Go slow before thinking the carbine is all that; carbine gas and short handguards on a legal 16" barrel are exactly what created some problems. The result was the industry as a whole inventing midlength - even tho there was no military application at all.
The little thing consumer shooters miss is that the issue M4 uses a 14.5" barrel. That's a NFA item to you or me, with BATF stamps and paperwork to possess. Gas length isn't a bunch of different sizes like everyone thinks - it's ALL about 5-7 inches from the MUZZLE, which gives the optimum timing and best reliability.
Moving the gas port an inch and a half earlier works for some guns ok, but in the big picture, opens the bolt too soon, and speeds up the carrier to a higher cyclic rate, which has been a issue from day one. The rifle gas system was never intended to handle it.
Cutting down the HBAR barrel won't help at all, it would be rifle gas on an overweight carbine barrel. The gas port timing would be late, with reduced power because the bullet leaves the barrel and dumps it too soon. It needs that 5-7 inches, which is why the guys building rifle length sights on 16" barrels use a low profile gas block at midlength under the handguards, and the FSB out at rifle. You get the correct operation and long handguards to reach further out on the protected barrel to shoot.
PSA and others offer drop on uppers for $400, converting that 20" HBAR to 16" midlength. Another factor is that a 4" shorter barrel loses about 50fps per inch in 5.56, and the loss of about 200fps does shorten the range and reduce the terminal effects. It's the heart of the M4 debate about whether it hits hard enough in combat, being 5.5" shorter in military issue. It's also why alternate calibers like 6.8SPC were created, to boost power back up 40% out of 14.5 to 16" barrels.
Since the AR doesn't come with a fancy adjustable gas block, and relies on port size and location, plus a one specification ammo load to achieve unfailing use in the field, it's best to use the proper combinations in shorter barrels that guarantee results. And that means low powered cheap import ammo can malfunction.