Whoever did the bad work on the 66 probably had reliability issues and got rid of it for that reason.
Let us hope that Bubba, the trigger job guy, did not damage the sear engagement in his zeal to do his kitchen table trigger job. If he did, you may end up with push off, in which case, let us also hope that Bubba, the trigger job guy, did not read on here about how you don't "need" the hammer block anyway, so you remove it to make the best trigger job.
If he did, let us hope when your revolver discharges when you do not expect it because a safety feature is removed that: (1) Bubba has plenty of liability insurance (not likely); and, (2) your muzzle is not pointed at anyone or anything you care about.
Pretty strong accusations without seeing the gun. As I noted earlier there are plenty of comp or race guns built and tuned for a specific load —a load to compete with. Another load with a magnum primer may not ignite but this has nothing to do with the competency of the gunsmith. Maybe the gun has been hacked but I would not suppose it base on what we have heard and certainly not seen so far.
I wonder if the OP would comment and tell us if this main spring resembles any of the three in this photo. The spring on the right is a factory K. The others have been reworked and tuned by a very highly respected Smith & Wesson gunsmith who may or may not have done them on the kitchen table.
http://smith-wessonforum.com/attachm...1&d=1364432705