I have a MM53 which at a 100 yards appears to have similar accuracy to my HK93. Will need to scope and work with loads to know more.
Like US Praetorian said, the accuracy is not effected as a first order function by barrel length with in reasonable limits (hate to try and model the gas exit effects on the bullet at or below the 53K barrel lengths), with iron sights the 53 will have sorter sighting radius , but can just ad optics to correct this ;-).
In the 2 platforms you mention, any difference will be immeasurable by the user.
Consider this, say you have a wooden yard stick. Break it in half. Now break one of those halves in half. As you continue on, your effort required to break the piece increases until you can't physically do it. It's basic physics and leverage. To further demonstrate (there is a Daniel Defense M4 video clip that I can't seem to find), If you watch a carbine with a high-speed camera, the barrel will whip around like its made of rubber.
Now, as mentioned above, barrel length will affect muzzle velocity and performance. A barrel can be too short to the point where a round can loose effectiveness and stability.
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