Well, boys, out there in .com land I need, or at least want, some ballistic coefficient info. First the rambling.
Today I fire formed two boxes of 7MM STW using 130 grain G.S. Custom H.V. bullets. Two boxes of ammo were taken from the safe. One box was wrapped in a couple of towels and put into an insulated lunch box. The other, with the lid off, was laid on the windshield between the wipers. I’m sure by the time I went fifteen miles to the bank, stopped to mail some “T” shirts and drove back a dozen miles or so to the range the ammo was down to 27 degrees like everything else outside. The 80 grains of IMR7828 were sparked by Federal 215 Magnum primers in Midway bulk cases. The home made muzzle brake
with seven rows of seven holes (.7x7mm diameter) drilled at 2x7 degrees angled back WORKS! The sky screens for the Ohler 33 were centered twelve feet from the muzzle. I was delighted to see the bullet holes at 300 yards dispite the light fog. The 3-15X Sightron II constantly gives me buyer’s congradualtions. The range is about 1,000 elevation. There was heavy overcast with fog limiting visibility to about half a mile.
The room temperature loads averaged 3,568 feet per second. The cold ones surprised me by achieving 3,516 feet per second. It appears one looses about fifty feet per second when the temp drops 45 degrees. Someone wanted to know what the velocity would be at 200 yards so I shot a three shot group at that range then placed the sky screens under the group with the center six feet from the target; or 198 yards from the muzzle. Of the eight cold shots fired at 200 yards, seven gave a reading which averaged 2,958 feet per second. Maybe some of you computer whizzes could calculate the ballistic coefficient from this data. But there is more.
Both 100 yard groups were 2 5/16” above center. The seven shot 200 yard group was 3 3/8” above and the 300 yard four shot group was 9/16” above center. The first shot at 200 yards was about 2” higher than the group. The first shot at 300 yards was 3 ¼” higher than the group. The 200 yard group was fired after about twenty minutes of cooling and the 300 yard group after another half hour. Neither were included in the measurements. The four I did measure at 300 made a 1 3/16” group.
I certainly hope there is enough data to calculate the B.C.