ᗝ BC Test of .25cal Polymag

[JungleShooter]

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.

● Chrono: Caldwell with lights. 1 chrono only, with consecutive velocity measurements.

● Ballistic Calculator: GPC Ballistics:

GPC Ballistics Applications for Windows, MacOS and Linux

A few ballistics applications for Windows, macOS and Linux written in the PureBasic programming language.

gpc.fotosoft.co.uk

➧ 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

 

[Vetmx]

I was curious about the BC of the Polymags. I never needed the actual numbers because you can’t shoot them far enough for it to matter. The accuracy just doesn’t hold up much after 50 yards. I did recently shoot them out of a .25 RPB like I promised. Best accuracy was 880fps. I could shoot them more accurately farther and faster out of a RTI CZ barrel. Thanks for posting.

 

[JungleShooter]

I was curious about the BC of the Polymags. I never needed the actual numbers because you can’t shoot them far enough for it to matter. The accuracy just doesn’t hold up much after 50 yards. I did recently shoot them out of a .25 RPB like I promised. Best accuracy was 880fps. I could shoot them more accurately farther and faster out of a RTI CZ barrel. Thanks for posting.

Thanks for the accuracy velocity of 880fps in the .25cal RPB barrel.

I will try the .22cal in the CZ barrel sometime next month.

Matthias

 

[Vetmx]

I have no experience with a RTI .22 CZ. But a Taipan .22 CZ will shoot a Polymag in the 930’s out past 50 yards with very good hunting accuracy. I shot them out of a .25 RTI CZ at 910fps.

 

[dizzums]

mainly, i like the 'cookie cutter' hole and deep penetration i get from a polymag, expansion and shallow penetration is never what i want from a pellet .. its nice to know precise bc for my apps though thanks ..

 

[18.13]

JSB list them at .027

 

[Long_Shot]

Good job checking for yourself.
Outstanding presentation as always.
Large velocity drop for 55 yards. approx. 140 FPS
Your velocity ES at 50 yards is still about the same. That's good.
140 FPS loss shows how much BC does matter for down range velocity.
You said: "➠ If a HP has a low BC, it will loose velocity rapidly and reach its
non-expansion threshold very close to the muzzle — reducing the HP pellet to a short range projectile. "

Not necessarily apples to apples here.
But, a higher BC does make a big difference in velocity at POI
just as you pointed out.

Recently tested a .25 cal. 48 gr. HP slug as a comparison here.
5 shots ea. Shooting any more than 5 gets too redundant.
Average: 887 FPS @ 1 yard - 3 FPS ES
Average: 806 FPS @ 100 yards - 4 FPS ES

Keep testing, and don't shoot the chrony.............