Bob's Boattails for Airguns

[HollowPoint]

if I remember right you were going to shoot this form a magnum springer. The replies you were referring to suggested that the twist rate of your barrel was a problem. I doubt a springer would get a bullet with that much bearing surface and weight to the intended target.

If the slug I was shooting weighed in at the estimated 96 grains that the OP has listed in his graphic, I believe you're absolutely right; out of my springer. They most likely wouldn't even make it all the way down the bore before stopping.

Although they have a pronounced arch to their trajectory, I am able to shoot the 25.4 grain monster pellets accurately enough for rabbit and feral pigeon work out to 50 yards. The estimated weight of my design only came in at 28-point-something grains. (mine were intended to be hollow pointed to bring down the weight) With the power mods I've tested in my springer I'm more than sure that my design would have no problem making it to "The Intended Target." Making it there accurately is something else all together though.

I have shot the sized-down NOE 35 grain cast bullets out of it, indoors; just to see if my Umarex Octane had the balls to get them out the barrel. It seemed to do just fine but, admittedly I was shooting into a ball of old rags, not at any distance or target. When I sized them down, it completely shaved off all the drive-bands so I was essentially shooting a solid slug of lead.

I've acquired another toy to play with for now so I'll look forward to the progress that rsterne achieves with his design. I did have plans to to buy an AirForce Condor with my tax return but I opted to spend it on a new Tikka T3 instead. That's the toy I'm playing with for now.

Incidentally, I think my barrel twist is 1 in 16. I believe that would be plenty of spin to stabilize pellets up to 30 grains out of my gas springer, regardless of what the computer generated calculations estimate.

HollowPoint

[rsterne]

Interesting results.... I take it the "sound barrier" doesn't really exist, and the difficulty in breaking it was a figment of the imagination.... I wonder what Chuck Yeager would think of that.... I guess the "Drag Divergence Mach Number", as shown in the diagram below at about Mach 0.85, doesn't really exist....



I didn't state that the BC decreased by 4-5 fold when you go supersonic, I stated that the drag increased by that amount.... In fact the actual drag increases much more rapidly than the Cd, and to calculate the total drag, you have to multiply the drag coefficient by the square of the velocity.... The G1 Ballistics Model (which has a BC of 1.000) takes into account a drag curve like the one below.... In other words, a bullet is expected to behave like that.... BCs are a measurement of how the bullet being tested compares to the G1 Model....



I have also done quite a bit of velocity testing with diabolo airgun pellets (which admittedly are not bullets), and I have found that the BC drops off rapidly as you exceed a certain velocity.... That actual speed depends on the shape of the pellet, and a wadcutter starts it's decrease in BC at about 700 fps, whereas a round-nosed pellet starts a drastic decrease in BC at around 850-950 fps depending on the SD, with heavier pellets closer to the higher figure.... I have numerous measurements that show a BC in the 0.04 range up to about 900 fps, dropping to 0.02 by 1050 fps, and down to about 0.01 at Mach 1.... Those are done by measuring the muzzle velocity and the downrange velocity with a Chrony, and then calculating the BC....

I have very little experience with cast bullets, nor have I done any velocity measurements downrange to test the numbers predicted by the calculator (yet).... I wouldn't be at all surprised that the actual BC is lower than calculated.... However, considering the credentials of the author of the program, Robert McCoy, and the fact that the program has been checked for accuracy at the Aberdeen Proving Grounds, I feel it is a worthwhile tool.... The bullet maker Sierra must trust his work, as they list his .22 rimfire BCs on their website.... http://www.exteriorballistics.com/eb.../22rimfire.cfm .... Note that just between 905 fps and 1047 fps the BC drops by about 25%....

I fully understand that airguns are looked at as toys by the majority of the PB community.... so rather than continue to argue the point with no measured BCs to provide, I'll just let the thread die.... Thanks to all for your comments....

Bob

[HollowPoint]

Threads come and go. Even if you had all the data to prove all your points there would still be those well meaning souls just chomping at the bit to inform you otherwise.

