BC extremely wide variance between barrels ??

[jrsandiego12]

Guys - have a question about how a BC could be so different. I am pretty experienced with external ballistics, familiar with many solvers -- AB, Kestrel Elite AB, Ballistic ARC, Hornady. And familiar with all the variables. HERE is the situation - it seems like the BC between two barrels is extreme.

COULD THE BC be .050 higher on one barrel versus another?? Seems extreme. I've done loads to tune ballistics between guns before and the difference was always minimal. So this is surprising to me.

6.5 Creedmoor
LOAD - (same thru both barrels) Hornady 140 ELD Match - new Petersen Brass - CCI 450 primer - 41.0 grains H4350

26" Impact Precision action and M40 profile barrel - fat bastard break. (Have been running this for several years over several barrels) (NF NX-8 4-32 - tracking checked and on)
Muzzle velocity = 2830 fps ES = 4 SD = 2.4 (verified on two Labradars)

22" Bugara medium weight barrel - Area 419 break (Leupold Mark V scope - tracking checked and on)
Muzzle velocity = 2780 fps ES = 16 SD = 8.4 (verified on two labradars)

140 ELD standard G7 BC = .326

846 yards target, white with horizontal waterline - so impacts are easy to spot. Using G7.

IMPACT 26" barrel - calculator called for 6.2 mil elevation (with 11mph 270 degree cross wind) - my typical ELD BC for this bullet has varied on several barrels between .291 - .316. Trajectory validation only need 6.0 mil - so adjusted my BC to .310 - Just as expected. Verified back at 600 yds and perfect ballistic solution.

BUGARA - started with .326 BC - calculator called for 6.03 mil elevation. Impact only required 5.8 mil elevation, occasionally only 5.7. (MV still verified at 2777 - 2785 during these shots. Adjusted BC is .364 - verified back at 600 yds too and very close on the solution - within .1mil.

It seems strange to me that the Bugara barrel (length may have nothing to do with it clearly) is having such a higher BC, significantly higher even than .326 bullet library starting point.

 

[acourvil]

FPS and twist rate will both have an effect on BC. There may also be other differences in the barrel that affect BC, like if one is harder on the jacket of the bullet. .050 seems like a lot, but a bunch of small differences could add up.

 

[jrsandiego12]

Yeah - both barrels are 1:8 twist. Understand that BC differences between barrels arises from varying bullet deformation and rotation. I wonder if one is 4 lands and the other 5 lands. I'll check.

 

[Feniks Technologies]

Keep in mind, velocity is a bigger factor in the 600yd area. So validating at 600 won’t help much with BC.

Barrel shouldn’t give a .050 BC swing.

 

[Feniks Technologies]

What was the temp and elevation?

The true dope data along with your velocity isn’t jiving on any quick software checks I did.