Mentioned this in another thread but since it seems to be a reSOUNDing success, I figure it merits a thread, with the hope that others can follow on with a more professional approach and parts.
Background: The GK1 is a fabulous device as many of you know but it does make quite a bark. Oddly, Huben chose not to give it an active shroud and initially, not even a moderator option, which makes it PB pistol loud. I have found that Impulse Air mods work very well, first using IA1200 and then IA1350. Still, it’s substantially louder than my K1 rifles which benefit from full shroud, built in baffles and 2-section Huma Mod30s. The stock shroud on the GK1 is open at the base where it meets the air tube and the adapters that fix the shroud to the barrel do not have any capability to strip air back into the shroud. So, the full force of air from the shot is projected forward, into the moderator (or not). In the spirit of experimentation, I decided to “fix it” and make the shroud functional in terms of providing a reservoir to reduce pressure of the exiting air.
Procedure: This is relatively simple and not by any means conducted in a professional manner. It’s an experimental hack. The first step was to mod the NEAG moderator collar that I have as a spare after buying the nicer adapter from Zach at Ares. A basic stripping function was provided by drilling four holes (eventually 9/64in each) at an angle into the adapter so that they are exposed in front of the barrel to allow air to pass into channels indented in the exterior of the adapter. Basically a bunch of careful drilling and dremeling. I then cut 5 pieces of CF from a template and sanded them to press fit into the five (let’s call them apertures) in the base of the shroud. This took a couple hours of careful crafting. Thankfully, all 5 apertures are the same size but this step could be made much easier by having 3D printed plugs/inserts made that could be fitted from the inside. Anyway, I press fitted my pieces and then glassed them in from the inside. I then drilled 2 holes in the rear most sections at 7/64 to provide venting. I really should have taken more pics but I tend to get on a tear with these activities. Here is a pic of the shroud and adapter collar showing the mods:
With the interior glassing, the shroud was deemed to be air tight and very solid so then it was just a matter of putting things back together. While the mod adapter collar is irreversibly modified, the shroud could be reverted by knocking out the pieces from the outside. The only other addition was a piece/plug of magic eraser foam (about 1 in long) fitted inside the shroud and around the barrel at the magazine end to disrupt a pressure wave.
Testing: Initial test involved dry firing with a sound meter 3ft away and at 45deg forward of the muzzle with no moderator. Having the unmodified Ares adapter, I could perform a comparison because the Ares adapter has no way to pass air into the shroud. An average of 10 shots with each adapter provided a difference of 4.7dB in favor of the active shroud. To put it into context, if you own a GK1, you’ll know that it is louder dry firing than it is with a projectile. I would say that the difference made by having the shroud active is about the same as dry vs. live firing.
This AM, I had a chance to do some real testing and configured the GK1 with my widescreen (grotesquely large) Holosun dot and IA1350. Shooting GTOs at 905fps/21fpe. Note that the GTOs (for reasons I don’t understand) are louder than lead pellets even at a lower power output. Anyway, here’s the rig and the “control”, Ares adapter:
The same testing approach was used with the active mod collar (leveraging the shroud) and the control Ares collar. 10 shots with each taken from the same starting pressure (290bar) gave a 3.7dB average difference, again favoring the shroud. With the shroud in play, to the ear, there is a notable difference and I can say that the GK1 is now midway between its unshrouded state and my K1 rifle in terms of noise. There is no resonance from the shroud and the glassed CF inserts show no signs of movement or other deterioration.
Of course, another key test is to determine that the pistol still shoots accurately. For this I shot the GK1 with functional shroud into a duct seal target from supporting bags at 35y. I know from past experience that it makes <1/2in groups in this manner with GTOs. To be thorough, I wanted to make sure that it was accurate at both the top and bottom end pressures of my typical shot string, which has an ES<10. Therefore, I made 5 shots from 290bar to 270, then shot off target at a spinner then returned to the same testing target putting in another 5 shots from ~230bar down to 210. As usual, the accuracy was top notch and I can confidently state that the shroud has no negative effect:
3/4 inch sticker on the duct seal, previously damaged by a couple sighter shots on left that were removed (I’m a terrible cheapskate with stickers)
Moving the sticker, you can see more clearly and yes, this is actually 10 pellets, mangled together!
