Having all of the moving parts enclosed inside the frame and slide reduces the chances of dirt and debris messing up things. Exposed hammers are susceptible to damage if the firearm is dropped. In close combat clothing, hair, or fingers can get between the hammer and firing pin preventing the gun from firing. Exposed hammers can be accidently cocked when they come in contact with objects while being carried.
All of these reasons are why exposed hammers fell out of favor with long guns. And are why striker fired guns are taking over with handguns.
And striker fired handguns don't have to have a long and heavy trigger pull. In fact most have trigger pull weights very similar to out of the box factory 1911's. The 1911 CAN be made lighter. And just like a 1911 trigger can be improved so can most striker fired guns. I have a couple of Smith M&P's with aftermarket Apex triggers that will rival my 1911's. They even have 1911 style thumb safeties, and with a trigger that light I wouldn't want them without the safety.
To the first point, the US military had pistol trials before the adoption of both the 1911 and the M9. In both of those trials there were striker fired pistols, at least the Luger and then the HK P7M13 respectively (there may well be others, that’s what came to mind). They didn’t win. Now that may not be solely due to reliability, but when you read the trial information both the 1911 and the M9 performed pretty admirably in terms of dealing with external fouling. You can also watch people do their own pseudo dirt, mud, and water trials on YouTube. One that makes a decent attempt at consistency is the Military Arms Channel. He’s had hammer fired pistols do very well and striker fired pistols do very poorly. The reverse is also true. I don’t know that hammer fired pistols are as a rule less reliable in the “elements” as striker fired pistols.
I’m not sure how overly common it is for a dropped pistol to land exactly on the hammer, but I think it’s a fair point. Some designers, such as SIG with the P6, included a deforming hammer as part of the design so the armorers would know if that happened.
It’s also possible for hands or clothing to get in the way of a falling hammer. At the same time I think it may be more likely in a close quarters struggle that you end up with a pistol out of battery, and in that case the pistol won’t fire even if it is striker fired (I remember that happened in the Michael Brown shooting). To that point though it can be easier to hold a striker fired pistol in battery with say the palm of a hand than a hammer fired pistol.
I’m just not convinced that the reasons outlined are areas where exposed hammer fired pistols are so deficient that they represent the reason why striker fired pistols have become so predominant (even if I personally carry a striker fired pistol and do agree with you to some extent). The domination of the striker fired pistol in the commercial market didn’t happen until some time after Glocks became more popular. As others have pointed out, there were striker fired pistols long before Glock, even polymer framed striker fired pistols. If exposed hammer fired pistols were so much more deficient than striker fired pistols there were a number of points in history for them to have taken over in that regard. Personally I think the current state of the pistol market in terms of striker fired sales has more to do with the relatively simple manual of arms and affordability.
To your last point, I do agree that striker fired pistols don’t necessarily have long and heavy pulls, certainly not compared to the DA on a lot of hammer fired pistols. They’re not what I would consider “pulling a stick through the mud”. I still don’t think they’re in 1911 territory or other hammer fired pistols in SA. While the resulting weights are often close to production 1911s, the amount of pretravel, length of the reset, and the crispness of the break often aren’t what I’d call close, but I admit that’s subjective. I have had M&Ps with Apex kits and they are quite nice, but my 1911s still put them to shame (in fairness I never tried the forward set sear kit from Apex, if you are talking about that kit).
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