Nozzle Design Questions

[Fredd3039]

This is a Muzzle Brake for a rifle barrel that uses rocket nozzle type porting that reduces felt recoil. The "Nozzles" are machined at a 30 deg slant towards the rear. The explosive pressure behind the bullet gets vented into the nozzles as the bullet passes them. The nozzle venting seriously dampens the recoil effect. I guess my question would be, Since this is drilled into a metal rifle barrel with a hollow core, the 30 deg angle reduces some of the throat volume or area, does this effect the function of the nozzle in a negative way? Oh I am an absolute beginner with Nozzle design so please go easy on me.
Thanks

 

[Baluncore]

Oh I am an absolute beginner with Nozzle design so please go easy on me.

Comments.

Drilling those diagonal nozzle holes will be difficult and expensive. The differences in machining and metallurgy, between a barrel and a brake, suggest it would be easier to make the brake separately, then attach it to the end of the barrel.

Very little gas will change direction, to escape backwards. I expect those small diameter holes will draw in more air, than they vent gas. There needs to be a reflector step internally to direct the propellent gas, backwards through the jets.

Better to have several axial discs with holes, like flat or conical washers. The projectile passes cleanly through the hole, while most of the gas pushes on the annulus, pulling the barrel forwards, countering the recoil. Gas that remains in the cavities between washers, may be released backwards through ports.

It is important that the operator not be blinded by the backward jets, and that dust is not raised from the ground when operating prone, that could make the operation dangerous to the operator.

 

[berkeman]

and that dust is not raised from the ground when operating prone, that could make the operation dangerous to the operator.

Interesting point. I did not know that.

 

[Fredd3039]

This may illustrate my question better, which design would produce more thrust A or B. Note the throats of each. At a 30 deg. slant the throat can either be straight inline with the nozzle As in the A example or an actual throat like in the B example.

 

[Fredd3039]

Forget that this has anything to do with a firearm and consider my question as if this was all the knowledge you have to go on: If a Nozzle Tilt of 30 deg. is necessary, which design would produce more thrust A or B. Note the throats of each.

 

[Baluncore]

I guess by combustion chamber you mean barrel, and the bullet travels from left to right. Your A has a small reflective corner, while your B has larger ports. Neither is optimum. Propellant combustion should have completed before reaching the muzzle brake. I believe what you are thinking of is called a ported-barrel, but is being used as a muzzle brake.

The brake cannot be machined into the barrel, because the ports will either be too small to operate, or be so large that they weaken the barrel. You really need to separate the brake from the barrel.

Take a look at the schematic of various forms of muzzle brakes: https://en.wikipedia.org/wiki/Muzzle_brake
Your concept is like Fig. a2 as it has backward holes.
Fig. b1 would be quieter, while Fig. b2 would make a better brake.

 

[Fredd3039]

Not to sound condescending because I do appreciate your feedback, but I am a full time machinist and gunsmith. I know what muzzle brakes are, I know what porting is and I know how hard it is to drill a barrel. Forget I ever said drill the barrel. I was trying to simplify this for people who don't know much about guns.

I just wanted an answer as it pertained to nozzles. Weather it is a gun barrel or not does not matter. It can be a pipe and I am trying to make a The picture is of a muzzle brake that was made many years ago and never mass produced. It was designed by a retired propulsion or rocket engineer, who is now passed on.

The brake does everything it is supposed to do. It takes a 55 Ft lb recoil impulse and lowers it to around 13.5 Ft. Lbs. It does not blow hot gas in the shooters face and I am not worried about a dust trail from prone position shooting. I am merely interested in trying to duplicate what he did. He used a "de Laval nozzle" to increase the thrust pressure to make it greater than that of a simple cylindrical hole like in a typical port or brake design. I am asking about the two different throat styles because modern machining a through hole into a cylinder at a 30 deg angle can only be done two ways. The drawings I supplied show the two possible outcomes for what the throats would look like after they were machined.

Since an actual CD Nozzle is not possible because there is no access to machine the convergent section at the combustion chamber, I am guessing that his design is more a Divergent only chamber. So, if it is a divergent chamber, what would make it more efficient, the triangular throat produced by drilling and milling with the form tool and bit at 30 deg like in the triangular cross section, or drill the throat hole at a 90 Deg, and then use the form tool at 30deg. so that you get the throat walls even?

I guess what it all comes down to is If you were going to build it what would you do?

 

[Baluncore]

This is a Muzzle Brake for a rifle barrel that uses rocket nozzle type porting that reduces felt recoil.

The example you show in post #1, seems to be an attachment to the muzzle, not a drilled or modified barrel. That makes it possible to form CD nozzles in the attachment, that redirect the gas backwards, and through the nozzles.

There is no requirement I see that requires the nozzles to be drilled or circular. I would consider turning segments that were mounted with spacers. The faces of those segments would be the front and rear faces of an annular slot, that forms an annular CD nozzle. The internal reflector discs could be turned on the same segments.

 

[Baluncore]

I see no way to machine a convergent-divergent nozzle with a bend in the middle, or fed directly from drilled barrel ports. So employ a common annular chamber that holds the used propellant gasses, then exhausts that gas reservoir backwards, through gaps between a stack of profiled discs. By mounting spaced solid discs, the spaces between the discs become the ports. The front profile of each disc is the rear wall of the port, and the rear profile of the disc is the front wall of the port. That makes it possible to have CD nozzles pointing backwards with optimised thrust.

It will be necessary to specify the pressure profile in the chamber before designing the annular CD gap nozzles, but that is true of any nozzle design. The advantage of a common chamber is that the jet exhaust pulse will become better established, and last longer.

There is a parallel. The aerospike is a rocket engine that employs the same inverted topology, as the muzzle brake I am suggesting.
https://en.wikipedia.org/wiki/Aerospike_engine

 

[jrmichler]

I see no way to machine a convergent-divergent nozzle with a bend in the middle

But such a nozzle can be made by additive manufacturing. Rifle suppressors (AKA silencers) are now made using additive manufacturing.

 

[Baluncore]

Rifle suppressors (AKA silencers) are now made using additive manufacturing.

But they are not an integral part of the barrel.

We do not talk about silencers here in Tasmania, as they are illegal. We only have muzzle brakes, AKA compensators. When legitimate hunters are at work, well-designed compensators do suppress the number of nuisance calls to the police, but we are not required to use one. I believe suppressors or silencers are now compulsory in some European regions.