Fastbolt:
Any ideas where a guy should start looking for clearance issues? It's hard to believe the little trigger bar is causing the problem, maybe it's slightly adding some parasitic drag, but is there a bigger area of drag I can look to minimize?
Is it possible the extractor / bolt face clearance is too tight? Where would I find a spec for these types of things?
The smaller you start making pistols, the more the shorter recoil springs and mechanical leverage conditions during "slow manually-induced cycling" can change. When it's done significantly more slowly than how the gun was intended to be cycled (for either normally loading the chamber or actual live-fire operation), it may manifest differently than in full-size pistols of similar design. Not something that's surprising.
I've seen a well-used, consistently reliably functioning little .380 pistol (2.75" barrel) repeatedly exhibit the slide & barrel being unable to return to battery just by spring tension when the slide & barrel have been manually retracted slightly out-of-battery.
On the other hand, sometimes the largest pistols may develop their own unexpected quirks when manual operation of the pistol occurs.
For example, a lot of folks are familiar with Glock's field-check of the recoil spring assembly strength. This bench/field check is fine for the 9/.40 & .357 Glock guns, but armorers have been told that it
isn't a reliable indicator of RSA (
Recoil
Spring
Assembly) strength for the .45/10 guns.
Why? Because the heavier slide mass of the .45/10's, relative to their proper recoil spring rates, is enough to hold the slides & barrels out-of-battery if manipulated in this manner. And
that's with an empty chamber/no magazine, and the pistol pointed slightly upward at an approx 45 degree angle. I've seen it occur with a new G21SF, using a couple of new RSA's.
So, even though a sufficiently tensioned recoil spring (even brand new) often won't have the strength to return an out-of-battery .45/10 slide & barrel back to into battery during a manually performed bench/field check, it's still fine for normal operation during live-fire. (presuming any other indications of a weakening RSA aren't present, of course.)
As long as the little pistol (Shield 9) is properly operating when used as described in the owner safety manual, and how the engineers designed it to operate & function, I'd not be losing sleep over how it "functions" when trying to manually induce problems in a manner other than how it was actually intended to operate & function.
If you're concerned about it, call S&W and arrange for a shipping label so the particular pistol can be checked and examined for proper tolerances, specs and functioning under warranty ... but don't be surprised if the gun passes the inspection & production tests just fine.
As far as gauging the guns? Sure, it's always possible for tolerance to be on the tight end of things in some particular gun, or even tighter than is normal.
While I haven't been through the Shield class yet (last I heard, it was awaiting approval by legal), I've been through the regular M&P pistol class twice.
S&W has been telling armorers for the regular M&P classes that extractor gauges aren't needed, due to the improved tolerances. Yes, they're still used by armorers for the 3rd gen pistols, and the standard SW1911's have their own extractor bar gauge (I don't know about the Enhanced models, yet). I have armorer extractor gauges for all calibers of the 3rd gen guns, as well as the SW1911. Only the original .40/.357 bar gauge for the M&P's, though.
They were originally recommending M&P armorers buy the .40 extractor bar gauges for the first classes, but nowadays they're saying the parts are being produced within such precise tolerances that gauges aren't needed by armorers. I bought one of the early .40 bar gauges, but I've been repeatedly told they still aren't making "armorer" extractor gauge tools for M&P's in the 9 & .45 calibers, nor have any plans to do so. BTW, they've also made a revision of the M&P extractor within the last year or two, refining it. I'd imagine the new Shield benefits from any recent extractor revisions and improvements.
If you're wondering about extractor clearance issues, the factory can check it (as I was told they use production gauges), as well as any spec/tolerance issues in the rest of the gun (including the trigger bar, safety block plunger, locking block, etc). Let them check it under warranty if you're concerned about (or just suspect) an actual problem. They're good about customer warranty.
Another issue where tolerances can vary is with the ammunition, though. I remember several years ago when some LE agencies reported some feeding issues with the SW9940's. While a revision of the magazine and follower design eventually resulted (related to an occasional reported early-slide lock issue), it was also discovered by S&W that some of the ammunition being used (contract ammo) exhibited some unexpected case rim tolerance variances which I was told might have contributed to some feeding issues.
This was discovered after S&W engineers couldn't get some of the affected SW9940's to exhibit similar described feeding issues with an assortment of common JHP ammo used at the factory ... but once they requested an agency send them the specific ammo they were using, the factory was able to get the "problems" to occur with that ammo.
I was told the Walther-provided 99 extractors were revised, and subsequent extractors I received appeared to have slightly beveled angles on the bottom of the hook, and were more polished.
I don't known what else to say, other than rather than chasing your tail and fiddling with the gun, let the company inspect it for any tolerance/manufacturing issues ... but consider that it may be possible that your expectations may not be considered realistic by the factory. Dunno.
I've only had the time and opportunity to handle and use one Shield 9 for an afternoon. It ran fine. I'm considering ordering one (as if I don't already have a surfeit of small 9's). Some of the other guys who have bought them have experienced similarly normal & reliable operation, as well.
I like the Kirk/Spock thing, BTW.
) , falling while running away and landing on your hands which are holding the gun, hitting your seat belt while in a car, a second bystander (maybe the perps girlfriend) grabbing at your hand while you bring your gun up, deflecting something thrown at you while the perp charges.... I could go on forever, but that's not the point. 
) caked on the top/front of the barrel, in front of the slide's front sight post.
