Yesterday, a fellow who frequents AGN contacted me via GTA PM, asking if I could design a muffler for his .25 Huben pistol. Specifically, 1.5" OD x 5" long. It needed to have an offset bore, so the stock sights would not be obscured.
I whipped up the design below in about 8 hours; then made some improvements to include a printed 1/2-20 thread version, and a version that would accept a 5/8" - 11 / 1/2 - 20 thread insert.
As I did this design for free I retain the right to share it as I see fit. Anyway, I notice you guys asking about offset moderators for the Huben pistol. So here is a potential candidate that you can 3D print for yourself.
No one has printed this design yet; let alone tested it. I have no control over your material choice or print quality. So, should you print one for your own use, you assume responsibility for your own safety. If I was selling the design or parts, I would have test results indicating acceptable performance, strength, durability and grouping ability.
The design uses a "can in a can" approach to have a longer path that "looks conventional" to the projectile. This is to reduce the time the projectile spends travelling through asymmetrical turbulence.
The design has 4 mm thick walls around the primary blast chamber. That chamber communicates with a forward offset expansion space via 16 x 2 mm diameter vent holes. The rear of the primary blast chamber is cored out with slots around the barrel stud thread, These slots are to reduce pressure wave bounce in the primary blast chamber. Ahead of the primary blast chamber the wall thickness is thinned down considerably because the bulk pressure is lower there; and to keep the unit mass close to 100 grams.
The forward-most expansion chamber vents downward into its own offset space, via a single large triangular opening. The triangular shape is so that the unit can be FDM 3D printed, while standing on its front end; threaded end up. That is the only position in which this part can be FDM printed.
The two STL files are attached in a ZIP file.
You will need to use shims from 0.025" down in perhaps 0.005" steps to "clock" the offset OD out of the sight-line. The muffler version that takes a metal thread insert may be clocked by rotating the insert, or with a shim of the right thickness.
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