I spoke to a retired law enforcement officer ta few months ago and they are going to 9mm because the ammo is cheaper . plus it's easier to shoot a 9mm than a 40 . I'd say 40 is a better round than 9mm. 9mm will work but if I had a large dog trying to make me into an afternoon snack I'd rather have a 40 than a 9. I remember back in the day the New York police were armed with 38 revolvers and sawed off Savage Stevens 12 gauge double barrel shotguns . so I red in an article . they were trained to use them properly and an article said they faired very well due to the training . then they went to a semi pistol .
I don't think most police should have a patrol carbine . the bullet carries too far . i think they would be better served with a pump shotgun . Sergeants and others with many years of experience who are trigger savvy and have proven so could be issued a carbine . if they wish . how many criminals have AR rifles ?? maybe in a drug raid but not on patrol .
most agencies are converting to 9mm for these reasons:
1 - when comparing terminal performance of modern JHP and better yet barrier blind ammo, 9mm penetrates as deep as 40 S&W and 40 will give you about .05-.10 wider frontal area of expanded ammo. so no much "extra" wound incapacitation ability. When stuck with FMJ, the rule of wider is better is still valid.
2 - 9mm is easier to shoot than 40S&W
3 - the life of 9mm guns is better than 40S&W guns - especially when aluminum frames are part of the equation
4 - 9mm is cheaper - in the order of 18-22% cheaper in fleet volumes. When I did pricing for my agency - 1600 sworn - the savings in one year's budget of ammo was enough for 46 free 9mm pistols with the savings.
5 - 9mm carries more rounds. not a huge issue but it is a slight benefit
6 - 9mm is slightly more available than 40S&W - both require ongoing advanced ordering when talking fleet volumes though.
It's the one time - very rare - that Officer Safety/bean counter savviness actually match.
In the realm of wound trauma incapacitation - Dr Fackler was stymied when there was a push to adopt 223/556 vs 12 ga. He was of the opinion that LE had the best wounding tool already available - the 12GA. the issue with the 12ga is limited distances/not 100% against body armour/need upgrading to be viable today (sighting/lighting/adjustable stocks) and they still have heavy recoil. the demographic of officers in the 40's-80's is different to the ones today - rifle is a better fit - period. With regards to having AR's on patrol - AR's are a multipurpose rifle. they don't come across many AR style rifles on patrol, they do come across all kinds of other rifles though. having a rifle to match a rifle is not possible. LE requires a side arm and long gun.
Boltgun