Re: Glock 27 or S&W M&P 40c...........................
We were issued the G22 1997 through my Department, and the G27 became the carry of choice for plain clothes. I am a large guy with big hands so the the G27 with the pierce extension was my carry choice in the Bureau for years. If we were allowed to carry a .45, the G30 fit my hand better, but we weren't. A very solid gun, point and shoot practicality, and very accurate for its size and use. The M&P is nice, but I still prefer the G27, though that preference is due to years of use and training with it, Glock's KISS mentality. Admittedly when we went to the Glock I was an unwilling participant, but through the years of service I have grown to fully appreciate the weapon.
The S&W M&Pc is very similar to the Glock with a few added features; slide release, magazine safety, and a thumb safety (decocking plate). It also has three palm swell pieces to adjust grip, a built in tool for stripping the pistol, magazine extenders, and a better rear sight for sight radius. The trigger safety is also very similar to the Glock and is the equivilant to the NY Stle trigger at about 7 pounds total. The thumb safety and magazine safety are options. I personally do not like either of these mechanisms on a striker-fired pistol, but others may. In my opinion, you train how you fight, so either pistol with proper and consistant training are fine. However, for the average person who will be shooting at the range, if a situation presents itself in real life, those feature would be a hinderance and more things to think about in a situation were response is essential.
The palm swell replacements are a very nice feature for proper fit, and the included disassemby tool is also a nice feature. The Glock Gen 3 has these as well, but the dissassemby tool is an extra you can buy. Most people will never completely field strip their pistol, but it is a nice feature, though a paper clip will do the same. For practical field stripping for basic cleaning, the S&W is a bit more complicated, you have to lock the slide to the rear and use the tool to release the slide and move the slide lever down. This is a bit more than the Glock, however you do not need to pull the trigger. With the Glock you simply clear the weapon, pull the slide back just far enough to clear the the slide lock, allow the slide to move forward and pull the trigger, and the slide comes right off. Many people have hap-hazardly has an AD because of this with the Glock, but again that is a training issue. I will say this regarding the field strip, The S&W can be field stripped by pulling the trigger also, though S&W doesn't tell you that. I did find the following on youtube, it is a pretty good overall of both guns.
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Over all, I still like the simplicity of the Glock for ease of shooting and field stripping. The few features that I do like on the M&P are easily purchased as aftermarket items relatively cheaply; ie: the disassembly tool, rear sight, and grip extenders.
Regarding accuracy and ammunition, I has seen little difference in either pistol.
Hope this helps you out