I know that this question pertains to modern weaponry but I was wondering why police and military units still use different types of repeaters (bolt-action, pump action, and lever action). Some examples are the bolt-action sniper rifle and the pump action shotgun , when I spoke of autoloaders I meant any firearm that is semi-automatic or fully-automatic in nature. The question that I have is why are reapeating firearms still being used by police and military units because semi-automatic or fully-automatic firearms are much faster and more accurate. Are repeaters more common because they are less expensive and easier to use or are the semi-automatic or fully-automatic firearms difficult (complex) to use, are they prone to jam up or are they just more expensive? Why are verious forms of breech loading repeaters still in use to this day and age?

Jean summed it up nicely.

I'd like to add that the majority of sniper rifles in use are bolt action for 2 reasons. Semi-automatic weapons tend to be less acurate than their semi-automatic counterparts. The mechanical complexity of an automatic reloading mechanism adds vibrations to a weapon when it is fired, reducing its long-range accuracy and consistancy. An inherent problem with semi-automatic weapons is a tendancy for the shooter to "rush" the shots, relying on many easily-available rounds instead of pin-point accuracy to bring down a target. A second issue with semi-automatic weapons has to do with the way they reload. The spent shell casings typically fly far from the weapon, reflecting sunlight off the o-so-shiny brass, and giving away the position of the carefully concealed shooter. A bolt action rifle allows the brass to be extracted from the chamber slowly, allowing the sniper to remain concealed.

In the case of the pump-action shotgun, there are several factors at play. The most obvious is cost; you can have a high-quality pump for much less than an equivalent semi-auto. But beyond that is reliability; pumps have historically out-toughed semis. Nowadays there are plenty of semi-auto shotguns that are reliable enough, but even they have their quirks and preferences -- semis are just more finicky about what kinds of ammo they digest. With a pump, you can shoot anything -- low-intensity training rounds, flares, blanks, gas rounds, rubber projectiles, etc -- and simply pump the action and the next round is ready to go. Semi-auto shotguns won't cycle most of these rounds.

You just can't go wrong with a decent quality pump. A cheap, beat-up Police trade-in Remington 870 will still last beyond forever while the newest "wonder semi" is choking on ammo it doesn't like.