Slugs distance to “stabilize”?

Ken, read this. It is on page 1 of this discussion. 

http://www.appliedballisticsllc.com/Articles/ABDOC104_EpiciclicSwerve.pdf

Click to expand...

Thanks, these are interesting topics, I will read up, our airguns seem to push the limits of accuracy... Although it is a little difficult to take reading any paper that isn't titled correctly seriously...

It's actually epicyclic curve, which only describes the path, not the forces that create it...

;-)

Ken

Bryan Litz wants to study this phenomenon, that’s why he has had this standing offer for years! Nobody, not a single person, has come forward to show that this phenomenon actually exists and can replicate it.

If I believed this phenomenon, which I do not, the flight path of an unstable bullet becoming stable between say 30 and 100yds would be minuscule anyway. Maybe a tiny fraction of the bullets diameter, certainly not inches, so the difference in group size would be negligible anyway!

I think it comes down to this possible effect is simply "noise" compared to all the other inputs to accuracy, such as shooter input, wind, velocity...etc

All I have is this...?? without any explanation of why.

And it's firearm related.

When working up a load for my new custom ELR rifle in 375 Cheytac at 100Y I got pretty angry and frustrated because after many attempts to achieve sub moa the rifle wasn't up to the task, or so I thought, although it'd do 1" on a regular basis. At $2.50 a pop that gets very expensive and after the 4th time out I was about to give up, thus resolving myself to send the rifle back to Lawton the builder of it.

I had 10 rounds left so for the heck of it I tried 400Y with the load which seemed the most promising. Results were two back to back 2.5" groups which is about 3/4" moa??!! Scratching my head a bit on that I tried that same load farther out successfully.

The rifle had a special bore made for Lost River solid alloy projectiles. These bullets were very long but very precise and I suspect the twist rate could have been a bit faster. I also tried the.375 caliber 350 grain SMK, a standard bullet, which shot horrible in this rifle/3" at 100Y for whatever reason???

The best group with the LRB, but only a 3 shot, was 6" at 2050Y. Shot a couple 3/4 moa groups at 2000Y and 2500Y. 

Later on another thing happened that was weird, a solid projectile as well, although I think twist rate was the culprit?? because Lehigh bullets 330 grainer listed a 10 twist minimum for this bullet and mine was a 11.5 twist. At 1000Y these bullets did two sub 6" four shot groups but by 1 mile they wacked out badly??!! I didn't even try the 330's at 100Y because by that time in the future I had learned to work the load up at 1000Y instead. So these 330's shot better than the 350 solids at 1000Y but the 350's sailed so good at ELR distances it was hard to fathom??!!

I'm not saying all 375CT's are like this but this is what happened to me.

Ok, getting back on track with airguns & their respective projectiles... best example I’ve come across (I’m sure there’s better) is airhunters youtube vid on testing 25gr. Jsb RD’s out of a impact .22 w/slugliner? If you watch the slowmo vids you will see almost all of the 25’s vs. the jsb 18.1’s the 25’s are not stable at all!, in his comments he’s referring them destabilizing after 50yds? My money is they were never stabile to begin with, why the slug barrel? To fast a twist rate?,to slow fps? Choke of slug barrel? This goes to show that that pellet or slug is not going to fly any more true (or go to sleep at 50,75,100yds) it’s only going to intensify with distance?, in my mind anyway! If its not stable coming of the barrel there’s no hope! “It can’t auto correct” plus your Cd is increased? IMO!

Also as far as slugs, I feel there’s much more to be learned as shooters use and test them, but feel to be stabilized quickly as they leave the barrel at the velocity’s pellet guns can shoot them (850-960fps?) so much depends on twist rate, slug dia, profile of rifling, seating depth of slug into rifling or “jump” before rifling?, also I believe the big one is seating the slug as squarely (concentrically as possible to land and grooves) also bearing surface of slug? One more thing, did anyone notice with the moderator vid. a small amount of gasses leaving the barrel ahead of theBullet?, this is the expanding gasses getting around the Bullet before it completely seals around the lands & grooves! This phenomena is more likely to happen with airguns shooting slugs vs. pellets because there is no thin skirt like a pellet and if this air bypass is not even as the slug exits the barrel well guess what! So softness of lead plays a factor as well! The list goes on and on and on...

Where's Myth Buster's when ya need em??

If you think of it this way can you make sense of it ?

Your line of sight is a straight line. No question. A fired bullet is on a path relative to that line of sight. Again no question iIt’s not the same path as the line of sight but it’s related to and our goal is to approximate that line of sight.

Now for this idea to work the bullet has to some how get off it’s related path ( wobble) yet some how consistently get back on the path. The critical word is CONSISTENTLY. If you think that possible then it could happen 

It would have to happen at the same distance and velocity and time every time Possible??? The bullet has to get from point A to point B CONSISTENTLY. It in therory could stop in mid air turn atround fly back and turn around and go back towards the target as long has it did it every time

Interesting to think about for sure

Im sure there are some Chinese whisperers going on. So imagine the original message is. 

