friction

[JAMES L.SMITH]

what would happen if icould reduce
friction between the barrel and
the bullet? would pressure go up?
or could the bulletbe forced past
lands grooves? thanks.

 

[bergie]

Hey James,
Reducing friction between the barrel and the bullet is desireable, as it results in increased velocity without the increase in pressure that is usually needed, an added benefit is reduced fouling. Methods for reducing friction have usually involved lapping the bore, lubricating the bullets etc., with most recently the use of "moly" coatings on bullets. The fit of the projectile to the bore is such that the rifling will still firmly grab and spin the bullet, the bullet just slides through the tube a little bit easier. It would take a pretty significant increase in velocity or reduction in friction for a proper sized bullet to skip past the rifling without being spun.
Bergie

 

[KOG]

Hypothetically, what about a teflon barrel and a teflon bullet? I know the coefficient of friction is really low for both.

 

[aztec777]

James-When I was in the Army, I got lucky enough to be assigned as a driver to the Sgt. Maj. He had worked on a project in where a projectile would move down a 'bore' without touching anything. The concept had to do with a magnetic field within the barrel and the projectile riding an electromagnetic 'rail'. The theory is sound, IMO, although he did not reveal how momentum was attained. He did mention incredible velocities were attainable. Anyone else heard of this?

Steve

 

[Bud Helms]

Yup,

And just a few weeks ago there was an extensive thread on that very subject. Maybe one of the moderators will be kind enough to provide you with the link to it. It may be archived by now, so ...

As of fairly recently, you can buy bullets, loaded cartridges or the kit to treat your own bullets with a dry form of molybdenum disulfide. It is a surface treatment. One method I saw is by physical impregnation (it's rolled on/into the sutface). Another is a spray can that you spray on to the bullets, let dry and then load as normal. I think. 'Haven't had time to try it yet.

Any time you can reduce friction between the barrel and the bullet you are getting ahead. I once read that on average (?) 35% of the energy during the internal ballistic cycle is lost due to bullet-to-rifling friction, engraving pressure, centrifugal force, and the force spent to move the mass of the bullet itself.

A teflon barrel wouldn't last long, though, even teflon-to-teflon. Look at the bottom of your teflon cooking pans. The moly treatment works because it is embedded into the surface, not a coating, as I understand it.


[This message has been edited by sensop (edited February 27, 2000).]

 

[KOG]

Aztec, I think what you are talking about is the railgun. I think it works like a particle accelerator. You have magnets in line and as each one fires off it pulls the projectile along, something like that. I don't think it's very practical yet.

 

[James K]

Hi James,

Magnetic guns aside, in the normal rifled firearm, the bullet is groove diameter. In other words, the bullet is not forced into the grooves by gas pressure (as the old Minie ball was); it is the same diameter as the groove, and the land is forced into the bullet. This requires pressure. Friction and its reduction is a separate issue.

Jim

 

[Bud Helms]

How do you mean a separate issue Jim? You mean cutting vs sliding friction?

 

[Gale McMillan]

A bullet that has reduced friction will have lower pressure with the same amount of powder. To obtain an advantage the volume of powder must be increased back to the original pressure figures and the increased velocity will be apparent There were a lot of disappointed shooters that found that their velocity went down with the same load once they started molly coating bullets. In my eyes I haven't signed on to the molly coated bullets due to the molly fouling created. Time will prove or disprove the process

 

[Bud Helms]

Gale,

I didn't know there was a fouling problem.

Is there any feedback from users on accuracy or any other characteristics?

Good to see you posting again, sir.

 

[Gale McMillan]

Sensop: The fouling I spoke of is wax and molly. It is so hard that a brush and solvent won't touch it, The only way that it can be removed is with an abrasive like JB. I fired eighty rounds of coated bullets through new 762 sniper rifle and when I bore scoped it the molly build up was from the top of the vertical side of the rifling out to the center of the groove. It almost looked like a ratchet rifling. We tried every thing in the shop and nothing but JB would remove it.I am of a mind that you are exchanging copper fouling which isn't too hard to remove for Molly fouling which has to be cut out. Not a good exchange!There has been a lot of good BR rifles quit shooting because of it.

