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BUILDING AR15

timhill100
my next project is going to be build my own ar15, been pricing lowers,
my question how does one know what uppers and lowers are compitable, does it even matter, ive been trying to match parts up but i can find anything that says you can use this lower with this upper or the other way around, i dont want to buy a lower than a upper to find out they dont work together, any help on this out there
thanks
tim
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Comments

7 comments

Date Votes
  • mark christian
    These days virtually all uppers and lowers are compatible. Those of us who've been around for a while can tell you about off-set and reverse off-set pins to adapt for the different sized holes in Colt products, but those days are mostly gone and virtually all production uppers and lower will match. The difference is finish colors still present a problem.
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  • timhill100
    awesome thanks
    tim
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  • timhill100
    These are mil spec forged lower receivers from R Guns. These receivers are ready for your 223/556 build. The have a nice matte black finish and are unique in that they have horizontal grasping grooves on the front of the mag well. They will accept all standard AR parts/uppers.

    IS THIS A GOOD RECEIVER WHAT DOES THE 556 MEAN, I WAS THINKING OF STARTING HERE WITH THIS ONE, ANY THOUGHTS OR ADVICE
    THANKS
    TIM
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  • ern98
    The .223 is the caliber in inches and the 556 is the caliber equivalent in milimeters. Can't advise on the brand you are asking about as I have never worked with one. As long as they can show that it specs out to milspec specs then it is probably ok. Good luck with it........
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  • beantownshootah
    Mark has it.

    Historically, there have been some differences in terms of receiver pin hole size (mostly with Colt parts), but more or less all the uppers and lowers in .223/5.56 mm are standardized nowadays and should fit together OK.

    If your receiver is "milspec" you should be go to go.

    Note that if you want to build a gun in 9mm luger, you can't just throw any upper on any lower and expect it to work. . .there are differences there that need to be addressed.

    In terms of the receiver you mentioned from R guns, its probably fine. AR-15 guns have literally exploded in popularity over the past few years, and now everyone and their cousin is putting out receivers to build on.
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  • timhill100
    THANKS, GREAT INFO, JUST GOING TO STICK WITH THE 223 FOR NOW, MAYBE A 308 FOR MY NEXT ONE,
    I NEVER HAD A INTREST IN ARS TILL I SHOT ONE AT THE RANGE LAST WEEKEND AND LOVED IT,
    NOW IM ONE OF THE AR15 NUTS LOL
    TIM
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  • cwi555
    quote:Originally posted by ern98
    The .223 is the caliber in inches and the 556 is the caliber equivalent in milimeters. Can't advise on the brand you are asking about as I have never worked with one. As long as they can show that it specs out to milspec specs then it is probably ok. Good luck with it........


    There is more to it than that.
    800px-_223_Remington.jpg
    800px-5_56x45mm_NATO.jpg

    Look at the r1 and r2 radius at the case mouth.
    it is 0 for the 5.56
    it is ,56 on r1 and 2,54 on r2.

    There is in fact a difference in the cases, and a difference in how they will seat, and headspace. A small difference, but enough to of concern.

    Now lets look at something else from clymer.
    the chamber reamers are as follows:
    Max variation between .223 and 5.56 reamers.
    Shank 0.0000
    Base Diameter 0.0020
    Shoulder Diameter 0.0007
    Neck-2 0.0000
    Neck-2/Case Mouth 0.0010
    Freebore Diameter 0.0025
    Pilot Diameter 0.0000
    Base-to-Case Mouth 0.0030
    Base-to-Shoulder 0.0040
    Neck Length -0.0020
    Freebore Length 0.0250
    Rim/Belt Thickness 0.0000
    Shoulder Angle (Degrees) 0.0
    Throat Angle (Degrees)-0.6

    The end result is their is a distinct difference.
    If you want accuracy and reliability, you should take that into account.
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