How to tell if a pellet is over or under spun?

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Arzrover

Arzrover

Member
Nov 28, 2017
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Arizona, United States
I have 3 examples I'm curious about .....

1. Jsb 177 .... 16.1 grain. I'm shooting it out of 5 different barrels... all w 1 in 17 twist. A couple are unchoked but the others are choked. At 900 fps, it shoots quite well at 50 yds but seems to get blown around quite a bit at 75. At 930 fps, it's better, maybe even really good at 75 but seriously bad at 100. At 970, it's still good at 50 and 75 but only okay at 100. Will not hit much of anything at 150. Some barrels are better than others but none really seem to break the 100 yd barrier well with those. By contrast, in a zero to low consistent wind, several of my 20 ft lb shooting 10.3s still seem stable past 150 in the same barrels. They ARE wind sensitive though. I know there are MANY of us that would like to figure these out.

2. Jsb 22 Monster Redesign 25.4 grain. Out of my Daystate barrels (LW), the more , the merrier till somewhere over 1k fps. Mine seem stable as far as I can shoot them and still see. ... 1 in 17

3. Jsb King Heavy MkII ... 33.4. As stated in another post, at 900 fps muzzle velocity, they hold together till somewhere beyond 200 and then really fall apart. I've not run them faster because of the air usage and rifle behavior. 1 in 17 and 1 in 28 have been tried.

I've read most of what has been posted in theory about twist rates but still find these puzzling. 

I guess what I'm asking is whether each could benefit from more or less spin and what are realistic expectations?

Bob
 
I don’t know much about this other then heavier projectiles require faster twist rates. It would seem to me the test would be what twist rate provides the best accuracy at more reasonable distances thus identifying the ideal twist for that pellet. My thinking is that changing from that identified best twist is not likely to benefit you as far as getting longer range stability.
Does that make sense or add anything to your quandary? And I could be wrong.
 
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Pellets do act differently than bullets (slugs)... Well, except for the .22 RD Monsters which tend to act like a pellet/slug hybrid. I think if anything, its a case of too much spin vice not enough. What I think happens (and its been mentioned on a few posts here on AGN), is that there is a specific speed to RPM ratio when it exits the breech. But the pellet slows faster than the RPM, so that ratio increases the further out the pellet goes. And once it passes a certain ratio, it loses stability. Obviously for some reason the RD Monsters in .22 don't act that way, but all other pellets that I've shot do tend to act like that. Probably one of the reasons you could shoot the older FX ST barrels with an effective twist rate of 1:50 and the pellets would remain stable until they hit the ground, however far away... Just a guess, and not based on any empirical data...

Mike 
 
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Bob, I’ve been wondering that also, if you look at SorenSD posts or YouTube videos he is shooting the 16’s @ 1020fps and are incredibly accurate to a 100yds! I believe that would indicate these are underspun in my gun at 920fps, as you’ve seen I got no where with them at 100yd, but yet would shoot the 13.4RD’s quite well to 100? It would be interesting to see if a faster twist barrel at the lower velocities would give same results as slower twist higher velocity? The heavy long waisted small flair skirt seem to pose a challenge at longer distance’s? as of now I’ve basically bowed out of the long range game! I’ll be staying tuned to this thread though! ( I know nothing about ballistics So can’t help directly in answering your question but it’s a good one to ask! )
 
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Thanks guys. This stuff has been bantered about several times and I think I've read them all. Azuaro wrote some pretty good verbage about it in one post but most of the theories typically related are specific to slugs. Just trying to figure out why and see if there is something I might do to get the 16.1s and 33.4s going further before coming apart. For that matter, the 22 Jumbo Beast would be a good one to have work better. Not even sure I can get a quality barrel in a different twist if needed. Those 16.1s are KILLER at closer ranges.

Bob
 
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Perhaps an ART barrel test in .177 is in order with the 177 16.1's ??!! 

