Never understood why people like a SBR in 5.56. not all the powder burns by the time the round exits the barrel and this gravely impacts velocity. Gas tube has to be shortened a LOT, and is way closer to the mini-explosion of a discharging round, thus overpassing the action and beating your gas key apart. This could be fixed by a piston kit, assuming they even make one for SBR AR, which I’m sure someone does, but that won’t fix the muzzle velocity you just lost.
The entire point of having a rifle is to utilize it’s round to the fullest extent of the given rounds physics. Lopping off 8 inches of barrel length decreses velocity, range, and many foot pounds of energy.
Want something short? Get a tavor.
Want a compact rifle that give you full power. Try a Kel Tec RFB 26.2” oal, 18” barrel, .308 caliber. I’ve had one for 6 years plus an AAC suppressor. It is accurate and hard hitting, and no $200 tax stamp.. It is shorter than my three SBR’s.
Probably because I can’t have one here...TBH. :)
Had a CX4 Storm in .40 that was nice. Mags usable in either the carbine or the pistol. Good combo.