“Don’t be to worried if your groups with slugs are a bit bigger than pellets at 50y. This is because the better bc will mean they won’t open up as much when they reach 100y”

So this is true. An inch group at 50y could end up not to bad at 2 inches at 100y and out preform the pellets by a long way! 

Now pass the message on through 10 people and we end up with 

“Dont be to worried if your groups are a little bigger at 50y they will be tighter at 100y”

I see this happen all the time. 

I got one for ya! Why doesn’t fx sell custom twist rates for there slug barrels instead of A or B? let us decide for ourselves which twist rate stabilizes the slug we choose (weight & profile) for long or short distance and the speed we can attain through the gun? We know that a heavier/longer slug requires a faster twist rate to stabilize the projectile? they have already offered a longer barrel (which didn’t exist before they started testing slugs in their barrels?) someone (manufacturer) is going to jump on the “gain twist” bandwagon probably the Daystate and LW partnership already has? for all we know maybe fx is doing it now? Kreiger or Bartlein probably have it patented though? fx already touts how adjustable and user friendly their guns are, take it a step further! I understand what’s being talked about in this topic and my comments are directly related, I think in the ranges we are talking about in airguns we need the projectile to stabilize as soon as possible leaving the barrel (however this is accomplished?) we shouldn’t have to just accept that a slug hasn’t gone to sleep @ 50yds but will by the time it reaches 100yds! Where’s the accuracy in this? It just doesn’t cut it with me! I’ve said enough...

Here's some good reading from Hornady...

https://press.hornady.com/assets/site/hornady/files/ballistic/hornady-4dof-technical-paper-v2.pdf

There's some very good reading about these subjects on page 7...

And here's what the US Army Research Lab published about spin stabilized projectiles...

View attachment 1566400870_7589049835d5d6166b20d71.34775127_1037832.pdf



There are some great high speed camera images of projectiles in actual flight at subsonic speeds... And a lot of reading...

Ken

Last week, I came across one of @Bob_O''s videos on YouTube showing slugs being shot in slow motion at water. I noticed some of the bullets starting off a little unstable at first, until stabilizing downrange through their descent into the water. 

I had just finished reading Brian's book Applied Ballistics for Long Range Shooting a few days earlier. I started thinking about what was happening to the bullets as the left the barrel in the video, and my first thought was that the bullet was transitioning through turbulence and different air pressure as the gyroscopic motion began to stabilize the projectile after its barrel departure.

With that said, I've seen similar shots start off like that, and then stabilize closer to 30y than 50y. I was shooting one day with targets at 15y, 40y, and then 100+ - my groups were off at 15y, but touching at 40y and sub-MOA at the long one. It's hard to pinpoint what it really is, and there's not a whole lot of publications out there that discuss pure subsonic external ballistics (it always seems to be a smaller topic working towards the deeper material on transonic and supersonic states in external ballistics literature).

Anyways, here's the video I was talking about:

https://m.youtube.com/watch?v=EvJA3MdFCUY

It comes down to an incorrect twist rate for that Velocity. Too much twist stabilizes faster and too slow stabilizes further out. The air hunter guys are just saying you need to adjust the speed of the bullet to the point you get the best balance of close range stability and further range stability.

Rpm (twist) and velocity are the two parts of the equation that work off one another so if your twist is close changing the velocity can put it on by slight adjustments up or down. The only other thing Airgunners should also understand and Matt dubber and air hunters are is when to cut off the pressure behind the bullet, this is why they are adjusting the regulators. Powder burner world changes to slower or faster burning powders. Our slugs suffer when the air is chasing them out the barrel, you want it cut off just before it leaves.

So if the bullet wobbles a little out to 50 yds the group opens to say half inch, but from that point on it has stabilized and is now flying true so the groups at 100 can be the same size as the 50 yd group but not better. You may also get a bullet stable at close ranges but becomes unstable further out so groups are really good up close but fall apart further out. So ideally you want to tune in a way to just be stable up close and keep that stability further out, which can be harder trying to fine tune for that perfect balance but is possible.

I've never believed in the "settling down" or "going to sleep" bit at all. IMO a projectile is either stable or not from muzzle exit-all will lose stability at some point due to spin decay but none will become stable further out if not stable at the muzzle. All JMO in deference to those who "know" what is happening.

It depends on the definition of accuracy. Whether you are stating absolute group size as a measurement of width, or group size in measurement of angle. I can see that through epicyclic swerve, the group size measured in degrees could theoretically be larger at a very close range when measured in angle. But the width of the group will always be larger at longer ranges even if the group angle is less. Probably more apparent in long range centerfire rifles which offer a more stretched out comparison of 20:1. It's hard to get any meaningful measurement of group size in angle for an airgun at 5 yards in order to compare it to 100 yards. And environmental factors are a much bigger influence for an airgun slug at 0.1 bc verses a bullet at 0.5 bc

So airgunners are never going to observe this but a 1,000 yard rifle shooter might

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https://youtu.be/KH9SCbCBHaY



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