Backspin to extend range of round ball projectiles in air rifle barrels

[UnderPressure]

The moderator who closed my thread told me I should start a new thread in order to answer the post below:

https://www.gatewaytoairguns.org/GTA/index.php?topic=175694.msg155989225#msg155989225

Russ,

I think for an external magnet to "see"  a steel BB inside the barrel to apply the rotational friction, the barrel needs to be non-magnetic, and thin walled.  So, steel is out; unless you somehow magnetize only the upper "strip" of the barrel.

My concern is the amount of blowby you will get from a ball that is so loose that it makes contact only with the "friction" side of the barrel.  Even more importantly; loose fitting projectiles are anathema to "accuracy".  So, perhaps a short tight section at the muzzle would be required (that does not brake out all the rotation you battled to induce). While clever and all, how much velocity can one get from such a system, using ball of sufficient weight to do more than puncture paper?

This thread started with you asking for the most versatile caliber.  While some might lament the scope drifting away from that, tolerating such drift is how new ideas are spawned.  For instance; what if you used the principle that applying a vacuum to a barrel before shooting, enables much higher velocities at lower driving pressures?  How do you like 2500 FPS delivered by 80 PSI input pressure? (third video below)

Yes, this is more of a lab arrangement, than something to keep the wolves at bay.  But since this thread has taken a turn, so to speak; perhaps more turns can't hurt:

Subscriber, yes a .177 steel BB used in a .230" smoothbore occupies only 59% of the bore's surface area thus allowing 41% of the bore's area for the gas to escape around it. (information about bore diameter referenced here--> https://www.gatewaytoairguns.org/GTA/index.php?topic=175694.msg155989151#msg155989151 )

Yes, I could see a lot of gas being wasted in that scenario.

However, the airsoft BBs (sized 5.95mm +/- .01mm, reference here--> https://www.gatewaytoairguns.org/GTA/index.php?topic=175694.msg155988803#msg155988803) are still getting backspin despite being in barrels as tight as 6.01mm (normal barrel size is 6.08mm).

5.95mm = .234"
6.01mm = .237"
6.08mm = .239"

5.95mm BB in a 6.01mm barrel occupies 98% of the bore's area.
5.95mm BB in a 6.08mm barrel occupies 96% of the bore's area.

So much much better than 59% of the bore's area.

So with that noted can a person reasonably obtain steel round balls with the same roundness tolerance as air soft BB's....and thus being able to use a tighter bore? I'm thinking it would be possible via buying steel slingshot balls (if not that then definitely steel ball bearings).

[rsterne]

Vacuum cannons work because the Sectional Density of the projectile (eg. ping pong ball) is extremely low.... ie it has very little mass to accelerate and a large cross sectional area for the air pressure to work on.... This would mean that the mass of air in the barrel in front of the ball would be a large percenage of that of the ball, and not only would that mass have to be accelerated along with the ball, but it would provide resistance to the passage of the ball down the bore.... Using a vacuum applied to the muzzle eliminates both problems, and in addition increases the pressure difference across the ball by 15 psi.... In a 3000 psi airgun, that would make little difference to the total force, but when you are powering the vacuum cannon with a shop compressor, it adds about 10% to the force (or more), while eliminating the drag and air mass in the barrel....

Trying to apply these same principles to a PCP shooting metal balls is a waste of time, because their SD is much too high, and the larger you make the caliber, the higher it gets.... It is simple physics, that mean that what works in a caliber of over 1", with one type of (extremely low SD) sphere, will not work in a (practical) PCP....

Bob

[rkr]

Nickel plated lead shots is what I shoot from my Drozd, much more accurate than steel BBs as it gets spin from rifling. There were discussions of using various types of muzzle mounted spin creating devices rin the old Drozd forum but IIRC no working prototypes ever appeared.

[UnderPressure]

Nickel plated lead shots is what I shoot from my Drozd, much more accurate than steel BBs as it gets spin from rifling. There were discussions of using various types of muzzle mounted spin creating devices rin the old Drozd forum but IIRC no working prototypes ever appeared.

Do you remember how they planned on implementing backspin with a rifled barrel? Did they plan on using undersize BBs as part of the strategy? Something else?

