Introducing the 1322MLT (Medium Length Tube) 13xx/66 Hybrid

[K.O.]

It took a few hours of work but here it is...

The only testing so far is a soup can in a chili can in a spaghetti sauce can, it went through  5 layers of 6 at 10 yards 15 pumps with 14.3 hunting points.

The only mods to the 13xx valve are angling the exhaust  passage,matching the nose to the cup and a sleeve in the intake passage, barrel port and

transfer port are both .160

[bgmcgee]

Cool custom. 

[targettgii]

Nice work looks like it has some power too.

[KevinP]

Looks nice ....   

[K.O.]

First groups all at 12 pumps. The 30 yard groups was hurried because I was trying to beat the rain I could see coming. Will chrono soon.

I am guessing  630-650 fps @ 12 pumps from trajectory.  I am sure that the 30 yard groups will be a lot better it was me not

the carbine I expect they will be very near to like the 20 yard group.  They were shot sitting side rested...


Thanks Guys


  I am pretty happy with it

[Ryan]

K.O.

Did you get the tube from a 2100/2200 or it is a custom-cut tube. It looks like you have a 2100 pump handle fitted to your MLT. You mind telling us the tube length?
So if everything is stock, all you are gaining is a bit of stroke length. The Boyd law that you showed me is still ingrained in my head. Now I am eager to know the tube length so that I could figure out the compression ratio.
Thanks,

[NoviceGunnar]

Nice! Looks like a lovely shooter.

[K.O.]

K.O.

Did you get the tube from a 2100/2200 or it is a custom-cut tube. It looks like you have a 2100 pump handle fitted to your MLT. You mind telling us the tube length?
So if everything is stock, all you are gaining is a bit of stroke length. The Boyd law that you showed me is still ingrained in my head. Now I am eager to know the tube length so that I could figure out the compression ratio.
Thanks,

Hi Ryan it is a 664/66 pump assembly it is ~4.2" stroke.

I am about to copy and paste  how it went and it probs...

[K.O.]

 this was a rifled 664/66  BUT this one had accuracy probs because it was almost what they used to call ghost rifling. This 66 also had

other problems. the valve would move back and forth some because it did not contact the piston cup, there was a full .052 of head space

which lead to two problems one was it limited velocity to about 570-580 fps(not the 640 it should get) with large variations which will show

as vertical spread.  The second was that when the hammer hit the valve's exhaust stem it made it move a lot which made the whole gun

shake throwing off my aim. my aim with it sort of sucked any ways the plastic trigger was heavy but mushy and I could not get a feel for

when it went off. OOps it also caused a third problem it leaked at the valve exhaust port/breech nipple. This was all fixable and with a better

straw barrel or turned down Disco barrel I am pretty sure I could have gotten it to shoot very well...   

BUT

http://www.walmart.com/ip/Crosman-66-Powermaster-Plus-Backpack/29329648


I bought it on clearance from Wally world for 30$ (the add said smooth bore and a model # of 664 gtbbk) for the purpose of  becoming the

power plant for a 13xx because its pump stroke is  ~.7"  longer. So once I had to open it up well then it was time to do the deed.

I had a 1377 that one of the members here sold me for 25$  so I decided it was time.


Ok so here it is

I pulled apart the 664 and basically only used the pump tube, linkage and pump handles.

so I stripped it down to a bare tube, it is longer than the 13xx tube so using the back edge of the hole for the transfer port I measured  and

cut it down to match the measurements of the 13xx tube (3"). It would have been easy with a chop saw to get a nice straight even cut but

what I have is a die grinder and cut off disk. I had to cut it a touch long and check square with a carpenters square while grinding to length.

Next was a rat tail file to round the edges and get rid of the grinding burr and then check the fit of the 13xx pump tube end cap. it was good.

So I next drilled the hole for the rear grip frame screw (drill press makes it easy but could be done by hand) I then used my Dremel to make

the sear slot as long and wide as the 13xx's. You also need to widen the guide slot for the wider hammer pin so do it now also.

I used this  http://www.dremel.com/en-us/Accessories/Pages/ProductDetail.aspx?pid=541

Now I could mount the grip frame using the rear hole and use the front hole to let me mark for the front grip frame hole (which is smaller

than the rear hole, important! helps keep the valve from moving). I got lucky and it lined up just right with the 13xx valves screw hole

without having to enlarge the hole .


