GTA
General Discussion To Gateway To Airguns => Gamo Gate => : Splash January 25, 2007, 06:46:33 AM
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enlarged the transfer port hole on a breakbarrel. I noticed on my S1K that the transfer port hole is about 1/2 the size of the barrel. I am fixing to take it apart to lube tune it and thought about opening up the hole to about 3/4 size of the barrel. Should I do this or leave well enough alone. Seems that if it were larger it would put alot more air behind the pellet while it was still at the breech end of the barrel. First 1/2 to get up to speed 2nd 1/2 to stablize it for accuracy. What do you think or am I totally lost. TIA
Mike
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Someone did something similar on the YF with a CFX breech block, and different sized ports. As I recall, it made virtually no difference. I fuess the small volume of air produced by a springer just doesn't need that much room :-). However, if you were going to do some serious testing, drill out the port, then tap for various sized inserts. Of course, you'd have to make inserts too. I think something similar is done for power tuning on some of the PCP guns. If you do just decide to drill her out, keep us posted on the results. Just remember, it might be kind of hard to un-drill it if it doesn't work as planned. Good Luck!
Dave
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In my experience (with a Shadow and the very similar B19 and Quest) is that there is something to be gained - but only in .22 cal. The original hole, BTW, is just about 1/8"
My B19 was shooting a smidgen under 700 with CPHP's. I yanked the barrel off and spring out, pulled the piston back a bit, and brought the hole out to 5/32" (which translates into a 56% increase in cross-section). I didn't even take the gun apart to clean it out - didn't wanna screw up the test by changing more than one thing at a time. After reassembly, the gun was shooting in the low 720's.
I did the same thing again, this time bringing the hole to 3/16. Essentially no change, so I did not take it out any further.
Doing something similar to my .177 Quest and Shadow yielded no change at all.
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just make sure you don't drill it so big that there is ANY chance of a pellet or pinched pellet piece dropping into the compression chamber.....THAT would be bad!
Dan