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Need advice


I have been building a new AR15 in .556 for a while now... I got nearly all my parts but I waited too long to get my upper assembly and thanks to covid you cant find any now.

Here is my problem, I found a upper from Aero Precision that is an XL upper, for the 458 socom. I ordered it along with a .556 barrel 16" with carbine gas system... my question is this. Will this upper give me any issues in a .556 build. I know it will fit on my lower just fine. From what I am told it should work ok with .556 parts but I haven't got it yet to tell. Will the barrel fit ok and all the other .556 parts, just a bigger ejection port or if there something else that will mess me up on this build.

I kind of like the idea that if this works I could always change out the bolt and barrel later on to make this a 458 socom or even 50 baewolf later on down the road. Any thoughts?


New member
Its an XL upper, it won't be compatible with your 5.56, which is what I am pretty sure you meant to say instead of .556. Maybe you should do a little more research before asking easy questions on the forum.


New member
Yup, you have an XL upper. You probably just wasted your money unless you want to make a 5.56 build and a 458