My 1325XLT becomes a 1322XLT

[K.O.]

And will not dump more than 10 pumps...

with the .25 barrel and .180 by  .219 barrel port  and  .220 transfer port it would dump 22 pumps...

well anyways I shortened the disco barrel to 22" in honor of the pump tube being from a 2100 (21.8"), plus I had to get rid of the boogered

up muzzle portion (come on Crosman ).

did a quick crown...

Milled a .25 sealing flat for the .220 transfer port.

Ported the barrel to .160  ( it obviously need at least  .160 by .180-.190 oval port)

Oh yea I finally stuffed the 13xx portion of the piston.


According to the spreadsheet (Boy do I wish I had a copy) it was 67% efficient pushing the  20.1gr .25 pellets to 630 fps.

I am hoping to hit at least 725-750 fps with 14.3gr pellets.

maybe my ears are fooling me but at 10 pumps it sounds faster than my 1322MLT at 15 pumps

will soft chrono in a while and then again after I  oval port the barrel...

[K.O.]

I have some thinking to do maybe add a bit more preload to the 13xx striker/2200 spring it already has a 25gr .25 pellet smashed in the striker.

I ported and it did not make a bit of difference it still will not dump more than 10 pumps


pumps      fps

5              495, 500, 498
7              591, 585, 592
8              626, 616, 616
9              654, 656, 657
10            673, 687, 680
11           653-580 wonky as heck did not measure 2nd shot just cock and dumped.


I guess  stuffing the 13xx portion made a bigger difference than I thought and pump effort is way up way sooner...

well  It is sneaking up on  700 fps at ten pumps not bad but I am power hungry I want it to dump 14-15 pumps...

I know it can be done a friends dad did one(2200) for me in the 80s.

[K.O.]

Just in case for those that do not know what I am talking about when I say my 1325XLT.

http://www.gatewaytoairguns.org/GTA/index.php?topic=60800.0

[UCChris]

It's all over my head, but atta boy! Keep on trying!

[plinker99]

Hey K.O.
      Reading this, I'm confused as to what  you did.  What I get is you swapped barrels so now you have a .22 instead of a .25.?  And now you are retaining air @ 10 pumps while before it could fully dump over 20?
       If that's correct, my hunch, guess is now with the smaller barrel volume, the amount of time the valve is open is too short for the added back pressure that the barrel is making.  Sounds like the valve spring is too strong or too long.   Do you have to cock before pumping? If no, spring could be too strong.  If yes spring could be too long.i say too long as that what I experienced with my 2100 modded to .22.  I trimmed 1/4-1/2 of a turn from the valve spring & it could dump over 20 pumps when previously it retained @ 15.
    Just my stab at what you got.
    I'll be watching on your further progress.

Plinker99

[K.O.]

yes I just did two things changed to a  22" .22 barrel. hey it is a .22 now and also a stock 2200 has a 20.8" barrel it just seemed fitting

The other thing I did was to stuff the 13xx part of the piston.

I actually think that it is building pressure much more efficiently now and that is most of why, basically it is building the same pressure it used

to in 20 pumps but only taking ten pumps to do it. I think the smaller bore is part of it but not a whole lot.

I could put the .25 barrel back on and find out a bit.

It has a very light valve spring (cock then pump) and that is not the prob 99.99% sure

I think that the striker/striker spring is having a hard time knocking the valve open with the higher valve pressure it now builds.

I had a modded 2200 in the 80s that hit over 750 fps so I know  it is possible all I remember was the flat top piston and no leaks.

I do not remember what else was done.

So far I have gained about 90fps over what a stock 2200 in good shape gets a ten pumps.

[K.O.]

added about .25" of preload at striker spring and think I can add about .125" more before coil bind.   

dumps 11 pumps now but not 12

will test fps again Sunday afternoon...

[plinker99]

Yes, stuffing the 13xx part of the piston could be making the pumping more efficient. It may be worth your effort to put  back the .25 barrel & to see if there is any gains with the stuffed piston
As for the valve spring, I was thinking that it was getting coil binds when being hit from the striker with all the extra pre load & weight that you added.  That was just something I experienced.

