Canadian Airgun Forum

Hi.This is my first air rifle that I am trying to convert from 495 fps to full power,{I do have a PAL}.MY results have been not too good.So far I have welded hole in piston,new seal,NP214-012 gas spring.around 600 fps.I noticed transfer port seems big.5/32 drill bit fits easily into port 11/64 will not fit.In my searching i found material that said transfer port sizes larger than 1/8 can hurt velocity.Since this is my only gun and i have nothing to compare it too does anyone have a full power NP2 apart to measure transfer port.Is this another way they detune Canadian guns?Thanks

just tried to measure port size with a caliper.hard to get in there but it looks like it is .160"

Sounds like you need a full power spring and or nitro piston.

The gun has a short piston,ie cocking stroke approx 140 degrees ,breach almost touches compression tube. I installed the full power gas spring # NP214-012,put a new seal on even though original looked good.The piston did have a hole which I welded shut.Plugging the hole gained me about 30 fps.installing replacement gas spring bumped me to around 600 fps.I have gone through ever thing several times and every thing looks good.even measured space between piston face and main seal.025".I am starting to think this large transfer port is a way to detune that is not easily fixed.ie requiring a new compression tube with smaller transfer port.

I did test different port sizes on a chinese springer once, which was giving only around 400 fps in .177. The original TP was about 9/64'', and the best fps I got (430 fps) was with a 1/8'' TP. I drilled and threaded the original port to 3/8-24 NF and made different inserts, from 3/32'' to 5/32'' ID, in 1/64 increments. The 3/8'' OD of the inserts allowed the breech O-ring to seal against the receiver face without touching the insert. Just make sure the insert does not protrude in the compression chamber or on the receiver face, but is still the maximum length possible. That could be tricky with a canted TP. I used red LocTite to secure the insert in place. If you have the tools and capability to do the job, it may be your best bet, short of buying a new receiver or welding the TP shut and re-drilling.

Another trick that could help would be to sand the seal face to get 0.012''-0.015'' of clearance instead of 0.025'', that would raise the ''compression ration''. If you have an old seal to test, that could be handy.

Hope that helps!

Edit: There could be some other things you could check: Even though you de-burred it, is there a gouge in the receiver tube that could allow some blowby? Does the piston seal fits tight or loose in the receiver tube? Is your breech seal leaking? Have you pushed a pellet through the barrel by hand to see if there's a tight spot in it?

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If everything's so lovely yeah, then why don't I, why don't I, why don't I, why don't I feel lovely?

i will prob just use it how it is.I dont think I can drill and tap that accurately enough by hand.Machine shops in my area charge $125-$150/hr with a 1/hr min.A new receiver tube is $52.99.Mostly just wanted to get info out there so others dont make same mistakes.

Well i made up some inserts for transfer port.Just trying to get courage to drill into a new gun that is only 1 week old.

FWIW, I admire your willingness to improve your rifle . Are you using threaded inserts or plain tubing? Keep us posted on your results!

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If everything's so lovely yeah, then why don't I, why don't I, why don't I, why don't I feel lovely?

That is one of my faults.I just cant seem to leave anything alone if improvements can be gained.I got a suggestion to make a flat washer with smaller hole and put in compression tube.i actually made one of these too,but not sure about it just floating in there even though it is a friction fit.I really am starting to wish I bought a full power gun and then ordered the stock I wanted.

A transfer port of .125 is more ideal for a generic B18 Crosman, which in my testing can be as much as .140 which is where power started to drop for me but keep in mind that test gun was making 19ftlbs, not 16 or whatever most guns do. I consider it best to go the smallest possible to clean it up, so the next size bit and sand it smooth. Only if it's still horrible would I suggest going a set larger, and even then it might be a coin toss as to whether a size up but smooth is better than smaller an sketchy.
Anyway, different guns use different port sizes based on the guns specs so you might see .120 to .170, maybe more. It isn't about the diameter of the port, but the volume, so another gun with a shorter port would use a larger dia, assuming all else is the same. Larger magnums like the Trail XL, Diana 350 etc use ports ~.160 or more because the gun physically has more air to compress and move. The NP2 is kinda a semi-mag so somewhere between 125 and 160 is what I'd expect but again it depends on the port length. The gun the NP2 is based on has a .120 port, so assuming the port length is the same I'd imagine the NP2 would be 130-135. Not that doesn't mean it's ideal since I think the old guns 120 was too small, plus misc specs we don't know... Long story short is I wouldn't about the 160 right now.

