag action which is why Remington shortenned it slightly. When guys shot the two side by side on my range I never got another order for a 338-300 RUM barrel. Everyone went with the cheaper standard cartridge. After all the work I had put into the 338-300 RUM for three years it was over at my shop with the introduction of the 338 RUM in 2001.
Times change and as new cartridges become available for wildcatting and new powders become available that change the parameters of existing cartridges or make new ones better you just got to go with it. It doesn't mean the others are not good and will not do the job all of a sudden. But it does change the perspective of a new guy wanting the best at the time for what he wants to accomplish with the rifle. I have a room full of wildcat cartridges that were the best I could do 20, 30, 40 years ago but with new cases coming out and new powders most I wouldn't do now. Not that they are not good, I can still kill anything with them, I can just get to the same peformance level better now with something else more efficient.
The 338 SIN will find a niche as a short barrel big 338 with plenty of punch that fits easily with bullets seated out on any standard mag action. There is just hardly any difference performance wise from the 340 Weatherby through the RUM's and into the standard Lapua. The 338 SIN fits right in there. My accuracy load with a 300 smk is 2735 fps with my 28" barrel 340 Weatherby, 2830 fps with my 28" barrel 338-300 RUM, 2730 fps with my 26" barrel 338 RUM and 2820 fps with my 26" barrel 338 Lapua. I have pushed the 300 grain smk over 2700 fps with my 24" barrel 338 SIN. There is just not a lot of difference between any of these.
I shot some great groups over the weekend with the 338 SIN using my accuracy loads with H-414 powder pushing the 185 Barnes ttsx over 3500 fps. Re-19 is still doing very well with the 225 Cutting Edge bullets around 3160 fps with low velocity spreads. I shot some 4" groups at 600 yards with these loads which is great for a lightweight 24" barrel rifle. I am using one of these loads for caribou in August. Just can't decide which one yet.
