Transfer Port Adjustment

[rr_shooter]

I've come across several threads that discussed narrowing the transfer port on B3-1 rifles to help smooth out the firing sequence, particularly if the barrel has been shortened.  I was reading some back isssues of Tom Gaylords blog on Pyramyd Air, when I came across a review he did on a Whiscombe.  He noted you can vary the diameter of the transfer port by changiing out the removable screw in the port.  (They look like hex head set screws - see photo)

Has anyone heard of a DIY conversion of this type on other rifles?  I don't know how difficult it would be to drill and tap the compression sleeve on say, a B3, or to drill out various size holes in the hex head screws.

Any thoughts on this?

[Gene_SC]

I have seen this before. Some have great success but most of the time I have read where it has done nothing or lowered the performance of the gun. But if you are gonna try it I could not think of a better gun than the B3 to try it on.  Good Luck

[RedFeather]

Ask on the Yellow.  I believe someone there fabricated a set for testing.  Thing is, you can't get around how the hex hole for the wrench affects performance on those pictured.  Maybe put two shallow holes into the face of the plug and use one of those tips with the two tines to screw it in and out with?  Let us know how it turns out.

[kiwi]

that would work....i can't see the hex section of the screw having any efect...
as the pellet is fired by a quick pressure increase rarther than air flow..
think of the pellet as a saftey plug.....
just make sure the port is bore straight as some are drilled on a angle...


Pete

[shadow]

Been there and done that on a B3. A few of us B owner's messed around with different port sizes a few years back and only gained a slight increase. We found a fine line of a little gain in FPS but after that the FPS dropped like a rock. We figured in the end that the slight gain wasn't worth the mod time on them, one of my B's still has a brass sleeved port in it. Ed

[rr_shooter]

Ed -
Can you elaborate on the B3 with the brass liner? I.D., O.D., length, how installed, etc...

Thanks!

[mjb108]

I like RedFeather's idea of getting rid of the hex wrench socket in favor of a spanner drive.  Drilling and tapping the B3 should be straightforward as the receiver is most likely mild steel.  

Real set screws or socket-head screws are hardened ~35 Rockwell C and will be slightly challenging to drill but not impossible.   The cheap screws of this variety sold by Harbor Freight in their "Storehouse" variety packs are not hardened in my experience - and that's OK for this application and will make drilling easier.

Good luck!

Mike

[shadow]

Honestly I could not remember so I went back through the China Gate since we all were posting the spec's on it but the China Gate only takes me back so far.:( Basically I took the ID dimensions from the port hit the hardware store  and found some brass tubing with with the next size up on the ID. I drilled out the port, cut the brass tubing to length and pressed it in. That port mod is the one that is still in one of my B's, had several other port mod's made and tried them but the FPS started to drop so I stuck with the first mod. Ed