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Magwell · January 22nd, 2017, 00:38

Another gearbox post...

Over the summer I was at a couple games where the FPS would spike at the chrono, and in some cases nearly too high to be allowed to play. While my chrono was reading a field legal FPS, the field chronos would peg it right below the limit and then spike over occasionally. Turns out my chrono had been shot one too many times and bit the dust haha.

So with a brand new chrono in hand, the tests yielded 353-356 FPS with 0.28g bbs (418-422 FPS with 0.20g) With the field limit being 355FPS with 0.28g a change was needed.

The simplest solution... reduce the cylinder volume with a Sorbo Pad. Deciding this would be a good idea as well for my ICS M4's as well (which are prone to upper gearbox cracks on M120 springs once you put a few hundred thousand rounds through em), I grabbed a few from Airsoft Store Canada. I had also picked up a Madbull poly piston with treated steel rack to help reduce my RPS further, and installed this at the same time. One great advantage of the Sorbo Pads is the AOE correction. I'm a little ashamed to say this is my first time using one on an AEG I've owned, but this will now be something I'm doing to all my guns haha.

A few other gearbox items to note as well:

1. The slipping bushings I mentioned in post 14 seem to be permanently remedied now with the JB Weld. No more slipping or squealing.
2. My Anti-Reversal latch is not compatible with Siegetek gears mentioned in post 13. I'm not sure any AR latch is to be honest, not unless it's hardened steel or something. What ended up happening is because the bevel gear has the smaller gears teeth run all the way to the shaft, opposed to the gradient on a normal V2 bevel, the AR latch gets worn down extremely quickly. Once worn down, it will lock into place with the force of the spring jamming it into the bevel gear. The entire gearbox then locks up as the motor lacks the torque to free the AR latch from the bevel. It took a surprisingly large effort with a screwdriver to release it via the AR release opening in the side of the gearbox. As such, my 249 is now running with no AR latch, but should be fine with the AB mosfet in there.

So, now with it all back together I hooked up my box mag and started doing some tests.

FPS was better, with a 5 FPS drop using 0.28g bbs...

Test before beginning work: 0.28g - 349 FPS (413 FPS w/0.20) & 20.3 RPS
Test after completing work: 0.28g - 342-344 FPS (407 FPS w/0.20) & 19 RPS

Quite happy going into the 2017 season with a comfortable RPS and nice buffer in my FPS

Finally a couple notes on the weight of my MK46. Note that this was not done with a precise scale, but rather a typical household bathroom scale.

1. With the reduction in box mag size, dropping the upper rail, front sight, and clamp from the ready mag my LMG is at a nice, comfortable 15.9 LBS now. Much of this can be attributed to the smaller box mag. This is fully loaded with all accessories and dummy rounds.
2. The MK46 with box mag and dummy rounds removed comes in at 13.3 lbs.
3. The upper rail weighs in at about 0.5 lbs.

January 22nd, 2017, 00:38	#26
Magwell Trader rating Join Date: Sep 2012 Location: Edmonton, AB	Another gearbox post... Over the summer I was at a couple games where the FPS would spike at the chrono, and in some cases nearly too high to be allowed to play. While my chrono was reading a field legal FPS, the field chronos would peg it right below the limit and then spike over occasionally. Turns out my chrono had been shot one too many times and bit the dust haha. So with a brand new chrono in hand, the tests yielded 353-356 FPS with 0.28g bbs (418-422 FPS with 0.20g) With the field limit being 355FPS with 0.28g a change was needed. The simplest solution... reduce the cylinder volume with a Sorbo Pad. Deciding this would be a good idea as well for my ICS M4's as well (which are prone to upper gearbox cracks on M120 springs once you put a few hundred thousand rounds through em), I grabbed a few from Airsoft Store Canada. I had also picked up a Madbull poly piston with treated steel rack to help reduce my RPS further, and installed this at the same time. One great advantage of the Sorbo Pads is the AOE correction. I'm a little ashamed to say this is my first time using one on an AEG I've owned, but this will now be something I'm doing to all my guns haha. A few other gearbox items to note as well: 1. The slipping bushings I mentioned in post 14 seem to be permanently remedied now with the JB Weld. No more slipping or squealing. 2. My Anti-Reversal latch is not compatible with Siegetek gears mentioned in post 13. I'm not sure any AR latch is to be honest, not unless it's hardened steel or something. What ended up happening is because the bevel gear has the smaller gears teeth run all the way to the shaft, opposed to the gradient on a normal V2 bevel, the AR latch gets worn down extremely quickly. Once worn down, it will lock into place with the force of the spring jamming it into the bevel gear. The entire gearbox then locks up as the motor lacks the torque to free the AR latch from the bevel. It took a surprisingly large effort with a screwdriver to release it via the AR release opening in the side of the gearbox. As such, my 249 is now running with no AR latch, but should be fine with the AB mosfet in there. So, now with it all back together I hooked up my box mag and started doing some tests. FPS was better, with a 5 FPS drop using 0.28g bbs... Test before beginning work: 0.28g - 349 FPS (413 FPS w/0.20) & 20.3 RPS Test after completing work: 0.28g - 342-344 FPS (407 FPS w/0.20) & 19 RPS Quite happy going into the 2017 season with a comfortable RPS and nice buffer in my FPS Finally a couple notes on the weight of my MK46. Note that this was not done with a precise scale, but rather a typical household bathroom scale. 1. With the reduction in box mag size, dropping the upper rail, front sight, and clamp from the ready mag my LMG is at a nice, comfortable 15.9 LBS now. Much of this can be attributed to the smaller box mag. This is fully loaded with all accessories and dummy rounds. 2. The MK46 with box mag and dummy rounds removed comes in at 13.3 lbs. 3. The upper rail weighs in at about 0.5 lbs. __________________ Last edited by Magwell; April 22nd, 2018 at 15:45..