Author Topic: Whats the Science behind shooting heavier projectiles? (like .247, .30, .357) (Read 12724 times))

zandrew · « **on:** October 16, 2015, 07:05:01 PM »

I have been throwing the idea around in my head for some time about adapting a larger caliber to my Airforce talon and seeing what can be done. I would love to be able to shoot accurately at longer ranges. I like the .257 but I am really interested in seeing what can be done in a .223 with say 50 grain projectile. I figure the lighter weight would be easier to get going fast enough to travel further more accurately. At the same time I am not trying to reinvent the wheel.

I am interested in any info regarding this topic.

Motorhead · « **Reply #1 on:** October 16, 2015, 07:28:57 PM »

With the smaller calibers like .22 ( .223 ) the limited area for air to work against limits power to some degree.
Larger calibers are more efficient in harnessing the same pressure to make more energy.
Being were still shooting +/- the transonic speed range ideally 950 or less .... You will find MUCH MORE power potential with larger diameter and heavier weights so long as rifles valving can provide sufficient air volume while maintaining reasonably short dwell time.

JMO,
Scott

zandrew · « **Reply #2 on:** October 16, 2015, 09:20:05 PM »

Quote from: Motorhead on October 16, 2015, 07:28:57 PM

With the smaller calibers like .22 ( .223 ) the limited area for air to work against limits power to some degree.
Larger calibers are more efficient in harnessing the same pressure to make more energy.
Being were still shooting +/- the transonic speed range ideally 950 or less .... You will find MUCH MORE power potential with larger diameter and heavier weights so long as rifles valving can provide sufficient air volume while maintaining reasonably short dwell time.

JMO,
Scott

I am wanting to shoot paper strictly so I have no need for energy. I am strictly looking for accuracy and hopefully distance. Thats my interest in the smaller .223.

Motorhead · « **Reply #3 on:** October 16, 2015, 09:25:18 PM »

Quote from: zandrew on October 16, 2015, 09:20:05 PM

Quote from: Motorhead on October 16, 2015, 07:28:57 PM
With the smaller calibers like .22 ( .223 ) the limited area for air to work against limits power to some degree.
Larger calibers are more efficient in harnessing the same pressure to make more energy.
Being were still shooting +/- the transonic speed range ideally 950 or less .... You will find MUCH MORE power potential with larger diameter and heavier weights so long as rifles valving can provide sufficient air volume while maintaining reasonably short dwell time.

JMO,
Scott

I am wanting to shoot paper strictly so I have no need for energy. I am strictly looking for accuracy and hopefully distance. Thats my interest in the smaller .223.

Plenty to read on the GTA about pellet BC / Velocity / what required for best accuracy.
You start shooting LONG & Heavy .22 cal stuff the barrel twist rate changes up making specialty barrels a go too for the serious target shooter.

Good Luck

rsterne · « **Reply #4 on:** October 17, 2015, 01:06:01 AM »

The practical limit is about 950 fps, above that the wind drift increases dramatically.... That works out to 2 FPE per grain of bullet weight, so power is a no-brainer, the bigger the better.... Now you don't need power, so the smaller calibers appear attractive, but for a given projectile shape, the Sectional Density, and hence the Ballistics Coefficient, are proportional to the caliber.... So, in terms of reducing wind drift, once again bigger is better.... There is one thing where the smaller calibers have an edge, and that is the other side of the SD issue.... For any given pressure and barrel length, there is a maximum SD to reach 950 fps, and when you hold the SD constant, bullets in larger calibers get shorter and fatter, and hence have more drag.... This swings the balance back towards the smaller calibers again when you are trying to fight the wind....

Bottom line, if you really want to fight the wind, you need high pressure and a long barrel, to drive the SD to the maximum.... because BC is proportional to SD.... The caliber is secondary, to a large extent.... but the one that gets the most attention, and has the best overall results at long range, is currently the .257.... That is where I would put my effort....

