I do not think that there is any reason in this day and age that a patrol rifle cannot be individually issued versus a pool rifle, or at the very least allowed as a personal purchase item with specifications. I feel any barrel length from 11.5-16 inches should be allowed for patrol purposes. Guys with motors and smaller vehicles that compete for space may be better suited with shorter 11.5-12.5 inch guns, while 14.5-16 may suit another agencies preferences better. So long as it is a quality purchase that is kept in the front compartment where it can be accessed when needed, those minimum and maximum lengths do not have any huge ballistic advantage or disadvantage or another for these environments.
I disagree with Bourneshooter and Failure Drill on the requirement for a freefloat handguard. Lots of badguys have died from non-freefloated equipment. It adds $300-400 to the cost of the carbine, and that may mean the difference between having and not having a RDS for some agencies. The POI shift that can be caused by sling tensions is to be considered, but I feel its lower in priority for a basic patrol capability. Now, if it was a DM/PPM/DMR rated LEO, then I can see pushing it up on the priority list a bit. My opinion along with 89-cents for that cup of coffee is that the Magpul handguards are actually a decent choice for a minimum patrol rifle standard. They have the capability of attaching light mounts and sling sockets and are affordable.
I am under the belief that irons are mandatory for patrol. I've been around Aimpoints long enough that I've never had to transition to a BUIS because of a optic being broken. But I have seen optics that batteries crapped out when they were needed. Plus, if an optic has to be taken out of service for some reason, whether it be the zero is affected, or repair, etc, the whole weapon isn't deadlined because there are sights still. This is important for the LEO that supplies his own equipment.
I personally feel irons ran in the up position should be the minimum standard. In the winter, I start a day shift in hours of darkness, which change to a possible bright sunny day against a white snow backdrop, and finish my shift again in hours of darkness. It is impractical and nearly impossible with weapon locks to continually change my RDS adjustment to match the current light during the day. If I set it to be seen in the brightest part of the day, its blooming when I go inside a dark structure, or forgot to change it when it gets dark. The same goes for guys that work afternoon shifts during the entire year. The main reason for using an Aimpoint besides durability is the ability to leave the dot on so an LEO doesn't have to consider his dot setting when he's deploying it under stress, such as backing up another officer on a high risk stop or coming to the aid of one that just called "Shots Fired." I can see the iron sights just fine in daylight conditions. I cannot see them in low light, which is also where the RDS dot gives me an advantage. So the dot gets set each shift to a level for lower light at the time. If I cannot see the dot because the daylight outside is too bright, then my irons are right there, just like my handgun sights.
Like the other guys, sling, light, RDS. When it comes to an optic, agreed from my experience is that Aimpoint is the standard for a patrol optic. I know of some people that have been running the EoTech XPS's with success for them. I have a very very hard time considering them based on previous performance from other models. I personally feel other optics like magnifiers or low powered variables are ok with patrol officers, but I am in favor of a policy of increased training and demonstration of skills first to help avoid Walmart 3x9's mounted with a bipod on the front.
Sling needs to be a 2-pt that can be adjusted one handed. I prefer the VCAS, but as slings are a highly personal choice, I'm ok with any quality choice that allows the weapon to easily be secured to ones person through quick adjustment like VCAS & VTAC slings prove they already do.
For me, the Surefire EAG Fury with the click switch sets a standard, with either the 500 or 1000 lumen options. Costs are reasonable.
I don't think lasers need to be on a basic patrol rifle, but I am in favor of patrol LEO's that have demonstrated a compentency level to be allowed to use them, similar to what I think should be needed for low powered variables. The more accessories like lasers and optics are allowed, however, the more a basic minimum equipment standard needs to be set to keep guys from opening up the CTD catalog or putting stuff on that they don't understand the requirements of. I know of a PITA doctorate student/PT LEO of all of 2-3 years try to spec out a departments pool rifles with a Streamlight TLR2, amongst several other issues. <sigh>
I would love to have every officer issued with some form of barrier blind ammunition. I think someday more LEO's will get there. But with costs these days of $1 per round, some agencies that have purchased these rounds will only issue enough for 1-2 20-rd magazines at times. On the other hand, a minimum standard needs to be set as well. I was once issued Silver Bear crap, and I know of other departments that still issue FMJ's due to costs. Doc Roberts has tested various loads over the years, and at a minimum I feel the Black Hills 55gr SP's should be issued if costs are a factor. This also allows remanufactured training ammunition to be purchased that's very affordable.
I've been working with a patrol rifle for about 18 years now. I'm rated as a patrol rifle instructor in my state, and I've been working on building some programs on the side for agencies in my region. While I would love to have the ideal standards a lot of us work with, I also know the realities of Yadontneeditville politics and budgets. The standards above to me balance out realities and desires the best, and still allow the job to get done.