Remington 700 trigger

 

That probably has a lot to do with the intended application of the rifle and the philosophy of your former Marine smith.  A typical 3 lever trigger like the Jewell, being more mechanically complex, is less tolerant of grit and residue.  It is a very precisely fitted mechanism, and if dirt, grease, or gelled oil residue gets inside the trigger housing, it can gum it up and make it not work.  This is much more likely to happen on a hunting rifle than a target or "fair weather" varmint rifle.  I'm referring to a M700 style drop-in trigger, not a Jewell AR trigger.  I've even seen this happen with a stock Remington 700 trigger, in fact.  In the instructions provided with their triggers, Jewell advises against using any oil whatsoever in their trigger and recommends that it be flushed out periodically with lighter fluid.  The main virtue of the old style Winchester M70 trigger for hunting use is the fact it was incredibly simple and wasn't enclosed in a housing, so it was totally reliable and virtually immune to getting gummed up.  I would imagine a former Marine would likely place more value on ultimate foolproof reliability than the best possible trigger pull.  It's a tradeoff -- simpler triggers with fewer moving parts are less affected by dirt and residue, but cannot provide as good a trigger pull as more complex designs with compound leverage and a separate actuator lever.