Getting Technical With Barrel Twist Ratios - Pellet Stability & Env. Variables

OVER STABILIZATION being ALLWAYS better than UNDER STABILIZATION

Maybe, maybe not. What are commonly called super-explosive varmint bullets have been around a very long time. They were designed to disintegrate upon impact at relatively low velocities, like those shot from a Remington .222, with a twist rate is 14:1. Most 22-250s have the same twist rate, yet, you can't shoot the SXs in a 22-250, because the rotation speed (RPM) is much higher due to the much faster velocity. This fact should be obvious, but it isn't typically.

You could say the same thing for pellets, but I don't think there is an airgun capable of shooting a pellet fast enough to have it fail due to rotational forces (RPM). But what does happen as I mentioned above, the pellets tumble. And, we need to realize that pellets aren't made very well, their diabolo shape notwithstanding. In fact, if we put pellets within the same exacting standards varmint hunters demand, they wouldn't fly! Or they would fly—as in off—depending on your point of view. 
 
I think moving away from firearms comparisons and simply using fact based info for airguns would be highly beneficial to this conversation. It is evident that airguns with diablo pellets act much different than a CF or RF. Contrasting is fine but comparing is making these discussions more confusing for the majority since we really can't compare powder to air in this instance.

A pellet can "fail" in the sense that it is no longer accurate and is spiraling. Proven many times in .177 that too high of velocity(which I would assume produces higher RPM's) will make a pellet spiral out of control. No, the pellet will not self destruct from over spinning but it will get out of control.

Maybe I am totally off base, but I really think airgun discussions need to move away from firearm comparisons based on the fact that they really don't apply and tend to cause more confusion. Theory and math formulas are great but most of us want facts as theories and formulas are worthless unless proven!! Guess this is a common problem world wide and on all subject matter as facts seem to be a thing of the past and pissing contests filled with theory and BS now take center stage.
 
With shooters regularly engaging 100 yard and further targets, this TR discussion is more important than say 5-10 years ago. I will agree that many variables can be nearly useless out to 50 yards. That I will agrre on, but alot of us are shooting much further and those variables that didn't matter before, now matter a whole lot!! I can easily see that with certain projectiles at 75 and 100 yards between a 1:18 and a 1:22 twist. That is not alot of difference in twist and really doesn't matter much out to 50, but I have first hand experience that it indeed does matter at 75 and 100 yards!! Again, we need more fact based airgun info in these discussions and keep the theories for beer drinking campfire talk!!
 
AZ, I do appreciate your experience and input and I don't mean to come off as rude, but it seems there is alot of confusion regarding this subject for airguns. I understand there are alot of variables and I also agree that proper and "adequate" testing needs to be used to prove or disprove anything. However, some instances have held true to conventional TR formula wisom, while many other examples seem to disprove those same formulas in my experiences.

It is my understanding that most of the commonly used TR formulas are based around velocities that no airgun will ever reach. DO diablo pellets need a specialized formula to correctly calculate TR? Could the large variance in pellet tolerances be a leading cause in the lack of good solid TR info for airguns? Airgun pellets and airgun bullets seem to prefer different TR's. Is that simply due to an airgun bullet usually being much longer than a pellet in the same caliber or is it something much deeper as to the mechanics of a diablo pellet vs a non diablo bullet? Most of the bullet shooters seem to have the proper TR figured out per caliber for a given range of commonly used bullets. This doesn't seem to be the case for those of us playing with TR's and diablo pellets.

 
Things I learned from this excellent thread:
  • diabolo pellets have different needs than bullets
  • The FASTEST effective twist rate imparted on a pellet out of an FX smooth twist barrel is ~1:44" (many test at 1:60", 1:70", etc.)
  • typical twist rate for a conventional rifled airgun barrel is ~1:18"
  • smooth twist barrels shave/skid pellets as they pass through the rifling
  • pellets fired from a smooth twist barrel end up with slightly worse ballistic coefficient when measured at 50 yds
  • gain-twist barrels don't seem to offer any advantages over fixed-twist barrels

It is obvious that the diabolo pellet shape is incredibly forgiving, but that we still don't know as much as we should about optimizing barrels for it. The engineering mind wants to know MORE:
  • Does the smooth twist pellet shaving aid in accuracy or is it just an unnecessary side effect of the current design?
  • Has anyone tried a conventionally rifled barrel with a REALLY slow twist rate like 1:40" or slower?
  • Has a smooth twist barrel with rifling pressed at a MUCH slower rate like 1:40" been tried? (current smooth twist rifling 1:16")
  • Has anyone tried a high quality smooth-bore barrel just to see how it compares? (maybe smooth twist with rifling cut off. would lack choke, though)
  • Has any one determined the point at which a diabolo pellet is over-stabilized?
 
Wow. Thanks for bumping this post, TDK. Agree, this poses a whole new light on the question. Previously I have read through the entire string of blog posts on Tom Gaylord's blog, resulting in his final summary seen here:

http://www.pyramydair.com/blog/2013/07/how-does-rifling-twist-rate-affect-velocity-andor-accuracy-part-13/

which seems to be somewhat contraindicated from the smooth twist results that Harry has posted, i.e. that the pellets (let's just compare JSB 15.9 grains) remain quite stable at 1:64 twist rates, whereas the Talon SS barrels got noticeably worse at long ranges when deviating either faster or slower from the factory 1:16 twist rate.

