TargetTalk

What are the regulations concerning devices fixed to the barrel and extending beyond the muzzle?

Specifically, can a 'bloop tube' bore be baffled? Can the tube be perforated? Can the tube be open / perforated at its back end, where it is attached to the barrel? Does the bore have to be parallel? Can the front sight be hung forward on a rod? What about several rods, parallel to each other, angularly disposed at the same radius from the bore centre-line, or does this become a slotted tube? When does a bloop tube become a muzzle brake (illegal)? Etc...

ISSF Rule 7.4.1.2:
"Barrels and extension tubes must not be perforated in any way.
Any construction or device inside the barrel or tubes, other than
rifling and chambering for the cartridge or pellet, is prohibited."

Seems pretty plain to me.

Eric U

Pretty plain, but by no means comprehensive...

So, nothing is said about an extension tube bore having to be parallel or of circular cross-section, nor about the termination of the tube. What if the extension isn't a tube? How is 'tube' to be interpreted?

Sounds like a rule inviting some interesting challenges...

[quote="Shooting Kiwi"]Pretty plain, but by no means comprehensive...

So, nothing is said about an extension tube bore having to be parallel or of circular cross-section, nor about the termination of the tube. What if the extension isn't a tube? How is 'tube' to be interpreted?

Sounds like a rule inviting some interesting challenges...[/quote]
This must be a southern hemisphere abberation

Shooting kiwi, maybe in NZ they don't get so nervous about supressors as they do here in the US. In the US they would interpret any kind of baffle in a bloop tube as a supressor and that could get you a spot sleeping with bubba.

Hi Kiwi there is a sight extension around, the name escapes me; I think made by Anschutz just a flat Metal bar extending off the top of the Barrel.Sorry cannot be more explicit, can you explain what you want to achieve the Benchresters seem to like a clean unobstructed tube?
Martin

the "hammerhead"

pdeal, we like the quiet life here: suppressors are not a problem, at least on long arms.

Martin, I don't want to reveal exactly what I want to achieve, but I'm happy to share further thoughts on the problems...

The muzzle blast exiting a 'bare' muzzle (in other words, unshrouded, with no bloop tube, etc) forms a roughly spherical shock wave, with a very turbulent forwards jet of gasses, which fans out from the muzzle. The exiting gasses have a velocity higher than the projectile. Therefore the projectile is flying backwards, with respect to the escaping gas, which isn't ideal, aerodynamically. The shock wave has an unobstructed escape path.

Now, if you shroud the muzzle, the shock wave will be reflected off the walls of the shroud in a complex manner. Also, the escaping gasses will be constrained into a narrow jet, of even higher velocity, through which the projectile must fly 'backwards'. It's possible that the constrained gas jet will behave itself because the shroud produces laminar flow, but I would think that it would be more likely that it would be horribly turbulent, with chaotic and significant velocity gradients across the bore of the shroud. With luck, down the exact centreline of the shroud, there might be no transverse gas velocities, because the system is symmetrical, but I wouldn't bet on it. Also, because of recoil, the shroud will move relative to the projectile's path, causing a small, but finite, deviation of the shroud's centreline from the projectile's path, thus destroying symmetry.

I think I read that high-velocity rifle testing in sewer-pipe tunnel ranges had problems with reflections of shock waves off the tunnel walls. Not an issue with ISSF rifles, but it illustrates one possible aspect of the problem, perhaps.

Careful design of the exit nozzles of jet engines has been a major component in quietening them. The noise is due to turbulence. A bloop tube is a nozzle, of sorts.

So it seems to me that a bloop tube is an aerodynamic device which will cause significant and difficult to predict aerodynamic (for want of a better term) effects. Some may be beneficial. Perhaps the detrimental effects are insignificant. Do we know? Has the science been worked out? Are they designed to produce aerodynamic benefit, or have they just been made, fitted and found to be OK. My guess is the latter. Or is it just a fashion? I think there may be benefits to be had from a bit more thinking, but we are chasing tiny benefits...

There may be benefits to such modifications, but to a competitor who abides by the rules, why invest time and money on development of something that cannot be used.

