Poly tube mod attempt

[akula8608]

Hi Fellas, over the weekend I tried out the poly mod on a spare .22 barrel (18") I had. I ported valve and barrel port to 11/64 (.171). I used a piece of poly tubing that was pretty much the same ID. During assembly all went well and I really expected to see some positive results. I am using an 1100psi regulated source. I went to run it over the chrony and the best I got was 670fps. I took it apart, checked my work, poly tube was in good shape, performed tissue test. 670fps was as good as it got.
  Then I re-assembled with an unmodified barrel and TP, still using the bulk valve that I ported to 11/64. went to run it over the chrony and I was getting 930-935 fps (27.5 fpe)consistently (CPHP). I've never achieved this with an 1100 psi source. The only thing I can attribute this to is venturi effect. Has anyone else seen this?

[targettgii]

Dang that is a high fpe what is the base gun of the build.

[akula8608]

The base gun is a 2260. I'm @ work right now but I'll try to get a pic up.

[mr007s]

Are both barrels 18"?

[targettgii]

Nice I have a 2260 project in the works with a Bna boss valve and cothran pcp tube hope I can get power like that from mine.

[akula8608]

The new barrel is a 24"