Home Forums Hunting & Shooting Ask The Gunwriters unusually flat trajectory with just one load in a particular rifle????

Ed,

While for many years most bullet companies calculated BC's, partly due to the very reason you suggested, many are switching to actually shooting them under controlled conditions. So it depends on the company.

On the other hand, recent research by Bryan Litz indicates the actual BC varies more to rifling twist than was previously believed. Actually, until fairly recently a lot of shooters felt too much twist "over-stabilized" a bullet, reducing BC, by Litz's research (involving actual shooting) indicates that over-stabilizing actually increases BC up to a certain point.

Litz's shooting essentially shows Hornady's listed BC for the 7mm 175 Spire Point Spire is spot-on, but I don't think he's tested the 150 TTSX. As noted earlier, however, I doubt its BC is the .450 Barnes lists. Among other things, Nosler's listed BC's are pretty good, and they claim .435 for the 150-grain Ballistic Tip, a noticeably sleeker bullet than the 150 TTSX. And Berger's BC (derived from Litz tests) for the .30 150 VLD is similar.

I don't know if this is what's in play here, but in the history of long range shooting, there is a phenomenon known as "compensation" where a barrel whipped differently for different loads, and released bullets at different initial trajectories. The Enfield with it's flexy rear locking action was one such rifle, and companies such as Fulton of Bisley (not Fulton Armory in the US) would "regulate" Enfields to allow rounds to converge at the desired range (generally 800-1000 yards). The standard barrel M14 was another rifle documented to "compensate" (though to a lesser degree than the Enfield).

My guess is if you play with BC's in JBM, you won't see the POI differences the OP is showing. I'd bet other than BC.

Tested BC is a reliable predictor of bullet performance, and inaccurate measurements and haphazard testing does not affect BC or how the bullet actually performs.