I don't keep up on the different pellet shapes but those JSB 22 Monster Redesign 25.4 grainers seem to perform the best at long range??!! JSB should copy that same exact shape in all the calibers and let the weight be what it comes out to be. Then let optimal barrel twists follow. Maybe a joint effort between barrel manufacturers and JSB to bring out the optimal combo ??? 

I have very limited experience with pellets and twists but we were both there that day at John's shooting our various AG's at 210Y and 289Y. My 25 caliber 1st gen smooth twist FX Impact with 34's totally fell apart by 140Y or so, it was luck if I hit anything farther. The same gun does okay at 100Y as witnessed shooting that 225 on CC's target. I think that's the limit with my combo, I might be able to get a 230 but that would be super hard to do because of the vertical. 220 was my previous best.

The AAA EVOL in 30 caliber did extremely well at 210Y and 289Y??? It had a 27 twist that's all I know about the barrel. It didn't shoot exceptionally at 100Y though???

It seems like most of our 177's do well at 70Y with JSB 10.5's around 900 fps.

I'm surprised there hasn't been more experimentation published about this subject. 

Tacticam and slow mo might be revealing?!
 
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Daystate seems unlikely to spend the money that kind of test when their barrel is shooting so well already. The 16.1s , Jumbo MRDs, and King Heavy MKIIs seem similar in design to me already. Not sure how to go about procuring different twist w the same interior dimensions without spending a lot of money . Not ready to do that yet. I know there is at least 1 manufacturer that can hammer forge different twist rates from the same mandrel but unless you get your own mandrel made, no guarantee of dimension consistency (from second hand source). Just fishing for some theories that might help decide what direction to go. I do have a Phonskope adapter but I don't think I could get good enough video at the distance they break down. Not sure what it would help, as we already know they're becoming unstable.

Bob
 
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FX has / is doing this. Their barrel manufacturing method of imprinting the rifling from the outside of a polished tube allows full control and adjustment of groove/ land ratio, twist rate and choke without any new tooling. And then slide the liner into any rifle in 5 minutes and shoot it at 50 yards indoors from a vise in the next room. Now if they could put more rigidity into the barrel system with a Carbon sleeve and beefier breech entry of the housing. I am thinking that the new super light barrel system may end up being a step backward with just a couple big spacer discs locating the liner in the shroud/ housing. Let's see how many competitive shooters choose a Crown with a long barrel.

It was a much longer manufacturing process for Daystate but they did the same trial and error with the newest ART barrel.
 
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Using the resources and tools at hand ( no new barrels etc.) using the phonescope and shooting against a background that allows you to see the pellet all the way through flight and then slowing these footages down, may allow you to see at what distance and speeds the pellet is loosing stability? ( similar to ted Biers examples, particularly the jsb 18.1 Video ) now I think this would be a incredibly time consuming process I believe you Would need to find The yardages that pellet looses stability then increase speeds incrementally at these distances and so on... You would obviously need the Daystate tuner or heliboard for the RedWolf ,but maybe you can use the Huma regulated model and put your art barrel in it? I would think it could could give you more control and speed this process up considerably ( if the huma reg. Can push these pellets at speeds you need them to be ) I think I’m just rambling but something to consider?
 
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Thanks, both of you, for your thoughts. Putting anything FX on my rifle doesn't appeal to me but in my limited testing on my Crown 25, it yields a worse bc than the ART barrel anyway and neither will stabilize a 33.4 much past 200. Joe... I do have a Heliboard installed and have experimented quite a bit with velocities. They do seem better at longer ranges going faster.. but why? Could a faster twist stabilize them better or are they already being overspun.... that is the question. The photography would only show that it's destabilizing and at what range, but can you figure out if it's over spun or under spun , that's the problem. Now I know I could get a stack of barrels made at different twists but having all barrels EXACTLY the same except for twist could be a real challenge and that's not something I want to afford.

One challenge with the barrels is that the twist and bore size has been the same almost from the beginning and was likely developed for the lighter projectiles of the time and WAY shorter ranges.

Anyway, thanks for the thoughts. That's what this thread is about.