Bob

zandrew · « **Reply #5 on:** October 17, 2015, 02:51:45 AM »

Quote from: rsterne on October 17, 2015, 01:06:01 AM

The practical limit is about 950 fps, above that the wind drift increases dramatically.... That works out to 2 FPE per grain of bullet weight, so power is a no-brainer, the bigger the better.... Now you don't need power, so the smaller calibers appear attractive, but for a given projectile shape, the Sectional Density, and hence the Ballistics Coefficient, are proportional to the caliber.... So, in terms of reducing wind drift, once again bigger is better.... There is one thing where the smaller calibers have an edge, and that is the other side of the SD issue.... For any given pressure and barrel length, there is a maximum SD to reach 950 fps, and when you hold the SD constant, bullets in larger calibers get shorter and fatter, and hence have more drag.... This swings the balance back towards the smaller calibers again when you are trying to fight the wind....

Bottom line, if you really want to fight the wind, you need high pressure and a long barrel, to drive the SD to the maximum.... because BC is proportional to SD.... The caliber is secondary, to a large extent.... but the one that gets the most attention, and has the best overall results at long range, is currently the .257.... That is where I would put my effort....

Bob

I figured there was a good reason the .257 is the hot ticket. Since we have established there is no logical reason to deviate from the known caliber whats the logic behind twist rate and more importantly grooves and lands? My understanding is that heavier grain bullets like slower twist rate. Why I do not know but that is what I have come across in my research.

I guess I am attracted to the lighter grains since you can accelerate them easier.

Motorhead · « **Reply #6 on:** October 17, 2015, 02:58:28 AM »

Quote

I guess I am attracted to the lighter grains since you can accelerate them easier.

It is a two way street, low mass & weight gets up to speed quickly ... tho also slows down quickly.
Thus the "BC" issue we so frequently speak of.

Sectional density as Bob speaks of above is well worth wrapping your head around, as it is key in long range shooting no matter what launches said bullet / pellet.

39M · « **Reply #7 on:** October 17, 2015, 04:24:26 AM »

Funny thing about Sectional Density. Doesn't matter if it's a round ball, a wadcutter, or a pointed pellet, if they're all the same caliber and all the same weight, they'll all have the same SD. But the pointed bullet would normally have a higher BC thanks to the lower wind resistance built into it's shape.

PakProtector · « **Reply #8 on:** October 17, 2015, 08:01:40 PM »

hey-Hey!!!,
I have a .224 boolit-shooting Marauder. The barrel is a .224/.219 liner from TJ's. It measures on the small side( .2234/.218 ) and thus will want sized boolits if they're to avoid large drag. I just got a mold from Lee. With soft alloy, they weigh 56 gr( 55 quoted by Lee ). They have a bore riding section of the nose that gets a fine bit of rifling engraved on them...but they'll be needing a 3k fill to move properly.

39-40 gr is much easier to deal with, and from published BC of 40 gr rimfire bullets traveling at 1080 fps around .095..slowing them down to 950 probably bumps them to a bit over .1. That is still huge compared to pellets. the best of them, the King Heavy sports a BC of ~.05...

cheers,
Douglas

rsterne · « **Reply #9 on:** October 17, 2015, 08:05:14 PM »

Actually, a roundball will have a different SD in every caliber, and in fact proportional to the caliber.... The BC is the SD divided by the "Form Factor", which is lower for bullets with less drag.... So, yes, a Spitzer can have less drag, although the difference when subsonic is not as great as you might think.... The largest portion of the drag when subsonic is the base drag, which is why I have been working so hard on boattails for airguns.... At our velocities, the back of the bullet is MUCH more important than the front.... but the SD is CRITICAL to improving the BC....

As far as twist rate is concerned, the longer the bullet (for a given caliber) the FASTER you need to spin it (shorter twist rate).... and heavier bullets (for a given caliber) are generally longer.... so need a faster twist, not slower....

Bob

39M · « **Reply #10 on:** October 17, 2015, 11:14:05 PM »

Yes, a round ball could be a different SD for every caliber.

What I meant was that a 15.43 grain .22 caliber round ball will have the same SD as any other .22 projectile with a weight of 15.43 grains, no matter the shape.
Or, for any given caliber all projectiles of the same weight will have the same SD no matter the length, shape or the BC.

A boattail pellet with a high BC is a great idea. I think I have seen these, but I can't remember what company was making them.

rsterne · « **Reply #11 on:** October 18, 2015, 01:29:43 PM »

I think you are referring to the Prometheus Piledriver pellet.... I am working on cast boattail bullets for high powered PCPs.... Search "Whiteout" on the GTA....

