AR polymer lowers

[mitch1]

Over the last couple years I have written some reviews on lowers that I personally have used, some have been great some not so much.

I have put several thousand rounds through the EP armory and polymer80 with no problems and their quality has been good.
This week I was going to use a TN Arms lower that I had received as a warranty replacement. The upper wont fit. I emailed TN arms and their reply was "just pin your upper with the pivot pin and then sand down the curvature of the buffer tube to allow the upper to lay on the lower. there's extra material at the curvature to allow the receiver to be more versatile with uppers"

And all this time I thought that mil spec receivers were all machined the same,
all of mine seem to interchange .

[dwalker]

Meh, some folks like a "tight fit" thinking it aids in accuracy. FWIW there is no such thing as "mil-spec" as any sort of standard, which is why some AR parts fit loose, some fit tight, and some do not fit at all.

[Oldmandan]

And all this time I thought that mil spec receivers were all machined the same, all of mine seem to interchange .

I think the term "mil-spec" has been used very loosely the last few years....

I have several polymer lowers, i prefer them. Never had a problem with them

[Pofoo]

. FWIW there is no such thing as "mil-spec" as any sort of standard, which is why some AR parts fit loose, some fit tight, and some do not fit at all.

I see this pretty regularlly. AFIK, the US gvt and military have specs for EVERYTHING. Helmets to shoe laces.