upper reciever

[gregr266]

What makes one upper reciever better than the other if they are all supose to be "mill spec." Not talking about the whole uppper, but just the reciever.

Thanks.

[X-NewYawker]

With LMT Uppers, the secret ingredient is love...





IF they're actually Milspec, they are pretty damn equal.

[pacrimguru]

the only thing i have ever saw was an upper that was not cut correctly. i saw a flat top cerro forged "keyhole" upper machined where the rails were completely not to spec. the rails were too shallow and spread apart so that nothing could have been mounted on it. too bad the owner had no idea who the manufacturer was. so becareful if it isn't being produced by a known manufacturer or if it is of unkown origin - even if it sports a keyhole. be sure that the rail has the correct dimensions.

[Fjold]

Milspec is the minimum acceptable quality. It is the "assembly line" standard so that all MilSpec parts will fit together. Many manufacturers build their products to better specifications which make their assemblies fit together better but may have fit issues if you interchange among differnet manufacturers.

Think of MilSpec as "Ford quality" and some of the other builders specs as "Ferrari quality".

[wash]

Some AR builders true the face of the upper so that the barrel is held on the exact centerline of the upper receiver bore.

Some people also use blue locktite (I think) to ~bed the barrel extension in the receiver for the best possible fit.

If you do those two things, the only spec that would be nice to tighten up is to make sure the picatinny rail is alligned parallel to and centered over the bore but it's not critical because the adjustment in your sights or scope can accomodate the tolerance.

[berg]

According to this video, some uppers have out-of-spec barrel threads making it difficult or impossible to properly install a barrel.