13xx with the steel breech – how to get it to sit flat

[WyoMan]

I call it the “floating breech”... the main bearing point being the transfer port sleeve. No amount of clamping or tightening or shimming really fixes the problem. The problem is caused by the TP sleeve (combined with the gasket seal) that is too long.

The 13xx, 22xx Crosman steel breech was originally used on the 7/8” o.d. tubes, and the radius for the tube was milled accordingly. It will fit the 3/4” tubes but not as well. Best case scenario – there will be a narrow contact area down the middle.

But the real problem (in my experience) is that the TP gasket sits higher off the tube in the ¾” tube. It’s just geometry and the design does not provide enough clamping pressure to overcome the problem. This may be why there are so many stripped 4-48 breech screws. And if you have the rear location breech screw, it's even worse for clamping the breech to the tube.

Some solutions if you have this problem…

Drill the countersink of the barrel port a little deeper with a #8 drill:

This matches the top of the TP sleeve pretty well.



Ideally, the flange of the TP sleeve should be just proud of the bottom of the breech:


Alternatively, you can shorten and re-chamfer the top of the TP sleeve.

Or, make your own TP sleeve:


Whatever you end up with, the breech should only rest a few thousands off the tube before it is clamped down. You should be able to “pinch” the breech onto the tube with just some light finger pressure. Gasket o-ring seals don’t need much compression to seal.

And while you’re at it, get a better 4-48 breech screw. You can get a bunch of St/St 4-48 x ½” for a few bucks. You’ll have to turn the heads and cut them to length:


I use the ½” length so I can chuck the very end (for turning), and then part-off the mangled threads.

Using a flat head screw that’s designed for a countersink is a little unorthodox in a counter-bore... the screw head will sit higher, like this:

But you don’t get the pellet snag problem with the breech screw hole.

In summary, you want your breech to sit “rock solid” on the tube without the need for excessive clamping force – and that will improve accuracy


Wyo

[Back_Roads]

 That deserves a thumbs up button

[Tater]

Great tips there Gary. Nice looking breech and tube too.

[cobalt327]

Good stuff- thanks.

[avator]

Thanks Gary.... your guns always make me drool.

[Mr. Panther]

 I just bought  some of those stainless screws from Amazon in .250 length so they are the right length. just need to trim the heads , and being a phillips head they are perfect. For  $17 for a pack of 100 beats, $3 or more a piece every where else. Great tips by the way and WAY too cool of a pistol  .
 

[Gipper]

Wyo is the king of Crosman pistols....glad to have him here. Have seen many of his outstanding builds on Crosman forums in the past. Always willing to share his knowledge as well.

Brian

[2K1TJ]

Well done, sir.

[Tater]

Wyo is the king of Crosman pistols....glad to have him here. Have seen many of his outstanding builds on Crosman forums in the past. Always willing to share his knowledge as well.

Brian

Well said, and all true.

[jim p]

Would shortening the metal transfer port also lower the breech onto the tube?

[WyoMan]

Hi Jim, yes shortening the transfer port sleeve would net the same result as drilling the barrel port deeper. I've done that very thing and it works. It's a good idea to reestablish the chamfer after the cut... you'll most likely get a better metal on metal air seal that way.
Thanks, guys... always appreciate the feedback -

Wyo 

[BillK]

Hi Jim, yes shortening the transfer port sleeve would net the same result as drilling the barrel port deeper. I've done that very thing and it works. It's a good idea to reestablish the chamfer after the cut... you'll most likely get a better metal on metal air seal that way.
Thanks, guys... always appreciate the feedback -

Wyo

Thanks Wyo.  Now I have to check 5 or so guns to see how they are doing.  I appreciate your info.  I think?

[GumpIsrael]

Thanks, Gary! I noticed this on my PC77 and was wondering what to do about it. Now I can't wait to take care of it tomorrow lol

[jim p]

I have not researched this and I don't have the equipment or skill to make this mod.  It seems that an extra breech screw about 3/8" from the barrel end of the breech would be helpful to secure the breech better to the tube.

currently I have floated the barrel on my 1377 and the breech is about 1/32" off the tube at the barrel end.  For testing I am using e6000 glue to help steady the breech on the tube.  If I get great accuracy from floating the barrel, I will have to come up with something to keep everything snugged up.

[anti-squirrel]

Now that I'm falling down the rabbit hole with my 2240, 2400KT, and potentially my 1377, I'm considering going this route. 

Thanks for sharing the information.