GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: SpiralGroove on September 09, 2019, 07:10:43 AM
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Hey Bob or Lloyd,
We've got an interesting discussion going over on the German Gate, dealing with pellet wind drift.
We're trying to determine whether a regular domed pellet would experience more or less wind drift when comparing standard .177 & .22 caliber pellets - using the same power plant.
For sake of arguments, let's say we have a OEM HW95, shooting .177 cal. at 860 fps while it's .22 counterpart goes 650 fps.
How can Chairgun be doped to calculate this?
Do you have any simple graphs which tell the story?
My basic thought was the higher ballistic coefficient pellet (.22) would experience less drift from the same crosswind. However, does the longer .22 pellet's flight time negate the ballistic coefficient advantage?
Any thoughts or graphics would be appreciated ;),
Kirk
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The BC is the primary consideration in wind drift.... higher velocity may, in fact, hurt.... particularly if over 900 fps.... because the drag increases so quickly in the Transonic region (Mach 0.8-1.2)…. You can do a quick confirmation of this with Chairgun…. My article on wind drift in HAM covers this in detail....
https://hardairmagazine.com/ham-columns/the-external-ballistics-of-diabolo-pellets/
For the velocities you chose, and assuming JSB Express pellets (7.8 gr.in .177 and 14.3 gr. in .22 cal)…. Chairgun calculates a 50 yd. drift for the .177 at 860 fps of 5.5 in.... and for the .22 cal at 650 fps it is 4.65 in.... so a 15% edge in favour of the .22 cal.... The .177 is right in the velocity "sweet spot" at 50 yards, but the .22 cal would benefit from being driven faster.... At 830 fps the drift would drop to 4.09 in.... At equal velocity, the drift is basically inversely proportional to the BC....
Bob
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Hey Bob,
Question:
Can ballistic coefficients for a given pellet change with velocity and therefore change wind drift calculations in Chairgun? Hence, does the BC change for the same pellet over different velocities?
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Some people just make you want to quit, I swear.
Yes I agree, across the board .22 pellets have better bc and do better in the wind. If you include wadcutters, hollowpoints, etc.
Today's top .177 domes meat or beat the .22's on the low end of the power spectrum.
It's been discussed ad nauseum on this very forum, among the HFT crowd. Only explanation they could come up with- demand drives supply, and they gave us superior .177 domes for power restricted countries. And probably HFT.
And for the record I was emotionally attached to the .22 and .25 at the time.
But yeah, that's the german gate thread in a nutshell.
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It depends on how well the shape of the pellet matches the drag model used to calculate the BC.... ChairGun has a model specific to Diabolo pellets called the "GA" drag model, and that is what I used for the above calculations.... The drag model already has the drastic increase in drag in the Transonic region built into it, and while it may not be perfect, it's the best we have at the moment....
Years ago, some calculators used a constant drag model, which up to about 900 fps is not too bad, but over that it is very, very wrong.... drastically underestimating the drag, and hence overestimating the BC.... I think a couple of the BC calculators on airgun sites still use it.... Using such a model will lead to huge errors in the BC, and hence in wind drift calculations, particularly over 900 fps.... Since the GA model is based on the drag vs. velocity curve of a "typical" pellet, it is the best tool we have at the present time.... and IMO good enough to answer questions such as you posed....
Bob
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Bryan, you are absolutely correct, a heavy, well designed .177 pellet can have a better BC than a light (for caliber) .22 pellet.... That is exactly why my answer stated that the BC is the most important factor in determining the wind drift.... However, the OP specified velocities for the two calibers that in a single powerplant (the HW95) precluded that as being the comparison in question.... Had he asked how a 10.4 gr. JSB Heavy pellet in .177 cal, travelling at 750 fps, compared to the other two, the answer would be quite different.... At 50 yards, it would have a drift of 4.17", or 10% LESS than the 14.3 gr. in .22 cal.... However, had the choice in .22 cal been the 18.1 gr. Heavy, with the drift being only 3.95" at 50 yards, it would better any of the other three choices.... despite the MV being only about 580 fps to have similar FPE....
For the record, for a 13 FPE Springer, I prefer .177 cal, shooting a mid-weight (~8.4 gr.) pellet.... for the best balance between trajectory (which is based on velocity) and wind drift (which depends primarily on BC)…. That assumes you can find one your gun likes, as accuracy trumps all, of course....
Bob
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Yes sir.
Very specifically, the argument as I presented it is at a given, lower power level- given the same power level in both calibers- the top .177 domes meet or beat even the best of .22's. Especially 10.3 jsb and 7.9 brown box premiers.
I would bet that, put to the test in the balkpark of 8-10 fpe, all else the same the .177 would have it. Even vs 18.13 jsb or 21.1 barracuda.
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Quite likely.... If the velocity of the .22 is low enough, the drag starts increasing again.... and a 21 gr. pellet at 8 FPE is only 414 fps.... Pellets have the least drag at about 600 fps.... and more either side of that....
In Canada, without a PAL we are restricted to under 500 fps.... however, that gives the ballistics advantage back to the larger calibers.... At 495 fps, a 44.8 gr. JSB is 24 FPE.... but that is no longer an apples to apples comparison, because the velocity is a constant and the FPE varies.... 8)
Bob