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PRESENTING THE GRT-4G TRIGGER FOR THE GAMO LATE MODEL WITH PLASTIC TRIGGERS

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notsure:
Recently installed the GRT4G trigger in a Gamo Swarm Whisper .22 with production date 11/27/2019, and the factory trigger on mine was also of the updated design with the integral pivot pin. Based on the number and timing of posts I've seen mentioning the need for a replacement pivot pin, I suspect these were phased into production at some point in recent years, and any new Gamo will likely require a pin.

I purchased a 50-pack of 4x12mm hardened steel dowel pins from McMaster for $10, based on the dimensions others have posted of the factory pin, but the molded-in pin on mine turned out to be a bit smaller in diameter than the 4mm that seems to be the consensus - it measured 3.84mm. This isn't much of a difference, but the ones I got from McMaster were 4.01mm diameter, and as a result, they are a very tight fit into the metal side of the trigger housing. The GRT4G trigger itself fits perfectly on these 4mm pins, as does the plastic trigger cover, but I needed to use a hammer (carefully!) to drive the pin into the corresponding hole on the metal backing plate. It will fit but you'll have to hit with some force - just make sure the metal housing is supported directly underneath the pin or you could easily bend the entire thing. A good gunsmith's hammer and nylon block are great for this purpose. The hole has a "stop" at the back to locate the pin correctly along its axis; you can look through the narrower opening on the back side of the plate to see when it's fully seated. You'll see what I mean when you get the trigger apart. Sorry, I don't think I can post pictures yet.

I sent the leftover 49 pins to Cathy so hopefully she can include them with orders going forward.

I ended up setting mine up in the single-stage configuration, where the first stage screw releases the sear before the second stage surface even touches the intermediate link. It is much lighter than stock now, and I do miss the two-stage feel, but the pull is just too heavy on the second stage due to the geometry of the Gamo trigger.

notsure:
Oh and one more thing, I found it much easier to compress the gas piston by removing the barrel, which simply involves removing the T25 screw that serves as the barrel pivot, and also removing the linkage from the receiver tube. You'll see that in the slot at the bottom of the receiver tube that the linkage travels along, there is a round opening - if you pull the linkage away from the receiver tube, the "foot" of the linkage that contacts the piston inside the tube can be moved to this opening, and you can then pull it through to remove the linkage from the receiver. Then the barrel comes off, leaving just the receiver tube with trigger assembly. Again, pictures would help but I can't post them yet.

After removing the barrel, a 24" bar clamp can be used with a 5/8" socket against the back of the trigger assembly to compress the piston (go to Lowe's website and search for "jorgensen 24 3700" and you'll find what I used for $18). No need to build a contraption to serve as a one-time-use spring compressor, although I admire the ingenuity some have shown here; personally, I do not feel comfortable putting much force on the plastic muzzle device of these Gamo barrels. After removing the cross pin, the gas piston does not travel as far out as a spring does, only a fraction of an inch, so you don't need a fixture with 2-3" of travel.

Booder98:
I just installed the GRT-4G on my Swarm Maxxim .177.  The old trigger did have the built-in pivot pin, but a replacement pin was provided, so that wasn't a problem.

I didn't remove the barrel, just used a trigger clamp pushing at a not-quite 90-degree angle.  That Maxxim had the gas piston as well, so as mentioned above you don't need a lot of travel.

It felt a lot smoother than the old trigger, even with the 10mm screw replacement.

juke:
Just replaced the trigger of Gamo Replay/Swarm 10 Magnum IGT GEN2 .22 with GRT-4G and the difference is noticeable.
Thanks to my compatrtiot Hank for his excellent pictures in this thread whitch were invaluable help during modification.
Regards,
Juke

GlennS1956:
Got my GRT-4G trigger yesterday (thanks Cathy) and just installed it in my Gamo Silent Cat. Old Bessey (36" sliding clamp) compressed the spring easily. I put the muzzle on the stationary end, and the screw part matched up to the spring perfectly. Didn't even need a 5/8 inch socket.

It was as easy as everyone says it is. I used the two easy to find installation videos on YouTube, which helped greatly. I shot one pellet afterwards to make sure everything works. I haven't had time to play with it yet. So far I am a happy boy!

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