I'll be watching for more results.

[K.O.]

698,694,696 at 11 pumps and the rest stayed the same.

Tried some stuff but it will still not dump 12 pumps more in a while got chores to do...

But I just figured out why in a quick flash as I was getting up....

the exhaust poppet seat was made flat( stock it is on a raised seat) in an attempt to get every little .001 ci of space so there is more force

holding it closed now, duh, it just was not building enough pressure before to show up...

[rsterne]

So you increased the OD of the sealing surface of the valve poppet?.... Yes, that would increase the force required to open the valve and require a stronger hammer spring....

Bob

[K.O.]

I was thinking time to get out of this seat and get busy and that triggered thinking about the poppet seating as I stood up.



It is probably best that I do not pump past 11 pumps any way the pump effort is more than what it was at 22 pumps  and I think without

more valve volume it will start egging out the linkage or pump tube.


I think he must have given up some pump stroke to get more valve volume to hit 750+ with the one that was built for me in the 80s. I was

told  but I just can not remember.  I  am pretty sure  it  took 15 pumps and the pump effort was pretty stiff, about like this one feels at 11.

I will try the .25 barrel back on it but have to go to the hardware store and get another piece to make the transfer port I had to shorten this

one for the smaller barrel.

From where I was as a .25 I am up 70fps with about  5.8gr less lead and still down a couple fpe...

 wonder if I will get 660-670 fps and 19-20 fpe with the 20.1g H&Ns?



Ten less pumps though, I just can not believe stuffing the piston had that big of an effect...

I do not think I will go to a Disco spring I think the 13xx hammer pin is having trouble with the 2200 hammer spring at full bind.

Before I figured out  what my problem is I shortened the back of the bolt just a smidge and lengthened the bolt slot in the breech a smidge...


I really wanted to hit  725-750 fps but I guess for durability's sake I should be happy with almost 700 at 11 pumps with 14.3g pellets... 

[K.O.]

how to explain that my testing today was well

I started by switching to a .190" nylon  t-port,

Down 10 fps across the board and was back to dumping 10 pumps but not  11

I thought Hmm did not expect that

so

switched back to the brass .220 t-port,

still down 10fps and will not dump 11 pumps

what the he

took a min to think and

yesterday was using Benji Discovery pellets which seated very well fell just past t-port with a tap

today I was using the last of a tin of CPHP and needed a bit of force with my seating tool to seat...

so

I switched back to the disco  pellets and sure enough  got my 10 fps back...

so

went to 11 pumps

no joy  600 to 650 fps with a second of 430-450... (tried 3 times)

huh

It rained this morning and humidity is at 65% the other days had been hot and dry for a week plus(and running Ac I test indoors)

and humidity was way lower like in the 40-50% range...

? ? ? ?? ?   

confusing but it seems that pellet fit cost me fps and the oversize t-port does not...

and a big swing in humidity made it build pressure even quicker?

 

[K.O.]

Will test .160-.170 t-port tomorrow still not feeling my best.

then  the .25 barrel and  .177 barrel.

[K.O.]

On the subject of why it is having trouble dumping more than 10 11 pumps

I need to clarify things.

it is not actually that I increased seating area it is that the equalizing area was taken away.

the exhaust passage throat area stock is about .200 we (me and Bart) opened it to F drill bit size  .257 

here is a quick and dirty drawing...  so only opening up a bit say to .21"-.22" might help

[K.O.]

Well I finally had a chance to test with the .25 barrel back on.

pumps    fps

7           503
8           540, 538
9           580, 580
10         593, 597
11         610,  548-378,  580-no capture...

So yep even though the valve volume is much more suited to a .22  I think if I get off my rear and do some work and make another exhaust

half for the valve I should be able to dump closer to 15 pumps and just maybe hit  640 650 as a .25 and 750 or so as a .22 but that is more stress than I think is good for it and 12 or so is about as far as I want to push it and only a bit here and there...

So the .22 barrel is going back on and most of the time will be pumped to 8-9 pumps.

