The individual gun matters more than an inch or 2 of barrel. Some 4" barreled revolvers shoot the same ammo faster than some 6" revolvers.
I don't keep those revolvers around long anymore. Too many more of them out there along with I just don't want to fix/replace cylinders/bbl gaps/bbl.'s anymore. There's something to be said for dan wessons.
There's a lot of experience with MP-300 on this website, their advise is spot on. Last year I did testing with different 35cal bullets and a little head to head testing with 2400/MP-300/H110.
Typically there's huge differences in velocities between plated/jacketed/cast/coated bullets. Add to that the bullets design itself will play a huge role in getting the most velocity out of a given load/revolver combo. I used these 8 bullets along with 2 hollow based bullets not shown in pic.
I used 5 different powders for the bullet tests, along with 1x brass, hot primers and max p+ loads with heavy roll crimps in a 2" bbl'd snubnosed 38spl revolver. You wouldn't think that a bullets design would make any real difference in velocities especially with a 2" bbl. At the end of the day the cream rises to the top & after a 500 round/10-bullet test these 4 bullets consistently outperformed the other 6 bullets.
The bullet 2nd from left is a cast 148gr hbwc that was turned/loaded backwards. These bullets outperformed other bullets by as much as 70fps & while 70fps doesn't sound like much. The difference between a 158gr bullet doing 850fps and 920fps in a snubnosed 38spl is huge. These bullets outperformed the others because they had the ability to seal the cylinders/bbl quickly/more efficiently with their large bottom drive band (cast) and the long bodied home swaged bullet (right).
I decided to use the green bullet (top picture, top row 2nd from left) in testing 357 in different bbl length 357 revolvers and a 10" tc contender. It was +/- 20fps slower then the bullets in the bottom picture/38spl test. I chose that 158gr mihec 640 hp to test in the 357's because I can cast a 170gr fn bullets by simply changing pins in the mold.
I was looking for a 1200fps+ load for a 2 1/2" bbl'd s&w 586 l-comp. S&W lists the 586 l-comp as a 3" bbl'd revolver. That to know what holsers to look at, the revolver itself has a comp at the end of the bbl' shroud and the revolver really only has a 2 1/2" bbl. So I loaded up a bunch of full house loads using 2400/MP-300/H110 and that 158gr hp bullet pictured above. The bbl lengths used in the test was:
one 2 1/2"
two 4"
two 6"
one 8"
one 10" (tc contender)
While not doing a lot of test loads because this was the initial/1st/beginning tests with those bullet/powder combo's. I ran 20-shot strings in each firearm/bbl (used a dw 15-2 with the 4"/6"/8" bbl.'s).
In the 2 1/2" bbl the 2400 load outperformed the MP-300 & H110 by +/- 50fps and did 1200fps+ (I was looking for a 1200fps load in that 586)
In the 4" bbl.'s all 3 powders were about even doing 1300fps+
In the 6" bbl.'s the MP-300 & H100 started to pull ahead of the 2400 with the MP-300 & H110 doing 1450fps+
In the 8" bbl the MP-300 & H110 really started to shine doing 1510fps+
The contender did 1620fps+ with both the MP-300 & H110
I really couldn't tell much difference between the MP-300 & H110 loads, they were within 20fps of each other throughout the entire testing. I'm sure that a different bullet (1 of the 4 pictured above) would bring out the most with the MP-300 & H110 loads.
With careful bullet selection, excellent neck tension and heavy crimps I see no reason the op couldn't get in the +/- 1400fps range without too much effort. After that everything counts.