 

[George Hill]

I havent used Moly since talking to Gale at the SHOT SHOW...
I dont know about you guys - but I cant afford to replace barrels for the little bit of gain that Moly is supposed to give me.

Oh - and I now have a full selection of Shooters Choice. Thanks Gale!

 

[DOCSpanky]

Had the privelage to speak to a Naval weapons designer who had tinkered with the RAILGUN concept. The Navy had intended it for use as an antiship and anti-shore emplacement type round. Problem was, the power source needed to push the magnets and everything was totally impractical. About the size of a 2 story house and needs a nuke reactor to be able to be used in a repetitive manner. They were also supposedly very fragile which has no place in a combat setting. But easily penetrating 28 inches of solid steel is a wonderfull pro, as was the nearly 40 inches of concrete.

------------------
DOCSpanky HM3 USN
Happiness is a smoking gun and a dead criminal

 

[James K]

Hi, Sensop,

I don't quite understand the question. forcing a bullet through a barrel creates both sliding friction and cutting. If friction were magically reduced to zero, the bullet would still have to be forced through the barrel because the lands still have to cut into it.

Magnetic guns (or at least the ones I have read about) are smoothbore and don't rotate the projectile. Rotation is not needed for high velocity, it is needed for stability. Modern smooth bores stabilize the projectiles by means other than rotation, such as fins.

One use for smoothbores is on tank and anti-tank guns. Since these use shaped charges to penetrate armor, they can't spin the projectile because spinning reduces the effectiveness of the shaped charge. (Yes, I know there are shells that spin the outer part without spinning the charge.)

This kind of stuff is not necessary in a simple rifle.

Reducing friction will obviously reduce pressure and may raise velocity but, as others have pointed out, there are drawbacks to some of the methods used. Nor do the advantages seem to be as great as some claim.

Jim

 

[JAMES L.SMITH]

Thanks to all on input on friction.

------------------

J.L.


JLS

 

[Bud Helms]

Jim,

I think the crux is right here ... and I may have a misconception.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>If friction were magically reduced to zero, the bullet would still have to be forced through the barrel because the lands still have to cut into it.[/quote]

I din't know, maybe I'm picking nits, but ... the lands "cutting" into the bullet is still friction. Isn't it?

Jim:
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>... it is the same diameter as the groove, and the land is forced into the bullet. This requires pressure. Friction and its reduction is a separate issue.[/quote]

sensop:
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>How do you mean a separate issue Jim? You mean cutting vs sliding friction?[/quote]

Jim:
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>I don't quite understand the question. forcing a bullet through a barrel creates both sliding friction and cutting.[/quote]

 

[James K]

Hi, Sensop,

I guess the lands cutting into the bullet would be friction of one kind, but once the bullet is forced into the rifling, that friction is reduced, and what we have is sliding friction between the bullet and the barrel as the bullet moves forward. There is also the friction of the edges of the rifling cut against the rifling as the bullet tries to go straight while the rifling turns.

My point was only that even if the sliding friction is reduced, you don't have the effect of a smooth bore barrel as there is still a lot of pressure required to force the bullet into the rifling. Some of the folks were comparing a rifled barrel to a magnetic gun, which has no rifling.

Jim

 

[Nestor Rivera]

The CRYO-Treatment of barrels is also an attempt to reduce friction

As for Rail Guns I think there is some confusion between a linear Accelerator and a Rail
gun.

a Linear Accelerator uses multiple magnets to push/pull particles at high speeds, uses
include super coliders

a Rail Gun is just a motor of sorts, if lay out the stator of a motor flat (the rails) and place
the rotor (projectile) on them and add DC the Lorenz force will accelerate the Rotor
(projectile) forward. the more DC the faster it goes a variant is a Coil GUN the uses a
coil tube shaped rotor which allows for the use of rod type projectiles


I hope I got all that right.

 

[JAMES L.SMITH]

Thanks again to everyones replys.
the reason i asked this question,is
that i am experimenting with a new
product to see if will work
onguns.the inventor gave me a large
sample to try.i'll let you know
results after tests.

 

[Bud Helms]

Okay, Jim. I gotcha.