At 3050fps the dasher would need 38gr of 4350 giving 59Kpsi. The 6x47 to get the same speed with the same powder needs 41.5gr at 54Kpsi. I can tell you they will last just as long at that level at best, but the extra powder vs the slightly lower pressure will most likely mean the 6x47 will last a bit shorter. I'm getting 2000-2500 from the 6x47 and got 3000-3500 from the Dasher. I am not shooting soft loads on the 6x47, but that will not account for doubling the barrel life, let alone tripling it.
The only way to get longer barrel life is to select a powder that has less energy, but that will mean more volume of a slower powder, kind of negating things. Avoiding double based powders is the thing that will save barrel life, not so much the larger case. I shot N165 in my 6.5-284s and they lasted 2000 rounds easily at <0.5moa level for f-class.
You refer to the 6.5-284 as being shot "hot" and the 6.5saum as being shot "not as hot". Hot refers to pressure relative to the case. You might have less pressure with the 6.5SAUM, but you are using more powder to compensate for the loss of pressure, and slower powder to spread the pressure and still get the required gas volume for the same speed.
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Rhino: There are more options, no need to call anyone a liar, that is quite a black/white view of matters... it depends on what your expectation for accuracy is, hence the "I believe you're getting 3000 rounds" line. I know people that got 7000 rounds from a PPC barrel, where 1500 is the norm for changing them out. But if you take the same accuracy for both cases, there will not be a difference between the 6.5-284 and 6.5saum in terms of barrel life. This is just like the 6.5 SLR debate that magically doubled barrel life by adding more powder.
PS: My 6.5-284 barrels (and several other shooters here) got 2000-2500 rounds from it before not grouping adequatly anymore for my purpose (<0.5moa). Yet I know people that only got 1200-1500 rounds from theirs, using the same powders etc. I know why there was a difference, time between rounds, and it has nothing to do with more/less powder. I've been wildcatting and shooting BR/F for 15 years, I know when something sounds too good to be true, it always is.