I have one of the original Appleseed Tippmann rifles (elite version with aluminum handguard). Serial number starts with 003.
Out of the box, this is a very capable rifle. However, I've always been a little irritated by the way the buffer system sounds and feels. It is a proprietary captured system, like a JP silent spring. However, it feels like the buffer and the buffer stop are colliding too violently and causing unnecessary noise and vibration while the action is cycling.
I wanted to slow the cycle down. Rather than adding mass to the system, I decided to try to make the spring stronger. It is a proprietary spring, so replacing it would probably be tough. Instead, my son and I 3D printed a spacer made from TPU. This goes around the end of the buffer (near the head) and compresses the spring. After some preliminary testing, we found that 3/4" was too long and prevented the gun from cycling properly. 1/2" allowed a full cycle and the bolt reliably locks back on empty. We printed a 5/8" one, but it is kind of a pain to take the buffer system out so we did not test that one. 1/2" did seem to quiet things down, which was the goal. I plan to shoot the rifle a lot more to make sure everything runs and that I continue to notice a difference in the way the buffer system feels.
Note: removing and re-installing the buffer system is a pain. Especially if you don't remove the trigger and the bolt catch. I left those in and worked around them. In doing so, I found that using the spring like a screw and turning the whole assembly helped walk the buffer past the part of the bolt catch that gets in the way. You have to hold the hammer down while doing this, as it gets in the way as well.
Anyway, happy to share the specs with anyone who has access to a 3D printer. TPU is very tough stuff and has a bit of squish to it, so I'm confident that it will last a long time. I'd be especially interested in trying this out with a suppressor at some point.
I did somewhat the same thing, but after installing a rifle length buffer tube for a A2 stock. I made an aluminum spacer, then drilled and tapped a 5/8-11 hole through it and used an Allen bolt to adjust the final length of the spacer. It takes up the difference between rifle and carbine length tubes and allows for adjustment.