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.

[DavidS]

Nice build.   I have thought about doing the same.  Though I just have not been able to talk myself into either getting a tube, and linkage from Crosman, or sacrificing one of my 66's.

Nice build.

[Trigg603]

That's awesome!!!  I'd love to know how to do that!!!

[AK73]

It sounds pretty nice. I guess there is no limit to what you can do with those Crosman pumpers.

[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.

"That's awesome!!!  I'd love to know how to do that!!!"   Thanks I will post about how this afternoon but right now I have to eat and then run

some errands.  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

[stonykill]

 very interesting. Can't wait to see the write up and chrony results.

[Skunk Shampoo]

The powermaster 66? Isn't that a smooth bore barrel? Does this mean you can shoot pellets and bb's without the concern of messing up the rifling?

[Big Bore Bart]

The powermaster 66? Isn't that a smooth bore barrel? Does this mean you can shoot pellets and bb's without the concern of messing up the rifling?

  There are currently two versions of the 66.   The 66SB and the 66GT.   The SB is smooth, the GT is rifled, but in this case, it makes no difference, all that's used is the pump and tube.    The rest is 13xx.

[K.O.]

The powermaster 66? Isn't that a smooth bore barrel? Does this mean you can shoot pellets and bb's without the concern of messing up the rifling?

  There are currently two versions of the 66.   The 66SB and the 66GT.   The SB is smooth, the GT is rifled, but in this case, it makes no difference, all that's used is the pump and tube.    The rest is 13xx.

Yep and 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 stunk 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.

[K.O.]

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.



Have to go for a few will finish in a few...

[K.O.]

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. (1/27/16 edit* ( they ended up being to soft )  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.

[K.O.]

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.]

Had to add a family pic.

1325XLT 1322MLT  1322