The 66 uses a 760 valve which is the same as a 13xx valve but has no screw hole in the nose for the grip frame front screw. point is they

interchange, you could drill and tap the 760 nose but you need the 13xx exhaust half to be able to use the stock transfer port sleeve so  just

use the 13xx valve. I then matched the valve nose to the cup and sleeved the intake hole with 1/16 brass tube.



The only other valve mod I did was to angle the exhaust passage 3/4 of the way to the poppet seat. I will finish those mods but wanted to

see what I got without them.  I then put the valve in without the exhaust poppet to make shimming the pump cup easy it needed .052 worth 

of shim. I then pulled the valve and mounted the breech using the rear screw and barrel transfer port and barrel band,  it made it easy to

mark the hole for the forward breech screw which I then drilled and tapped.  From there it is just a matter of assembling.

the 66's trigger pivot pins are just right for use as a solid pump lever pin.   I used a drilled out 13xx barrel band but that will be replaced

with a 2289 barrel band. The barrel is a cut down 18.75" .22 Disco barrel ported to .160. The stock transfer port is  opened up to .160also       

(used a slightly worn 5/32 Dremel chainsaw sharpening bit).

Because I did not use a lighter valve spring I am getting hammer bounce above 10 pumps but it does not retain air until 16-18 pumps.

I also think that coning the exhaust poppet helps reduce opening force needed more than an air flow benefit and so will help fix hammer

bounce just a bit.

I did not thin the exhaust poppet shaft and am not sure if it will matter that is why it is next after a lighter valve spring & the poppet.

I  am thinking those three wil fix the wonkiness past 10 pumps and I should get a fps increase from the air dumping whenits needed rather than to late to help.

Also I will be removing a couple threads for more valve volume depending on what I get.

Chrono results...

Pumps      Fps


5              405
6              450
7              481
8              509, 517
9              523
10            555, 542
11            550, 568
12            585, 598
13            625
14            580
15            625, 616
16            592,
17            620
18            640, 497  big burp instead of small after 497 shot...
19            620

So that's the story so far I think I should get close to 650-700 fps @ 15-17 pumps with 14.3g CPHP when I am done.





I now think it might have been the carbine some on the 30 yard group. The velocity spread would show as the  vertical spread. and that is

right where  it seems to start getting into problems...

[K.O.]

Ryan I wish the 2100 pump tube was a bit more like this one...

I had to cut off about an inch of the breech end the thing is that it uses the 760 valve which if you go all out you can hog it out to about .2 ci which

would really help my 1325XLT get the 20.1g hunk of lead to around 700 fps on 17-20 pumps or so.


I could use this for my 1325 but because the pump stroke is 4.2" rather than 5" it would take about 30 pumps...

I have figured out how to get .17 or so ci for my 1325 though and should be getting that done soon   cross your fingers for 690+ fps for me will ya...

I will also reduce headspace just a touch  on that project at the same time.

[K.O.]

by the way the 20 yard groups  the top is zeroing the scope

and the bottom is a five shot group the large opening is a 3in one large hole...

[Ryan]

K.O. Thanks for the write-up. I have a 2100 and a 760 pump tube. I haven't decided which tube I am going to use yet. All I need is to find some time and to ask a machinist friend to drill the holes for me to make it into a hybrid pumper. I would sure like to use the 2100 short valve for higher compression ratio, but I haven't figured out a way to fasten the 13xx grip frame onto the tube without being able to screw it into the 13xx longer valve nose. I was hoping time will find me a solution.

Nice work that you have done to the MLT.

[KevinP]

Nice work 

[Ryan]

K.O.

The 2100 gives a 4.27" stroke
The 13xx gives a 3.545? stroke
The gain is .72" stroke as you said

If this is the case, I might as well cut the 2100 tube to the same length as a 13xx. This will make the hybrid more compact while gaining a .72" stroke. All it needs is to adjust the piston length to compensate the increased .72 stroke length. This may accelerate the wear of the pump arm/linkage due to increased pressure though.

The above said, I still wished there was a way to fasten to fasten a tube to a 13xx frame so that I could make use of a 2100 value - the best of both worlds.

[K.O.]

Ryan the only reason to build a hybrid is the longer pump stroke.

13xx & 760 pump stroke ~3.5"
664/66  pump stroke      ~4.2"
766/2100 pump stroke    ~5"

On the 66 I had to shorten the breech end not the pump end.

the 2100 could use about a .6 longer breech end