1322 velocity after FTP and valve mod

[CarsonRatSniper]

The bolt needs to be threaded 8-32. I forget what # the pilot bit is - either #21 or #29. I will look in the morning.

[Rivers3Plinker]

there's always a next project 

+1 And when there doesn't seem to be any, get another gun to modify!

[Perry01]

So I bought a 8-32 tap and #29 drill bit then threaded my new extended bolt probe. Only minimal gains were seen at 10 pumps but using 14.3 gr. CPHP pellets, it now shoots:

15 pumps 616 FPS
20 pumps 648 FPS
22 pumps 662 FPS or 13.8 FPE

With the extended bolt probe, it gained 27 FPS at 20 pumps. It dumps all air at 20 pumps but retains a little at 22 pumps. My goal when I set out was a 10 FPE pistol and if it reached 600 FPS I would have been pleased but I had no idea I was going to get it to shoot 662 FPS.

I'm done with the performance mods and am waiting for my 2289 shoulder stock, TKO and compact 4X32 scope to see how accurate it is at 20+ yards

[K.O.]

 

[DavidS]

I am still waiting to hear the numbers at 10 pumps.   I power mod to get the most power from the fewest pumps, preferring to keep under 8 pumps for high power shots .

[Perry01]

I am still waiting to hear the numbers at 10 pumps.   I power mod to get the most power from the fewest pumps, preferring to keep under 8 pumps for high power shots .

550 FPS at 10 pumps

[DavidS]

Not bad at all.  Nice work.   You are getting close to my 2289g, I better watch out.   Last I chronied it my 2289 was doing about 560 on 8 pumps and I have an 18 inch barrel on it.

So you are doing great.

[Perry01]

Not bad at all.  Nice work.   You are getting close to my 2289g, I better watch out.   Last I chronied it my 2289 was doing about 560 on 8 pumps and I have an 18 inch barrel on it.

So you are doing great.

Thanks David. Maybe I spoke too soon as for performance mods. I totally forgot about the lighter valve spring. That's something I was meaning to do and I'm wondering if it's possible to cut a little bit off the one currently in there now. If so, any idea as for how many coils to remove from the spring?

Also, since I just bought a #29 drill bit and 8X32 tap, I'm going to pin the valve. That should keep the ports lined up under pressure. With the pinned valve and lighter valve spring maybe 700 FPS is possible.

I'm really just hoping for 600 FPS with 12 pumps.

[DavidS]

Not bad at all.  Nice work.   You are getting close to my 2289g, I better watch out.   Last I chronied it my 2289 was doing about 560 on 8 pumps and I have an 18 inch barrel on it.

So you are doing great.

Thanks David. Maybe I spoke too soon as for performance mods. I totally forgot about the lighter valve spring. That's something I was meaning to do and I'm wondering if it's possible to cut a little bit off the one currently in there now. If so, any idea as for how many coils to remove from the spring?

You are likely better off severely over compressing the spring 20 to 30 times. Slide it on the shank of a screw driver and compress it until the coils are touching, hold for 30 seconds or so, release, repeat 20 or more times.   This is what I did in mine and it works well.

Also, since I just bought a #29 drill bit and 8X32 tap, I'm going to pin the valve. That should keep the ports lined up under pressure. With the pinned valve and lighter valve spring maybe 700 FPS is possible.

Depends on how much you want to pump.

I'm really just hoping for 600 FPS with 12 pumps.

Have you already inserted a rod in the front of the check to partially fill the valve intake hole?

[Perry01]

You are likely better off severely over compressing the spring 20 to 30 times. Slide it on the shank of a screw driver and compress it until the coils are touching, hold for 30 seconds or so, release, repeat 20 or more times.   This is what I did in mine and it works well.

Have you already inserted a rod in the front of the check to partially fill the valve intake hole?

Not yet, reducing headspace is always good but I'm not sure what kind of gains can be achieved by doing it.

As for the valve spring, maybe I'll compress it in a vise and let it sit for a few minutes?

Also, pinning your valve with two 8-32 set screws will ensure your piston head space doesn't come out of adjustment.

I decided to tap a hole on the top of the tube for a set screw so it's covered by the steel breech. Any idea as to what length set screw to use? 1/8"?

[DavidS]

You are likely better off severely over compressing the spring 20 to 30 times. Slide it on the shank of a screw driver and compress it until the coils are touching, hold for 30 seconds or so, release, repeat 20 or more times.   This is what I did in mine and it works well.

Have you already inserted a rod in the front of the check to partially fill the valve intake hole?

Not yet, reducing headspace is always good but I'm not sure what kind of gains can be achieved by doing it.

As for the valve spring, maybe I'll compress it in a vise and let it sit for a few minutes?

I think that the repetition is needed (not 100%).   So if you are willing to do that 20 times then I guess so.

Also, pinning your valve with two 8-32 set screws will ensure your piston head space doesn't come out of adjustment.

I decided to tap a hole on the top of the tube for a second set screw so it's covered by the steel breech. Any idea as to what length set screw to use? 1/8"?

