Starting my new project 1325XLT carbine

[K.O.]

When I first came here I had just pick up my 13xxs and a 2100b  in my intro thread I had some goals...


In this thread
http://www.gatewaytoairguns.org/GTA/index.php?topic=53940.msg514392#msg514392


is  the statement
___________________________________________________________________________
want to keep the 13s to long pistol 14.5   and have 1399 stock on the way

.22 first probably 14.5 barrel stuffed piston ,match valve and cup/shim, porting(?),valve work(?), crosman breech, barrel band last( home brew 3 piece)...

@ 14.5 barrel ,  valve interior (cut a few threads off) volume increase help?

need to understand better!!! mods trade offs...    willing to pump a little (15) to get 625-650fps 1322 or so   I think is doable?   valve and  valve stem mods...

Do not know enough yet...

Low budget but sound an dependable is the theme...

Thanks for your time...

Dreaming of self contained  .25 and/or custom up to .30 self contained pumper 20-25 pump max,  650- 700 fps with mostly commonly available parts... (crazy?)

All for fun  Informal...
_______________________________________________________________________________________________

well I came close with the 1322   

I will have to put an  18" barrel on it  making it a carbine and not a long stocked pistol but am very happy with my results...



So My Dream goal...


Well I tore down my 2100 and it will become the tube for a 1325XlT and I have moderated my hopes to 575-625 fps for now but do think at some point I might reach more...

In my research  I was inspired by,

http://www.gatewaytoairguns.org/GTA/index.php?topic=37401.0

in which over 600 fps  is doable on 1200 psi  (I will go out on a limb and guess that is about what a 2100 can reach?)

but that was with a .3356 ci  or so valve  so I am hoping that I can hit closer to 1400 psi because I at best will have about .14 ci to work with.

and that will take Big Bore Barts assistance...


I checked how far back I could mount the breech on the tube and found  that I could move the port back .3"  so I pm Bart and tell him my

idea(inspire by research here and other places but mainly here) about notching the exaust end of the 2200 valve  to move it back and then
 
make an extension to expand the valve by .3...

Well Bart know his Crosmans,  and let me know that a modded 760 valve nose would be the best way to go about it.

That was my biggest hurdle  I needed to jump so today day  I put in an order for a 18.75 .25 barrel  turned down on the end for Crosman

breeches. 

I am going to go eat dinner and will say more in a few but wish me luck.

[kj]

hi, where you get the barrel ? can a 1/2" barrel be turned down to fit a croaman breech ? just asking cuz i built a few 2540 , and have barrel/breech bolt for a 1325, just haven't gotten around to it. in any case my point being that none of the barrels i bought/used were turned down. the breeches were made bigger to accomadate the larger diameter. i just wonder if the barrel will be too thin there or somethin. just somethin to think on. good luck

peace
kj

[Big Bore Bart]

   The Crosman breech is too thin to open to 1/2", you break out at the bottom.     A 1/2" barrel can easily be turned to .437, and will still have .093" wall.    It will be very close to touching the pump tube.

[K.O.]

http://www.bryanandac.com/

Here is a link to a capof thread  that let me know that I will have to drill my own port and transfer port sealing area and that it is a  np barrel.

http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,10989.0.html

It is a 9/16ths barrel,

.25 to .435 leaves .1 or wall thickness, which is double what the straw barrels in the 2100 have.

It is steel... and these are not powder burners... so yep I think it will be fine and only the breech area is turned down.

[K.O.]

I may have to shim the breech just a touch but it will be only a little if at all...

I may have found a 1377 trigger group and grip handle like new does any one know how much Crossman wants

and do you have to order it as separate parts?

I did spot this on ebay   http://www.ebay.com/itm/Crosman-Pistol-Frame-Grip-Trigger-Assembly-2240-2250-1322-1377-2289-2260-/331049479535?pt=LH_DefaultDomain_0&hash=item4d14162d6f

[K.O.]

To start with this will be a budget build (plastic breech for a few months) but I will upgrade as I can.

[K.O.]

I do like a challenge and do know that in the end well if I do not get it right well I will just have to build a regular short stroke 1325...

I am decent at working with wood and no machinist skills

this is a lap slide I am working on for my daughter,

It is done with all hand tools even though I have all the power tools needed except a  thickness sander ( do have a friend/ex boss with one)

[K.O.]

I have read that a 22 bolt works so that is what I plan on Does anyone have any experience  with that?

grip handle and trigger group fell thru guess I will just get it from Crosman.

[Big Bore Bart]

   No experience with the bolt, but the PRod/1701 frame unit is 25-30 bucks complete.   Alliance Hobby is a usually quite a bit higher than Crosman.

[K.O.]

For now I have to go low budget besides I honestly do not have a problem with the 13xx trigger.

