I just bought a Tristar Viper G2 Turkey in 20 gauge and wanted to improve the trigger. I did some research and found out the trigger return spring that M*Carbo sells for the Mossberg SA-20/SA-28 will also work in the Tristar G2 models in 20 and 28 gauge. I ordered one along with the silicone grease they sell and just installed it. The whole process took me maybe 15 minutes and that included a good cleaning inside the action since the gun was new. The spring definitely helped and reduced the trigger pull from 6lbs 3oz down to 4lbs 3.7oz. It still has some creep in the trigger but it's definitely lighter and breaks smoother as well. I thought others that owned the Tristar Viper shotguns might find this information helpful, M*Carbo doesn't list the Tristar brand on their fitment guide so you wouldn't know this worked unless you contacted them to ask.
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Awesome! What is the LOP on that gun?
Did same with mine...Remarkable difference!