Definitely get the cutout. Imperceptible weight gain is far outweighed by the benefits of having more rail to work with grip and accessories.
Ghetto comparison of a 7" vs cutout
Are these rails easily user installed or is a gunsmith required? Does one need to take off the front sight off?
I believe you do have to cut off the delta ring. Which you can do.
That and cut off/rip off/remove the handguard cap. A pair of vise grips and a Dremel worked for me.
OK, just installed a pair of Centurion C4 Carbine Cutout rails I ordered last week on a pair of Colt LE6920’s
This was a number of “gunsmithing” firsts for me…
1st time removing a factory flash suppressor. No problems here. I used a vise takedown block
http://www.amazon.com/Aluminum-Upper-Receiver-Takedown-Block/dp/B006QMYVLK/ref=sr_1_5?ie=UTF8&qid=1327803829&sr=8-5
clamped in a Rockwell Jaw Horse and the flash suppressor broke loose without a huge amout of effort.
Next came removing the tapered pins in the front site post. This was a little more tricky. Brownell’s is sold out of the pin blocks for front site posts. I cut out some pieces of 1x4 pine and put the barrel in the gap between two pieces to get a solid support to hammer the pins.
I took the advice I read on a forum to use a FLAT steel punch about 2x the diameter of the pins and a 16oz brass hammer. Had to pop them a few times but they came out without much problem. Once you hammer the pin flush with the surface of the front site post (the pins stick out maybr 1/64 of an inch then switch to a small nail punch and the pins will practically will fall out. They are not like roll pins where you have to hammer them all the way through. The hard part with the tapered pins is getting them to move the first little bit.
On my LE6920 I had to hit the pins on side opposite the ejection port.
If you aim the rifle that would be the left side. If you are looking into the muzzle it would be the right side. I used a micrometer to verify which side the smaller end of the pins was on. You want to hammer on the smaller end.
Once the pins were out, the front sight post slid off the barrel without any hammering as the the metal piece that the handguard snaps into.
The gas tube slides out as you slide the front site post off, no need to remove the gas tube from the front sight post.
As this point I was felling pretty good and figured what mess with cutting off the delta ring when I can just break barrel nut loose, take the delta ring off, and put the nut back on.
I had bought a really heavy duty barrel nut wrench from Spike’s. It’s one of those that you put on the end of a 1/2" drive ratchet.
With the upper clamped to the vise takedown block which was clamped in my Jaw Horse I attempted to break the barrel but loose. No go. I put as much pressure on it as I felt I could without fear of ripping the pin posts off that were holding the upper to the vise block.
I think you would have to have one of the plastic clam shell things that allows you to clamp the upper into a vise to get the barrel nut off.
So I broke out the dremel and a small cutting wheel and cut through the left and right side of the delta ring and then put a screwdriver in the cut and twisted and the delta ring popped right off.
The spring was easy. Just grab it with some needle nose vise grips and tear it off. The spring is somewhat brittle and breaks easy.
The snap ring was a little more trouble. It’s too thick to just break and if you try and wring it off over the barrel nut it will scratch you barrel nut all up if you care. Easy way it to use the dremmel and cut it about 1/2 way through then it will break easy and fall off.
Putting the Centurion rails on after that only took a few minutes.
So how do I like the C4 Carbine cutouts?
Very well made and the rail locks up to the barrel nut very tightly. The hex nuts on the C4 and larger and MUCH easier to tighten than the tiny little hex screws on the Omega rails I had on.
That said, I’m still not sure I made the right choice with the C4 Carbine cutout instead of the C4 7".
My goal has been to build a M4 that was lite as possible while still being accurate. The 2 extra oz. in the C4 Carbine cutout compared to the C4 7" is already bugging me.
I’ve been so anal on weight that I actually went with the aimpoint comp ML3 instead of the newer ML4 just to save a few oz.
The ML3 is 7.8oz compared to 9.3oz for the ML4. There’s also the difference in the AA battery (.5 oz) in the ML4 and the button battery in the ML3 (.01 oz).
I’m probably going to go ahead and order the C4 7" and EBAY the C4 Carbine cutouts. I don’t plan on attaching anything to the rail. The only reason for the rail is for the Free Float.
I’ll trade ya:D
I don’t THINK you have to remove the front sight to install the C4 cut out rail.
You don’t. If you’re even a little skilled with a tin snips you can get the handguard cap off without a problem. Obviously mind the gas tube.
I just installed a c4 12" FSP on my 6920. Instead of taking the FH off, I removed the taper pins from the FSB, removed the gas tube, dremeled the delta ring and springs off, and used snips for the handguard cap- -a pretty easy install for a first timer such as myself.
Here’s a pic:
I’d like the personally thank you for putting me out the cost of one C4FSP rail - that is pretty!
Without question, that is the first time I’ve ever heard anyone mention scratching a barrel nut as a concern. 
Stick that pic is amazing, is that a 10.5" or 11.5" barrel
Stick’s is 10.5"…
Mine is 11.5" for comparison…
thanks for the reference pics
so why don’t you carry his rails and other products?..
Do they sell their stuff at any [online] retail stores?
Sounds like Bravo Company just picked them up as well.
Stickman, I can’t tell for certain due to the angle of your pictures, but on your 10.5" can you tell if the rails on the side would interfere with an AAC 51t Brake and the mounting of a M4-2k?