<< Previous Topic | Next Topic >>Return to Index  

.22 Pildrivers (part 2 of at least 3)

June 15 2017 at 7:49 PM
gubb33ps  (Login gubb33ps)
YF

A little home-grown BC check at short range for the Piledrivers.

Life suxs with only one working Chronograph. I had two (guess what happened to the "far" one).


So you "work around" the problems and get ther most from what you got (in this case, one working chronograph and 25 yards of clear space to test fire in).

Distances measured as close as possible with a 100 foot steel tape (it's within 1/16 of an inch).

Distacnes measured to the MIDDLE OF THE CHRONOGRAPH (exactly 1/2 way between the screens).

Unregulated rifle, so shots only taken inside the prooved (by previous test) the best possible pressure range (the "sweetest of the sweet spot")....the plateau....the spot where varation between shots is the least over just 5 shots.


So fot first 5 "best of the best" shots were at exactly 1 yard from center of the chronograph:
1 yard distance:
30gr Piledrivers
Average = 660fps
Lowest vel. = 659fps
Highest vel. = 663fps



The moved the chronograph back to 24 yards to chronograph center, refill to the best-of-the-bst sweet spot, and fired another 5 shots.
24 yard distance:

Average = 637fps
Lowest vel. 634fps
Highest vel. = 639fps


Used this calculator:


http://www.pyramydair.com/airgun-resources/widgets/convert.php?BCalc&u=17So

Connecting the FASTEST 1 yard to thew LOWEST 24 yard vel. (not that they DID happen that way, but they COULD have...which is the curse of the one-chronograph-BC-calculation):

663 - 639fps = BC of .0643

Connecting the SLOWEST 1 yard vel to the FASTEST 24 yard vel. (again, the curse of one fucn tioning chronograph)

659 - 639fps = BC of .093

AVERAGING the 5 shots at 1 yard vs averaging the 5 shots at 24 yard:

660 - 637fps = BC of .081



While I was at it, did the same thing with 18.1gr. JSB's.

With this rifle, over just 24 yards of travel, the AVERAGE BC came out to be .037.


That seems a reasonbly VALIDATION of the test process...the 18.1's are pretty ding-dang close to the publihsed/predicted BC.s


I will give you that at closer ranges, the BC's are likely to be a bit LOWER than they are at farther distance. Either of them would likely gain some BC if measured from 24-54 yards.

But unless the pellet "goes stupid" and gets into that ballistic "death spriral" it should stay pretty proportional.


We'll talke about accuracy after I've done some compartive tests with a 1" target as reference.


Lets even it all out at 29 foot pounds (and sure I could manage that with the Beeman Chief test rifle with both pellet weights)>

So well will start the 18.1gr. JHSB (BC .037) at 850fps and the 30gr. Piledriver at 660fps.
Scope height at 1.5" over bore line.
Sight in at 25 yards and projected to 50 yards (pick a ballistic program)

18.1gr. JSB start at 850fps

Arrive at their 25 yard zero at 782fps / 24.6 foot pounds/ zero sight in
Arrive at 50 yards with 721fps / 20.9 fpe/ 2.06" of drop / 1.36' of windage (5mph 90degree wind)


30gr. Piledrivers at 660fps

Arrive at 25 yards with 636fps / 27 foort pounds/ zero sight in
Arrive at 50 yards with 613 fps / 25 foot pounds / -3.8" of drop / .75" of windage ( 5mph 90 degree wind)

SOOO..are the los speed/high BC pellets of any use?

Maybe.


Gravity is one of the constants in life. So if you know the range (or can range-find) whould be able to handle that reasonably will with a mil-dot scope with some preperation (and maybe a drop chart taped to the stock).

So for a 25 yard zero and a 50 yard shot, would give up nearly TWICE THE DROP....(for n about 40%)ain in windage (and energy).

Thats a BAD CHOICE for hunting at odd/ill defind ranges (at leat that this low speed0, but mioght be ueful/ at known ranges;


All of that it "moot" if theaccuracy isn't there, which is what I'll look into just as soon as I can get to 50yards of open range.


    
This message has been edited by gubb33ps on Jun 15, 2017 8:20 PM


 
 Respond to this message   
AuthorReply
JD
(Login JamesDingle777)
AR&P

That's a lot of hard appreciated work Gubb. Hey, besides Chair Gun,

June 16 2017, 8:16 AM 

where can a list of most pellets BC be found? There was a guy doing close up photography and listing all info of pellets; but I haven't seen hide nor hair of that in awhile.

 
 Respond to this message   
BillE.
(Login garczar)
YF12

BC's..................

June 16 2017, 1:15 PM 


 
 Respond to this message   
Miles
(Login Miles_M)
YF12

Personally

June 18 2017, 5:31 AM 

I would not use that BC calclator for a Piledriver shaped projectile. You need to base the BC on a suitable drag law for the Piledriver shape which will not be the same as a drag law shape for a normal pellet and certainly will not be a constant value. That is why a number of different values of BC will be obtained for the different speeds.
The calculator does not take into account any changes in air pressure, temperature etc. or wind speed and direction during the tests all of which can and will affect the values of the calculated BC if you ignore them. It would be better to use Chairgun which gives a choice of reference drag laws and the ability to input the atmospheric conditions.

 
 Respond to this message   
gubb33ps
(Login gubb33ps)
YF

Not a big fan of Chairgun...

June 18 2017, 8:19 AM 

..the older versions were more user friendly, last ones I tried were a bit over complicated for my use...but I'll try the current version.


 
 Respond to this message   
Miles
(Login Miles_M)
YF12

If you use Chairgun

June 19 2017, 3:12 PM 

I would try to use the G1 drag law as being possibly the nearest though even that is not going to be very similar. The nose for the G1 shape is a little too long and it has no boat tail, though I don't believe the boat tail on the Piledriver does very much as it is the wrong shape and angle for the speeds of interest. The thing to remember is if you use the BC you have obtained using the G1 drag law, you need to use the same reference drag law in any calculations using the BC.

 
 Respond to this message   
gubb33ps
(Login gubb33ps)
YF

Doubt it you will...

June 20 2017, 8:16 PM 

..but the real world, measured to the inch, chronograph numbers come up close (within 10%) to reported figures.

Still not a Chair gun fan, even after trying the current version.

You get the urge, can compare the measured speeds(1 yard and 29.5 yards / 89degees F / +5 feet elevation, and use 1.5" over bore line foe both pellets)

 
 Respond to this message   
 
  << Previous Topic | Next Topic >>Return to Index  

Airgun Calculators    Num of fills calc    Capacity Calc

******** Kalibrgun High quality, superb Accuracy, outstanding Value. ********





D I S C L A I M E R
JK's Airgun Forums, moderators, and administrators are not responsible for any problems that may occur from reading or using content posted on this forum, as they are the exclusive responsibility of two parties: the person who posted it and the person who acted on said posted information.Use of our forums by people under 18 years old is allowed only with legal guardian(s) present.