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Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by alcesgigas, Jul 5, 2013.
Shooting 30' from my screens what to add to my velocity? Thanks
Post up your enviro, load and gun data and we can easily give you a good number.
Bright sunny 58*F 640' above sea level 66*91mN, 151*W 338 Edge
Berger 300 Hybrid OTM/91.6 H-1000/GM215M/BertramBrass set at 3.880
M70/Hart BR-1000 (1.125-.900) 30"
The way I back calculate actual MV from a chronograph reading is as follows. Set your ballistics software to out put in one yard increments, enter your recorded MV under the shooting conditions, edit the MV value upwards until your measured velocity is shown at the distance you had the chronograph from the muzzle.
I didn't see what velocity you were recording, but with that projectiles advertised BC of 0.419 at say 2949.4 fps recorded on a chronograph 10 yards (30') from the muzzle you would have 2961.0 fps at the muzzle. The atmospherics won't make that much difference to the output when your solution is only 0.1 fps in resolution and mearured over ten yards.
This method is acually very simple to do, just remember to reset your ballistics program or app back to ten yard increments afterwards, or you will end up with very large drop tables
If you go to jbm ballistics and input your numbers and change the "distance to chronograph" box to your distance it will show you your actual muzzle velocity on the trajectory chart if you look down to the drop chart you will see that at 0 yrds your muzzle velocity will be higher than what you put in because of the distance to chrono!! Here is the link: JBM - Calculations - Trajectory
Highest average (three shot groups) was 2892.
Lowest average (three shot groups) was 2861 with 2843 as the lowest speed recorder; 2925 the highest.
I continue to have unusual (for me) experiences with this rifle: With 20* in the base and 20* in the rings I'm sighted in for 100 yards. Cartridge necks are loose; I have to measure each shot at the range. Nosler brass holds up better than Bertram brass. Primers are set to .010 below case head and still once in a while I have to use the priming tool to drive the primer back down so as to fit in the press shell-holder. Last year's dime sized groups are now two inch groups with an occasional one inch group. I worked up loads (above variety) from 88 grains of H-1000 to 91.8 when I encountered tight bolt and lift behavior. Last year the more H-1000 used the slower the bullet and I loaded up to 97.0 with CCI BR-2s in Nosler and RP brass. I'm getting best ES with 91.6 and 3.880 OAL. I've been shooting every other day since mid-June...
It's frustrating, but I'll keep looking for solutions and I appreciate all the responses received.
Since 6/10/2013 171; all but three Bertram Brass. Last year I began shooting as soon as the rifle came together in early August and in spite of the moose season I had 196 rounds down the tube by November 4. I figure it will be anywhere between 350 and 600 rounds before I feel confident enough to shoot game consistently at long range.