My Berger 7mm hybrid BC test

E

elmerdeer

Guest
Hi guys I bought some berger hybrids 180gr bullets with a G7 BC of .345 and I decided to run some tests on them at semi lomg range 625 yards to see if they would get that BC. I have a Hoover metplat trimmer and poining die, so I sort 150 bullets and there is .002" variance at the ogive, pretty good so far. I start to metplat trim them about .005" and then point them. So if theory is correct I should loose about 2% BC and gain lets say up to 8% BC, so were 5% gain on BC which would bring the BC of this bullet up to G7.362 BC.
Well I shot them out to 625 yards and was low about 1.5 MOA, so I come back look at my speeds from my chrono at 12ft and decide to put a chrono at 200 yards to see what speed I am getting out there. Then I run those numbers with my 2 average velocities and I come up with my ne BC for these 180gr hybrid Bergers and I am a little off Bergers numbers.
The BC I got was .327, so it seems they are not as high as I thought.
Has anyone seen the same thing with these bullets?
But as far as acurracy they are pretty good if I do my part and the conditions are good, i get Half MOA or less at 200yards.
And when I shot at 625yards the bullets went through a quarter inch of steel like it wasnt there. So I think it should be a good hunting bullet. I shoot a 7mm Dakota caliber, Stiller predator action, with a 24.5" Rock barrel 8.73 twist and my load is 74.5grs Retumbo seated .015" off the lands and I am getting 2979 fps avg with low es and sd numbers.
Let me know if what I did was the right, as I am pretty new to long range shooting.
Thanks
Elmer
 
Hey elmer,
I shoot 7dakota also, actually, I'm starting again after a hiatus from 7 and focus on 308 now pretty much perfected so back to my Dakota work. I have a 9 twist heavy contour Lilja on a blueprinted 70 action, using RL22, N560, MagPro, and various custom 185 & 190 VLD's. My best experience with G7's however are slight jam rather than off the the lands. Just thought I'd share that.
 
"My best experience with G7's however are slight jam rather than off the the lands. Just thought I'd share that."

What is G7's I don't understand?
I like Retumbo and RL-25 in my gun. I have a #4 contour and with the Hybrid 180's and Matrix custom 190's I shoot half moa all the way out there>
Elmer
 
You might want (or not) to do a little reading. http://en.wikipedia.org/wiki/Ballistic_coefficient
As you will read in the article that I have given the link to, G7 refers to the model that a bullet is compared to to determine its BC. It is not the difference that distinguishes Berger's VLD bullets from their Hybrid designs. VLDs have secant ogives that tend to make them touchy about seating depth, but are an advantage in that they give high BCs. Tangent ogives are less sensitive as to seating depth. The Hybrid designs incorporate both, tangent where the rifling engraves and secant where it does not. Any long range bullet can be given a BC that is based on the G7 model, secant, tangent, or hybrid.
 
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