Crazy theory

[wannabe_shooter]

Hi all,
I'm new here so if I'm breaking any protocols I apologize in advance.

I know a guy who has this crazy theory about rifle barrels that seems kind of hard to believe, so I thought I'd bring it here to the experts.

His idea is that the bullet does not need actually to touch the rifle barrel through the last part of the barrel, and in fact he claims it's better if it does not. It's based on some wild notion of "supersonic boundary layer" which supposedly allows the bullet to be supported and guided by a high pressure film of gasses. Well I know that the heads of hard disk drives are supported by an air film, basically the same idea as an air hockey table, and some really high speed bearings are gas lubricated, but does this work for bullets?
What do you think, will that actually work or is the guy just wacko?

 

[Keith Glasscock]

We will only know once it is tried and either succeeds or fails.

I can guess, as anyone else here can, but in the end, an experiment will tell the truth.

 

[357Mag]

Wanna -Be -

Howdy !

What is meant by the statement.... " better if it does not " ?
Better accuracy ? Better barrel life ? Better/higher vel compared to a standard barrel of otherwise similar specs ? What would be the perceived benefit(s) ?

Rifling in the barrel is utilized to impart spin to the bullet; as bullets are typically spin-stabilized.
By necessity, this means the bullet must contact the rifling in a useful manner.

As an observation: with " squeeze bore " and hand-lapped accuracy barrels, they strive to make the barrel "tighter" in pretty much the same area where the theorized smooth section would be.
Two opposing ideas, fer sher.

If nothing else, I'd think the theory barrel would produce a tad les vel than an otherwise comparable conventional barrel; because of additional expansion space provided the powder combution gasses by the smooth section.

I do like the challenge to exisitng norms.


With regards,
357Mag

 

[JPeelen]

Where would the air gap between bore and projectile come from so that there is space for a boundary layer?
Bore diameter near the chamber and the muzzle is the same; if anything, its a little tighter towards the muzzle. A fired bullet has the same outward dimensions as the bore dimensions of the barrel. If the theory were true, its diameter should be much smaller.

Why exactly does your friend think it would be better if the projectile did not touch the rifle barrel in its last part of travel?

 

[CJ6]

Sounds like a tight bored "Bloop Tube".

 

[wannabe_shooter]

so I guess "better if it does not" means that the muzzle velocity would be higher. The theory being that there is essentially no friction between the bullet and the barrel in the last several inches. I guess I wasn't clear about that, but the plan would be that the bore in the end of the barrel would be a small amount, maybe .001" larger than the bullet diameter. So there would be a tiny gap between the surfaces.
However, would accuracy also be affected? I've come across several posts which tend to indicate that barrel length is not correlated to accuracy. So apparently, as long as the portion of the barrel which does contact the bullet is of high precision, then anything that doesn't contact the bullet doesn't matter. Yes??
Is it true that sometimes the muzzle is counterbored to improve accuracy?
Keith, I like your suggestion. The best way to know for sure will be to try it.
It seems to go against everything I've read, which admittedly is not a whole lot. I wonder whether anyone else has ever tried it.

 

[357Mag]

Wanna Be

Howdy, again !

Don't think the air gap could hold powder combustion gasses and pressures at bay.

For experiments, perhaps use of a highly precise screw-on ( " smooth-bore " ) false muzzle ?


With regards,
357Mag

 

[JBO]

Sounds like a tight bored "Bloop Tube".

Many guy's on other 22 rimfire forums have experimented with this and found they just add more weight on the end of the barrel turning them into an extended tuner with no increase in accuracy shooting through dead air space. One of the well known experts that expresses this theory is Bill Calfee.
I'll make a prediction you won't see people on the shooting line with short barrels and "Bloop" tubes in the near future.... I do think you'll see more and more with tuners.

 

[Dusty Stevens]

All youd have to do is chamber up a barrel and forget to cut that inch off the muzzle to see. Hint: that loose 1" really kills accuracy so his theory is 180deg out

 

[GrocMax]

There's merit to the theory. I challenge anyone to push a bullet down a cold dry bore at 1" per second and tell me there's less copper deposited than 100 rds fired, with NO heat. Rub a piece of 101 copper across a piece of smooth steel, it'll mark it like a crayon. At the gaps we're talking about (molecules) there's virtually no significant leakage forward of the bullet even at the pressures encountered. If there was 100% metal to metal contact stuff would wear out FAST. Why do throats/leades show wear? Duh. Moving too slow to form a boundary layer, deforming the jacket and metal to metal contact. Bore taper at muzzle, over a short distance, metal to metal contact. Ever recovered an intact fired bullet? (think fired in the air, dropped in a lake) Smooth as silk, slight marking in the corners of the grooves. Ask yourself why very smooth polished bores copper up quicker.

Food for thought- I watched 3 20 Practical rounds get fired at a 100 yd target, while chronographed, thru a 223. Take a guess at what the group size was, and what the velocity was. None of them keyholed.

 

[wannabe_shooter]

A couple more dumb questions - thanks for your patience

What is a bloop tube?

GrocMax, in the experiment you mentioned, do you mean that a .20 caliber bullet was fired through a .223 caliber barrel? So in that situation, would the bullet ever have been in contact with the rifling? Oh, and I give up, what was the group size and velocity and how did it compare to "normal"?

 

[ab_bentley]

While the theory may be true, our projectiles aren't perfect. This would lead me to believe that if the bullet wasn't guided via lands the imperfections would take over and send that bullet right or left. I could really only seeing it work for FB bullets with a short ogive and longer bearing surface. I mean we are experimenting with bore rider bullets and muzzle loaders are using similar tech. But each of those instances we're still using the lands to prevent bullets from crashing into the bore.

Adam

 

[1lnbrdg]

Is it April 1 yet?