Some airsoft guns have rifled barrels, but the BB is sized smaller than the lands:

"How is it physically possible to have a rifled barrel impart a spin on the BB and combine it with the Magnus effect of the hop-up? It is two totally different axes of rotation!" A1. Actually, the barrel ISN'T "rifled" in the standard sense of a real gun. Yes, the inner barrel has spiral rifling grooves in it, but the BB does NOT touch the groove. The purpose of the TWIST inner barrel is not to put a rifling spin on the BB. It is to put a "cyclone" of air around the BB, to help float it through the inner barrel and PREVENT the BB from touching the side walls of the inner barrel at all.

[rkr]

Nickel plated lead shots is what I shoot from my Drozd, much more accurate than steel BBs as it gets spin from rifling. There were discussions of using various types of muzzle mounted spin creating devices rin the old Drozd forum but IIRC no working prototypes ever appeared.

Do you remember how they planned on implementing backspin with a rifled barrel? Did they plan on using undersize BBs as part of the strategy? Something else?

Some airsoft guns have rifled barrels, but the BB is sized smaller than the lands:

"How is it physically possible to have a rifled barrel impart a spin on the BB and combine it with the Magnus effect of the hop-up? It is two totally different axes of rotation!" A1. Actually, the barrel ISN'T "rifled" in the standard sense of a real gun. Yes, the inner barrel has spiral rifling grooves in it, but the BB does NOT touch the groove. The purpose of the TWIST inner barrel is not to put a rifling spin on the BB. It is to put a "cyclone" of air around the BB, to help float it through the inner barrel and PREVENT the BB from touching the side walls of the inner barrel at all.

There was talk about a short rubber cap that would grab the BB and cause spin + stabilise it. IIRC the bottom of the cap was longer for back spin - or perhaps it was top. Similar things but made of steel were considered as was 1" rifled section screwed on the muzzle (that was actually before we had ST barrels).

[UnderPressure]

Deleted.

[Chris USA]

I played around with putting small, very strong magnets on the 499 barrel to induce back spin. It seemed to help,.. most of the time. The 499 trigger is not the best. I also did it on an 880 barrel (had cut the shroud/cover off to make it into an arrow-over barrel shooter. Another story,... but did work,...sort of. Not enough air blast)

I also tried it on a 760? that had a solid barrel.

Results were mixed, but overall seemed better. The 499 showed the most consistent improvement. The 880 and 760,.. not so much.

A slight oil film on a bb can help any perceived blow by. I tried spiral, all at muzzle, all at breech, spaced, all at top, all at bottom,. etc. Like 6 magnets.

It was a fun experiment but I can't say that it yielded any earth shattering results. Oh well,.... 

[Bryan Heimann]

I Am pretty sure there have been backspin barrels of some sort implemented on paintball guns successfully.  Maybe look in that direction

[UnderPressure]

I Am pretty sure there have been backspin barrels of some sort implemented on paintball guns successfully.  Maybe look in that direction

Yep, backspin has been used in Paintball via flatline barrel and Apex tip:

https://www.gatewaytoairguns.org/GTA/index.php?topic=175694.msg155988621#msg155988621

https://www.gatewaytoairguns.org/GTA/index.php?topic=175694.msg155988995#msg155988995

It has also been used in .177 BB guns:



Also from the comments of the above video:

Victrola Fix
2 years ago
I was also very surprised to find an actual hop-up unit in my KWC Tanfoglio Witness 1911 .177 cal. It seem to work very well with the steel BBs, this gun shoots with the same muzzle velocity as my Daisy Red Ryder, yet the BB drop happens much further down range.

[Nomadic Pirate]

I still don't think that backspin on a lead ball, especially on a big bore lead ball will even come close to the benefit imparted by the standard rifled barrel, ....not even close.

[SilentMatt]

I still don't think that backspin on a lead ball, especially on a big bore lead ball will even come close to the benefit imparted by the standard rifled barrel, ....not even close.

That's for sure.


I remember when the Flatline paintball barrels came out like 20 years ago. You could dial in the amount that the nub hung in the barrel to get optimum range. If you added too much, the ball would curve up pretty drastically. None of the pro's or the woodsball snipers used them, a barrel with fitted inserts that matched the balls you used was always more accurate.

