Anyway, let me start by saying that this is, in my own humble opinion, the COOLEST GUN EVER! The auto-rotation, the pump ON the barrel, the goofy color scheme, etc. Too bad that the Sm1k is very rare and fragile.
Edit: Pump only up to 3 times max!
Hotglue gun w/ sticks
Sch 40 PVC / Sch80 PVC depending on FBR fatness
O-ring from a 2k pump (or another with similar dimensions)
My Highly Informative Guide on the SM1k Internals
Ok, here is the completed gun, which is not that different looking from a stock one.
Start by gently prying off the orange rings on the pump and fake barrel. After that, open her up. Be careful when doing this, as springs inside are likely to pop out and get lost forever. Take your time and hold the blaster by the red tank part. This will take pressure off of the spring resting on top of the turret, which will fly out, unless you do this. For more info, look at the internals guide.
Here are the over all internals of the gun, when everything is assembled.
After opening it up, start by plugging the over-pressure release valve in the pump. Load up the center with hot glue. Let that dry, and lube up the plunger.
If you have a Dremel, you should cut the trigger spring down to about 1.5". It will make it much easier to reassemble and operate the gun. A good picture of the cut spring is in my internals guide.
Now, on to improving the seal. For some reason the white piece sitting on top of the airtank which is supposed to provide a seal, was completely blocking the air, making it come out of the sides. I ripped off that piece and glued on an O-ring from a broken At2k pump. Perfect fit!
To improve the barrel fit, but still allow a working turret,
From this point, the only thing left to do is rebarrel the turret. Now this part can be a little tricky. I used about 2" of Dremel'd CPVC in each barrel, and haven't looked back. The only problem is that the turret was too heavy for the auto-rotation mechs to continue working. After only a few trigger pulls, the end of the trigger snapped. I tried gluing it, re-melting it, and nothing held. The trigger was too hard to pull and was unreliable.
So if you are desperate to keep the auto-rotation, DO NOT USE CPVC or most likely, BRASS. You should use a lighter barrel material like PETG. Be warned that if you do use CPVC or brass, you will most likely end up needing to manually rotate the turret. This was fine for me, but I am just warning you.
If you happen to be using brass or PETG, you can skip the next few steps, but you will need to glue your barrels in.
Ok so, cut 6 lengths of CPVC to this height.
And Dremel out one end like so. Picture is blurry, but sand down until the walls are pretty thin.
Rinse and repeat 6 times until your turret is full. You don't need to hammer them in, just push firmly. No glue necessary, and you can take out the barrels in a moment's notice with needlenose pliers.
If you used CPVC, then take out the pieces that make it auto-rotate, and then follow my internals guide to put it back together.
I pump it mainly 3 times, 4 and the firing pin closes up again before all the air is out. Manually rotating the turret isn't too bad, I can squeeze off all 6 shots in under 20 seconds with 3 pumps. It also makes the gun more reliable. I can confidently say that I am getting ranges of 80' or more. Accuracy is dead on, mainly because of the excessively long barrel.
I measured in my street how long each graduated line on the rain gutter thingy next to the asphalt was. I used a yardstick and each was 20'. I am a short little asian kid, 5'5", and took 6 level (or as close as I could get) shots. Including dart skip, the ranges were between 100'-120' by counting how many lines it passed. I eyeballed where each hit the ground and the ranges were between 80'-90'. Before I replaced the Sch40 with Sch80, the ranges were probably around 70'-80'. If anyone disputes these ranges, I guess I could make a video, but it's not like I'm claiming consistent 100' shots.
My airtank busted from overpumping so I am no longer able to prove any claims. I would highly recommend pumping only up to 3 times, maybe even 2.5
As requested, here is a comparison of a 2k airtank and the sm1k one.
Here is a size comparison pic next to my 2nd favoritte gun of all time, my SM5k.