Planning to run out and shoot my first 22 NRL club match in the morning. I have cases of this old Gemtech 22 Subsonic 42 grain ammo and trying to find a BC (ballistic coefficient) to get started. Not even finding any 42 grain rounds in any of my apps or kestrel that list a 42 grain projectile for reference. Has anyone used this ammo for an NRL style match and have a starting point? This ammo seems fine in the Kidd Supergrade I will be shooting but tomorrow is going to be a dash to the range, zero the scope and get velocity so will be a busy morning shooting a new match with a new club. Getting this figured would be one less thing to resolve in the morning.
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Gemtech 42 grain Silencer Subsonic BC?
- Thread starter Texascbr
- Start date
You will need to calibrate your Kestrel to the real world ballistics of your gun and ammo. To do that, you need bore over height for the optic, actual muzzle velocity, a zero distance (at say 50 yards), and then what you have to dial to make it shoot another distance (say 100 yards). Then you go into the Kestrel put all that data in and adjust the BC so it matches what you dial for point of aim at 100.
Edit add: For instance, on my Vudoo, Bore over Height is 1.95", MV 1082 (SK PM), zero at 50 yards, dial 1.8 mil for POA 100 yards, DM is G1, and I adjusted BC to 0.157 to "calibrate" my Kestrel. I've compared that to what other people got out of their chronograph #s and similar ammo, near identical rifle, and random target distances reveal that our Kestrels are both spitting out the same answer.
Edit add: For instance, on my Vudoo, Bore over Height is 1.95", MV 1082 (SK PM), zero at 50 yards, dial 1.8 mil for POA 100 yards, DM is G1, and I adjusted BC to 0.157 to "calibrate" my Kestrel. I've compared that to what other people got out of their chronograph #s and similar ammo, near identical rifle, and random target distances reveal that our Kestrels are both spitting out the same answer.
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Then what is it? Since you seem to know what it isn't, that would mean you know what it is...please share with the group.
Update: I spent 3 minutes on Google and found it...from the 2019 Gemtech Catalog, the BC is 0.120. Sectional Density is 0.120, fps is 1,050.
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Please go back and read my first response in this thread. BC calculation from the manufacturer isn't the same as what you will see in the wild.
The BC ammo makers "publish" is unlikely to line up with what a random rifle does. They use a very specific chamber, who knows what that is; a very specific barrel/length, who knows what that is? Button rifling, single cut rifling, who knows what they use for the testing?
I was expecting it to be within a few thousands (0.001) or so, for my Vudoo it is more than 3 hundredths (0.157).
