What lasts longer in EBR-types--SN'ed upper, or SN'ed lower?

[Eightball]

Just started thinking.....with the recent crop of "modular" rifles and such springing up, each has their own take on what constitutes a "receiver" to be SNed--should it be the "upper" (the SCAR, the Masada), the lower (AR15s), some middlin' part?

So, I started thinking.......what offers more modularity & longevity, having the upper serialized or the lower serialized? Which can have more rounds put downrange before there's meaningful wear-and-tear?

Sorry if this is a dupe, but I wasn't meaning to compare specific platforms, but more of the concept of where the SN should go--and the search function didn't turn up exactly what I was going for.

 

[taliv]

lower will last a LOT longer in most guns

 

[Dr. Tad Hussein Winslow]

what offers more modularity & longevity, having the upper serialized or the lower serialized?

I don't think there's any set answer to that, as far as longevity is concerned - it's gonna depends more on the specific materials used, the specific design, and thickness of the material than just whether it's an "upper" or a "lower".

Modularity? It would seem to me that the lower being the serialized part offers more modularity, but I'm not sure - I'd have to think on this one some more.

 

[Maelstrom]

The AR lower is actually a stress-free part, which primarily serves to house the trigger-groups and very little else.

The recoil is handled by the buffer tube which (granted) does thread into the lower, but that's really about it.

 

[Eightball]

The AR lower is actually a stress-free part, which primarily serves to house the trigger-groups and very little else.

The recoil is handled by the buffer tube which (granted) does thread into the lower, but that's really about it.

This is my thinking about it, but why, then, do SIGs (I think), SCARs, and the ACR/Masada all have a SN'ed "upper" unit?

 

[expvideo]

what offers more modularity & longevity, having the upper serialized or the lower serialized?

I'm pretty sure the serial number doesn't do anything for the longevity of the gun.

 

[WardenWolf]

The ATF could step in and say "The upper on this design is the firearm and will receive the serial number." It may depend on how much of the equipment is in the upper receiver.

The serial # matters because uppers wear out, and if a new upper is considered a new firearm it can cause problems. In a gun ban situation where they're not allowed to make new weapons of that type, but can still manufacture parts, replacing the upper would not be allowed because that would be considered a new firearm. Also new firearms transfers have to go through an FFL, get a background check, all that fun stuff.

Effectively, it determines whether the parts that wear out are considered just parts, or the firearm itself.

 

[HorseSoldier]

This is my thinking about it, but why, then, do SIGs (I think), SCARs, and the ACR/Masada all have a SN'ed "upper" unit?

It's not up to the manufacture, it's up to the ATF. Their general preference on rifles with discrete uppers and lowers has been to put the S/N on the upper receiver. I've heard AR lowers are basically grandfathered on the serial number issue -- the military has the serial number on the lower and the ATF followed that pattern.

If the AR were to be introduced today, they'd probably make the upper the S/N'ed part.

 

[jason10mm]

In some of those newer modular rifles isn't the upper just a shell that easily allows barrels and bolts to be swapped out for different calibers? If so, it makes sense, as the lower has to change for different magazines. Swapping an AR upper makes sense because changing the barrel is a lot of work.

 

[Shear_stress]

I don't think there's any set answer to that, as far as longevity is concerned - it's gonna depends more on the specific materials used, the specific design, and thickness of the material than just whether it's an "upper" or a "lower".

Exactly. The question totally depends on the design of the gun.