Vent holes in AirMax shroud...things to consider

May 19 2017 at 1:30 PM
H.E. Potter  (Login Hepotter)

Response to What about drilling new holes forward do you think that would work?

First...I considered drilling more holes above the barrel threads, but I lack the drill press equipment to firmly secure the font bushing in order to drill it, so I decided reducing the thread length on the barrel might be the better method. The first thing I would do is find a nut that fits those threads and put it on the barrel threads BEFORE I cut off the excess. That way I can unscrew that nut and force any disturbed threads back into proper alignment after the cut.

There was evidence of loc-tite on my front bushing. I used two small stiff nails, placed them into opposing holes, held them in place with my fingers, then put a screwdriver between them and turned slowly. That additional leverage broke the loc-tite loose and off it came.

Once those bushing holes are opened, one way or another, I do believe that adding a few small vent holes in the back of the top rail/shroud will help reduce air pressure on the LDC/SRS system. It might change the "tone" of the muzzle exhaust, or simply reduce the air pressure coming out of the muzzle, perhaps making it a bit quieter. Maximizing the efficiency of the LDC is done by permitting air expansion in the shroud, and lightly venting some of the pressure out before it gets to the LDC baffles.

My experience with venting shrouds goes back several years. One thing I learned is a few small vent holes work better than numerous or big vent holes. I suggest 1.0mm to 3.0mm size, buy a new drill bit to do the job cleanly, and after examining the AirMax shroud, I'd go about an inch forward of the breech block to avoid that small nylon sleeve on the back end of the barrel, and this would still permit the high pressure air to use the full length volume of the shroud to expand before it vents out.

Starting with two 1.5mm holes on each side of the shroud is what I'm considering. Keeping these holes small keeps their exhaust noise very quiet.

Another forum member is considering placing his vent holes in the SRS tube. If you decide to try this...keep these holes especially small and few! Too big/too many and they will produce their own noise, or adversely affect the SRS system function.

I can't over emphasize that venting is not a total's just one efficiency aid for the LDC, and it's very very tempting to over-do it. Be satisfied with the results from a few small vents strategically placed!.

(Afterthought: If you over-vent, and get excessive exhaust noise, you can always plug excess holes with JB Weld epoxy putty. It fills holes nicely, can be sanded smooth, then touched up with a black permanent marker to make it disappear.)

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