I want a .308 AR. Will a .308 upper fit on my standard Bushmaster lower or does it require a purpose made lower. Where can I get a 308 upper as my searches on the net have been less than succesful. Any help would be great as it's tax time and I need to spend some loot. I want it to be on a .308 upper. HELP!! Thanks.

The length of the mag well is different.. I have an AR10 and My upper will not fit anything but an ar10 AFAIK.

Damn!!! I guess I'll have to try and find an affordable M1a or maybe go with a .50 Beowulf upper. I know they work with standard lowers and I reload. My friend says that the .50 will cause alot of wear really fast on the lower and I say it's BS. Any opinions.

I don't personally own a .50 but from what I understand they do put a lot of stress on the lower and the advice is to use a forged lower if you do... I prefer a dedicated gun instead of having to swap out parts..

I have had my 50beowulf upper on an older DPMS lower and a RRA lower both worked out just fine,  I don't think you can live long enough to wear out the lower from the upper performance wise, go ahead get the Beowulf its a ball to shoot and wow what a hard hitting round but remember its not for open range shooting its more for woods hunting effective range is abt 200 yards is its ideal kill zone. I live in Minnesota so most of your kills on deer are under 100 yards and this makes a perfect brush gun it has about the same balls as a 45-70 government round

I thought the 458 socom had the same bullets as a 45-70 not the 50 beowulf?

Edit: to your 308 question if you build out an eagle arms ar10 lower and then add the upper it's about the same price or less than an M1A unless you get the chinese M1A.