AR-15 Mid-Length vs. Carbine Upper: What’s the difference?

There is a slew of misinformation on AR-15 upper configurations on the internet, but sometimes it’s more a lack of information than anything.  When it comes to the somewhat unknown mid-length upper for the AR platform, the latter is the issue. While there are mid-length uppers for even the LAR-8, AR-10, SR-25 platforms, this article will concentrate on mid-length uppers for the AR-15 platform.

In basic terms, the A3/A4 mid-length upper is typically identical to the A3/A4 carbine upper with a few exceptions.

1. Both typically have 16″ barrels (other length models are around, but not as common)
2. The mid-length has the gas block and front site post (if equipped) further down the barrel (closer to the muzzle end of the barrel)
3. The mid-length has a longer gas tube
4. The mid-length has a longer hand guard (to cover the longer gas tube)

Now for the stuff you really care about…

Myth: The Mid-Length Upper has a longer barrel than the carbine

FALSE. The mid-length designation isn’t about the barrel length – other than the fact that is not a full rifle-length barrel (20″). Mid-length actually refers to the length of the gas system (placement of the gas block and length of the gas tube), not the barrel or overall length

Mid-Length Uppers Have Lighter Recoil

While felt recoil is largely a subjective measure, the recoil impulse of a mid-length upper where all other things are the same should be obviously smoother. The reason for this is the difference in the “dwell time”  of the bullet after passing the gas port. The mid-length gas port is 7.5″ from the muzzle, the same distance as the 20″ rifle length gas system. The carbine gas port is 9.5″ from the muzzle which increases dwell time which increases the pressure in the gas tube, against the gas key and puts more force on the bolt thereby causing harder cycling and a sharper recoil impulse.

Mid-Length Uppers Are Better for Accuracy

Depends on shooter and optics: If you shoot with iron/open sights, the mid-length will put the A2 front sight further out which gives the shooter a longer sight radius (distance between the rear sight and front sight). This gives the sighting system greater accuracy. If you are shooting with combat optics (ACOG, red dot, HWS, scope), it won’t make much difference. The smoother recoil should certainly help with follow-up or quick shots.

Mid-Length Uppers Offer Better Reliability

Because of the lower pressures in the receiver due to the shorter dwell time, the BCG and buffer components should take less punishment. Hard data on extended lifetimes is difficult to come by, but anecdotal evidence from security teams and police force armorers gives the idea credence.

Another consideration for owning a mid-length upper is the fact that the hand guard is 2″ longer. For a longer-armed shooter, this could make the rifle feel much less cramped. If you use a tactical hand guard, it will also give you some extra room for all sorts of gadgets on the rails.

 

 

Category: Learning Center, Tips and Techniques