Let the thread die but, please keep the project alive. At PCP velocities, the possibility for success is much greater than those of present day Gas Spring velocities; although I do believe that may change given enough time. The need for more efficient projectiles in both Air Rifle designs will never change.

Give them hell Bob; and thanks for posting your idea.

HollowPoint

[GARD72977]

Do not misunderstand my post. I think rsterne is making a case for why his bullets will work. I like the idea and will follow this thread. Your post puts you in the same situation that rsterne and that is not the case.

[K.O.]

http://www.gatewaytoairguns.org/GTA/...?topic=96713.0

[Tom_et]

Just a thought?
You inventors should try a sabot that does not separate in flight
using a bb or similar

[rsterne]

Not sure what would be the point?.... If the goal is to reach a higher velocity from lighter weight for a given caliber, then you will sacrifice Ballistics Coefficient for exactly the same reason.... While there is a practical limit on the Sectional Density for any give air pressure and barrel length, a sabot that doesn't separate would have a low SD, and hence a low BC, throughout its flight.... losing velocity and energy too rapidly to be useful, IMO....

Bob

[LongRangeAir]

For all the Nay Sayers out there, Rstern's design, just won 1st and 2nd place at the Extreme Bench Rest comp In Arizona. A 200 yard match for high power AirGuns!

As far as whether an AG can shoot Sub MOA regularly or not, LOL, seems many are ignorant here of what is going on in AG's these days. On a good day, I can shoot that at 200. yards. And usually under!

A fellow who use to frequent here, shot long range with Sharps for years. He stated that at 200 yard, and under, his High Power Air Gun was more accurate than the Sharps. (He won a LOT of Comp's with his Sharps, including his State Championship) He managed to shoot Pepsi cans at 600 yards with his .257 J. Haley Air Gun.

My custom .257 built on a Cheap Air Force Frame will shoot 1/2 to 3/4" at 100 yards all day long. And often, well under 3/8" for five shots.

Say that under MOA on a regular basis isn't what an ag can do? No, what it can and does do, is every once in a while, it will shoot under one tenth MOA or less, as in .009". THAT is what it does on a NON Regular basis. Best Group to date was .027". This is far beyond what a typical .22 long rifle can do, and it does it at 200 fpe. In the world of High Power AG's, it's a light weight!

For plinking fun, I shoot PB hulls off a perch at 100 yards. Shot gun hulls? Nope, .22lr hulls. And have run many a 10 for 10 at that range! Show me a .22 long rifle Powder Burner that can do that! And I'm pushing a Lot more Energy, and enjoying casting for it. Where .22 LR is hard to come by now days, With casting and reclaiming my lead, I shoot darn near for free! Well, except for the RCBS Pro Melt, and NOE Molds. LOL!!!

Knife

[HollowPoint]

This only verifies what I've believed for some time now. I knew it would work.

How did I know?

Because; unlike some of the arm-chair-experts we encounter in some of these chat forums, I
(and many others; like rsterne) actually take the time to do the designing and testing.

A similar phenomenon also occurred when I posted a subject on Boat-Tailed Gas-Checks placed on Boat-Tailed
cast bullets. I got them to work and outlined how I did it but it only received mild interest. It's only recently
that others with a greater post-count and more recognizable name within this cast bullet forum have started mentioning
this same subject of Boat-Tails that it seems to be more plausible to us all.

No matter; as long as we move forward with our dreams and designs. If we stagnate, we loose interest
and loose out on what could have been.

For the most part, I quit posting my ideas because there always seem to be those well meaning souls who's life mission is to
stifle creativity as politely and courteously as possible.

Congrats to the guy who proved the validity of the guys who came across as invalid to so many.

HollowPoint

[LongRangeAir]

Yep! See a LOT of that!

The greatest minds in History have all been plagued with the short shortsightedness of others. (Know-it-All's). LOL

[PAT303]

I find your results staggering,my absolute hats off to all of you,brilliant work. Pat