Sure the trigger isn't just out of adjustment? If it's set too light it could just be not engaging all the time. Has anybody fooled with it, trying to adjust it?
Installing a trigger is a little more then just a bolt in thing. Call Ahlman's in Morris Town Mn. They are very good..know their stuff.
http://www.ahlmans.com/
No I am not!!! Took it to a gunsmith and 2 days later he called and told me to send it to Weatherby!!!!! When it did catch you could hit the bolt with a rubber mallett and it would release!!!!!