Barrell twist questions...?

[Mike West]

 Hi my first post here.

I wasn’t sure where to post this because this board is a little different than the ones I’m use to... so feel free to move it if necessary.

 Anyways I come from the Center fire Bench Rest world... competed for eight years and have been OCD about accuracy all my life...I’m 60

I haved pellet guns and BB guns all though my teens and early 20’s.

 I’m just getting into this and I’ve been researching for probably six months reading,window shopping etc.

 I did a search on this topic and really didn’t find what I was looking for.

So in the benchrest world shooting a 6PPC with 68 to 72 grain bullets you use a 1/14 twist Barrell ...that’s it end of story..oh some guys will mess around with a 1/13 twist or a 1/15 twist But 98 out of 100 shooters shoot a 1/14 twist because it’s been figured out eons ago that’s what works with those bullet weights.

 So why don’t we have this info in the pellet gun world?

 I can only assume guys that compete competitively with $3000-$4000 pellet  rifles know all this stuff.... but I can’t find it shared or talked about.
Couple little snippets here and there that’s about it.

Lets throw some hypothetical numbers out there...
I have gun X in .22, manufacturer states it will shoot 800 FPS with lead.
(An other pet peve...what 10 grains of lead or 15 grains of lead?)
They never state that so it’s absolutely useless information.  I’m really not into the FPS anyways...other than muzzle energy...I’m into the accuracy.
 I’d rather have a gun that shot one hole groups at 20 yards doing 600 FPS than one doing 1000 FPS and 1.5” groups.

 OK I’m getting off track here.
Right before I posted this just to make sure I went to pyramid and looked guns costing $100 up to $4000.....Not one manufacture listed their barrel twist rate....hey!!!!!

I can understand that on a Walmart gun but not when you’re buying a $3000 pellet rifle.

 Back to my paragraph above.
 It just blows my mind watching all these pellet gun review videos and reading threads on accuracy with pellet guns  nobody ever mentions barrel twist I don’t think I’ve seen one thread or one video where the guy talks about barrel twist.

 All you ever see is guys talking about you have to find the pellet the gun likes to eat by buying  a shooters pack or buy 10 packs a different brand pellets and weights and figure it out.

I’m calling BS.

I read one thread where a guy posted he had a 1/19 twist barrel.
 That’s insane to me. I had 1/8 twist barrel for a 6 mm to shoot a 1000 yards with VLD bullets.

I can Only asuume that twist rate is because the pellet is going so slow.

 Back on track again.
 So my gun is a 22 caliber with a 1/19 twist shooting 700 FPS.
The info should be out there to tell you that gun is going to like pellets in the 9-11 grain range ( hypothetical numbers again) so  don’t bother shooting pellets that are 7 grains or 16 grains they aren’t going to group with that FPS  and that Barrell twist.

 I’ve gone on long enough  my next thing would be talking about pellets themselves....Walmart pellets, high end pellets I guarantee you the quality control is not there.

 I made my own bullets for benchrest I spent close to $1000 on dies to do it.
Even then I would weigh every bullet and group them in groups of 10 to .1 grain of each each other.

 I can only assume you have to do this with pellets if you want to drill one hole.

Thought? Feedback?
Thx.

[RDB]

Welcome aboard Mike. You'll get some good technical answers here shortly. But for pellets, they are drag stabilized. So twist rate can very quit a bit and not be as critical as with shooting slugs. A well machined barrel can be capable of one holers at 25yards. Sometimes much farther. Its the elements that effect the trajectory of the light drag stabilized pellets most of the time.

[Taso1000]

Welcome Mike,

There was this recent thread with people submitting twist rates:

https://www.gatewaytoairguns.org/GTA/index.php?topic=117383.0

There are diabolo shaped pellets and lead bullets used in airguns today.  Each projectile type requires a different twist rate.

I have come across this barrel twist calculator that was brought to my attention by Bob Sterne:

http://www.geoffrey-kolbe.com/barrel_twist.htm

It is the only and best twist rate calculator that I know of that models bullets at subsonic velocities.  I do not know if it's good at modeling diabolo shaped projectiles.

Matt Dubber has quite a few educational videos on the subject on his Youtube channel too:

https://www.youtube.com/user/MoshDubber/featured

I hope that helps.

Thanks,

Taso

[Mike West]

OK I want to reply and quote some stuff... I see how to quote but don’t see how to edit my own post for typos or editing.

[Mike West]

 I can’t see how to edit my first post
There is no modify or edit button,there is on this post but not my first post.
?

[Taso1000]

I can’t see how to edit my first post
There is no modify or edit button,there is on this post but not my first post.
?

Mike,

There is only a short time after you originally post that you can edit.  Just add or make corrections in your following posts.

Thanks,

Taso

[rsterne]

HI Mike....