I have sent a couple more pm to you to try and talk you into modding a 760 nose for me( hey you are an ARTIST) and I also have pm'ed another  member about some pellets but I think

they may not be getting thru?

If I can't get a modded valve I am stuck with unscrewing slightly and washers which gains me only .11 or so which translates to a valve

volume of about .11 and that is with cutting down the poppets,  compared with just over .13 or so with the modded  760 nose  which is 

probably barely(if) enough at .25...

[K.O.]

oops pm is working

I will be ordering tomorrow and just remembered I need  advise


Transfer port size  I need  .170-.185?   is there a Crossman part?

[Big Bore Bart]

  A 1322A026 T-port can only go about .160ish.  To go larger needs a custom port.   Delrin or Teflon works nice.

[kj]

@bart , i have 3 after market breeches fitted with .25 barrels in 1/2 dia., none turned down the barrel.  so, i'm not sure about that crosman breech thing.  but what do i know ? is that thin wall strong enough for the extra wieght of a thicker barrel.? note that i'm not a machinist, not even a hobby type machist-wish i knew how..lol.

peace
kj

[rsterne]

If you turn down a 1/2" barrel to 7/16" to fit a Crosman breech, that will work fine, and the barrel will JUST touch the top of the tube.... Therefore, if you use a 9/16" barrel, it will stick out 1/32" below the bottom of the breech, so you will have to shim the breech up by 0.032" to compensate.... If you want to figure how much larger valve volume you need, that is in the ratio of the bore AREA, which is the square of the diameter.... so to go from .22 cal to .25 cal you need a valve that is about 1/3rd larger in volume.... That means 1/3rd more pump strokes to get it to the same pressure, if the .22 valve took 15 pumps, the .25 cal valve would take 20 to reach the same pressure....

Bob

[kj]

thanks for your input bob. you're a wealth of info.

peace
kj

[K.O.]

Today was full of other tasks but I did get my order in with Crosman and got the rear grip frame hole drilled. Tomorrow I will see a buddy that

has a nice tap and die collection but knowing my luck I will probably have to order a  4 48 tap because I live in a smaller town and I doubt

anyone  will carry one. Then I will be able to mount the breech.

I am sort of stuck with  about a .13 ci  max for the valve volume,

But I do have some hope that it is enough...

@ Bob

Using Boyle's law,

 and  pi X  r² x l


  3.14x (.25 x .5)² x 18.75= .9199  ci  for barrel  volume

so

  .9199 + .13 =  1.0499 ci  for total  volume

so

  1.0499 / .13 = 8.076   for expansion factor (ending volume is 8.076 times larger than starting volume)

 Boyles law says   "At a fixed temperature, the volume of a gas is inversely proportional to the pressure exerted by the gas."

which means

assuming a starting pressure of  1400 psi

1400 / 8.06 = 173.69  Psi left at end of barrel...

Similar work tells me that pump swept volume vs valve volume gives a compression factor of 10.85 ( end volume is 10.85 times smaller than beginning volume)

so I live at about 2000 feet above sea level and will use 13.9 apsi  as beginning pressure

that gives  150.8 psi per pump

now here is the thing  pump efficiency? I will use   95% but feel that may be high especially at 800 psi on up...

but   150.8 x .95 = 143.26

so 

  143.26 x 10 = 1432 psi at 10 pumps  ( in case I am way wrong lets add 2 pumps and call it 12)

and

   143.26 x 15 = 2148.9     ( I am going to take a  W.A.G. that the stuffed plastic piston and pump cup will only handle 1500-1700 psi though?)

 as long as I get the porting right I have hope of hitting 575-625 fps with 21g-24g pellets at around 15 pumps I think ?


?

[K.O.]

Oh my measurements for the 2100b's pump where .61 id and 4.83 for stroke.

I did not use  ideal gas law because I feel Boyle gets close enough...

[K.O.]

Another thing that is giving me hope is I found this thread on the Capof,

http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,4528.0.html

For those that have not become  members a Mountain air 1325 is checked using a chrono.

It looked to have a 12" barrel.

I do not know what was done to the valve but my guess is it was just ported...

I used to accept that a 13xx valve was .1 ci as I had seen posted but when I measured (with some estimation) I came up with .13 ci and that

is subtracting the space taken up by the poppets...


So  if the valve is stock and it is getting 490 or so fps  @ 15 pumps  with a 12" barrel,

and I gain 10-15 fps per inch of barrel   that puts me close to 575fps @ 10-12 pumps with  an 1325 eXtra Long pump Tube.

But there is a real world and this is just hopes and conjecture...

[K.O.]

No luck on the tap closest he had was 4 36ns...  Darn.

[rsterne]

I've found trying to calculate the final power of a pumper just about impossible.... so based on that your numbers are as good as any.... *grin*....

Bob