BC Test of .25cal Polymag
Well, I'm finally getting serious in measuring and documenting BC numbers — especially for projectiles where few BC numbers are out there.
But first:
Why is the BC of the Polymag so important?
● We shoot hollow points (HP) because we want them to expand.
But HP do not expand if their impact velocity (IV) is too slow.
I have a lot more testing to do, but usually above 750fps IV many HP expand well in animal flesh and 10% ballistic gel.
➠ If a HP has a low BC, it will loose velocity rapidly and reach its non-expansion threshhold very close to the muzzle — reducing the HP pellet to a short range projectile.
PREVIOUS BC TESTS
ᗝ BC (GA) 0.026 — with the eye watering muzzle velocity of 1372fps down to 740fps @90y (though only 1 shot, Labradar)
ᗝ BC (GA) 0.029 — MV 913fps to 30y (10 shot average, Labradar)
MY TEST
ᗝ Projectile: .25cal JSB Polymag
26.00gr
Gun: RTI Prophet 2 Compact Performance
▪Barrel: RPB, 1:20" twist, very lightly choked, 510mm (=20")
▪REG 130bar
𖣠 Range to Target: 50m (55y)
Atmospheric conditions: Outdoors, light swirling winds, 1002mB local, 30⁰C, 65% Hum.
● Chrony: Caldwell with lights. 1 chrony only, with consecutive velocity measurements.
● Ballistic Calculator: GPC Ballistics:
[URL unfurl="true"] https://gpc.fotosoft.co.uk/ [/URL]
➧ V @0m = ∅ 955fps (52.6FPE)
10 shots: 962, 959, 959, 953, 959, 950, 950, 953, 954, 952, 951.
➧➧ V @50m = ∅ 709fps (29.0FPE)
7 shots: 703, 710, 714, 708, 712, 710, 706.
➧➧➧ RESULT:
BC (GA) = 0.0239 ≈ 0.024
Comments:
This is disappointingly low for a 26 grainer, also considering the test results of others.
Even if — through an error — my actual V @50m would have been 15fps faster (724fps), the BC still would only have been 0.026.
Matthias
