Some Ballistics Comparisons

[MicErs]

Idle hands and all of that.


I've compared the ballistics of a .308 165gr SPBT at 2750 fps muzzle velocity to the ballistics of my four springers with their favorite pellet.  I modeled the .308 over 1000 yards with an optimal zero setup for a 10" kill zone.  I modeled the pellets over 100 yards with an optimal zero setup for a 1" kill zone.  Wind is 5 mph full value.


First picture is a the .308,
second d460 .22 shooting JSB exact 18 grain heavies at 712 fps (~21 fpe)
third d48 .22 shooting JSB 16 grain at 635 fps (~14 fpe)
fourth is d350 .177 shooting Kodiaks at 954 fps (~21 fpe)
fifth is d36 .177 shooting H&N FTT at 857 fps (~14 fpe)

At the bottom I've run some of the data through a spread sheet so that I could get some approximations of how these two shooting problems compare and how they differ.  The real nugget is the average differences for all ranges and all rifles.  The average difference in drop in mRads of all pellets in all rifles at 100 yards is about 81% of the drop of a .308 at a thousand yards.  So clearly range estimation requirements scale reasonably well.  The average difference in wind drift in mRads for all pellets in all rifles is about 213 percent of that for the .308 so wind doping is more important for the air rifles.  Time of flight averages about 1/3 of the time of flight for the .308.  The average of the averages is about 123 percent.


I realize this is not a scientific study.  It is just a model to give me some numbers to think about.


I'd say it is just about as hard to shoot a MOA group at 100 yards with an air rifle shooting pellets in the smaller bores as it is to shoot an a MOA group with a .308 at a thousand yards.  Unless it is a springer, then it is probably twice or three times as hard.

[rsterne]

Interesting way of doing the comparison between a high performance PB and a springer.... When I have some time I might do something similar for PCPs.... I usually figure roughly 1/6th the distance is pretty close for a high performance PCP with a good pellet.... 100 yds. vs. 600 yds.... but I have never done it using mRads....

Bob

[Deckard1973]

Thank you for posting that MicErs.
I shoot .308WIN so the comparison is appreciated. 

[rsterne]

I just ran the numbers for my 2560 HPA, which shoots an 18 gr. pellet at 960 fps, and the drop and drift in inches at 100 yards are pretty much identical to the data for your .308 at 400 yards....

Bob

[MicErs]

I just ran the numbers for my 2560 HPA, which shoots an 18 gr. pellet at 960 fps, and the drop and drift in inches at 100 yards are pretty much identical to the data for your .308 at 400 yards....

Bob

That's cool.  Definitely different.  That is likely the JSB exact heavy?  What a great pellet!  I might have made some mistakes in setting things up to be honest.  I did not select a different drag model when I ran the .308 data, probably should have.


Drop and drift in inches? You mean mRads, right?

[rsterne]

Nope, in inches.... at 100 yd. for the 18 gr.JSB Heavy, and your data for the .308 at 400 yd.... so roughly 1/4 that in mRads....

Bob

[MicErs]

Nope, in inches.... at 100 yd. for the 18 gr.JSB Heavy, and your data for the .308 at 400 yd.... so roughly 1/4 that in mRads....

Bob

That makes sense.  It is an HPA gun shooting 250 fps faster than anything I modeled with the same pellet.  So it probably matches up pretty well with a .308 at 400 yards.  Factor in the ease of shooting a PCP and yeah.  Totally down with a 1:4 ratio.  Maybe I should get my Lonestar out and do some shooting to see how it compares with my D460.  It will probably be better.