The short barrel isn't the cause. All the powder that going to burn, burns within a short distance in front of the chamber, because that''s where pressure is highest.
Instead it's lower pressure than the powder was designed for. In my 32" barreled trapdoor Springfield a 1300
fps load of IMR4895 with 400-grain bullets shoots great--but there are still plenty of unburned (or only partially kernels, because the load isn;t anywhere near the 50,000 PSI or so IMR4895 was designed for.
Why is it a problem? Is accuracy poor, or inconsistent?