1322 velocity after FTP and valve mod

[Perry01]

I recently installed a flat top piston and modified valve in my 1322 and have read that a 100 fps gain is what to expect. I also installed a 14.5" barrel and went from 400 fps at 10 pumps stock to 530 fps at 15 pumps using 14.3 gr. pellets. Does 530 fps sound about right for what I've done so far? There is a little compressed air leftover after 15 pumps.

My question is: what kind of gains are possible at this point. Will a stiffer hammer spring help and if so how much? I'm not looking for a 650 fps pistol but am curious as to the potential of the 1322.

I'm at 9 FPE right now. 560 fps or 10 FPE would be a nice goal.

Thanks...

[DavidS]

That seems about correct for what you have done.

If you have another original style valve, shaving about 4 thousandths off of the valve cone, and using the original cup piston and shimming, or using an aluminum adjustable piston that uses the original pump cup can get greater gains than using a flat top piston.

Also boring the transfer port a little and a slight angling can help.

Then add an even longer barrel (mine are 18 inch [on my 2289's (2289 is a 1322)]), if you want to keep it a pistol then a 14 inch barrel is likely your limit (some like even longer pistols).

For some secondary references:
http://www.network54.com/Forum/275684/thread/1226290086/my+2289%27s+official+introduction+%28lotsa+pics%29

http://www.network54.com/Forum/275684/thread/1169082692/I+just+did+another+%26quot%3Bstuffed%26quot%3B+plastic+piston%2C+this+time+in+a+bone-stock+2289---

http://www.network54.com/Forum/275684/thread/1353701149/Secrets+of+the+Stuffed+Piston+Revealed+%28Surprising%29

[bigfish123]

I have the DBO 2289 12" barrel. I installed a flat top piston and valve from A C Custom mods. Stock it shot Crosman Premiere HP 14.3 at 460 fps with the flat top it shoots 14.3gr at 525 fps all on 10 pumps. I haven't shot over the chrony with 15 pumps yet. With 10 pumps this pellet goes thru 2 tin cans at 10 yds, 15 pumps it goes thru 3 cans at 10 yds. I've got the steel breach waiting on my work bench to be installed, and a Leapers 3-9x40 to top it off

[Perry01]

I have the DBO 2289 12" barrel. I installed a flat top piston and valve from A C Custom mods. Stock it shot Crosman Premiere HP 14.3 at 460 fps with the flat top it shoots 14.3gr at 525 fps all on 10 pumps. I haven't shot over the chrony with 15 pumps yet. With 10 pumps this pellet goes thru 2 tin cans at 10 yds, 15 pumps it goes thru 3 cans at 10 yds. I've got the steel breach waiting on my work bench to be installed, and a Leapers 3-9x40 to top it off

Sounds good.

My 1322 came with a damaged transfer port seal and was leaking air right out of the box (I performed the tissue test). I'm going to make my own transfer port out of poly tubing tomorrow and check the velocity afterwards. I also ordered a stiffer hammer spring that should arrive by Friday.

Boy this platform is fun to tinker with.

[ray1377]

If you have another original style valve, shaving about 4 thousandths off of the valve cone, and using the original cup piston and shimming, or using an aluminum adjustable piston that uses the original pump cup can get greater gains than using a flat top piston.

can you please elaborate on this sir?
Do you know of someone who makes a pump air/piston design like this, that uses a factory cupped end with metal construction instead of the factory plastic?
And whats removing the 4 thousandths do?
Thanks
Ray

[Big Bore Bart]

   Actually on some valves it's over 40 thou. (.040")   It fits the valve to the cup better to reduce headspace.  Properly done it also causes the cup to mate with the valve at the outer edge first, then roll the air to the center.    Any adjustable piston for using the factory cup will be a one off, usually made by the end user.

[Rboss75]

Hello. I am new to the some air gun mods but very curious. Why does the flat face valve give you more power the the cone type ? 

[Big Bore Bart]

   It's a matter of compression and headspace.    The rubber cup of the stock setup has a lot of give.   A flat-topped metal piston only has the O-ring that can compress, which can be reduced by proper design of the groove.   Also removing the cone of the valve, removes that amount of the inlet hole's headspace, a large portion of the remainder can be eliminated by adding a pin to the check poppet.    Reducing the valve's top to within .012" of the O-ring groove removes even more headspace.   Ultimately it all adds to the pressure in the valve.

[Perry01]

So instead of waiting for a replacement transfer port seal from Crosman, I decided to fabricate a transfer port using poly tubing. The original seal was damaged and leaked but now there is no leaking air and the velocity increased as well. Thanks Nervoustrigger.

14.3 gr. CPHP pellets

10 pumps 519 FPS for 8.5 FPE
12 pumps 539 FPS for 9.3 FPE
15 pumps 580 FPS for 10.7 FPE

Not bad for the mods I've done so far. It dumps all air at 15 pumps but there is very little gain after 15 pumps. I'm pretty happy with this little shooter.

[Rboss75]

   It's a matter of compression and headspace.    The rubber cup of the stock setup has a lot of give.   A flat-topped metal piston only has the O-ring that can compress, which can be reduced by proper design of the groove.   Also removing the cone of the valve, removes that amount of the inlet hole's headspace, a large portion of the remainder can be eliminated by adding a pin to the check poppet.    Reducing the valve's top to within .012" of the O-ring groove removes even more headspace.   Ultimately it all adds to the pressure in the valve.

