Transfer Port ID Question

Eaglehorn · Jun 29, 2017

What would be the maximum effective ID for a transfer port if you were using a .25 1/2" OD barrel? I'm trying to find out how big a hole I'll need to make for a high-power build. I've read that .25" is ideal, but wouldn't this cause the pellet to fall through the bottom of the barrel? Should I be thinking ovals? What should I say to my local machine shop?

Alan · Jun 29, 2017

There is a limit, but there is a whole lot more to it than just the transfer port size. What is the rest of the gun like, and start with the valve and pressure.

ackuric · Jun 29, 2017

.25 cal can handle UP to 5.4-5.6 mm / .212"-.22" WIDTH provided the bolt probe is designed to aid in loading the pellet into the chamber.

Most people feel the SAFE max on porting WIDTH wise on a .25 cal is around .1875" and then they oval the rest of the porting to obtain bigger ports.

My barrel port is currently .21" (width) x .23 (length) which makes for a .22 port on the barrel...the .23" was a stretch as I started getting into the rifle chamber by a .01" or .02" but I didn't obtain any ill effects, but this is just what was necessary on my rifle due to design...(.25 marauder)

I have no pellet loading issues but I had to deburr the port very well and smoothly

Eaglehorn · Jun 29, 2017

"Alan"There is a limit, but there is a whole lot more to it than just the transfer port size. What is the rest of the gun like, and start with the valve and pressure.

Gun I'm working on is a Marauder with a Cothran valve. He suggests (and the gun is rated for) 3000psi so I'm not going higher than that. Yes, I will be using heavy pellets, but still sticking with diablos. End goal is to have efficient, consistent air flow and regulate after initial tuning.

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Transfer Port ID Question

Eaglehorn

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Alan

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ackuric

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Eaglehorn

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