Meteor transfer port

[evert]

In my collection of .177 meteors, theres a wreck of an old mk3 Super that has had its finish removed by the previous owner..

Have done a few experiments on it, with different piston fronts and seal types, but right now I am planning to do a long-stroke version, with a steel piston front with original seal, and less lost volume in front of the seal. Will not increas stroke to where i have to open the cocking slot, just get a few mm's extra, and maybe increase the piston weight with a steel tophat.

So, now my question is: can anyone advice me to a good transfer port diameter on this setup? the port is already drilled out and has been sleeved down to 2,5mm's, which i think might be a bit too tight when I increase the stroke?

[mikewareing]

Work out the swept volume of the piston stroke and comaare it to that of the transfer port and submit it as a ratio.

ie 350:1 and search on this site for "static compression ratio" and follow the advice of "Hsing-ee"

Mike

[greenwayjames]

If it is a .177" drill it out to 3/16" but be careful the pellets dont fall into the air chamber when loadin. You may have to use skyhooks to keep the pellets in the breach.

[evert]

Will get around to measure swept stroke when I get the piston short stroke nose done..

3/16", that means above 4,7mm's, sounds a little on the large side- bigger than bore diameter, is that useful in any way? imagine that any port bigger than the bore is not able to give anyting more, and compression can probably be reduced by other means if one needs too?
On the other hand, the short meteor port will probably not need to be as little as many others to get good compression.

This project is partly inspired by the pictures I've seen of Bowketts 12fpe meteors, does anyone know what port diameter those conversions have?

[greenwayjames]

I made an attempt at humour which failed. Give Bowket a ring on his work number 0121 745 4287 and I am sure he will give you all the information you seek. He always rings back - even to Oslo. I collected my new .25" FAC toy from him yesterday and he is very busy despite the efforts of others to besmirch his name. While I was there doing the necessary paperwork the phone did not stop ringing with calls seeking Blueprint Tuning work on R10s, S10s and all of his other designs. He told me he has had to stop incoming Blueprint Tuning work for a few weeks to finish off a development project he is working on that needs to be completed by the end of this month. Since not having the entanglements of his association with BSA he has been able to delve into his 30 plus years old "bank of ideas" and finish projects which were stalled because of being unsuitable for production at the time. With new materials and methods of manufacture as they are things are different. I spent a very interesting couple of hours late yesterday afternoon terminating in shooting a revolutionary spring air rifle that he intends working on again. It was not like anything I have seen before, wasn't shown the internals, but was very,very compact. What recoil there was easily absorbed even by the lightweight sporter stock on the prototype.
Off to play today

[evert]

Sorry I didnt catch the humor.. but no problem, the advice didnt sound too good

I'm a bit reluctant to call people I dont know.. and anyway, im only a few transfer port sleeves away from finding out on my own!

Got the new short stroke nose done yesterday, an it measures in at 82mm's of stroke.. which should give around 41,5ccm's if the bore is an inch. Reading other posts on here tells me this should be enough for 12fpe if set up correctly?

Forgot to measure the length of the port, but I guess it is about 6mm's long.

the rifle became much softer too shoot than standard, and the gun gives 8.8fpe with 7.9grs JSB's at 710fps, and 8.4grs JSB running at 680fps, giving 8.6fpe.

The port is quite small, sleeved down to about 2.5mm's, but the nex move before I open it will be a heavier tophat, to counter any possible bounce.

[greenwayjames]

I forgot to mention that when I spoke to him he said that in his 12 ft/lbs Meteor conversions he left the port as standard at about 1/8 inch but just removed any sharp edges. He increased the weight of the piston and guaranteed between 800 and 850 fps in .177" with an Eley Wasp pellet The cylinders on the ones I had were just sheet steel folded to make a tube and brazed along their length. Hardly airtight

[Shed tuner]

As said tell use your new bore and stroke, length of TP, and piston weight, and we can make some sensible estimates of optimal TP dia based on SCR.
However, if you want a finger in the air, probably something around 3mm to 3.2mm will work. But don't drill anything until you have done the above.
PS Don't make a big thing of making the piston heavier, it probably doesn't need it.

[T 20]

As said tell use your new bore and stroke, length of TP, and piston weight, and we can make some sensible estimates of optimal TP dia based on SCR.
However, if you want a finger in the air, probably something around 3mm to 3.2mm will work. But don't drill anything until you have done the above.
PS Don't make a big thing of making the piston heavier, it probably doesn't need it.

Hi John

Bore X stroke = 25.4mm X 82mm

Transfer port 3.175mm X 4mm (iirc) --- I forgot to measure one today.



All the best Mick

[Shed tuner]

Hi John

Bore X stroke = 25.4mm X 82mm

Transfer port 3.175mm X 4mm (iirc) --- I forgot to measure one today.



All the best Mick

Wow - in terms of raw numbers that easy 12 FP territory already - identical bore and stroke to a MK1 TX or HW77, but with a transfer port less than half the length (of the TX). There must be some horrible inneficiencies - e.g. sealing - to stop it producing power. I;d work out if it's leaking / tube out of true etc first.

Sounds like it could handle a 4mm port, but I'd wait and test it out first... 3mm would be my starting point, 2.5 is pointlessly small if the port is that short.

In fact - lightbulb goes on - I've just remembered I actually have a fairly modern meteor someplace - should find it Then again I need to finish of testing my HW sealed TX first, then sort the RAM leak and shorten the stroke in the sirocco, fix the undeerlever catch on the goldstar, and there's a CFX in bits that needs at least 20mm taking off the stroke and the port sleeving - hmm where to start..

[evert]

The inefficiency is probably caused by the fact that the comp tube on these old meteors are really lousy, a piece of folded and brazed sheet metal.. And they seem to almost always leak a bit around the piston seal, the brazing joint is never completely even along the tube.

About drilling the port- its already drilled and sleeved, so no problem to re-sleeve it if I go too far.

25.4mm piston diameter and 82 mm stroke gives the mentioned 41,5ccm's of swept volume..

If the port is 2,5mm's by 4mm's long there should be a compression ratio of 41,5:0.0196, which should give a way too high compression ratio.

So the advice on 3.2mm's is probably not bad..

I think its time for port reaming

Will try to get the piston on a weight as well.

[T 20]

Hi Jon

The Meteor MK1 to MK5 cylinders were so poorly made I sort of Frankensteined one with a b2.

http://i1138.photobucket.com/albums/...2_05090138.jpg

B2 cylinder and barrel + Meteor piston, trigger and stock.



All the best Mick

[Shed tuner]

Ahh, I've seen that gun on a few pics, was wondering what it was
So a B2 is also 1" bore ? What stroke and power is that running ?
Could be a nice "99esque" lightweight full power gun...

[T 20]

Hi Jon

I went a bit too long on the stroke and ended up with piston bounce and never got round to sorting it out properly as the HW35LGV and then the Boinger bash got in the way.

I may revisit this one when I get time as it does put a smile on my face.




All the best Mick

[gedfinn 2]

Hi Jon

I went a bit too long on the stroke and ended up with piston bounce and never got round to sorting it out properly as the HW35LGV and then the Boinger bash got in the way.

I may revisit this one when I get time as it does put a smile on my face.




All the best Mick

Very nice Mick ,

I have a question !!!! ( This is tongue in cheek as I have a 75% meteor already made, Hence the wanted ad for a barrel )
How much power can be acheived from a meteor action ?
Thats question 1, But to appease the Mods, Is a realistic, Easy cocking , Low recoil 12 Fpe Meteor possible .

Just a thought , Ged.