Sounds like we are all in the same ballpark to me Ironmaker. Good stuff.
The info I was able to find showed a 50 to 80 fps difference between the two Short versions but I can believe as much as 100.
Yes... I think all the numbers throwing around certain are reasonable "worst case" figures. The reason I settled on the 150 and 200 is from several articles where they actually cronographed them. But I am sure the numbers of 200-300 could occur.
If you look around at some bullets you will see numbers listed like 150 grain going about 3000 FPS (in some particular load) so if you use my averaged numbers you could assume the Scout at like 2850 and the SOCOM at 2800 or using some other numbers posted here then perhaps 2850 and 2750...
It does appear that with both of these shorter variations it would be wise to chose a bullet around that size. Because the muzzle velocity of a 180 grain bullet (just for comparisons sake) is going to be down in the 2600 or 2700 fps out of the long barrel versions already.
But ya know... 2700 FPS out of a short barrel is pretty darn good when you compare it to some other rounds. But not terrific real extra long range good. But darn good enough for most things up to 300 yards.
I saw somewhere where someone did some testing that tried to determine when the muzzle velocity would finally DROP in a barrel due to length. And they came out with something like 30 FEET!
Also saw this posted on FireingLine one time
The Hornady Labs list an approximate variation in bullet velocity based on their experimentation. For bullets traveling in the range of 2000-4000 fps, the velocity will vary from 10-40 fps per inch of barrel, respectively (Hornady Handbook, 3rd Edition, page 401).
The Springfield Armory tests showed the 30'06 ball to range from 2709 fps in a 24" bbl to 2848 in a 32" bbl. Another Springfield Armory test indicated an *average* (5-shots) drop of 83 fps when shortening the bbl from 26" to 24" (Hatcher's Notebook, 3rd Edition, pages 399-400).
You may be hard pressed to get relevant data, short of measuring the differences between two or more rifles of the same make & model, but of varying barrel length. Bullet weights and powder burn rates may also be significant factors in this determination, especially if reloads.
If you use good commercial or MILSPEC ammo, I don't believe you will find the differences between the 20" and 16" bbl significant enough to cause you worry about trajectory drop or kinetic energy retention within practical employment ranges.
However I do think you will find a concern over 300 yards though...