Wow
I just got my June issue of Shooting Times Magazine in the mail yesterday. And the 1st article I read was the Night Hawk Long Slide 10mm. First off Bart Skelton talks about the 10mm and how powerful of a round it is and it's been one of his favorite handgun cartridge etc etc so I read the whole article and think, wow this is good press for the 10mm. Until I see that all the loads he shot were ALL on the soft side !!! My gosh not 1 load hit over 1100 fps :'( and that's with a 6" barrel !!
Now my ? is why would someone pay all that $$$$ for a 10mm when all your getting from the factory loads is 40 S&W performance ??? Even the Sig ammo which I have chrono in my Colt and Kimber was really slow and it wasn't slow in my 2 guns. It seems like the Sig ammo is all over the board. What gives ??
Frequently authors in gun rags have to test with the ammo they can get in the timeline the editor sets. It is possible that they didn't have time to find more suitable ammo than what was on the shelves of their Walmart or LGS.
It is frustrating that they didn't plan ahead and have some loads that would really shine in a 6" 10mm. Some Underwood or Buffalo Bore that would clock off a 180 grain at 1350-1400 fps or some 200 grain that reaches 1300 fps in a 6" barrel would be great.
There are lots of things that can influence velocity. Published specs from ammo makers are generally taken from a "reference" barrel. The barrel is carefully cut with minimum chamber and minimum specs in the bore, to a specific length, often 8" for handgun ammo. The testing occurs in a climate controlled environment at a specific temperature, humidity. I would think they would try to test within a certain barometric pressure range as well.
That all said, this results in frustration among un-informed buyers who own a chronograph. Like ballistics gel testing, the goal of this testing is to verify pressure, and to provide a comparison reference between different ammo. In a consumers actual gun, the chamber will not be cut to minimum spec, the rifling may be radically different, the barrel length will almost certainly be shorter, and the temperature and humidity may be different.
I like Kevin at Underwoods practice, at least with some ammo, of publishing the reference velocity, and then "real world" velocity from a specific gun. It would also be nice if he documented temperature, humidity, etc.
My guess here is that the testing Shooting Times did was last November/December/January. It was cold and the test gun had a bit more generous chamber. The result was lower pressure and therefore lower velocity. If the reference testing was at 65°, and your testing at 75° and there testing in Montana in January at 11°, I would expect some significant drops in velocity as a result.