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Posted: 8/9/2024 1:10:31 AM EDT
| I was playing around with my xm1773 and its a major pain in the ass taking off the handguard to change the battery. I put in a new barrel, bucking and nub had to use the stock hop up unit though (no biggie). So I was thinking F this pain in the arse hand guard to put the battery in. I even used a real steel hand guard tool and it still sucks! So has anyone put a polarstar Kythera in a ver2 gearbox? Looks fairly easy just curious. I already have a regulator (redline), hose and several ninja tanks. |
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Originally Posted By WTFShane: It'll still need a battery to operate, which will probably end up getting routed to the rear and into the receiver extension. Most of Polarstar's stuff is electropneumatic, but the Kythera is purely mechanical in function. No batteries, but still tethered to an air line. Looks like it's semi-automatic only, if that's a concern to OP. |
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What brand is the gun? I know a little bit about this. Attached File |
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Originally Posted By bnoji: What brand is the gun? I know a little bit about this. https://www.ar15.com/media/mediaFiles/95899/20200602_044302_jpg-3294437.JPG Well I guess you definitely know a thing or two in regards to the Kythera! It would be going into a E&C XM177 Xm177 |
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Originally Posted By firemed13: Well I guess you definitely know a thing or two in regards to the Kythera! It would be going into a E&C XM177 Xm177 That should be a standard V2 style gearbox so there's usually no modification needed unless there's some heavy reinforcement inside the gearbox shell. This can get in the way of the air line bending down towards the grip. Kythera has some "mass" moving around because of the necessary weight of the nozzle and momentum needed to cycle. If the cylinder head pins are on the small side this can lead to sliding back and forth in the shell even if it seems like it's pretty solid. This will lead to inconsistent chambering depths (sort of like headspace changing on the fly) which will usually lead to varying amounts of hopup. You can check this by either measuring the diameter of the pins (the mating groove on the Kythera cylinder is 0.182" wide) or installing it and loosely installing the gearbox screws then try to slide it back and forth in the cylinder window. We have some shims that basically sleeve the cylinder head pins to fit tighter in the cylinder groove or you can use aluminum tape. I don't normally recommend shimming forward or back since the "ideal" nozzle length was calculated based on the center of the groove and you might run into air seal or feeding issues if it's shimmed too far back or forward. Since we don't have the benefit of electronic timing the return speed of the nozzle is controlled by the fill rate of the dump chamber which is controlled by an orifice screw. The default size is 0.024" diameter. If you're using heavy BBs or your mag springs are weak the nozzle might come back into battery before the round is fed and you'll dry fire. In this case you might need to swap it for the 0.019" orifice to slow the fill rate which slows the nozzle. There's a trade off here though. Since the fill rate is slower you may out run it if you're pulling the trigger really fast. If I do make a change to the design it would be to increase the rearward travel distance so there's more time on the retract and we can afford to have less time on the return. Some people like to mess with the trigger/disconnector tuning to adjust the creep and overtravel. This also tends to be where the most mistakes are made. It's essentially an AR trigger system with a set screw to adjust the pre-pull of the trigger. Since you're also shifting the disconnector with it there's a second screw to adjust the overlap point. These have to be adjusted to match each other and it's easy to mess up. ETA: It's a fixed volume system so there may be more air in the dump chamber than what is actually needed for a shorter 12.5" barrel. We make some reducers that go inside and take up some space to lower the internal volume in 12.5% increments. You can 3D print these yourself too. Attached File If you decide to go this route let me know first. |
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Originally Posted By bnoji: That should be a standard V2 style gearbox so there's usually no modification needed unless there's some heavy reinforcement inside the gearbox shell. This can get in the way of the air line bending down towards the grip. Kythera has some "mass" moving around because of the necessary weight of the nozzle and momentum needed to cycle. If the cylinder head pins are on the small side this can lead to sliding back and forth in the shell even if it seems like it's pretty solid. This will lead to inconsistent chambering depths (sort of like headspace changing on the fly) which will usually lead to varying amounts of hopup. You can check this by either measuring the diameter of the pins (the mating groove on the Kythera cylinder is 0.182" wide) or installing it and loosely installing the gearbox screws then try to slide it back and forth in the cylinder window. We have some shims that basically sleeve the cylinder head pins to fit tighter in the cylinder groove or you can use aluminum tape. I don't normally recommend shimming forward or back since the "ideal" nozzle length was calculated based on the center of the groove and you might run into air seal or feeding issues if it's shimmed too far back or forward. Since we don't have the benefit of electronic timing the return speed of the nozzle is controlled by the fill rate of the dump chamber which is controlled by an orifice screw. The default size is 0.024" diameter. If you're using heavy BBs or your mag springs are weak the nozzle might come back into battery before the round is fed and you'll dry fire. In this case you might need to swap it for the 0.019" orifice to slow the fill rate which slows the nozzle. There's a trade off here though. Since the fill rate is slower you may out run it if you're pulling the trigger really fast. If I do make a change to the design it would be to increase the rearward travel distance so there's more time on the retract and we can afford to have less time on the return. Some people like to mess with the trigger/disconnector tuning to adjust the creep and overtravel. This also tends to be where the most mistakes are made. It's essentially an AR trigger system with a set screw to adjust the pre-pull of the trigger. Since you're also shifting the disconnector with it there's a second screw to adjust the overlap point. These have to be adjusted to match each other and it's easy to mess up. ETA: It's a fixed volume system so there may be more air in the dump chamber than what is actually needed for a shorter 12.5" barrel. We make some reducers that go inside and take up some space to lower the internal volume in 12.5% increments. You can 3D print these yourself too. https://www.ar15.com/media/mediaFiles/95899/KytheraVolReducer_JPG-3295016.JPG If you decide to go this route let me know first. Wow thanks so much for the heads up and recommendations. By chance do you work for a certain retailer who is located in Pittsburgh? |
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