Beginner Help Needed

[BCMEAG]

Just started getting into shooting bolt guns and ran into something that doesn't make sense to me. Hoping more knowledgeable people can help me out.

The guns and ammo are:

Bergara HMR-14, 6.5 Creedmoor, 22 inch barrel, shooting 140 grain Sig
Bergara B-14, 6.5 Creedmoor, 22 inch barrel, shooting 140 grain Nosler Ballistic Tip

At 200 yards the HMR has about a 2 inch bullet drop and the B-14 has about a 6 inch bullet drop. At 300 yards the HMR has about a 10 inch bullet drop and the B-14 has about a 24 inch bullet drop.

Does this make sense to have guns in the same caliber, same barrel length, and same bullet weight to vary this much? The HMR at 400 yards has about the same bullet drop as the B-14 at 300 yards.

Thanks

[davsel]

Velocities the same?
Optic heights (center of barrel to center of optic) the same?

[BCMEAG]

The velocities are the same on the ammo boxes, I don't have a chrono. The center of the optic on the HMR is about 1/2 inch higher than on the B-14. Thanks

[Gman]

I'm a little confused. When I look at Bergara's lineup, B-14 is an entire series of rifles.

The B-14 HMR I understand (can't find an "HMR-14"). Your second rifle, "B-14", I have no idea what that is.

Do the bullets have the same ballistic coefficient? Are the rifles zeroed identically? Same rifling twist rates?

ETA: Looked further:

The Sig ammo appears to use a Sierra MatchKing hollow-point bullet, made for precision shooting. BC - 0.535

The Nosler Ballistic Tip is an expanding bullet used for hunting. BC - 0.509

Have you tried switching ammo in the rifles to see if they're close using the same ammo?

[CS1983]

If you swap the ammo, does the inverse happen where the flatter shooting rifle is now the less flat shooting rifle?

[VDW]

I’m on my phone, but try using your posted velocity from the box and punch the BCs posted by Gman into an online ballistics calculator to see if the difference in the two bullets roughly corresponds to what you’re seeing on the range. When it comes to long range shooting, the same bullet weight with different aerodynamics can have vastly different down range performance. Also, don’t get too hung up on a company’s claimed BC, as there are probably millions of threads online about the validity of those. Real world performance is what is important, but it should give you a rough idea.

[Gman]

Also, don’t get too hung up on a company’s claimed BC, as there are probably millions of threads online about the validity of those. Real world performance is what is important, but it should give you a rough idea.

From what I was reading on the Internet (which is always true), the BCs also vary relative to velocity.

So many variables.

[BCMEAG]

One is the Bergara B-14 HMR and the other is a Bergara B-14 Hunter. Same twist rates 1:8. I have not tried switching the ammo.

[Gman]

One is the Bergara B-14 HMR and the other is a Bergara B-14 Hunter. Same twist rates 1:8. I have not tried switching the ammo.

Those rifles both have the same 1:8 twist, although the Hunter has a different barrel taper. Who wants to carry a heavy rifle while you're hunting, right? The barrel harmonics may be different between the rifles.

I'm still curious what happens when you try the same ammo in both rifles.

[VDW]

You need a chrono to verify, but CS1983’s suggestion should give you a good idea. If both rifles have the same drop using the same ammo, then the difference is likely from a difference in velocity and BCs in the two ammo types. I have some rifles with the same chambering and barrel length that shoot 100+ fps different with the exact same ammo. The difference comes from a difference in the tightness of the chamber and/or rifling between the two rifles.