The port is much more than a passage way, it's a storage area for the air that drives the pellet. Kinda like the valve assy in a pneumatic gun. The piston charges the port/valve, then that air drives the pellet. If you enlarge the valve volume of a pneumatic it'll lose power, unless you force more air into it to compensate, which your gun cannot do. It doesn't work exactly like that but that the gyst and if you keep it in mind it'll help the end goal. Other springers like a B1 do work like that and the port is just a passage way so bigger is better.
As a side note; making an orifice like the washer with a smaller hole will only hurt power since it's still whatever size port but now has a restriction to boot, kinda like adding a restriction to a pneumatic.

Sanding the seal thinner like airmec mentioned is better in more ways that one. That .025" is typical and I would sand it thinner, but it is not your main problem either.

I'm surprised they put a hole in the piston considering it's new design with all that stuff going on there, but if they did then they did. Filling the hole should net substantially more than 30fps so my first thought was it blew out, but you said you welded it... It could also be a clue that air is leaking elsewhere which would explain why the hole had little effect.
For example I had a Ruger where the welding of the scope rail left open areas for air to escape so instead of making 22ftlbs it made like 14. I was surprised what a drastic effect it had, but it was a lesson learned about leakage. Like your breech seal, is that thing sealing? Is the breech face smooth or does it look like a vinyl record?

Do you have the part # on the old spring and did you by chance compare the two visually and by compressing, or trying to compress by hand? And what did that new spring cost?
You said it was full stroke but are you sure? When it's apart can you measure the piston and take a pix?
I'm very curious and all the info will help others trying to convert to pal.

I will try to get pics of everything.I am glad I read this post before I drilled and tapped my transfer port.I was going to do that today but we got 14 " of snow I had to deal with.So tonight I will take apart and get photos and measurements.

I will try to keep related posts in this thread.I am in process of taking apart and taking pics and measurements as Chevota requested.It appears as I did not completely weld the hole in piston.Could not see anything but put a bright light behind and used magnify glass and sure enough light coming through,back to the welder.The main seal looks like it is melted in one spot too.good thing I have another.Not sure how long it will take for pics cause I am basically a computer illiterate.I have to go set up photobucket account and upload and supply a link.Wow.I probably have more success rebuilding a motor in a dark room with only a flat screw driver and adjustable wrench.

Canadian part prices from Gravel.NP214-012 full power gas spring $16.99.CRS5177-012 piston seal $4.50.NP214-121 compression tube $52.99. .22 cal breech/barrel NP214-108 $61.04. ELS 100 trigger assembly $29.99. both sears and trigger can be ordered seperate but are $9.99 each.NP214-009 plastic shroud cone $2.63.NP214-032 barrel shroud retainer $4.82 Canadian version of Trail baffle.NP214-008 shroud $13.11.NP214-131 piston $59.99

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Transfer port hole is .158" in dia. .668" deep from breech to compression chamber.6-NP214-012 201507 oem gas spring I can compress 2" with body weight.Full power gas spring Np214-012 201508 can not compress by hand at all.Found small pin hole in piston,fixed that,install new seal sanded to .015" head space.Cocking force on bathroom scale read 36lbs at start for first few inches then dropped to 32lbs for remainder of stroke. Phone app says 595 fps. not much different than yesterday.So I shot a piece of 1"x4" at 25 ft got about 95% penetration with CPHP pellet.causing big splinters out back of board.When installing shortened barrel shroud I found I could distort barrel enough[with the plastic barrel cap by hand]to not be able to see through barrel.back it off 1/4 turn good again.Not sure what happens next,prob just shoot it for a while.the gun seems accurate at 35 ft.1/2" groups but takes a lot of concentration on my part to pull that off usually 1".Gonna give up on phone app but would like to shoot it across a real chrony one day just to see.Sorry. Not sure how to link to the whole file of pics but the title of thread is transfer port so it is the one I picked.Hope the info helps.still wonder about the size of transfer port hole though.I have a friend who has a Golden Eagle Np2 in.177 but he wont let me take apart to measure.LOL.