Thank you

[Perry01]

Well I've had my 1322 for a couple of weeks now and the more threads I read here, the more ideas I get for new mods.

I got an envelope today from AC and in it was a new solid pivot pin as well as a new breech screw to replace that lame hex head one.  More important though was the new stiffer hammer spring. I'm now able to dump all the air at 20 pumps. So far I've got a FT piston and modified valve, poly tube transfer port, bored barrel port, a 14.5" barrel and some trigger work. I shot it over the Chrony with 14.3 CPHP pellets.

10 pumps: 541 FPS
12 pumps: 568 PFS
15 pumps: 592 FPS
18 pumps: 615 FPS
20 pumps: 621 FPS for 12.2 FPE

My next project is to make an extended bolt probe. I don't know of I'm going to get any more velocity but it will probably help accuracy. I'm already shooting 1" groups at 20 yards but there is always room for improvement.

On the way is a 2289 shoulder stock, a 5" TKO, and a 4X32 compact scope and rings. I also ordered a 12" barrel from Crosman for when I want to use it as a pistol.

I've tuned my springers and gas ram rifles but this little pistol sure is fun to play with.

[K.O.]

Hey not bad at all...

I think that is about what my 1322 with a 14.5 barrel gets. I went a different route tho, until  your bolt get to you you can use an allen


wrench or something similar to seat the pellet just past the  port, that is what I do.  I am guessing I will gain you about  10-20 fps...

[Perry01]

Hey not bad at all..  I am guessing it will gain you about  10-20 fps...

Another 10-20 fps would be nice. I have already gained 200 fps over the stock 1322. It's amazing how easy this platform is to modify.

[CarsonRatSniper]

You're about maxed out for what you have.
I get 570 fps on 10 pumps with a 16" barrel using a 14.3 grain pellet and I've noticed gains of 7-10 fps per inch in barrel length.

Gil Irvin used to make an aluminum adjustable cup piston - I wish he was still around as he made me some amazing stuff.

If you contact Roy Weid at Mountain Air Custom Air Guns he will make you a Delrin stem for your 1322.

I am using 1/4" steel brake line for my transfer port sunk metal to metal in my valve, the barrel is countersunk 1/4" with a poly tube washer and a 9/64" transfer port in the barrel.

I am making 16 ft lbs @ 20 pumps, but I usually just shoot her at 10 pumps for 10 ft lbs.
If I need more I grab my Steroid 392 or a PCP.

[Perry01]

You're about maxed out for what you have.
I get 570 fps on 10 pumps with a 16" barrel using a 14.3 grain pellet and I've noticed gains of 7-10 fps per inch in barrel length.

If you contact Roy Weid at Mountain Air Custom Air Guns he will make you a Delrin stem for your 1322.

I am using 1/4" steel brake line for my transfer port sunk metal to metal in my valve, the barrel is countersunk 1/4" with a poly tube washer and a 9/64" transfer port in the barrel.

I am making 16 ft lbs @ 20 pumps, but I usually just shoot her at 10 pumps for 10 ft lbs.
If I need more I grab my Steroid 392 or a PCP.

What's the advantage of a Delrin stem?

I countersunk my barrel transfer port so the ploy tube fits nice and snug and was wondering how big to go on the port itself without having the pellet drop through. I'll try 9/64" as you suggest.

[CarsonRatSniper]

The stem is flow enhanced behind the poppet. Are they using teflon from the factory now? My 1322 is an old model from the early 1990's that had the same seal as a 2240 just smaller.
If your poppet is white teflon just grind the stem down behind the poppet for 3/8" - take off about 30%. It will open up th flow path through the throat to the transfer port.

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

[Perry01]

I just inspected the stem and the guy I bought my FT piston and modified valve from (Airgunsmith) already grinded the stem down behind the poppet. He also bored and angled the valve port.

I like the idea of putting set screws to secure the valve. That may be my next project.

[D14Jeff]

there's always a next project 

[Perry01]

I built a nice extended bolt probe out of the original brass bolt but now I need to tap the bolt to accept the bolt handle. Does anyone know what size the threads are on the Crosman bolt handle and what size drill bit to use?

[DavidS]

Hello. I am new to the some air gun mods but very curious. Why does the flat face valve give you more power the the cone type ?

As others have said it is a matter of reducing head space, and there by increasing the compression ratio.  Less head space also means there is less air wasted in the lower pumps before much pressure is built.

Though flat top is not the only way to do this.   If you make the standard piston stiffer by stuffing the pockets with steel rod, and then shave a little tiny bit off of the nose of the valve (so the cup fits the valve nose better), add a 4mil thick washer between the cup seal and piston, add a thin O-Ring around the outside between the cup seal and piston, you will get much better results than any commercialy available Flat Top Piston + Flat topped valve and it will only cost you a little less than $5.   This reduces the head space more than the Flat Top Piston does.

For secondary reference see:
Secrets of the Stuffed Piston Revealed (Surprising)
New item on the dinner menu - Fresh Stuffed Piston!
And:
Washer O-Ring?