Author Topic: "Hop-upping" a round all  (Read 13262 times)

Short start

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"Hop-upping" a round all
« on: April 05, 2014, 07:19:44 AM »
In airsoft, a sport like paintball but using smaller plastic pellets, there is an innovation called "hop-up".  A  piece of rubber protrudes into the bore very slightly and puts a backspin on the outgoing BB which causes it to fly straighter for longer.
An idea I had was to try double patching the top of a ball in a smoothbore to achieve this spin. Has anyone experimented with something like this? I've heard of bending barrels to achieve a backspin, but that sounds iffy.

hpdrifter

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Re: "Hop-upping" a round all
« Reply #1 on: April 05, 2014, 09:44:02 AM »
Is that anything like backspin on a golf ball to make it "fly" longer"?

galamb

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Re: "Hop-upping" a round all
« Reply #2 on: April 05, 2014, 04:31:06 PM »
I think if you want to "achieve spin" you use a rifled barrel.

The method you describe may impart some spin but how would you control the consistency?

Unless you could duplicate it exactly for each shot the point of impact would be erratic at best.

That is why you work up a load/patch/ball/lube combination and stick exactly with that - so that you know with some certainty (or as certain as you can be) where the ball will impact at a given distance.

So maybe if you are horsing around punching paper you might fiddle with something such as this "just to see" what it does, but if you were shooting at game you owe it to your quarry to develop a consistently accurate combination that will allow you to impart a kill shot - you don't want to end up with a "curve ball" that only ends up wounding.

Offline Kermit

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Re: "Hop-upping" a round all
« Reply #3 on: April 05, 2014, 05:47:24 PM »
Seems to me there has been a lot of effort expended in trying to avoid what you are trying to accomplish in round ball flight. But go ahead on, and let us know what you determine.
"Anything worth doing is worth doing slowly." Mae West

necchi

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Re: "Hop-upping" a round all
« Reply #4 on: April 05, 2014, 09:39:39 PM »
Go ahead an try, nothing ventured,,,.
The different dynamics of the air soft pellet mass and it's velocity vrs a lead ball even at low charges is huge.
If I remember correctly, the military of several countries spent many decades trying to improve the accuracy and range of their infantry guns in the 17th, 18th and early 19th centuries.
But what da heck, you might find something they over looked.

DaveP (UK)

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Re: "Hop-upping" a round all
« Reply #5 on: April 05, 2014, 11:08:22 PM »
Hop up is the equivalent of putting massive back spin on a table tennis ball. I never understood the mechanics of it, but it has the effect of generating lift, and the light ball simply soars, travelling much further than you would get with a straight on hit.
Air soft pellets are light and small, a disastrous combination in ballistic terms. The idea of hop up was and is simply to get a bit more range out of the things.
I can't even imagine how much back spin you would need to make a heavy lead ball soar.
Just as well lead balls have better ballistic properties  ;D

gard72977

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Re: "Hop-upping" a round all
« Reply #6 on: April 06, 2014, 10:53:24 PM »
I don't understand how a patched ball can rotate that way?

Online smylee grouch

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Re: "Hop-upping" a round all
« Reply #7 on: April 06, 2014, 11:29:08 PM »
While your at it, why dont you devise a method to consistantly dimple the surface of the roudball too.    ;D

Offline George Sutton

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Re: "Hop-upping" a round all
« Reply #8 on: April 07, 2014, 01:10:02 AM »
Why do you think this would work? The rifling already puts an clockwise spin on the ball. If you could accomplish what you wanted to do, you would disrupt the spin of the ball.

Maybe it would work in a smoothbore if you could devise a way to hold one end of the patch (it would have to be a strip) at the end of the barrel and as the ball leaves the barrel the rest of the patch (strip) would somehow create a backspin.

One part of the patch has to be held in place in order for it to create a backspin.

I think any patch material would be torn to shreds doing what your thinking about.

I consider it an effort in futility. But hey, who knows maybe your onto something.

Centershot
« Last Edit: April 07, 2014, 01:24:27 AM by Centershot »

Old Bob

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Re: "Hop-upping" a round all
« Reply #9 on: April 07, 2014, 03:32:53 AM »
I personally don't understand the need for all this. Back before the Civil War some guys tried to improve the range and accuracy of smoothbore muskets, even including adding wooden sticks with fins (a la rockets) and nuthin' worked. A big part of shooting these things is learning to shoot them well in spite of their ballistic shortcomings and overcome them by practice and working up loads that make the most of the barrels. If you want to impart spin to a projectile you simply rifle the barrel or use a rifled slug.

