Easy Peasy transfer port reductionJanuary 25 2014 at 2:35 PM L D (Login lhd)
I've often needed to reduce the power of a precharged gun, yet found over and over that simply lightening the striker spring generally also reduces the shot count and requires a lot of work to discover the new ideal charge pressure. I also sometimes find that reduced pressure spoils accuracy.
Anyhow ... here's how I reduce a transfer port in a barrel with sufficient wall thickness, such as 16mm or 15mm diameter with .22 or less cal.
1. Clean the breach and transfer port area thoroughly with solvent and blow dry.
2. Find a fine thread tap just the size to start into the existing port.
3. Form some threads into the port, halfway is fine ... don't go all the way into the bore.
4. Clean again with solvent.
5. Mix up a small amount of "JB Quick" or similar metal filled epoxy.
6. Stuff a felt pellet cleaning slug, or some packed cotton into the breech leade until you see it plugging the bore under the transfer port.
7. Dap the JB-Quick mix into the port until its filled to the brim and let it set up for a few hours at least in a warm area.
8. Re-drill the port in the center of the epoxy mix, starting with a very small drill, say around 1/16". Push the felt or cotton plug out.
9. Ream the hole larger as required, slowly working up to the size you need (yes, you need to testfire over the chrono to verify).
The epoxy stays put because its hard enough, and the partial threads hold it from coming loose. It need be, it cna be removed back to original dia.
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