Extra-long slugs

I think you loose to much power, because of the friction from bullet on barrel surface. And difficult to load. I think a good BT or RBT wil give a very good aerodynamics. Cheers wimone

Don't waste your time. projectile length is limited by several factors. Space in the magazine, loading space in the breech, barrel friction, but the biggest factor is flight stability. The longer the projectile the more stabilization that is required to prevent wobbling. You can stabilize a projectile's flight in one of two ways. Either drag stabilize, like a Diabolo pellet and feathers on an arrow or spin stabilize like with rifling, your choice. If you choose spin to stabilize, the longer the projectile (cross sectional density) the more spin is required. In this respect, too much is just as bad as too little. Too much spin prevents pitch over at the apogee of fight which keeps the orgive always pointing in the direction of flight. When that occurs, the projectile will suffer pancaking as the projectile encurs changes in air density.Too little will cause wobble and tumble. This principle can be viewed by watching an American football or a Javelin flown with different rates of spin. If you elect to use both, you can suffer the loss of ballistic efficiency with drag and potentially an argument between spin and drag under certain circumstances that creates spireling in flight when they fight each other. 

Why are you reinventing the wheel? All these principles were discovered and quantified 200 hundred years ago. Your observation that there are longer PB projectiles is true, but they are propelled by SAAMI gas pressures not compressed air. Therefore spin rates can be much higher. Spin rates are controlled by both the rate of rifling and end velocity.

I wrapped some 6mm 100 gr sierra bullets with scotch tape to make them fit the land & grooves of my 25 condor. These was pulled bullets! so I had nothing to lose.

The majority (of course) tumbled! But they certainly done some damage to the target. The longest "lead" air gun slug I have shot is the NSA 55.5 gr. With a choked barrel, they foul quickly! Cleaning after only 10 shots is a must to retain accuracy. Longer bullets with a spitzer shape do generally have a high B.C from a powder burner! thats not always the case (as stated) with subsonic projectiles.

Let’s not forget these are basically pellet guns, not powder burners. That is what makes this hobby unique. If you need that much power get a powder burner. 

3x diameter for the length has been a good compromise between all the factors with a round front boat tail. Bob Stern has spent a lot of time designing just such an animal from 1.5x up to 3x and often compromising shorter 2x and 2.5x to fit in the breech.



If you are going to custom barrel something with an energy using 1 in 6 barrel, then give bullet design a go and let us know where you end up. But with air a 1 in 14 is probably going to be about as much energy as you want to use to accelerate the bullet rotationally.

Delooper, your expectations are way off the mark. It takes in excess of a 1 in 7 rifle rate to stabilize a 70 grain Sierra boatail .224 bullet and a muzzle velocity in excess of 3000 ft/sec. That translates to more than 300,000 rpm. How do you do that in an air rifle? I have some of these around somewhere, but as I recall they are around .5 inches long! Do your own research and get back to the forum.

I think you are confusing issues. You don't have to fire that slug at 3000 ft/sec.

If you have any actual research to present, please do.

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My info is first hand. I am a reloader and have been for more than 50 years. That sierra bullet would not stabilize in an FNC 5.56 with a 1 in 9 twist no matter how much powder I stuffed in the case. I was pushing these things well over 3200 ft/sec and I was still keyholing the target at 100 meters. Once rebarrelled to a 1 in 7 rate, it stabilized and I could reduce both pressure and velocity to do it.

My experience, not somebody else's taught me that I could stabilize up to 62 gr in .224 with a 1 in 9 twist, but not heavier. What is your experience that indicates I am confused?

The rotational rate is the direct factor in stabilizing a bullet (not pellet). That said, you can shoot a .750" long .357 145 grain out of a Bulldog at 750fps and have it be stable, I think it is 1:16 or 1:14. So what is that, a 2.1:1 ratio. I think the best you can hope for is a 2.5:1 or 3:1 ratio of length to diameter, and you still need a barrel that has the spin set for bullets, not pellets. Weight is also a factor, heavier bullets need a different amount of spin than lighter bullets, and I don't remember which way things go (heavier needs faster spin?).

Greg, check out this website. https://bergerbullets.com/information/lines-and-designs/bullet-reference-charts/

Minimum spin rate is quoted for various bullet designs and is generally dependent on the overall length and cross sectional density. Please note the quoted rate is stated as minimum. That is the minimum edge of the stability envelope. In my experience, the spin rate is always a bit more to the center of the stability envelope.

"Bob's 300 Whiteout" should give some insight on the subject. 

I think that's in .224 for a airforce 62g maybe 65g would be the max bullet weight you could shoot..counting with a Doug valve .. 30" barrel and 3,300 psi fill.. using 1000fps as you max speed.. TJ has my 218 ..224-1-8.5 twist mandrel on the works.. we will know soon enough..I managed to find 9 - 60g to 62g molds to test... I don't think there is a valve aviable for 70g+ if I want to shoot more than 60g I would go better with a .257.. way better bullet selection aviable.. there is almost no bullet molds aviable for purchase between 55g n 60g n those that I have found but not purchased above 60g have low BC..I have emailed arcenal 2 times with no response to see if a Spitzer BT that they have in .280 could be made in .224..

Have some friends the purchased. 224 -- 1-10 to test.. it should be good for 50g + hope it works to I have 5 mold in 50g.. that I would like to be able to use to..

This bullet in .224 .. would be great to try .. there is nothing like this aviable..the closest is the lyman 228-60 .. which I found in spire poin n flat poit...but only single cavity... 

In order to take any advantage of the higher BC afforded by "extra-long" slugs, we would need to shoot them at a decent velocity. Say at least 950fps? Because of the relatively low pressures, trying to deliver enough air volume becomes problematic. Lets say that we wanted to shoot a 100gr .217 caliber slug at 950fps. That's 200fpe. With a 200cc plenum and 3000psi of air, that requires dumping it all into a 62" minimum length barrel in order to get the required energy to accelerate the air and projectile to 950fps.

I have not done a .217, but I have done a .257 and experimented with relatively long slugs. Best way to start is pick the maximum barrel length that you can live with, and then work backwards, with the other practicalities: such as available air volume and pressure, desired shot count, gun weight, etc. It becomes a game of compromises. For my purposes, "medium-length" slugs (72gr .257) turned out to be the best compromise for my end goals.