Shoot On Purpose®


*** TSM4 Vs. TSM4C Most AR-15/M-4 model rifles use the “STANDARD” (.154) hammer and trigger pins which are included with the RTS TriggerShield TSM4. However, Semi-Automatic Colt AR-15/M-4 Lower Receivers manufactured between 1991-2009 may use the “LARGE” (.170) hammer and trigger pins. These Colt AR-15/M-4 Lowers will not function properly with “STANDARD” (.154) hammer and trigger pins. Potential malfunctions may include, but are not limited to; looseness of the internal trigger control group, multiple rounds fired on single trigger press, complete inoperability, etc. To determine whether your Colt Lower uses “Standard” (.154) or “Large” (.170) Hammer and Trigger Pins, either measure your pins with a caliper or call Colt directly at 800.962.2658 to confirm for the date of manufacture and exact Hammer and Trigger Pin size. If you determine that you have a “Large” Pin Lower Receiver, please order the RTS TriggerShield TSM4C. If you have any questions, please contact us at