Offline Daryl

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Re: "Hop-upping" a round all
« Reply #10 on: April 07, 2014, 07:52:57 PM »

The military's of the world found by swaging or casting the ball closer to the bore size (reducing the windage), although increasing loading problems due to the buildup of fouling with fewer shots, it also increased the musket's accuracy.  Thus, they found, as we know today, a tighter fitting ball increases smoothbore accuracy.

 Attempting to somehow improve smoothbore accuracy by causing a spin is easy - use VERY coarse emery or flint paper and scratch a spin into your bore- right or left twist, doesn't matter.   You can use another rifled barrel blank as a 'guide' - easy to do. 

This method actually works fairly well for a number of shots before needing to be reapplied - Dan has mentioned this method here at ALR as possibly being used to day, and definitely was used many years ago.   

This method might be construed as a move outside the flavour of good sportsmanship (by mechanical advantage, seeking unfair advantage in competition) and thus would/should remove that smoothbore from a smoothbore event, I'd expect.

If improved accuracy was desired from your favouite stock design, by all means - put a rifle barrel on that gun, saving the smooth one for shot.imho

Or - you might use a centre-punch and "punch" a DIVOT staight down from 12 o'clock into the bore at the muzzle or very near the muzzle. This "might" impart a backwards spin to the ball - however slight, which might cause it be more stable than normal and not take on the normal 'knuckle-ball' effect which badly effects accuracy, sooner or later depending on the velocity. If it worked, would it be a 'cheat' in competition?  It just might improve a smoothbores accuracy for hunting, as well as having no adverse effect on shot patterns.
Daryl

"a gun without hammers is like a spaniel without ears" King George V

Offline LH

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Re: "Hop-upping" a round all
« Reply #11 on: April 07, 2014, 08:25:05 PM »
do rifled slugs actually work in shotguns?   ???

Offline Daryl

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Re: "Hop-upping" a round all
« Reply #12 on: April 07, 2014, 08:36:05 PM »
sent you a PM, LH

Daryl

"a gun without hammers is like a spaniel without ears" King George V

Offline LH

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Re: "Hop-upping" a round all
« Reply #13 on: April 07, 2014, 10:24:52 PM »
Thanks Daryl,  interesting stuff.  On the smoothbore,  what would filing the barrel off out of square to the bore do?  Maybe impart some spin?  Seems like any spin other than around the axis of the line of flight would cause the ball to fly on a curved path?  I guess if it was a uniform curve it might  be usable.   

DaveP (UK)

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Re: "Hop-upping" a round all
« Reply #14 on: April 08, 2014, 01:10:36 AM »
As I understand it, when the muzzle face is not square to the axis of the bore, the gases will escape earlier on one side than another, and while this can push the projectile off course, I don't see why it might cause a spin.
I think that those of us who are less than totally conversant with maths and mechanics can overthink questions like this very easily. Right now I'm wondering why normal rifling induced spin doesn't cause the ball to follow a sideways curve  :o

Old Bob

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Re: "Hop-upping" a round all
« Reply #15 on: April 08, 2014, 01:38:50 AM »
do rifled slugs actually work in shotguns?   ???

I've never used one so I can't say. I have been told they do, some better than others.

Offline Bill Paton

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Re: "Hop-upping" a round all
« Reply #16 on: April 08, 2014, 02:14:23 AM »
DaveP,  As a spinning rifle projectile falls through the air due to gravity, it does drift sideways--to the left in a right twist rifle, and to the right in a left twist barrel. At very long ranges, this drift is significant. When shooting North or South in the Northern Hemisphere with a right twist barrel, this drift helps to cancel the Coriolis drift effect. The principal is the same as a pitched curve ball. This has to do with the air on one side of the projectile  speeding up because of the twisting, and slowing down on the other side as the ball passes sideways to its spin axis through the air due to gravity. In baseball, the pitcher spins the ball sideways to the direction of flight, causing the ball to curve left or right or up (or potentially down), depending on how he spins it. Like and airplane wing, the faster air has lower pressure effect on the ball than the slower air, thus the ball is pushed toward the faster air. Some military rifles with very long range sights (like my trap door .45-70) have a built-in cant to the long range sight to compensate for the drift.
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Old Bob

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Re: "Hop-upping" a round all
« Reply #17 on: April 08, 2014, 02:45:18 AM »
As I understand it, when the muzzle face is not square to the axis of the bore, the gases will escape earlier on one side than another, and while this can push the projectile off course, I don't see why it might cause a spin.
I think that those of us who are less than totally conversant with maths and mechanics can overthink questions like this very easily. Right now I'm wondering why normal rifling induced spin doesn't cause the ball to follow a sideways curve  :o

Yes, if the crown of the muzzle isn't square, it'll throw the ball off. The only way to produce a backspin would be to slow one side of the ball down. But to do that there'd have to be a hump or dimple and I think that would have the same effect as a damaged crown. I suppose if there was a way to do this near the breech but after passing that point a bare ball will still be "balloting" down the barrel and will go in the opposite direction of wherever it last contacted the barrel. If the ball was patched, either when loading or more likely when firing, a dimple would likely badly scuff or tear the patch.