For bullets in airguns, where we are almost always interested in Subsonic (under Mach 0.8 ) and sometimes in Transonic (Mach 0.8-1.2), the Kolbe Twist Calculator linked in Reply # 2 is great.... It may overcompensate on rebated boattails (predict too fast a required twist rate), but you can be pretty sure that if the Kolbe Calculator says it is stable in a given twist, it will be.... Unfortunately, you cannot input Diabolo (waisted) pellets into it, nor am I aware of any Twist Calculator where you can.... So from a theoretical point of view, we are pretty much in the dark....

As was previously mentioned, Diabolo pellets are primarily drag stabilized, just like the Badminton Shuttlecock they resemble.... They do need some spin, but I am coming to believe that most airgun barrels are MUCH too fast a twist rate.... One of the problems we see frequently is the pellet spiraling/corkscrewing as the range increases.... Any projectile loses forward velocity much faster than RPM, so as it moves downrange it flies like it was shot from a faster twist barrel.... Since pellets have a terrible BC, they lose forward velocity faster than a bullet, so this effect is amplified.... It is quite common to see pellets spiral past about 70-80 yards, sometimes even after 50 yards.... even though they fly perfectly and group well at 50 yards or less.... This is called "Dynamic Instability", and is probably one of the least understood parts of ballistics.... In fact, from what I have read, there is no computer program or calculator that can predict it !! …. 

When you see a pellet spiraling at long range, the classic solution is to reduce the muzzle velocity.... That reduces the RPM, and increases the distance at which it begins to spiral.... There is, of course a better way---use a slower twist rate.... Only relative recently have some of the top level, small manufacturers started to experiment with this.... The Thomas BR rifles (a $5K item) use a much slower (proprietary) twist rate.... The EVOL rifles being developed by American Air Arms have adopted (and to their credit published) much slower twists for pellet use.... They are using a 19" twist in .22 cal (and I expect may go even slower), and use a 32" twist in .25 cal and a 42" twist in .30 cal.... The original FX "Smooth Twist" barrels, which were a smoothbore with rifling swaged in the last few inches at the muzzle, although if you looked at the angle of the lands appeared "normal" (a 16-18" twist)…. The pellet in fact "skidded" through the rifling, and depending on the fit and alloy, ended up spinning as slowly as 1 turn in 13 FEET !!…. Yet they shot just fine....

I honestly feel that airgun manufacturers started out using twists similar to PBs, and never broke the habit.... However, some of the most accurate pellet rifles made today, are proving that the optimum twist rates are MUCH slower than we ever imagined....

Welcome to the revolution in technology necessary to take pellet rifles into the era of long range accuracy.... 

Bob

[Dairyboy]

With pellets it seems that twist rate isn't very important rather than the speed of the pellets. You can shoot at 30fpe since your example was .22. Ok that puts the JSB 18.13gr pellets at ~864fps. Or let's say your shooting the JSB 14.3gr pellets and that puts them at ~972fps. Regardless of twist rate I can almost guarantee that the 18gr pellets are going to shoot better (in a good barrel) as the speed for the 14gr is getting up there where pellets can usually destabilize (not always but usually). Most manufacturers though I think keep there twist rates between 1:16"-1:18" twists. But there are some 1:19" twists that I know of too one being the AAA EVOL Tac .22 non HP. It's there pellet shooter. They have a EVOL Tac .22 HP which shoots 30gr slugs and it has a 1:18" twist. WAR .22 barrels are 1:19" twists. Edgun barrels are 1:16" twists. Most guns with LW barrels are 1:17.7" twists. I think CZ barrels are also.

[KnifeMaker]

MIke


The Airgun world is an incredibly strange and convoluted world.


It is oddly charged with political leanings. Even though we can't comment on politics, it is strong in the AG community. 


Due to this strange bedfellow relationship, many consider airgun shooting not real shooting. Nor do they see air GUNS, as guns. People who would not touch a "real Gun" as they call them, are shooting ag's and thoroughly enjoying them. Where they would shake in fear if the projectile were propelled by gas generated by combustion rather than stored energy, whether by spring, for compressed gasses. 


For this and other reason, even though both are shooting sports, most of what has been learned thru the last century or so is being completely ignored.
It is truly an industry living in ignorance is bliss mode.   


What has been learned in Stock design, trigger design, twist rates, you name it, is virtually and conspicuously missing.


We end up with twist rates that are completely wrong.  Stocks that are awkward and very unnecessarily heavy. Barrels affixed to actions with one or two set screws. Barrels that would better serve as milk shake straws. Twist rates that are completely wrong. No rhyme or reason other than that is what worked 50 years ago with very low power springers in indoor shooting galleries, (in Europe), made of overly soft cheap steel. And I'm just getting started.


