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01 August, 2010

Spring may be the nicest season, but springs in adjustable triggers aren't so nice.

By Steve_in_NC

Adjustable triggers need adjustment screws, and trigger adjustment screws (especially when used in springers) need some means of locking in adjustments. When I originally designed the GTX adjustable replacement trigger in 2004, the best means I knew of for adjustment screw thread locking was a compression spring. 

Thread locking springs work - but they're less than ideal for a number of reasons... 

1. Newly made adjustments tend to drift for several shots as the spring "settles in" to a new position, sometimes requiring frustrating repeated adjustments. 

2. Space must be provided to house the spring. In the GTX this required a bulky "spring chamber" that proved problematic in manufacture. 

3. Spring-locked adjustment screws need a head for the spring to rest on. 

All these issues can be annoying, but the worst turns out to be #3. Screws with heads are invariably designed as simple fasteners, rather than as precision setpoint adjusting screws. Consequently, the manufacturing process leaves their tips rough, unfinished and uneven.

The rough tips have an unfinished non-circular edge which... 

1. makes adjustment a hit-or-miss process, 
2. generates excess friction that creates a draggy, creepy pull, and 
3. changes trigger-pull geometry in unpredictable ways as they skid, tilt, and roll on the contact surface. 

Fortunately in the intervening years, I've had the good luck to hang around with knowledgeable people, one of whom is "Big Ed" Stack, and learned some useful things. One of these (thanks Ed!) is the availability of reusable (aerobic) polymer thread lockers (eg, ND Industries' "Vibratite") that make adjustment locking springs completely unnecessary.

The new (Generation II) GTX's trigger adjustments are designed around this technology, making possible the use of precision finished bearing-tip setscrews for adjustment, which dramatically improve the adjustability and feel of the new trigger.

One glace at these (unretouched) side-by-side photos (old GTX and screws on the left, new GTX and screws on the right) should provide all the explanation needed for why the new GTX is better than the old, not to mention better than any unauthorized knockoff.


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This blog shares information, ideas and knowledge about air rifles. It compliments the information Stephen publishes on the Archer Airguns website, on YouTube and the Chinese Airgun Forum.

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