I use 3/16th length grub screws.

[D14Jeff]

here's a link a saved on valve pinning .

http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,10015.0.html

[Perry01]

You are likely better off severely over compressing the spring 20 to 30 times. Slide it on the shank of a screw driver and compress it until the coils are touching, hold for 30 seconds or so, release, repeat 20 or more times.   This is what I did in mine and it works well.

How would I know if I compressed the valve spring too much?

Jeff,

I'm not able to view that thread on the Crosman air pistol forum. I tried to register but wasn't able to. Bummer...

David, are the 3/16" grub screws flush with your tube or are they recessed a little?

[CarsonRatSniper]

Mine are flush.
Tape off .250" (1/4") on the tip of your pilot bit.
Carefully measure from the back of the tube to the center of the factory valve retainlng screw.
Repeat that measurement from the back of the tube where you want your valve pin screw located.
I highly recommend spotting your mark with a dremel ball tip deburring bit to avoid any drill bit walking.
Drill ONLY as deep as your 1/4" tape marking - not a hair more!

If your transfer port is angled you will want to make sure you aren't going to break through with your hole - I drilled mine between the breech and forearm.

Your tap will only start the threads - use some oil on it and when it stops, do not force it. Clear out any shavings. Start the grub screw and take your time - torque it down until flush. The grub will cut the threads as you go. A little turn, back it off, another little turn.....

Do one complete pin screw at a time if doing more than one. Drill, tap, install.
If you drill both and then tap, one will more than likely be off center and cause you grief.

If you want pics of mine PM me your e mail address and I will send them to you.

[Perry01]

Mine are flush.
Tape off .250" (1/4") on the tip of your pilot bit.
Carefully measure from the back of the tube to the center of the factory valve retainlng screw.
Repeat that measurement from the back of the tube where you want your valve pin screw located.
I highly recommend spotting your mark with a dremel ball tip deburring bit to avoid any drill bit walking.
Drill ONLY as deep as your 1/4" tape marking - not a hair more!

If your transfer port is angled you will want to make sure you aren't going to break through with your hole

Your tap will only start the threads - use some oil on it and when it stops, do not force it. Clear out any shavings. Start the grub screw and take your time - torque it down until flush. The grub will cut the threads as you go. A little turn, back it off, another little turn.....

If you want pics of mine PM me your e mail address and I will send them to you.

Mike, im following you for the most part but am wondering why just a 1/4". Don't I drill the pilot hole with the valve removed from the tube? Why is it important to just drill 1/4"?

I plan on using just one set screw directly above the valve retaining screw so I'll measure the distance like you said.

What do you mean by:
"if your transfer port is angled you will want to make sure you aren't going to break through with your hole"

Do you use 3/16" grub screws?

PM sent

[CarsonRatSniper]

I drill the tube and valve together so they are both threaded.
If you drill deeper than 1/4" you will blow through into the throat of the valve and ruin it.
Wyoman on the Green did his under the breech - all I'm saying is take an internal measurement where your exhaust port on your valve is located.
You need about 3/16" meat in the valve for the set screw.

If your set screw is not screwed into the valve and just butts against it like the barrel grub screw in the breech you're wasting your time....that will not hold your valve in place.

[Perry01]

I drill the tube and valve together so they are both threaded.
If you drill deeper than 1/4" you will blow through into the throat of the valve and ruin it.
Wyoman on the Green did his under the breech - all I'm saying is take an internal measurement where your exhaust port on your valve is located.
You need about 3/16" meat in the valve for the set screw.

If your set screw is not screwed into the valve and just butts against it like the barrel grub screw in the breech you're wasting your time....that will not hold your valve in place.

Thanks for the explanation. Its crystal clear now. I'll make sure to take accurate measurements and drill just enough to tap both the tube and valve without going too far into the valve taking my time as I go.

[DavidS]

You are likely better off severely over compressing the spring 20 to 30 times. Slide it on the shank of a screw driver and compress it until the coils are touching, hold for 30 seconds or so, release, repeat 20 or more times.   This is what I did in mine and it works well.

How would I know if I compressed the valve spring too much?

Simple put the spring on the shank of a screw driver, and with a washer compress it till the coils are touching.

Jeff,

I'm not able to view that thread on the Crosman air pistol forum. I tried to register but wasn't able to. Bummer...

David, are the 3/16" grub screws flush with your tube or are they recessed a little?

Close to flush.

[xtratoy]

How do you retain pin in valve inlet when reducing headspace?

[Mzq284]

Perry,
You're getting some good numbers, keep going!
For your valve spring, a 2240 or 13xx sear spring is a good one. I get similar numbers with similar mods. I used a sear spring in the valve, stock hammer spring with a brass guide in the hammer end of the spring. This adds a little weight and preload. I also used a Marauder exhaust poppet, they're harder material and easier to pop open. The Marauder poppet and sear spring are available from crosman, they're dirt cheap. Interesting build, I'll be following.