 Between the kids and I, we have five upper end airsoft guns that all have the Hop Up system. It's great for squeezing out a little more range, but far from accurate.

[VaporTrail]

I was big into airsoft at one point. Hop up caps/sleeves were in all of the rifles or pistols I owned. Basically just a rubber flap that the BB would rub over before going down the barrel.

Adjusting the hop up wasn't really for accuracy, it was more for linear trajectory. I say this because when you're firing a BB that is anywhere from .15 to .43 of a grain, even a fart can alter trajectory. So we'd adjust hop up to give us the longest straight path.

Accuracy was good enough to hit a player up to 30yds, but further than that you're basically having fun with the full auto function and sending upwards of 60 BBs in that general direction.

I still have a Sniper rifle that is good out to about 40/50 yards, but after that, there's so much backspin on the BB that it actually has a steep curve up.

[Doug Wall]

As Paul said, Hop-Ups don't do anything for accuracy, the backspin creates lift on the BB to make the trajectory flatter. You're much better off with a proper projectile in a good barrel. Any muzzle mounted device to try to make backspin would probably act like a bad barrel crown, and cause the accuracy to go to 43LL.

[UnderPressure]

I remember when the Flatline paintball barrels came out like 20 years ago. You could dial in the amount that the nub hung in the barrel to get optimum range. If you added too much, the ball would curve up pretty drastically. None of the pro's or the woodsball snipers used them, a barrel with fitted inserts that matched the balls you used was always more accurate.

Flatline barrel was not adjustable and a person needed to use undersize paint to make it work (re: it was an upward curved barrel with roughness at the top of the curve to impart backspin).

Apex, on the other hand, was adjustable and a person could size paint to barrel and adjusting the tip for backspin did not hurt accuracy:

https://www.pbnation.com/showthread.php?s=db396e2348ec24db4e01b8b68a933d0b&p=73337182#post73337182

[UnderPressure]

Nickel plated lead shots is what I shoot from my Drozd, much more accurate than steel BBs as it gets spin from rifling. There were discussions of using various types of muzzle mounted spin creating devices rin the old Drozd forum but IIRC no working prototypes ever appeared.

Do you remember how they planned on implementing backspin with a rifled barrel? Did they plan on using undersize BBs as part of the strategy? Something else?

Some airsoft guns have rifled barrels, but the BB is sized smaller than the lands:

"How is it physically possible to have a rifled barrel impart a spin on the BB and combine it with the Magnus effect of the hop-up? It is two totally different axes of rotation!" A1. Actually, the barrel ISN'T "rifled" in the standard sense of a real gun. Yes, the inner barrel has spiral rifling grooves in it, but the BB does NOT touch the groove. The purpose of the TWIST inner barrel is not to put a rifling spin on the BB. It is to put a "cyclone" of air around the BB, to help float it through the inner barrel and PREVENT the BB from touching the side walls of the inner barrel at all.

There was talk about a short rubber cap that would grab the BB and cause spin + stabilise it. IIRC the bottom of the cap was longer for back spin - or perhaps it was top. Similar things but made of steel were considered as was 1" rifled section screwed on the muzzle (that was actually before we had ST barrels).

If steel BBs are smaller than the rifling lands then maybe something like that could work. (I've read that steel BBs are sized .171" to .173")

But then it would still, of course, suffer accuracy problems being an undersize projectile as compared to the .177 sized nickel plated lead shot from Ballistic products which is .177" +/- .003".

Maybe some kind of magnetic hop-up system to help align the steel BB for accuracy (in addition to flattening trajectory)?

From the link in the opening post:

https://www.pyramydair.com/blog/2006/05/can-a-common-bb-gun-be-accurate/#comment-346629

Bought a Daisy Grizzly just for plinking but was astounded at the lack of accuracy. Watching the BBs fly was like watching Phil Niekro pitch. I was looking at a 1 foot pattern at 50′. I measured the bore: .230 so I started to think about sleeves and there is off the shelf precision tubing that would bring that down to .187 with an OD of .25… Then I started thinking about a magnetic ring to maybe center the shot?…It then occurred to me that pulling the shot to the top of the barrel might solve the problem. If I could get the BBs to roll out the top side of the barrel it would straighten out the shot and put a back spin on the BB thereby leveling out the arc as well (similar to a softballers rise pitch) I had a bunch of fairly powerful button magnets (1/8″ dia x 1/16″) which I lined up on the top of the barrel 3/8 of an inch center to center. Now It’s shooting less than 1″patterns at 50′ at a much flatter trajectory. Those magnets are just taped there now but I’l be breaking out the epoxy soon.