I have noticed, when shooting in crosswind at 50 yards, that the smooth twist barrel on my Wildcat .22 tends to not deviate up/down as much as my .177 Mrod, but I have no real data to share on the subject beyond my uncalibrated Mk 1 eyeball...yet.
 
With smooth twist barrels operating so drastically different than conventional barrels, but both being accurate, its almost like each is hitting a different rotational resonance (is this a thing??). This would explain why you can get worse performance on either side of 1:16" twist, but then get great performance again when you hit the 1:60" effective smooth twist.

I can't wait to find out more as research unfolds. There is something in there waiting to be discovered.

I think the first step would be to measure effective twist rate of an accurate smooth twist barrel and then make a conventionally rifled barrel with the same twist rate. That will prove whether it is the spin rate imparted on the pellet that is important or how it is achieved.
 
There are some assumption made here, that are quite accurate.

The average firearm twist rate is closer to 1:12, and a bit faster for the smaller caliber magnums. 

The twist rate for Benjamin's 392 and 397 is 1:14. Both of these airguns are very accurate right out of the box.

And we need to remember that diablo (skirted) pellets are BOTH spin and drag stabilized. Upset the skirt, for whatever reason, and accuracy decreases which should be obvious. 
 
"bent"
http://www.pyramydair.com/blog/2013/07/how-does-rifling-twist-rate-affect-velocity-andor-accuracy-part-13/

which seems to be somewhat contraindicated from the smooth twist results that Harry has posted, i.e. that the pellets (let's just compare JSB 15.9 grains) remain quite stable at 1:64 twist rates, whereas the Talon SS barrels got noticeably worse at long ranges when deviating either faster or slower from the factory 1:16 twist rate.


Bent,
Tom's groups are so poor that any conclusions about twist rate comparisons based upon such are spurious. ... Harry.
 
Harry,

Can't deny your statement. It would also seem that the data says "don't use an aftermarket barrel on a Talon SS", but again there's not a lot of consistency in the data to make even that a real conclusion. I'd think the best comparison test would use barrels made by the same techniques but in different twist rates. The elimination of other variable (barrel straightness, alignment and securing in receiver, "best pellet" for each twist rate...the list would be pretty large and the testing would take quite a long time and a fairly good chunk of money.

I am quite happy with the FX 'cat, I wanted a rifle that could reach out to 50 yards in gusting winds, and this one does that pretty well compared to my .177 Mrod.
 
Bent alluded to several factors which are not in evidence (normalized) with respect to the published article referred to above. As examples; The two "non-stock" barrels were not choked; The tests didn't address pellet sizes or weights; and nothing was said how the tests were run. All of this "input" would have to be known. Without it, the tests are, in Harry's words, spurious. 
 
AZ needs to get facts sorted before publicly insulting fellow shooters. I presume his libelous onslaught was aimed at me.

1. I have never attacked or initiated any discussion of the noted rifle builder Bill Calfee here or elsewhere. 
AZ, whoever you are, please do not again return to putting words in my mouth with a view to libel. "Libel", as in a false report maliciously intended to a person's injury. 

2. Then, I have never thrown any "punches" at Tom Gaylord and certainly would not. So please don't imply or infer that I have done so. That too is malicious false accusation.

What I did write in respect of Tom's data was simply, "Bent, Tom’s groups are so poor that any conclusions about twist rate comparisons based upon such are spurious".
That is all I wrote above.
One inch to near 2 inch groups at 25 yards; 1.25 inches to 3+ inches at 50 yards across the barrel spectrum indicates the rifle/ barrels combinations were suspect; or the wind conditions were very bad. Either one points to group spreads from which, in my opinion, spurious conclusions may be reached. 
See Tom's table below for you, the shooters here, to draw your own conclusions as to the groups' qualities and with reference to your own understanding and experience.

In respect of AZ's further slander in reference to my age, mental and shooting abilities: it is on public record (WRABF results) that at last year's 2015 World Championships, with 15 countries and 90 shooters competing in LV Air Rifle, I did creditably in beating the then current European Champion (GB) and also a current World Cup Champion (Ukraine). I was the second oldest competitor. I was also chosen to officiate in charge of the air rifle testing for compliance to the rules. As a spin-off, I got to meet with and further cement friendships with many, including the best from your USA. Tod Banks, Paul Bendix, Vipha and Doug Miller and I had much discussion and I'm confident they would vouch for my mental integrity. 
Harry. 





 
"azuaro"Whatever Harry....

This sport is about enthusiasm and you seem to be an enthusiastic guy and this is valuable for the sport and this forum, buy please keep it that way and restrain yourself from attacking our friends and institutions and avoid crashing and scrutinizing what other members say...Again, post whatever you want but don't invade and crash other people's ideas and beliefs...If you believe they are wrong, kindly and politely express your points of view.

Your "Spurious" adjective to Tom Gaylord's shooting groups is very arrogant, and insulting to him and to us who appreciate what Tom has done for the industry and mostly for helping shooters enjoy the hobby...

And yes. I have an issue with your claims, with your confusing and extensive posts/communications and this is why I don't participate where you are present and I won't, just to cross the line as you dd with Tom Gaylord and with Bill Calfee on another thread because I will be there.

I abide by respecting to other people's ideas as this means peace and getting along well. Turn the page and let's talk shooting and let's contribute positive things...No need to respond to this post. 

AZ
Azuaro

Your response hypocritically contradicts some of your previously slanderous comments (which were removed). I would like to see you honor your own words. Please, drop the agenda. If you want to participate... great. If you cannot play nicely then don't play at all. 

Thank you

-Michael