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sniper · Silver Status Member

ok. what is the formula (there has to be) of fps-fpe @ a given range?? i want to know as far as killing power. i don't hunt (rats don't count) the question is curious to my math brain.

my steroid throws kodiaks @ 715-720 fps for 24 fpe.
my tech 89 throws superdomes (14.5) @ 805-810fps for 21 fpe.

what do these numbers yield (accuracy aside) @ 25-50-100 yards??

pre tune with crappy trigger i've hit a small water bottle easily @around 75 yards with my gamo 440. Question

Amigo · Veteran Member

Sniper:
The easy and numerically accurate way to establish the answers you are after, is to put the chronograph down range at the distances in question.
Even though I might be confident in my accuracy I would put a shield in front of the unit just large enough to protect it and no more.

Give it a try,

Amigo

rsterne · Moderator

According to ChairGun2, the Ballistics Coefficient for .22 Kodiaks is 0.025, and that for .22 SuperDomes is 0.016.... Assuming that those numbers are correct:

Kodiaks @ 24 FPE (muzzle vel = 715 fps)

25 yds = 19 FPE (625 fps)
50 yds = 15 FPE (565 fps)
75 yds = 12 FPE (500 fps)
100 yds = 9 FPE (445 fps)

SuperDomes @ 21 FPE (muzzle vel = 810 fps)

25 yds = 14 FPE (645 fps)
50 yds = 10 FPE (555 fps)
75 yds = 7 FPE (460 fps)
100 yds = 5 FPE (380 fps)

The caculations are pretty complex.... much easier to just download ChairGun2:

http://www.chairgun.com/offset/products.htm

It's free to download and use.... If you like it and want more features you can make a donation to register it.... Wink

Bob

Amigo · Veteran Member

r:

The formula software will give good ballpark figures but does not account for air density. The lighter the projectile, the greater the error with changes in density due to the lessor kinetic energy.

sniper · Silver Status Member

!!!!!!!!!!! this is why i love all of you!!!!!!!!!!!

BIG THANKS!!

fritz · Silver Status Member

You guys are all right, I do agree to just download chairgun however. You can answer alot of ballistics questions yourself with it as I have.

Here are a couple links you may find helpful:

http://www.airgunforum.co.uk/forums/showthread.php?t=280 <pellet weight and BC

http://www.airgunexpo.com/calc/ <many helpful calculators

http://www.chairgun.com/ <need I explain?

rsterne · Moderator

ChairGun2 actually can compensate for air density.... it has inputs for temperature and altitude.... but since I wasn't given those, I couldn't input them.... Rolling Eyes

The biggest variable is Ballistics Coefficient.... they can vary greatly depending on the velocity.... I have never seen a satisfactory explanation of this.... but I have done tests on the same day, with the same Chrony.... at the same ranges (1 yd. and 26 yds).... and found wide variations in BC for the same pellet at 500 fps and 800 fps.... Shocked

That said, it's alot better than guessing.... Laughing

Bob

Jaxom · Senior Member

Some good tips in this thread!!!

I don't mean to hijack this thread, but I've a few questions that I do believe are related.

I've been thinking about getting a chrony to help keep a record of the mods and tweaks I'm doing. I know basically nothing about them other then they measure the speed of the pellet passing through the antenna's. And that's about it.

Can anyone give a brief over view of what makes a good chrony, and what features one should be looking for when selecting one?

Thanks,

Jax

rsterne · Moderator

Check out this site.... pretty well the standard setup in Canada....

http://www.shootingchrony.com/introduction.htm

I understand there is a eBay site with good prices on them if you are in the USA....

Bob

sniper · Silver Status Member

Slavia · Moderator

I got a Chrony F1 from the "bargain cave" at Cabela's (returns) about three years ago for $50.00 U.S.D. It is very, very useful.