A bit of an unusual happening this weekend I'm at a loss to explain and hope maybe someone here can explain.
Some background on the gun and ammo. Rifle is a custom Ruger No. 1 using a 1-16 twist stainless Shilen barrel, 24" length. Scope is a 2.5-5x Leupold Vari X III. Velocities were measured with a Chrony instrument places 10' in front of the muzzle. Ammo was made in Starline new brass, Hornady 200 gr RN, Rem 7 1/2 primers and powder was IMR 4227 and RE-7.
I took the loads from Hornady 7th edition for a 10" TC Contender. Charge #1 was 18.0 gr IMR 4227 with a velocity shown for the TC as 1450 fps. Charge #2 was 25.0 gr RE-7 for a TC velocity of 1550 fps.
Now the mystery......
Chrony velocity data for RE-7 was average 1815 fps for 6 shots or a velocity INCREASE of 265 fps. But, when I ran the IMR 4227 load the velocity was only 1410 fps or roughly 40 fps BELOW the 10" TC data.
What?? That's a first for me where 24" data was below 10" data. Before you wonder on charge weights, each load was hand weighed and the scale confirmed prior to throwing charges.
Ideas? Comments?
Some background on the gun and ammo. Rifle is a custom Ruger No. 1 using a 1-16 twist stainless Shilen barrel, 24" length. Scope is a 2.5-5x Leupold Vari X III. Velocities were measured with a Chrony instrument places 10' in front of the muzzle. Ammo was made in Starline new brass, Hornady 200 gr RN, Rem 7 1/2 primers and powder was IMR 4227 and RE-7.
I took the loads from Hornady 7th edition for a 10" TC Contender. Charge #1 was 18.0 gr IMR 4227 with a velocity shown for the TC as 1450 fps. Charge #2 was 25.0 gr RE-7 for a TC velocity of 1550 fps.
Now the mystery......
Chrony velocity data for RE-7 was average 1815 fps for 6 shots or a velocity INCREASE of 265 fps. But, when I ran the IMR 4227 load the velocity was only 1410 fps or roughly 40 fps BELOW the 10" TC data.
What?? That's a first for me where 24" data was below 10" data. Before you wonder on charge weights, each load was hand weighed and the scale confirmed prior to throwing charges.
Ideas? Comments?