Bob

grimeszee · « **Reply #12 on:** October 18, 2015, 01:52:00 PM »

H+N PYLE DRIVER .177 21 grain sold at PA

39M · « **Reply #13 on:** October 18, 2015, 02:46:29 PM »

Yes sir, that's the one. I considered that what I was aluding to might be off topic.
And I see the Whiteout uses heavier bullets than I had considered. But I had kind of switched my train of thought towards heavier bullets in 6mm and up.
Granted, I'm not well versed in big bore air rifles, but it would seem that similar principles would apply. Unless pressures prevent their use, a flow through bolt that directs air away from the boat tail and towards the center of the projectile could be advantageous. What I would invision for a large caliber long range air rifle projectile would be a hollow base boat tail with a fast taper hollow point tip similar in appearance to a blend of the Sierra GK and SMK.
I had considered a kind of a wide wasp waist with land width in between groove width rings just behind the tip and at the leading edge of the boat tail, but this design would lower the BC in my guestimation.
Or a more conventional design similar to the Lapua FMJ S, which curiously has a hollow base of sorts.

When talk swings towards SD and BC, it seems the 6.5 is always in the conversation. But I don't see any reference to it concerning air rifles. Fast twist barrels are prevalent here, and high SD and BC are achieved with relatively lightweight conventional bullets. A 110 to 115 grain bullet/pellet in 6.5 should be in the range of a 155g .308 SD, and high BC is the norm in 6.5

rsterne · « **Reply #14 on:** October 18, 2015, 03:48:19 PM »

Airguns are only just beginning to push the limits of SD, and there is good reason for that.... The higher the SD the more barrel length and pressure you need to drive it at a decent velocity.... If you want to reach 950 fps, and you have a PCP with a 24" barrel running 3000 psi, forget about anything with an SD over 0.17, you just won't make it.... For an SD of 0.25, you need about a 30" barrel and 3600 psi to get into the mid 900s.... and even then it better be a POTENT gun to have a chance of doing it (using air)....

As far as reaching the maximum potential in an caliber, a flow-through bolt will never do it, there is too much restriction in the port area, you need full bore-sized porting to get to the above numbers.... I use a retracting bolt with a square nose that seats the bullet past the port and then retracts completely out of the airflow.... The other suitable method is an axial flow design, like a Condor....

Bob

39M · « **Reply #15 on:** October 18, 2015, 04:41:59 PM »

I see. So low SD/high BC could be the way to go with a more conventional air rifle that doesn't have extreme pressures or super long barrel?
Maybe something like the Crosman Powershot is worth looking into, with it's long plastic base. Or an all lead pellet with a long hollow skirt to keep BC up and weight/SD down.
In .308, a 110 grain is about the max weight to keep SD below .17, and in a conventional solid base spritzer only gets about .260 BC. A long hollow base and possibly plastic tip could raise BC and keep SD at a minimum.

K.O. · « **Reply #16 on:** October 18, 2015, 07:29:37 PM »

There is a very close relationship between S.D. and B.C. so no that will not work, as you drop weight so you drop S.D./B.C...

I think the best that can be done for more normal power levels is to shorten the round as much as possible while keeping as much of the boattail as possible...

39M · « **Reply #17 on:** October 18, 2015, 08:09:18 PM »

From my limited experience, bullets with equal SD can vary quite a bit in BC.
While SD is in the equation for calculating BC, the shape of the projectile plays a heavy role in BC.
A clear example is the difference between two different designs of 175 grain .284 bullets. Both have an SD of .310, as do all 175 grain .284 projectiles. But the differences in the BC of the 175 gr Hornady Interlock RN(.285 BC) and the 175gr Berger XLD(.658 BC) vary wildly.

K.O. · « **Reply #18 on:** October 18, 2015, 08:51:57 PM »

yep but those are supersonic rounds... so the Form factor will play a much bigger role...

http://www.gatewaytoairguns.org/GTA/index.php?topic=70470.0

K.O. · « **Reply #19 on:** October 18, 2015, 09:00:34 PM »

Now at subsonic the boat tail config (more of Bobs work)...

http://www.gatewaytoairguns.org/GTA/index.php?topic=93524.40

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Whats the Science behind shooting heavier projectiles? (like .247, .30, .357)

Author Topic: Whats the Science behind shooting heavier projectiles? (like .247, .30, .357) (Read 12724 times))