Background: The GK1 is a fabulous device as many of you know but it does make quite a bark. Oddly, Huben chose not to give it an active shroud and initially, not even a moderator option, which makes it PB pistol loud. I have found that Impulse Air mods work very well, first using IA1200 and then IA1350. Still, it’s substantially louder than my K1 rifles which benefit from full shroud, built in baffles and 2-section Huma Mod30s. The stock shroud on the GK1 is open at the base where it meets the air tube and the adapters that fix the shroud to the barrel do not have any capability to strip air back into the shroud. So, the full force of air from the shot is projected forward, into the moderator (or not). In the spirit of experimentation, I decided to “fix it” and make the shroud functional in terms of providing a reservoir to reduce pressure of the exiting air.
Procedure: This is relatively simple and not by any means conducted in a professional manner. It’s an experimental hack. The first step was to mod the NEAG moderator collar that I have as a spare after buying the nicer adapter from Zach at Ares. A basic stripping function was provided by drilling four holes (eventually 9/64in each) at an angle into the adapter so that they are exposed in front of the barrel to allow air to pass into channels indented in the exterior of the adapter. Basically a bunch of careful drilling and dremeling. I then cut 5 pieces of CF from a template and sanded them to press fit into the five (let’s call them apertures) in the base of the shroud. This took a couple hours of careful crafting. Thankfully, all 5 apertures are the same size but this step could be made much easier by having 3D printed plugs/inserts made that could be fitted from the inside. Anyway, I press fitted my pieces and then glassed them in from the inside. I then drilled 2 holes in the rear most sections at 7/64 to provide venting. I really should have taken more pics but I tend to get on a tear with these activities. Here is a pic of the shroud and adapter collar showing the mods:
With the interior glassing, the shroud was deemed to be air tight and very solid so then it was just a matter of putting things back together. While the mod adapter collar is irreversibly modified, the shroud could be reverted by knocking out the pieces from the outside. The only other addition was a piece/plug of magic eraser foam (about 1 in long) fitted inside the shroud and around the barrel at the magazine end to disrupt a pressure wave.
Testing: Initial test involved dry firing with a sound meter 3ft away and at 45deg forward of the muzzle with no moderator. Having the unmodified Ares adapter, I could perform a comparison because the Ares adapter has no way to pass air into the shroud. An average of 10 shots with each adapter provided a difference of 4.7dB in favor of the active shroud. To put it into context, if you own a GK1, you’ll know that it is louder dry firing than it is with a projectile. I would say that the difference made by having the shroud active is about the same as dry vs. live firing.
This AM, I had a chance to do some real testing and configured the GK1 with my widescreen (grotesquely large) Holosun dot and IA1350. Shooting GTOs at 905fps/21fpe. Note that the GTOs (for reasons I don’t understand) are louder than lead pellets even at a lower power output. Anyway, here’s the rig and the “control”, Ares adapter:
The same testing approach was used with the active mod collar (leveraging the shroud) and the control Ares collar. 10 shots with each taken from the same starting pressure (290bar) gave a 3.7dB average difference, again favoring the shroud. With the shroud in play, to the ear, there is a notable difference and I can say that the GK1 is now midway between its unshrouded state and my K1 rifle in terms of noise. There is no resonance from the shroud and the glassed CF inserts show no signs of movement or other deterioration.
Of course, another key test is to determine that the pistol still shoots accurately. For this I shot the GK1 with functional shroud into a duct seal target from supporting bags at 35y. I know from past experience that it makes <1/2in groups in this manner with GTOs. To be thorough, I wanted to make sure that it was accurate at both the top and bottom end pressures of my typical shot string, which has an ES<10. Therefore, I made 5 shots from 290bar to 270, then shot off target at a spinner then returned to the same testing target putting in another 5 shots from ~230bar down to 210. As usual, the accuracy was top notch and I can confidently state that the shroud has no negative effect:
3/4 inch sticker on the duct seal, previously damaged by a couple sighter shots on left that were removed (I’m a terrible cheapskate with stickers)
Moving the sticker, you can see more clearly and yes, this is actually 10 pellets, mangled together!