I've wondered about the effect of rifling myself over the years. The old Ordnance Department tests with the new Minie rifles mention this. There is some lateral drift in rifled arms and from what I've read drift is liable to be greater when the twist is tighter. I'm sure there are other opinions on the matter. Gravity would overcome upward vertical drift and compensating for drop would take care of downward drift.

Online smylee grouch

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Re: "Hop-upping" a round all
« Reply #18 on: April 08, 2014, 02:50:46 AM »
If a ball is spinning left to right on top it should be spinning right to left on the bottom, wouldnt that negate any drift in one direction?  Don't know but am wondering as this has come up in conversation before.

Offline Bill Paton

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Re: "Hop-upping" a round all
« Reply #19 on: April 08, 2014, 03:05:52 AM »
Since the projectile is falling due to gravity, and with a right hand spin (clockwise as seen from behind), the air on the left side of the projectile is pulled up by the spin and "up" by the downward travel of the bullet. The air on the right side is pulled down by the spin, partially canceling the "upward" air due to the fall. So the air on the left is faster and on the right is slower. So the ball moves to the left.
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Offline smokinbuck

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Re: "Hop-upping" a round all
« Reply #20 on: April 08, 2014, 03:42:06 AM »
LH,
IMHO you are way off base with your thinking. First, bending a smooth bore barrel is done to change the POI, windage and elevation, not to make the ball spin. Second, filing the muzzle off center is going to do the same thing, change the POI, due to gas escaping from the muzzle at a different than square angle. File the left and it will push the ball right and vice versa.
Mark
Mark

DaveP (UK)

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Re: "Hop-upping" a round all
« Reply #21 on: April 08, 2014, 10:57:33 PM »
Bill, Thanks for explaining that point. I must confess, the thought only came to me while I was typing, my comment was ever so slightly tongue in cheek. Nice to realise it wasn't a completely dumb idea  :)
The club range only extends to 100 yards, and as I find that an adequate challenge for offhand shooting I have tended to ignore long range issues.

Offline Daryl

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Re: "Hop-upping" a round all
« Reply #22 on: April 09, 2014, 07:42:39 PM »
The muzzles on some American Double Rifles of the 1800's were filed to produce/induce regulation.   The outsides of the barrels were filed to bring the 'balls' together, or filed from the inside to outside to spread the impacts. Filing top or bottom will also influence the point of impact.

A MODERN double rifle firm called "Sabatti" 'used' to used filed muzzles or angled crowning to regulate their modern double rifles.  this received a LOT of bad press in some double-gun forums and now Sabatti is now apparently regulating the barrels before finishing them as is normal for high quality double rifles.

The reason for saying this about Sabatti, is to show you that a ball's or bullets poi can be altered by filing the muzzle - whether on purpose or not.

Gas escaping from one side, top or bottom before the opposite side, will tend to direct the projectile in the opposite direction of the gas's first escape - thus, this system does and has worked - but is NOT recommended.  This could be used to 'regulate' a smoothbore that needs correction and the owner does not want to bend the barrel to achieve it.
Daryl

"a gun without hammers is like a spaniel without ears" King George V

Vomitus

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Re: "Hop-upping" a round all
« Reply #23 on: April 09, 2014, 08:29:47 PM »
   To get away from "knuckling" in my .540 smoothbore, I've jacked up the charge from 60 to 80 grains of 2f. Shoots point of life size rabbit(gong)@100 meters.Tight ball/patch/lube/barrel combination is the first item to get correct.Then I started experimenting with charges. With 60 gr. at 25 I got three shots touching with 2 fliers,not good enough. With eighty grs., she brought them all together. My ball size is .513(a .510 mold that casts oversize perfectly)and a .030 tight woven Carhart type denim. Gives me 15-18 thou compression around the ball. Spinning a ball in a smoothbore sounds oxymoronic to my taste for smoothy fun. If they were made smooth,I shoot 'em smooth.JMHO.

Short start

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Re: "Hop-upping" a round all
« Reply #24 on: April 10, 2014, 02:13:31 AM »
Good responses. I would use this for target shooting and in the interest of science.
I only have rifles so I can't really try for myself yet.