Over sizeing transfer port

[CraigH]

Paul,

Looks like running a #20 drill (0.161") through all parts will likely put it right on with Carl's chart.

[quickster47 †]

Here is a really great article about FPE versus caliber and port size by one of thee airgun gurus R. Sterne.

Carl

http://www.airgunhome.com/agforum/viewtopic.php?p=78260

[RinCG]

What if one would apply an optimal port dimension of .160-.167(.22 caliber) to a reduced volume valve? Will it benefit the lower volume valve to expel air as quickly as possible? I'm guessing a 12-14.5" barrel is right at the raggedy edge with reduced valve volume in .22.
Really trying to get a 600-650fps 13xx but don't want to pump 15-20 times to get it. Something for nothing I guess is what I want.

[CraigH]

Carl,  Great article as you said.          Have to go over it a few times.

reduced volume valve
Something for nothing I guess is what I want.

I'll take some of that.         Don't know regarding the reduced volume, but certainly need more pressure to have the same fpe potential in the charge.

[quickster47 †]

Something for nothing I guess is what I want.

Wasn't it Dire Straits that did a song about this dilemma "Money for Nothing".   

Carl

[RinCG]

Close! Not discrediting Mr Knopfler, but am thinking Geddy Lee and Rush( 2112)is more my speed. That and the Rush of air through a transfer port  is more fitting to this thread. No derailment here. All things working together for a common cause. Will oversizing the port coupled with a reduced(or stock for that matter) volume valve cause more harm than good? 

[quickster47 †]

Will oversizing the port coupled with a reduced(or stock for that matter) volume valve cause more harm than good?

Hard to say.  Matching the port to the caliber cannot be a bad thing and the standard 1377 valve has been performing wonderfully for many moons now.

But then a transfer port is to an airgun what restrictor plate is to cup cars.  A given orifice can only flow so much volume. Even then, the maximum volume is only reached at the optimum pressure (whatever that is). The transfer port "transfers" air from where it's stored, into your barrel. Imagine if the port was the size of a pin hole. Now imagine it the size of a drinking straw. Obviously the difference would be dramatic. Somewhere in between lies the "optimum" size for that caliber, barrel length, pellet weight, working pressure, number of shots desired, etc., etc.. That's one of the things that makes air guns so fascinating. The "hot set-up" is often a moving target, in that it changes every time YOU change something (like barrel, caliber, pellet weight, etc.) So, for sure I'd say transfer port size is one of the critical elements involved in performance.

Carl

[RinCG]

Well alrighty then!
rather than "shoot for" a velocity & muzzle energy range, I'll set up my my gun and test out a few sizes of ports. Basically using the optimum chart as a guide and fine tune to my ag's set up and environment. There are plenty of individual variables to play with. More work, more fun- right?   

[UKairgunner]

so folks
final plan for this  first seasons mods on my new 2240
open out gas passage to 4mm......sorry for the metric thingy  but we only revert to imperial to confuse French tourists
cut off a few threads in the valve and make good
remove the unused  internal threads in the valve female part  with a dremmel 115 bit   ,( on order), quick de-burr and polish
stronger hammer spring( gma)
hollow probe(gma)
hawke red spot
and some 20 grain pellets

and a  swifty stumpy moderator to keep the eco campers happy


although with the amount of co2 i might be venting i might tell em its a fire extinguisher 

[Rualert]

     Not sure if you have restrictions where you live, but if so be careful as you make the gun more efficient it will produce more power. Reducing the restrictions in the gas / air flow from the valve to the barrel will make the gun more efficient, and generally more powerful. I have on many occasions made smaller transfer ports to squeeze more shots from a CO2 cart at a specific muzzle velocity. When you find the sweet spot with a CO2 gun you can get them to basically self regulate to the point of x number of shots at virtually the same MV. If you do live with the 6ft.lb. pistol or 12 ft.lb rifle restriction, this little trick will help you mod the gun, but still keep it in the range you need. If you don't have the restriction, you can adjust the transfer port size, staying within the 75% of caliber range to squeeze as much flow out of it as you can get.

Casey

[UKairgunner]

Completed most of the mods today
Drilled port out to 3.75mm...bottled out of using 4mm as the wall of the short end of the port looked to be getting too thin,valve and barrel at 4mm.lost 3 threads off  valve male part and internal chamfer and polish...didnt increase internal diameter of male part as it was looking too thin esp when you consider the depth of the threads...internal diameter of male part was 10mm.Nice gasket on port top made a nice solid  connection.
hollow probe also fitted well allowing plenty of room to load.

Co2 in and ...no leaks and firing really well

next thing is fix that truly terrible trigger wobble with a couple of brass shims and have look at fitting a stronger hammer spring or just popping a couple of small stainless washer in the recess at the back under the spring and thats it

heavy 20 grain pellets when im next in town me thinks..squirrels have had a day off whilst i tinker

thanks to all here for help and info

[ped]

on a UK 2240 I'd be wary of doing any power mods as you'll likely go over 6fpe which makes it a section 5 FAC far better to use a 2250
some info if you use a 2250
use the std spring and add a guide with 4mm of preload(a plain m4 nut added to the rear cap works as well)
a few lads in the uk will mod your valve for extra volume
for the tp use a John small two part one (available on e bay) http://www.ebay.co.uk/itm/HIGH-FLOW-TRANSFER-PORT-FOR-CROSMAN-2240-2250-2260-2289-1377-1322-/272254317200?hash=item3f639f3290:g:V-MAAMXQVT9S-TDY

[UKairgunner]

good advise from ped and rualert

yes ill be borrowing a small crony for tests next week and will be ensuring im within the law

were a mixed bag in the UK...whilst we are restricted in the  power  of  airguns and ownership of FA we can still freely buy, own and use moderators.And our restrictions are not as bad as Europe(god help us if we lose the referendum)