Speed Airsoft have released a turnable trigger for the M4/M16 AEG:
One of the most important areas of your airsoft gun is how the trigger feels each time you pull it. The more precise and easier the pull, the more confidence you have with each follow up shot. With more and more players upgrading to MOSFET systems for their AEG, the ability to shoot faster is limited by how fast you can actuate the trigger switch, which usually is limited by the trigger.
The SPEED Tunable Trigger is precision machined from billet aluminum, using hardened roller pin for a slop-free pull. Since each AEG has variations, the SPEED Tunable Trigger incorporates a setscrew for easy alignment to the trigger switch assembly unit. The spring guide also has a larger diameter for preventing the trigger return spring from moving around. The SPEED trigger have the same trigger geometry as the stock M4 so you will have the same feel but with more precision.
The SPEED Tunable Trigger will improve performance on a stock AEG switch unit, and will really excel with a MOSFET unit that uses a micro-switch. The SPEED Tunable Trigger can be adjusted for a shorter pull with a micro-switch.
The SPEED Tunable Trigger includes complete installation instructions along with tuning tips to make the most of each switch system. The SPEED Tunable Trigger is available in silver (SA3032) and black (SA3033).
For more info, visit SPEED Airsoft at www.SpeedAirsoft.com
