People have been shooting XP100s and Contenders in .223 with 10,12, and 14 inch barrels for years. Perhaps they know something about how to get good velocities from short barrles with reduced muzzle flash.

For one thing, they use magnum handgun powders like Blue Dot, Reloader7 and 12 ect. Maybe this is a key to getting the 11.5 and 14.5 inch guns to deliver good performance.

I know that with short barrels the .222 does well, compared to the .223. Not necessarily better, but it is more efficient. Might be something there too.

Be careful with using Blue Dot in .223.  There aren't too many loads out there that use this powder.  

I have used it.  4.0 grains at a time, to get a 35 grain bullet to about 1300 fps.  The inspiration for this endeavor was from a man searching for a low noise ground hog cartridge.  IIRC, ([url]www.jamescalhoon.com/tobee2.html[/url] Link doesn't work at this time) the max was about 11 or 12 grains, and the bullet (author used 40's) was moving in the range of a 22 Hornet.

Using a rifle sized charge of Blue Dot in a .223 Rem will probably destroy it.

Nope.  No real secrets there.  Handgun hunters are just used to lower velocities in general.  So even with the velocity lost in a short barrel they still think their .223 loads are very speedy.

The powders they use are the same ones you use in your rifle.  Never heard of a hunter being too concerned about their muzzle flash.  (You only get one shot, usually.)

The key to high velocity is the area under the pressure curve.  The longer the pressure is maintained at a high level the faster the bullet goes.  The problem with pistol powders is they burn "fast" and pressures peak fast but do not have the volume of gas (due to the lighter charge required to keep from going over pressure) to maintain that pressure level for long.  Rifle powders burn "slow", you can use more powder to create more gas volume because the volume is being created more slowly (per gain of powder used).  Thus, higher pressure is maintained until the bullet exits the muzzle (harder push on the back of the bullet = faster bullet).  Higher pressures at the muzzle equal a bigger boom (more muzzle flash too, maybe?).

So even though the barrel gets shorter you should not increase the burning rate of the powder unless you are trying to quiet the gun down, because doing so is counter productive if you are looking for velocity.

Kent

BTW: Reloader-7 & 12 are rifle powders. 7 is a medium burn rate I've used in my 30-30 and 12 is a bit slower yet.

Actually, Reloader 7 and 12 are rifle powders, not handgun powders.  I've never used Blue Dot in .223, nor would I ever unless I were using lead bullets for reduced loads.  I only load my 14" .223 Contender barrel with rifle powders.

I've actually had reasonably good luck with H322 as far as keeping muzzle flash down in my 14" .223 Contender Barrel, but I can't say how it would do in an AR of any flavor.  

4.0 grains of Blue Dot behind a Hornady 35-40 grain V-Max makes a great low noise/no recoil loading.  As I mentioned before, this is WAY below the limit, and the load doesn't cycle the bolt at all.

I use it for popping bunnies in the garden and quieting down the bluejays.  It isn't loud either.  I still wear ears cause the POP is a little louder then a .22 LR.

It is nice though for shooting out of a window, because the pressure wave won't rattle the house or hurt the ears of occupants.

H322 works great in ar-15s with 20 inch barrels.

I have never tried a shorter length ar-15.

I have a xp-100 with a 14 inch barrel in .223. I would say that H-4895 produces the largest ball of fire.

I don't fault anyone who does use Blue Dot in the applications you suggest, I'm just not going to do it.  I'm very much into fitting the gun/cartridge to the job at hand, even though I mostly shoot paper.

For reducing flash, here's my theory.  The shorter the barrel, the faster the powder you need.  If you've got a longer barrel, more powder will burn in the barrel rather than out past the end of it, even with slower powders.  

.223/5.56x45 is already restricted to relatively fast powders, but even then, a faster powder within the .223 burn range will give less flash than a slower powder.  

H/IMR-4198 is probably the fastest powder that you'll find any quantity of loading data for in .223 Rem.  It's a great powder for the .222, epspecially in a 14" barrel.  I'd say anything between 4198 and H-322 ought to do it.  AA2230 starts to give a little too much flash for me and anything slower than that would be worse.