QB Transfer port thoughts/advice?



Author Topic: QB Transfer port thoughts/advice?  (Read 672 times)

Offline Raizer

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QB Transfer port thoughts/advice?
« on: April 03, 2013, 10:36:54 AM »
Just looking for advice/thoughts on modding the transfer port on my QB79.
I've finally got my .25 blank coming and I want to ditch the stock QB oring arrangement on the barrel and was thinking a full length transfer port would be the way to do it.

So I got hold of some 5mm id tubing that matched the port in my valve, and was going to get a seat for the tube milled into the valve (and a matching one or flat done in the barrel when its machined) with the idea of running the transfer right through the main tube and breach.
But the seat on the valve would sit tight on the edge where the seal is so I don't think it would work to well?


Yes I messed up when opening up the valve end, I've got another coming  :-[



So yeah, I'm looking for any tips or advice I can get at the moment!
« Last Edit: April 03, 2013, 10:55:55 AM by Raizer »
  • New Zealand


QuarterBore79 - BSA Barrel - Hawke Varmint 4-16x44SF
Hatsan Striker 1000s .177 - Nikko Stirling Gold Crown AirKing 4x32AO
BSA Super Meteor mk3 .177
Rossi 4.5
Relum .177

Offline Bill G

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Re: QB Transfer port thoughts/advice?
« Reply #1 on: April 03, 2013, 12:43:11 PM »
Don't make the port in the barrel any larger than 75% of the bore.  This will ensure proper feeding of the pellets.  I learned this here from Bob.  Thought I'd try it out o an out broken, rusted, junk gun that a guy brought to me.  YEP, any larger than 75% of bore and the pellet gets deformed, shaved ect...  IMO,  try to keep the cross sectional area of the ports equal to the barrel port.  This, in theory, maximizes flow while minimizing dead volume.  Cross sectional area??....  The area of the throat, transfer port and barrel port, as I note them.  Others may have differing of better descriptive names. Pi(r^2)  Don't forget to subtract the poppet stem area from the throat area to get an accurate cross section.  This area should equal the port in the barrel as well as the transfer port.  If you need better explanation let us know.  Bob and Lloyd will surely be more articulate than I have been.  I've been up for 20 hrs after only 3-1/2 hours of sleep

Going tto bed
Bill
  • Nicholasville KY
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Offline Mattman

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Re: QB Transfer port thoughts/advice?
« Reply #2 on: April 05, 2013, 07:23:26 PM »
Hi Raizer I've don the same with mine but put a piece of 5/32 - 3.96mm brass tube through the silicon to act as a guide I used 5.9mm fuel tubing and still in .177 . I don't see no reason why it shouldn't work and Ive fired over 1500 pellets since Christmas with no problems ill try and post some pics soon. What happened to our NZ air gunners forum ?? Your name looks familiar.
« Last Edit: April 12, 2013, 07:04:51 PM by Mattman »
  • New Zealand - Wanganui

Offline Raizer

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Re: QB Transfer port thoughts/advice?
« Reply #3 on: April 06, 2013, 01:40:46 AM »
That looks like an effective way of doing it!

I'm unsure why Alan hasn't fixed the NZ board, hoping he does or at least lets someone have access to the info on there for the other Kiwi forum!
Most of us are now on http://nzairgun.com/forum/
  • New Zealand


QuarterBore79 - BSA Barrel - Hawke Varmint 4-16x44SF
Hatsan Striker 1000s .177 - Nikko Stirling Gold Crown AirKing 4x32AO
BSA Super Meteor mk3 .177
Rossi 4.5
Relum .177

Offline Raizer

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Re: QB Transfer port thoughts/advice?
« Reply #4 on: April 08, 2013, 03:27:03 AM »
Hey Matt did you seat the brass tube into the valve and barrel?
And do you still have the 3 orings around the barrel or did you ditch them too?
  • New Zealand


QuarterBore79 - BSA Barrel - Hawke Varmint 4-16x44SF
Hatsan Striker 1000s .177 - Nikko Stirling Gold Crown AirKing 4x32AO
BSA Super Meteor mk3 .177
Rossi 4.5
Relum .177

Offline Mattman

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Re: QB Transfer port thoughts/advice?
« Reply #5 on: April 10, 2013, 05:42:14 AM »
Hi Raizer the brass tube wasn't a tight fit more of a snug fit and I also slid the silicone tube over the brass tube and put one end into a drill press .
Used a sharp knife and cut a few seals at different lengths starting at 4mm and 4.5mm 5mm 6mm and tried each one out till i got the right height .
The washer in my pic was to lift the barrel and action up to clear the Co2 bottle there's also another washer at the rear end - the rear trigger bolt goes through it so the action is square with the bottom tube . The brass tube is chamfered at both ends on the inside done with a dremel .When I slid the brass into the silicone the outside expands 6.9mm - I measured and drilled the action tube 7mm not all the way through between 1.5mm to 2mm . The hole on the main tube above the valve I didn't touch it was just the right size ill post a pic with action and main tube together minus the barrel . the brass tube shouldn't stick above the inside of the action - the hole in the action and main tube stops both ends of the silicone tube from bulging out and also grips the brass tube and stops it from moving up or down . I put new o'rings on the barrel and I'm now getting sub 8mm groups at 20 meters and makes snipping mynahs and starlings out to 40 45 meters a breeze .
« Last Edit: April 12, 2013, 07:11:15 PM by Mattman »
  • New Zealand - Wanganui

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