Tx200 zero transfer port

[slugger]

I wouldn't worry about that, the tx has a nice sized lead-in and its all but impossible to push a pellet past this point with your thumb....... and I don't imagine for one minute you would want to upset this gun by deliberately probing the pellet past its natural lead-in point [would definitely have massive changes on shot feel and I imagine poi at range] ....... perhaps the way forward would be to pellet test prior to the mods, see if it likes [for example] AA fields, and then tune the guns shot feel to live on that pellet ?

[Shed tuner]

I was more thinking of not pushing it in properly !
Ref tuning feel for the most accurate, favoured pellet, for sure, we do that already

[slugger]

I would imagine [due to head size versus skirt size] that a pellet not seated quite right in the breach that [due to the lack of TP] the early stage of piston movement would probable seat it for you ? also the minute difference between lost volume quantities between a seated and not-quite-seated pellet would me minimal, and certainly overcome by the fact it hasn't got the usual 10mm or so of port volume when compared to standard setups ?

[wonky donky]

I love the idea of this, but I am left wondering about consistency... with no transferport are you not going to have massive variances in fps with different brands/makes of pellets ? surely some of the traditional transfer-ports job is to restrict flow/air-speed, without that effect I image it would be very pellet fussy in terms of fps to avoid slam ? or am I not thinking right ? seb

Right from the first shot there's been no more than 18fps variation with the pellets Iv'e used, had about 60 shots over the chrono now, & when settled less than 10fps.

Shot cycle & perceived feel will always be different from one pellet to another. you can tune for the most accurate pellet/s or you can tune for different brands to give the same power level within reason but the firing cycle will be better with some than others, rarely can you achieve the optimum with any one this way.

[FPoole]

Will I see any benefit in cutting the o-ring groove off the comp. tube end plug and opening up the TP in an otherwise factory MarkI stroke TX. Not worried about the 12 ft. lb. limit over here. I really don't want to carve up my nice MarkI piston to lighten it, but I do have a good straight MarkIII comp. tube I can work on.

[Shed tuner]

Will I see any benefit in cutting the o-ring groove off the comp. tube end plug and opening up the TP in an otherwise factory MarkI stroke TX. Not worried about the 12 ft. lb. limit over here. I really don't want to carve up my nice MarkI piston to lighten it, but I do have a good straight MarkIII comp. tube I can work on.

You will see a benefit in cutting off the sealing o-ring (and relocating / resealing it), but DO NOT open up the port at all. Saves 2.5mm of port length/lost volume, and also increases your mk1 stroke by 2.5 mm, both of which take out all the slam.

[T 20]

Just a thought Dave

When you have the gun set and bedded in could you chrono a few shots with the pellet seated 6mm up the barrel ?

Not very scientific or accurate I know, but it would give us an indication of the gain you've acheived from not having a transfer port.



All the best Mick

[Black Beard]

Jon/sluggerI don't think consistency will be a bigger problem than any other gun. Lost volume restricts the potential to tune before the piston crashes. The pellet still starts moving before the piston is fully forward and will be an inch or two down the barrel when the piston is turning around.At the very high tune that low lost volume will allow you will have high pressures. This might expand the skirts like the ones in one of the last chapters of Mr Cardews book. I think this makes the pellet expand in to the bore and grip the barrel, slowing it down a lot. This might apply on a reduced stroke TX with a very high pressure tune. Need someone to do some test firing and collect the pellets.

[greenwayjames]

I was recently shown a zero transfer port airgun which was surprisingly powerful for its size. It was a 19th century Bussey which used the barrel to push the piston back against a spring. The barrel was returned to its original position for firing. I guess it used a dart of some kind.

[wonky donky]

Just a thought Dave

When you have the gun set and bedded in could you chrono a few shots with the pellet seated 6mm up the barrel ?

Not very scientific or accurate I know, but it would give us an indication of the gain you've acheived from not having a transfer port.



All the best Mick

Did 10 shots Mick, 100fps loss almost exactly with the same spread over the string as I got with pellets seated in the breech.

If any one wants me to try anything whilst the rifle is together please say so........I will probably strip it at the weekend.

[wonky donky]

I was recently shown a zero transfer port airgun which was surprisingly powerful for its size. It was a 19th century Bussey which used the barrel to push the piston back against a spring. The barrel was returned to its original position for firing. I guess it used a dart of some kind.

Sounds like the one I made at school for my exams 50yrs ago! I'm disappointed now I thought mine was unique

[Shed tuner]

Did 10 shots Mick, 100fps loss almost exactly with the same spread over the string as I got with pellets seated in the breech.

If any one wants me to try anything whilst the rifle is together please say so........I will probably strip it at the weekend.

Only problem with this test is you also need to factor in that the pellet is no longer sat on the lead-in, so will tend to move earlier / under less pressure.

[wonky donky]

Only problem with this test is you also need to factor in that the pellet is no longer sat on the lead-in, so will tend to move earlier / under less pressure.

Absolutely, knowing Mick he's probably thought of that before he asked me to do it Jon

[Shed tuner]

Absolutely, knowing Mick he's probably thought of that before he asked me to do it Jon

I was thinking you could also do the same test 1mm into the bore, the difference between the two being the "short port effect", rather than the "no lead-in effect"

[T 20]

I was thinking you could also do the same test 1mm into the bore, the difference between the two being the "short port effect", rather than the "no lead-in effect"

That's what I was thinking as well Jon

Another source of data is Jim's old article from Airgunworld where he increased the transfer port length on a 77 bit by bit.

Another way for us to get a baseline off Dave is for him to push a pellet 6mm up the barrel and then push it back to the breech and then take the no transfer port velocity of the sized pellet.


It's all good stuff though.




All the best Mick