3 ms·

That is true, but I never understand why mix and match uppers and lowers? Why use a DPMS lower with a Sig upper? Makes no sense. Best I can figure is that in a

That is true, but I never understand why mix and match uppers and lowers? Why use a DPMS lower with a Sig upper? Makes no sense. Best I can figure is that in a war situation with a gun of questionable stability, swapping parts might give you an advantage in survivability.

megaman22 9y ago
I believe one of the biggest reasons is that nonsensical gun control laws make it difficult to purchase entire rifles in some states, while you can relatively easily buy the components and do the trivial assembly yourself.
- cptskippy 9y ago
  It is illegal to sell guns with certain characteristics (e.g. fully automatic fire, select fire) without possessing a Federal Firearms License which carries certain onerous requirements of the seller. It is not however illegal to own or make such guns. Because the AR15 is so modular in nature and parts like the stock and barrel don't dictate if the firearm is automatic, federal laws dictate that the lower receiver is what is actually considered the firearm. Since regulated and unregulated AR15 lowers are mostly identical, and the point at which they diverge is a nonfunctional state, manufacturers can make incomplete or 80% complete AR15 lowers that aren't considered firearms. You can then take these lowers and complete them yourself at home to have an unregistered firearm that you could not otherwise posses without registration.
cptskippy 9y ago
Lots of reasons! The US Army has interchangeability requirements for different rifles based around the AR-15. Different rifles use different barrels, gas systems, and ammunition requiring or eliminating the need for certain features. Civilians will also often have requirements that are unusual such as left side porting and assists. Not all manufacturers are going to make all of these variations thus you might choose to mix and match based on your needs. It's also quite common for civilians to make their own lowers to circumvent federal regulations around owning fully automatic weapons. The M4 has a shorter barrel and thus short and higher pressure gas system. This results in a higher bolt velocity and rate of fire. Because of this and the fact that you typically use M855s in the M4, you can run into feed issues since the bullet tip is more pointed. Because of this they altered the angle of the feed-ramp however that modification caused issue when machined into the upper and so it's preferred for your barrel to have the feed-ramp. Thus your upper and barrel have to be closely paired and are also M4 specific. None of this however affects any compatibility with the lower. The forward-assist and chrome-lined bores were introduced due to extraction issues experienced during Vietnam with the M16. These were attributed to improper maintenance of the rifle and quality issues with the ammunition. Since neither of those are really issues in civilian rifles and add complexity and expense, they not explicitly needed. So there exist options for uppers without. Left port and assist uppers are also relatively uncommon but sought after in civilian rifles.

megaman22 9y ago

I believe one of the biggest reasons is that nonsensical gun control laws make it difficult to purchase entire rifles in some states, while you can relatively easily buy the components and do the trivial assembly yourself.

cptskippy 9y ago
It is illegal to sell guns with certain characteristics (e.g. fully automatic fire, select fire) without possessing a Federal Firearms License which carries certain onerous requirements of the seller. It is not however illegal to own or make such guns. Because the AR15 is so modular in nature and parts like the stock and barrel don't dictate if the firearm is automatic, federal laws dictate that the lower receiver is what is actually considered the firearm. Since regulated and unregulated AR15 lowers are mostly identical, and the point at which they diverge is a nonfunctional state, manufacturers can make incomplete or 80% complete AR15 lowers that aren't considered firearms. You can then take these lowers and complete them yourself at home to have an unregistered firearm that you could not otherwise posses without registration.

cptskippy 9y ago

Lots of reasons! The US Army has interchangeability requirements for different rifles based around the AR-15. Different rifles use different barrels, gas systems, and ammunition requiring or eliminating the need for certain features. Civilians will also often have requirements that are unusual such as left side porting and assists. Not all manufacturers are going to make all of these variations thus you might choose to mix and match based on your needs. It's also quite common for civilians to make their own lowers to circumvent federal regulations around owning fully automatic weapons. The M4 has a shorter barrel and thus short and higher pressure gas system. This results in a higher bolt velocity and rate of fire. Because of this and the fact that you typically use M855s in the M4, you can run into feed issues since the bullet tip is more pointed. Because of this they altered the angle of the feed-ramp however that modification caused issue when machined into the upper and so it's preferred for your barrel to have the feed-ramp. Thus your upper and barrel have to be closely paired and are also M4 specific. None of this however affects any compatibility with the lower. The forward-assist and chrome-lined bores were introduced due to extraction issues experienced during Vietnam with the M16. These were attributed to improper maintenance of the rifle and quality issues with the ammunition. Since neither of those are really issues in civilian rifles and add complexity and expense, they not explicitly needed. So there exist options for uppers without. Left port and assist uppers are also relatively uncommon but sought after in civilian rifles.