I will also do my best to build another in .177 shooting for about 800 fps in 11 pumps...

Hey the pump tube and lever are only about  15 bucks... and I do have the rest as a 1377 18" carbine.

right now I just need to see if the Mk177 nose will work may not have to go custom.


I think not bad for sticking with a rubber pump cup.


The 1325XLT, well it is making way for the 1325MLT it is going to send the lead  down range faster(but more pumping which does not bother me)

it will use a 66 pump and modded valve...

Stay tuned...

[plinker99]

Hey K.O.
     I was reading your progress when a couple things hit me.....
1- you're looking for more valve volume?  How about trimming the back end of the check valve.  Depending how much you trim, doing the math will tell how much volume gained.
2- you seem to be having trouble getting a full dump of over 12 pumps.  Could it be that the valve spring is getting to full coil bind when the hammer hits  the poppet stem?   Quick check would be to measure how much travel the poppet stem gets when pushed in & bottoms out.  Then compare to a stock one.  I think that is the valve lift amount.  More lift, more air flow.
  If it helps, great.  If not, well just my $.02.
Keep posting your progress.  I'm still learning.
Thanks!

[K.O.]

Hi plinker

yes the check valve has been reduced to about half size and then drilled out some at the rear, the exhaust poppet had been reduced in diameter and shortened on the spring guide portion

I am surprised  the head has not popped off....

the exhaust passage has been opened to .257 stock is about .200, what this did was to take away equalizing area and now almost all the pressure is pushing the poppet against the seat.

there used to be more area that the air pressure on the exhaust side of the poppet could push on because it sits up on a little hill and there was area that overhung.

The effect is that it takes more cracking force to open the valve...

To much thought about flow and not enough on mechanics...

[plinker99]

K.O.
   Another thing  came to mind.....
   What doyou think about trimming a little off the end of the poppet stem?  That would give the hammer more acceleration distance & possibly a stronger hit to crack the valve open.

[K.O.]

Reducing poppet shaft length is a good thought and when I first built the 1325 I tried it after a fashion...

I used a 2100 exhaust poppet which is .220 shorter than a 13xx exhaust poppet.

It did alright at lower pressure but did not have enough lift at higher pressure to dump cleanly. (pic below)


So what is my solution...

well look at the above pics of the rear valve halves  one is .200 in exhaust throat diameter and the other has been bored out to  ~.220 with a

7/32 drill bit... and the raised seat area is preserved... and the poppet head is .34 so I will still have a good amount of overhang to equalize pressure and cracking force needed will only increase slighty

we could calculate it out to see a rough estimate of how much but I will trust my gut on this one.

ok so how about flow, well the 2100 pump makes a good .22 power plant  but the tube would need to be about an inch .9" longer to make a good .25 power plant.  (630-650 fps with 20.1gr is not to bad though)

so a .22 it will be,

as a .25 the valve exhaust was bored to .257 with a poppet shaft reduced from .120 to .1  so that left an effective throat diameter of .157

that is about 63% of bore size  ( and the valve half I am now using)

so now we have a .22  valve bored to .22 with an effective exhaust throat diameter of .120   

That is about 54.5 of bore size  (the valve half I will put in)

I am pretty sure is good to about 900-1000 fps and if not well  I can probably go to .23 ~ 59% bore size and still dump 15 pumps..

If I new just what pressures the system was actually producing I could figure out a rough charge velocity  for  finding the right port diameter

to use for the goals set but hey backyard engineering is not doing so bad...


I am pretty sure this will allow me to dump 15 pumps (which I will only do a couple times  to see what is possible) I will use 12 pumps occasionally and most of the time 8-9 pumps

I have a few nylon ports made to try .170-.180-.190  the   .170 should have the advantage by a touch at lower pumps...

So yep that's the .22 plan.

[K.O.]

I finished the valve and used a .170 transfer port sleeve,  no fps testing till tomorrow but it will dump 15 pumps and sink the 14.3g CPHP   .25"

past the skirt into a maple round(end grain) at 20 yards...   And I got rid of all preload on the 2200 spring but left the .25 pellet in the back of the striker.