AR-15 upper question about fit and function

[ACP]

I've got a mid-90's Bushmaster Patrolman's carbine with a 16" barrel and fixed sights. I dropped a Rock River match trigger into it some time ago; it's a very light, accurate rifle.

I'm thinking about purchasing a Bushmaster Varminter or Predator flattop upper and mounting a scope on it for plinking/target work at 100+ yards. I'd buy an upper with a dedicated bolt, of course.

Question: will swapping out the uppers back and forth cause any loss of accuracy (loss of zero)?

Or is it better just to go with a dedicated second rifle?

I've never swapped an upper on my AR before, I don't know what the pros and cons are.

 

[RickRandom]

Since the sights/optics are mounted to the upper, switching lowers has no effect on zero.

 

[Bezoar]

thenewrifleman.com is your new friend. Lots of these questions answered.

You have the modern ar reciever. 99.9999% of everything should line up perfectly with a currently produced upper. The worst ive seen tales of online is folks having to handream the holes so that the pins will fit without needing a hammer to install.

try a barska carry handle scope mount on your current upper? Apparently unless you get a true match barrel, im hearing you can get acceptable accuracy from a 16" upper with a decent optic.

 

[HammsBeer]

The barrel, bolt carrier, rear and front sights are all on the same upper. The lower is only there to house the trigger group and buffer tube, neither of which has any significance on accuracy. Unless you are switching between different lowers with drastically different buttstock cheek weld or triggers, the point of aim/point of impact for each upper will remain the same. Swap away.

 

[Davek1977]

try a barska carry handle scope mount on your current upper?

Seems like odd advice, both since you are recommending a scope of questionable quality, and that the OP said NOTHING about wanting to scope his original upper. A flattop gives one FAR more scope mounting options, and you aren't stuck with repro's of the "original" Colt AR-15 scope. With a flat-top, your imagination is the limit when it comes to optics, as red dots,reflex sights, scopes from 1x to 24x and beyond, lasers, etc are all valid options

 

[ACP]

thanks gentlemen, you have set my mind at ease.

I actually do have an ARMS #2 mount for the carry handle.. it's fun to use a red dot at 25-50 yards, but the cheek weld is non-existent

 

[cfullgraf]

Stripped lowers are priced pretty low these days, $50-$70 or so. Consider at least getting the lower and building it over time as you find deals on the remaining lower parts.

While swapping uppers is a pretty quick and easy task, boy it is nice to have a complete rifle.