Just showing a pic of a firearm can get you banned on most AG Forums. Yep, politics is forbidden, yet it is just behind the curtain like the Wizard of OZ. Pulling all the strings. Pretty much setting what people can think and ay. Strange and dangerous to say the least. But resistance is futile. you will comply. Period. LOL   (Never seen AG's banned on Firearm sites,odd).


Questions are ask in complete ignorance everyday on all AG forums, that have been simple basics in the Sport Shooting World for 200 hundred years.  So your questions are quite valid. It is almost as if the AG industry works over time to keep their customers completely in the dark.


A perfect example of this is the race to high velocity you see in the Big Box Stores. Seasoned AirGunners know full well that wasp wasted pellets cannot shoot well at all much over 900 fps. At any range other tan kiddy stuff, you know, cans at 10 feet, LOL, they spiral completely out of control.


The longer the range, the worse they are. Yet, there it is. High velocity with tin pellets, canned hunts being toted as proof of the superiority of the high fps. When nothing could be further from the truth.


It is one of the strangest sports you can fall into. Clouded in mystery, steeped in misinformation, and ignorance perpetuated by even the top manufacturers.


Enjoy the minefield. A real open minded experienced shooter will easily recognise the hurdles, and simply walk around them.


Ignoring it all, and going your own way, guided by what you already know from the Powder Burner world will go a long way in making the proper decisions.


Knife   

[Jonnie]

Ok, this guy has a dumb question.
What is considered a faster or slower twist rate.
Example, 1-10 and 1-20. Which one is faster?

[dmeguy]

Ok, this guy has a dumb question.
What is considered a faster or slower twist rate.
Example, 1-10 and 1-20. Which one is faster?

1:10 would be one revolution in 10" versus 20" for the 1:20. 1:10 is faster.

[Mike West]

Awww a sigh of relief.

Thank you the concise,honest and informative answers guys.
I now have the info. to figure it out from my own ballistic education and experiences.

 A lot of the nonsense I’ve been reading and watching kind of makes sense now.

Well at least this confirms what I was thinking in the 1st place.

Thx again for the help.

[SAGERAT NITEMARE]

There are only 4 parameters that are asked for with twist calculating software...

1.   VELOCITY
2.   BULLET LENGTH
3.   BULLET DIAMETER...and
4.   IF IT HAS A BOAT TAIL.

These parameters specify OPTIMUM TWIST...and anyone who has done this AG/PB game for any length of time understands that twists on EITHER side of this "OPTIMUM TWIST RATE" can work just as well, the pellets missed that school lesson...not sure why people get all anal over twist rates...most barrel makers/rifle makers understand this very well and also understand what bullet weight/pellet weights work the best for specific calibers.

Fast forward to today with AG's and all the changes in pellet design, velocity, profiles etc and SOME of that goes out the window but not all...as long as you stay with "common" usage you don't have to think and sometimes it is better if you DON'T think...just like the new and old pig farmers - the new one played Mozart to his pigs and the old one kept telling him NOT TO because it just upset the pigs and made them squeal louder.

If you want to take advantage of the newer "goodies" then by all means pick a pellet and a twist that works best for THAT SPECIFIC pellet and get going.  Again you really don't have to get headaches over it because it has been done already and the specific info is there/available for the using.

It's a bit humerus to watch and hear all the "stuff" coming out in vids with the 38/45/50 cal AG's and what the authors say what you can and can't use.  I have 32 to 54 cal BP rifles that toss relatively heavy, FN bullets at velos ranging from ≈750 fs to just over 900 fs and have NEVER had any trouble taking game up to the size of a moose(with the larger cals!!! ) and have the bullet pass completely through 4-6 ft of animal...basically what a 45 cal AG can do with a ≈400 gr pellet on Helium.

This AG sport is becoming more and more interesting the more I read.  I've spent 60 odd years experimenting with all kinds of powder burners starting in the early 60's but I'm somewhat burned out now and I will leave the experimenting to the younger members and enjoy reading about it online.

Good Shooting.

[Ribbonstone]

Do agree with much of this....it's as if the actual twist is a secret that don't want commonly spread about.  Custom barrels are more willing to mention twist rate than factory barrele,but even there I'll self-check.

[Mike West]

Good read guys and thx for the links.
 I got the information I need now to research what I wanna know and make an intelligent decision.

[rsterne]

Fred, you are only partially correct.... That is all that is asked for by the simplified calculators online, and in fact some don't even ask about a boattail…. In addition, most of them don't work properly Subsonic.... The Kolbe Twist Calculator asks for many more dimensions, including nose length and meplat diameter, boattail length and base diameter.... It is based on the "McGyro" software developed by Robert McCoy of the Aberdeen Proving Grounds.... It produces a chart giving the ideal twist (for an SF = 1.5) that looks like this....