Whatever he did worked.

With that noted, subscriber made some good points to the use of magnets. (I'm still trying to figure that out. Example: Steel acts to block magnetic field....but it can also be used to extend the magnetic field.)

[SilentMatt]

Flatline barrel was not adjustable and a person needed to use undersize paint to make it work (re: it was an upward curved barrel with roughness at the top of the curve to impart backspin).

Apex, on the other hand, was adjustable and a person could size paint to barrel and adjusting the tip for backspin did not hurt accuracy:

https://www.pbnation.com/showthread.php?s=db396e2348ec24db4e01b8b68a933d0b&p=73337182#post73337182

Like I said, it's been around 20 years since I messed with them, but thanks for clearing that up...

It didn't hurt accuracy because they weren't accurate to begin with. I still have a Tippmann A-5, it's minute of person at 30 yards.

[UnderPressure]

Flatline barrel was not adjustable and a person needed to use undersize paint to make it work (re: it was an upward curved barrel with roughness at the top of the curve to impart backspin).

Apex, on the other hand, was adjustable and a person could size paint to barrel and adjusting the tip for backspin did not hurt accuracy:

https://www.pbnation.com/showthread.php?s=db396e2348ec24db4e01b8b68a933d0b&p=73337182#post73337182

Like I said, it's been around 20 years since I messed with them, but thanks for clearing that up...

It didn't hurt accuracy because they weren't accurate to begin with. I still have a Tippmann A-5, it's minute of person at 30 yards.

We don't know what gun was used in the link.

All we know is that the shooting was done from a bench at 130' (i.e. 43 yards) and the same J&J barrel* (with Apex tip attached) was used for both targets. For one target the Apex tip was turned off (meaning no  ramp touching projectiles as the left they gun) and for the second target the Apex tip was turned on (meaning the ramp touched the projectiles as they left the barrel creating backspin).

Here was the tester's conclusion:

I think it's a perception thing...it's much easier for your eye to follow the flat trajectory of the APEX'd shots and notice the spread than it is to follow the highly arched shots from a standard barrel.

*Not the Tippmann flatline barrel which forces the user to use undersize paintballs in order to get backspin.

P.S. One thing that I noticed is that nobody disagrees that an APEX tip will allow paintballs to go a lot farther. However, with the paintballs being able to travel so far they now have a different problem: Not enough energy left for reliable breakage. (a paintball bouncing off a target doesn't count. It needs to have enough velocity and energy left to break the gelatin skin of the paintball capsule to release the paint.) Being able to shoot farther doesn't help anyone's game unless the paintball can also break at the farther distance.

[UnderPressure]

I still don't think that backspin on a lead ball, especially on a big bore lead ball will even come close to the benefit imparted by the standard rifled barrel, ....not even close.

I suspect rifling matters less at low speed for lead round ball.

For example, if shooting at 350 FPS I would expect less deformation of a lead round ball than I would at 950 FPS.

With less deformation of the round ball to another shape the need for gyroscopic stability should decrease.

[rsterne]

Be VERY careful about ricochets with metal balls at low velocities.... They don't seem bad at 500 fps, but at 300-350 fps can end up coming back at you with significant energy remaining.... depending on the target.... My personal opinion is that the whole concept of flattening trajectory via backspin is a non-starter for metal projectiles where a reasonable degree of accuracy is expected.... I would put my energy (and $ )elsewhere....

Bob

[UnderPressure]

I played around with putting small, very strong magnets on the 499 barrel to induce back spin. It seemed to help,.. most of the time. The 499 trigger is not the best.

You mention "It seemed to help.... most of the time. The (Daisy) 499 trigger not being the best."

Overall, did you notice improving accuracy via the method of using a magnet to induce backspin?