Bob
 
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Here's an example from today. I was replacing the GC1 board in my wife's RW HP with a GC2 so we can make it a competitive 22. I tuned the Low to shoot 1000 fps in an attempt to get the 177 stable at 100 yds. It was previously at 950 which was about 90% of max with the original board. It was very marginal at 950. I plugged the close ones to come up with a 219 in pretty nice conditions. 

1595389606_14676442775f17b6a6d02903.00156431.jpg


Note the extreme fliers went in sideways. Some of the 8s are slightly sideways as well. There is about a 10 ft drop from the bench to the target plus another 14" because it's 100 yds so they will be going in at a slight angle, regardless. So WHY are 1 of 10 or so spiraling but not the others? I shot a couple more cards and managed a 218 and 214 that had the same evidence. The wife shot a couple and we even cranked it back to 950 with the same result. I also shot out to 125 and mostly they followed the same stats with 80% or more being predictable.

Still searching....

Bob
 
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How do trans-sonic shock waves from shooting so fast figure into this? And does "nose up flight" become an issue if the twist rate becomes way too high as the down range velocity bleeds off much faster than the spin? Ted mentions turning his rifle down to 830 fps to eliminate the last hint of spiraling in windy conditions the year he won EBR with .25 King Heavy (not MKII).

.

https://youtu.be/TNONcrNmWDE?t=470

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Interesting, but doesn't seem to apply within the limits I have of this barrel. I tried from 813 to 1040 in approximately 20 fps increments yesterday with the best being about 1020. At 813 to 920, it was really awful, gradually getting less awful. Had approximately 10" groups at 813. Shot another 219 with 5x at 1020 with only a couple of fliers in the 7 and no 6s. The 7s were sideways and several 8s looked like the were slightly sideways. The non fliers sure seemed good in the wind. I'm kind of leaning towards a 1 in 15 or 14 twist as being the answer. The question was posed about the 13.4 Monster's. They were 1" plus at 50, so not worth pursuing in this barrel.

Bob


 
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How do trans-sonic shock waves from shooting so fast figure into this? And does "nose up flight" become an issue if the twist rate becomes way too high as the down range velocity bleeds off much faster than the spin? Ted mentions turning his rifle down to 830 fps to eliminate the last hint of spiraling in windy conditions the year he won EBR with .25 King Heavy (not MKII).

.



https://youtu.be/TNONcrNmWDE?t=470



.

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Is it the lower "trans sonic shock wave" or is it the lower spin rate? Or a combination of the two? A pellet shot out of a 1-17 twist will be physically spinning at a slower rate when shot at 830 and at a higher rate when shot at 1020. Which factor would be the cause of the issue, if either could be isolated from the other?
 
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Interesting, but doesn't seem to apply within the limits I have of this barrel. I tried from 813 to 1040 in approximately 20 fps increments yesterday with the best being about 1020. At 813 to 920, it was really awful, gradually getting less awful. Had approximately 10" groups at 813. Shot another 219 with 5x at 1020 with only a couple of fliers in the 7 and no 6s. The 7s were sideways and several 8s looked like the were slightly sideways. The non fliers sure seemed good in the wind. I'm kind of leaning towards a 1 in 15 or 14 twist as being the answer. The question was posed about the 13.4 Monster's. They were 1" plus at 50, so not worth pursuing in this barrel.

Bob

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13.4's, man that's pretty bad. What velocities did you try?

Had any success with slugs, just curious because I know that's not what this thread is about or what you are after?




 
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Again, I don't think it has anything to do with trans sonic shock waves. At 813 I'm FAR from trans sonic and even at 1020, it's still out of that zone. That Ted had luck with slowing them down is more dependent on individual barrel and pellet batch than trans sonic imho. I've shot Kings from 750 to 1000 in different barrels with good success pretty much the whole range. They seem BEST in the 880 - 900 area in my experience, but that's just me. 

Steve123 ... tried them at 880 and 900...... bad.

Bob
 
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