There may be benefits to such modifications, but to a competitor who abides by the rules, why invest time and money on development of something that cannot be used.

Err... that's exactly why I asked what the rules were - to ensure developments stayed legal. It sounds like the rules would permit a lot of development.

With people both with and with out bloop tubes consistantly shooting possibles and perfect groups, how are you going to prove any thing if you do make bloop tubes with either a megaphone, expansion chamber, or venturi as this is maybe what you are thinking of? Any difference in group size is likely to be more effected by quality of amunition or barrel.
Best regards
Robin

Yes, Robin, I agree. As I said before, we are chasing tiny benefits.

My suspicion is that these things are a fashion accessory, rather than a proven enhancement. In fact, I'm rather surprised they don't make inherent accuracy worse. These comments exclude the obvious effect on sight radius, of course. However, it would be nice to understand what's really happening, and I think there may be something useful to be learned, for instance even if the results only show up at long range. I also think that careful design might allow other phenomena to be manipulated, but I'll keep that to myself, at present. Even if progress seems pointless, you can't stop it!

Anyone got any figures for the velocity of muzzle gasses compared with the muzzle velocity of a .22 bullet?
A bit of elementary maths might determine whether an expansion chamber might have any beneficial effect.
I've also occasionally wondered if an exponential or constant directivity horn type internal profile would be any better than a plain tube.

Ken.

the gases expand at the speed of sound if that's any help...

There is probably some truth to the statement that bloop tubes are as much a "fashion" statement as anything else for shooters in their 20s to 40s. BUT they are helpful to older eyes and can give better definition to the front aperture and bullseye with the proper correction for shooting glasses. As far as I'm concerned that's a real benefit. Mike Barron

the gases expand at the speed of sound if that's any help...

Just to clarify, lest anyone is misled...

The pressure waves, including the shockwave previously mentioned, travel at the speed of sound in whatever medium they propagate through. I don't know what the speed of sound is in red-hot combustion gasses at whatever pressure they happen to be. The speed of sound will vary considerably near the muzzle at the time the projectile is around there because of the huge variations in gas density etc. If the medium is moving, as in a jet of gas, the velocities add.

The exiting gasses, however, are not limited to sonic velocity and overtake the projectile. Supersonic gas jet nozzles are interesting...

i was under the impression that gases cannot expand faster than the speed of sound unless there is as a special shape preventing expansion back.

http://en.wikipedia.org/wiki/De_Laval_nozzle

the gases you see exiting before a round does are because they got past the round and down the barrel before the round did.

robf wrote:the gases you see exiting before a round does are because they got past the round and down the barrel before the round did.

I find THAT quite remarkable... I would expect the air in the bore to be pushed out in front of the bullet but I would have thought that gasses getting past the bullet in the bore would be considered a huge failure and source of inaccuracy.

Ken.

i was under the impression that gases cannot expand faster than the speed of sound unless there is as a special shape preventing expansion back

That physics sounds right. The special shape is a DeLaval nozzle, and it looks nothing like the muzzle end of a gun.

Sometimes, if you watch ultra-slow film of a big naval gun firing you will see burning gases preceding the shell; I suppose the seal of shell to barrel is not quite tight and that there is some leakage. Then those burning gases are driven by their own thermal expansion and by the advancing piston that is the shell. Gases in the barrel still travel faster than the speed of sound in air because they are hotter, different chemical composition, etc. But they do not move faster than the speed of sound in their own neighborhood -- surrounded by hot burning gases. Even a choked muzzle does not look like a DeLaval nozzle.

OK, things are going to get confusing unless we are careful. It's potentially misleading to think about the speed of sound, because one is tempted to think only of the speed of sound in the free air around the gun and I apologise for my sloppy use of the term.

The combustion gasses certainly exit the muzzle faster than the projectile, even if the projectile is 'supersonic'. What the speed of sound is within the combustion gasses, I have no idea, but it isn't really relevant to what I was saying about the relative velocity of projectile and muzzle blast.

Those who choose not to believe a crank in the antipodes, can easily read about it: try Hatcher's Notebook, where he talks about muzzle blast in the chapter 'The Theory of Recoil'.