Quoted: It's probably something about CAR SP-1's not being all that common. As in, why cut up a collectable, when other barrels/uppers are so readily available. As for shortening a 16" barrel to 11.5", you take a significant loss in velocity and therefore lethality. I think Tweak was just asking why you would want such a short barrel. A CAR SP-1 is not exactly your first choice for a duty gun, so we would all make an asumption you just want to do that because 'chicks dig it' (CDI factor) The Noveske Krink is 3" long without the locking ring that holds the baffle. If you are thinking to permenant attach it to get to 16", your barrel needs to be at least 13.7" long. If you have an SBR stamp, then 11.5" is fine and certainly has CDI factor with a Krink hanging off the front. As mentioned further up in the topic, the Krink will certainly help reliability with an 11.5" barrel.

Thanks for your comments,Randall.
You make a good point about my barrels "collectability". My first thought was it would be much cheaper to have my barrel shortened rather than spend a bunch more money for something new. My ignorance is no excuse. I'll try to read more before asking questions,next time.
I just want the shorter,more portable OAL that the 11.5" unit allows. Even if it had something to do with the CDI factor,as others call it,so what. I've owned the gun for almost twenty five years and it'll probably be buried with me. Not to be a smartass but it's my funds and I'll spend them how I see fit. FWIW,there is no such thing as the perfect AR.
If I do decide on a 11.5" barrel,I'll do the paperwork and then build a SBR.

No,I'm not a LEO,,just a civilian rifleman. My AR just fits a niche in my armory as I own other .30 and .50 caliber ordnance.
Clint

You may want to checkout this Thread of mine:

Gone Shooting an 11½ Inch Upper

My groups were very near that of my 20 inch upper.
There were no malfunctions of any kind.

Quoted: You may want to checkout this Thread of mine: Gone Shooting an 11½ Inch Upper My groups were very near that of my 20 inch upper. There were no malfunctions of any kind.

At our 50-100 yard range, they make all "muzzle braked" rifles sit on the far left.

Ooops, my AK will throw brass 4-6 benches down. Oh well.

And for the guys who start complaining, I'll put away my AR, and bust out the "fireball" Mosin Nagant right next to them.

But then, I'm a prick.

Va_Dinger:
When the 223 and AR15 were developped, the barrel length and powder matched for a full burn - perhaps an optimum burn.
Where as longer barrels give some increase in speed, a too long barrel has the opposite effect. Shorter barrels don't provide enough length for a "full burn" inside the barrel.
My question was: if we went to 30 - 40gr bullets (and changed the load), wouldn't we be able to have a better performing 10 1/2" - 11 1/2" barrel system with also higher bullet speed as opposed to 55-62gr.

Tweak:
Assuming constant material construction, a heavier bullet would be longer.. is that you reason?
What I am thinking of is lighter bullets, slower twist in a shorter barrel. The velocity is the main interest in my case, not necessarily the overall leathality.

Quoted: instantaneous velocity doesn't matter as long as it imparts enough energy to the bullet to it to be effective. the heavier bullets do better out of short barrels due to their connstruction not their V.

In your opinion,what bullet or load would you consider an optimum in a 11.5" barrel w/ 1/9 twist?

I picked up a M16A1 large-pin upper with 11.5" M4 barrel w/ 1/9 twist that I'm going to use,instead of messing with my SP-1 Carbine upper.

twist is immaterial to lethality - I think effective bullet stabilization and their status and effect upon impact is a long discussion.
My only point is to have a short barrel to shoot lighter bullets reliably on a target - nothing else. Sorry if I lead anybody down the wrong discussion path.

My wife uses an 11.5" Bushmaster barreled upper on her M16.  We have both put around 5,000 rounds through the upper with and without a silencer attached.  

During the initial 100 rounds fired we had numerous failures to extract.  After replacing the standard weight buffer in the VLTOR stock with an LMT H buffer and adding a Colt extra power extractor spring we have had nearly no other failures.  The few failures to extract since I added the H buffer and Colt extractor spring occurred when we were firing Wolf ammunition.

I would also like to mention that her Bushmaster 11.5", 1-7" twist barrel is around 1.5 - 2" capable at 100 yards.  I have been very pleased with this barrels performance.

Tweak:
What would you use for buffer weight for the following scenario:
11.5" Barrel
14:1 or 15:1 twist
223 - 30gr or 40gr Berger MEP ammo (3600fps - 3900fps) from Reeds Ammunition.
Would you change the gas port hole? Change the gas tube?
Thanks