98 vs 98C vs 98C Pro?

"Tippmann recently introduced a feature known as A. C.T. (Anti-Chop Technology), which is a mechanical system integrated into the bolt system to reduce the chance of jams due to misfed paintballs. In the 98 Custom and Custom Pro markers, the hammer has a deep groove that the linkage arm sits in, along with the ACT spring to keep it in position (there is also a small hole to insert the linkage arm into if the user chooses not to use the ACT function). If a paintball is incorrectly fed into the breech when the bolt is closing, the bolt stops on the paintball with little pressure from the ACT spring, while the hammer continues on its stroke unlinked to the bolt. It hits the valve and is blown back open, where it re-engages the linkage arm and retracts the bolt, letting the paintball fall into the breech correctly. The marker is now ready to fire again.

An alternative to purchasing the Tippmann A.C.T. can be found here. This is a home modification requiring only the purchase of an inexpensive (approximately $5) spring. This mod has been tested many times, yielding good results 90% of the time. This modification, however, will not work with markers with Low Pressure Kits, or E-bolts (older style 98 customs are compatible with the discontinued E-bolt).

The Tippmann A.C.T feature is very similar to Spyder's ACS bolt."