In addition, you can input the twist rate of your barrel and it will also produce a chart of the SF, both are plotted against velocity.... Note the HUGE increase in RPM required to maintain stability as the bullet drops below the speed of sound....



NONE of the twist calculators take into account the drag induced stability of a Diabolo (waisted) pellet (they don't allow you to input the "waist"), and hence predict a faster twist than necessary for pellets.... In fact, if you use the twist predicted using just the velocity, length and diameter, you will very likely see the pellet develop a spiral flight path at some distance as it travels downrange, due to Dynamic Instability.... The available twist calculators simply DON'T WORK for pellets.... They only predict Gyroscopic Stability....

Dynamic instability is usually worse when the gyroscopic stability is too high (eg SF>4) and increases as the pellet slows as it goes downrange.... It is caused by an unstable combination of Precession and Nutation, which are the two types of yaw a bullet sees in flight....



The above diagram represents the position of the nose, relative to the position of the base (the center of the diagram)…. You can see the effect it causes when the pellet has dynamic instability, it flies like this....



The cure for dynamic instability is usually either a lower velocity or a slower twist rate.... Both reduce the RPM....

Bob

[SAGERAT NITEMARE]

Hummm...seems like my last post didn't come through...just as well, it sounded like I had my fangs out and my sword half unsheathed and it wasn't meant to come out that way.

My intent was that "too much information" isn't necessarily a good thing except to those with extensive knowledge of this subject.

All those "fancy" programs are really only useful to long range shooters...I mean LONG range...over 1000 yds and with guns and projectiles capable of accuracy in the 0.100" range.

Besides just how many "Illuminati" even have a "computerized" shooting system.

The simple twist, free for the taking, programs provide ALL the info needed for MOST shooters, AG OR PG...anything more just confuses the issue.

I went down that "twisty" road a long time ago when I was bench-resting and I could hardly see any positive results for the noise due to conditions.  If I had todays bullets and powders and other components that might have changed.  When things went good I could shoot a 10 shot 200 yd 22 cal group not much bugger than bulled size...WITH a standard 1-14 twist and 50 gr length bullets...when things went sour I was lucky to hit the ground.

For those experimenters with deep pockets all this specific knowledge is fun to play with and toss about...otherwise I think it should go into specialized links for those that just want to get their feet wet without getting drowned.

Good Shooting.

[rsterne]

If you know of a twist calculator that works for Diabolo pellets, not just for predicting that it won't tumble from too slow a twist, but that it won't spiral downrange from too fast a twist....PLEASE link to it, and I've been searching for one without success.... Apparently so have most of the airgun manufacturers, as their result, IMO, are not much better than a wild guess.... Why else would one of the top airgun barrel makers in the world use the same twist rate for .177, .22 and .25 cal.... and then a FASTER twist rate for .30 and .35 cal....

Bob

[SAGERAT NITEMARE]

I don't want to get into a protracted discussion on twist rates vs whatever... and I've never come across a SPECIFIC twist rate for SPECIFIC projectiles...that is WAY beyond the purview of the average shooter and doesn't matter one whit to any but the most SPECIFIC minded shooters. 

All that minutia doesn't work worth a hoot at the distances related to airguns...it might be additive, but I don't think many shooters, guns or pellets are accurate enough to cut through the noise and actually show any value.

Hey...If YOU want such a program I'm sure everyone with an interest in one would be very appreciative if you would do the research and build a software program...or maybe someone with the requisite skills will read these discussions and do one...although I'm not sure IF it would be very applicable... but who knows unless it's done.

I'm sure you are knowledgeable enough to understand and know the answer to your last query...over 22 cal pellets are LONGER(for the most part) than <22 cal projectiles and the simple twist programs provide adequate answers.

Not sure what all the hoo-haw is about anyway between diablo style pellet and some projectile with "straight sides". 

I would really like to see an ACTUAL high speed video of the air turbulence surrounding a diablo pellet and some ACTUAL test data over say 100 yds...NOT someones "ESTIMATED VIEW".

Good Shooting.

[Taso1000]

Not sure what all the hoo-haw is about anyway between diablo style pellet and some projectile with "straight sides". 

I would really like to see an ACTUAL high speed video of the air turbulence surrounding a diablo pellet and some ACTUAL test data over say 100 yds...NOT someones "ESTIMATED VIEW".

Fred,

Ballistic coefficient is a measure of, in our case, a projectiles ability to overcome air resistance in flight.  It is calculated and not an "ESTIMATED VIEW".

Diabolo shaped projectiles have very high drag by design to self stabilize in flight.  Their ballistic coefficients are very low compared to straight walled and aerodynamically tuned bullets.

I will agree that at short distances within 50 yards it's not really a huge concern.  But if you are trying to shoot beyond 100 yards the higher bc bullets offer a significant advantage of flight path and retained energy compared to diabolo shaped pellets.

Thanks,

Taso