Home Forums Hunting & Shooting Hunting Rifles 6.5's by the numbers

I am closely acquainted with the people who run two of the major piezo labs, which do the pressure testing for most of the handloading powders sold in the U.S. In answer to question with a slightly different context, they told me a couple of years ago that powder capacity is THE factor in how much velocity in possible in two cases of the same caliber, loaded to the same pressure.

I specifically asked whether they'd ever found any of the magic velocity some cartridge developers claim due to shoulder angle, or how long or short a case might be. The answers from both places were an emphatic no--both adding the detail that the only factor in potential velocity is powder capacity, everything else being equal. The corollary would be that larger capacity does NOT result in less velocity when cases of the same caliber are loaded to the same pressure, regardless of case shape.

Both of those labs have been running "experiments" along those lines for many years, with state of the art pressure equipment.

That's what I paid for mine a few weeks back. Can't hardly say 'no' to that!

Have you shot yours yet? If so, how did it do?

MZ5,

The reason one of the labs publishes CUP and PSI data side-by-side isn't because they're ignorant of the differences, but because SAAMI decided a few years ago to switch entirely to electronic PSI data. But so many new powders, cartridges and bullets appear constantly that pressure labs can't just retest everything in a month or two, since they're kept very busy just keeping up with new stuff. So they continue publish the CUP data, because it's still valid, even if the numbers are different.

Yes, different powders will result in different velocities in different cartridges, often enough that a "perfect" powder for a smaller round may result in slightly higher velocities than for a larger round. But that's basic stuff--that may change next week when another new powder appears that allows much higher velocities from the larger cartridge.

However, we were not discussing such powder-induced differences, but the basic overall trend in case capacity. Limited tests can also be influenced by individual barrels, which definitely can allow a smaller cartridge to reach higher velocities than a larger cartridge, but the millions of rounds and thousands of barrels used by big pressure labs would tend to even that out. Plus, there are so many powders these days that any specific advantage of one powder in a certain cartridge would almost certainly be eliminated by testing a wide variety of powders.

But since you apparently won't accept the results of two major professional labs, I'll note that Charlie Sisk, the well-known gunsmith, and I have performed quite a few experiments with his Pressure Trace that so far have confirmed their conclusions. These included rechambering the SAME barrel to different cartridges, to see what difference in pressure might result.

This was relatively easily done since Charlie's shop includes an indoor, air-conditioned benchrest room where pressure-testing (and shooting targets on an indoor 100-yard range) can be done in a controlled environment, only a few feet from his loading bench. The results of some of these tests have already been published, so I'm not going to repeat such "musings" here, but it would be relatively easy to run such test with same barrel first chambered in 6.5 Creedmoor, then rechambered to 6.5x55. However, I'm not particularly interested, since due to both the conclusions of the big labs and our own experiments, I'm sure what the results would be--and I'm sure Charlie is too.

My Howa 1500 in 6.5x55 has a long throat, so there is a bit of freebore with lighter bullets. I shoots good, but not as good as its brothers in 6.5 Creedmoor. I like the 140 grain BT and/or Partition over H4895 in my Remington 700 Classic and Winchester/USRA 70 Fwt, but haven't found the sweet spot for the Howa yet.

That .30-06 blend ain't that bad in a .30-06....

My money went for a 6.5-06AI.

130 Scirocco II, 3161fps with IMR 7828SSC
140g BT, 3075fps with Hodgdon H100V.