I was doing some pricing on two Colt carbines
today: MT6400C (with compensator and 1:7 twist) and the MT6731 (no comp and 1:9).  When I spoke to one of the dealers he made a comment about the addition of a compensator will make the rifle less accurate because "it throws off the round at the last minute".  Although I've never owned anything with a comp on it before I was under the impression that it made the rifle more accurate since it helped reduce muzzle flip.  It seems that if his statement were true, no one would want to use one, right?

I apologize of the second question has been beaten to death, but are the Colts perfectly happy being fed 5.56 even though the Colt website states .223?

I also understand that a 1:7 twist is made for heavier rounds and that the 55gr round may spin too fast and come apart or tumble.  Anyone have a 1:7 that can speak to this?

Thanks for helping a newbie.

Jeff

Other than internal case dimensions (which is only important to reloaders) there is no difference between the 223 and the 5.56. They are the same round. Military chambers are a bit different but the ammo is the same. Most colt recievers are marked 223 ont he reciever and 5.56 on the barrel. The round does not magically change during the feeding process.
PAT

I should have been more clear in the question.  I thought I read that the 5.56 rounds tend to have higher pressures than the 223 rounds and if the chamber isn't designed for these pressures, damage can occur.  That being the case, I wanted to make sure what I bought would handle both.

I'm not sure what you meant about magically
changing during the feeding process.

All Colts have 5.56 chambers and I shoot military surplus and commercial 55g bullets all the time in my 1/7 barrels without any problems.

You can shoot 5.56mm or .223 cal. through a Colt bbl.  5.56mm marked bbl.s are what you'll most likely run across!  Good luck!

Allow me to plagiarize Bushmaster.coms tech-support site. The overall physics’ of this scenario should be identical, and i believe you should find it very helpful.


"...In our experience, the most accurate muzzle is the post-ban crowned muzzle. Many competition and target shooters we have talked with confirm this. As the bullet leaves the muzzle, you want - for greatest accuracy - to have no alteration of, or influence on, the bullet's flight. With an 11 degree
competition crown, the gases behind the bullet flow out in an even pattern of dispersal at the instant that bullet exits the barrel. This affords the least chance of disrupting that bullet path..."



"...We have tested our brake on post-ban and pre-pan barrels to see what, if any, effect they have on accuracy - it does not affect accuracy to a great degree. When you send a bullet out of the barrel and then through a muzzle brake, you are influencing it with gas pressures from various directions (depending on the type of brake). These gas pressures can alter the flight of the bullet - and therefore its destination accuracy. Granted, we're splitting hairs here as the time spent by the bullet in the muzzle brake can only be measured in nanoseconds, and the amount of force exerted by gas pressures would be difficult to measure at all. But, these gas pressures do exist, as the purpose of a brake is to alter the flow of the gases and to use the energy of that redirected gas flow to control muzzle rise. This becomes an important consideration to an L.E. Officer when that 2nd shot may be the one that saves his life - and, the amount of accuracy lost to the muzzle brake may well be inconsequential at the distances involved in a firefight with a bad guy. However, at the distances a tactical team sniper or a competition target shooter is concerned with, the loss of any amount of accuracy may be the difference between success or failure. It comes down to a question of choice based upon intended usage of the rifle.
An AK Brake will add 2.25" to your overall length - it has no effect on bullet velocity. We also make a 5.5" version of this brake for use on our 11.5" barrel - to reach a total legal length of 16". We also have some new brakes  - called the Y Comp and the Mini Y Comp - that are very well designed...."