Transfer port sleeving

[Neil54]

After reading the excellent thread by mick regarding the rebuilding of an SMK B2, I thought I may have a try at altering the transfer port diameter.
I have a couple of questions.



Would it be better to sleeve the whole length of the transfer port as in diagram A?

Would there be any benefit in tapering the opening with a centre drill as in B?

Would it be better reducing the length of the sleeve to 16mm like some of the other rifles as in C?

Your thoughts

[Shed tuner]

full length, straight through. you want to limit lost volume

[CapitalBee]

That b2 is already sleeved. I drilled it 4.5mm x 26mm dp to the shoulder, so about 3mm of original tp left and inserted 0.6mm wall thickness brass tube. As the b2 tp is angular, it saved faffing about with the squareness of the front faces.

[Rich]

Personally I'd radius the inlet side, otherwise the sharp edged entry will cause a vena contracta.

[T 20]

I always do "B".

[MartynB]

Personally I'd radius the inlet side, otherwise the sharp edged entry will cause a vena contracta.

A what Rich ?

[Hsing-ee]

A what Rich ?

I'm guessing but I think it means that there will be a central area of the port which will flow air cleanly, and a layer on the periphery which will have stagnant or turbulent air. You can see this happening with people walking down the connecting tunnels at Bank underground station. Those walking in the middle will be going fast while those closer to the walls will be slower. Smoothing the edges of the port mean that the air will travel closer to the edge at the same speed, unlike the people in Tube stations. It was a poor analogy and it broke down soon after takeoff.

[BTDT]

There is always a turbulent boundary layer at the periphery of the transfer port; putting a radius into the inlet reduces the boundary layer's depth.

[Neil54]

That b2 is already sleeved. I drilled it 4.5mm x 26mm dp to the shoulder, so about 3mm of original tp left and inserted 0.6mm wall thickness brass tube. As the b2 tp is angular, it saved faffing about with the squareness of the front faces.

Thank you for that information.
I was thinking of sleeving it down further and maybe changing the piston seal.
Won't be doing anything yet. Working on another project as my time permits.

[Shed tuner]

You can see this happening with people walking down the connecting tunnels at Bank underground station. Those walking in the middle will be going fast while those closer to the walls will be slower. Smoothing the edges of the port mean that the air will travel closer to the edge at the same speed, unlike the people in Tube stations.

As someone who passes through this mess several times a week, I'd suggest you are confusing Brownian smoke motion with fluid dynamics. There is nothing fluid about the flow through bank station...

[harvey_s]

After reading the excellent thread by mick regarding the rebuilding of an SMK B2,

Hi

Got a link to the thread you speak of please?...couldn't find it

[CapitalBee]

Thank you for that information.
I was thinking of sleeving it down further and maybe changing the piston seal.
Won't be doing anything yet. Working on another project as my time permits.

No problem Neil

As I didn't have the means to manufacture an insert, I used stock tube size, but I think it would benefit from going smaller.

[Neil54]

Vena contracta
Vena contracta is the point in a fluid stream where the diameter of the stream is the least, and fluid velocity is at its maximum, such as in the case of a stream issuing out of a nozzle,.. It is a place where the cross section area is minimum. The maximum contraction takes place at a section slightly downstream of the orifice, where the jet is more or less horizontal.

[Neil54]

Brownian motion
Brownian motion or pedesis is the random motion of particles suspended in a fluid resulting from their collision with the fast-moving molecules in the fluid.

[Shed tuner]

Brownian motion
Brownian motion or pedesis is the random motion of particles suspended in a fluid resulting from their collision with the fast-moving molecules in the fluid.

yup, that's the one... fast moving commuters & slow moving tourists... all random, and lots of collisions