There’s a very good article in the new issue of Combat Arms on the new KMR uppers. It included a picture of the stripped ELW barrels as well. It stated a 0.625 oz. weight savings on a 14.5 barrel. An interesting note, it also discussed the Mod1 comp and described it as having an expansion chamber that improved reliability of the 14.5 midlength barrel. I had not heard that before. Overall, it’s a good article. The issue had some of the best written articles I’ve seen in a print magazine in a long time.
What does that even mean?
The article indicated that the Mod1 comp had a small chamber in the rear of the device, whose purpose was to increase reliability by affecting how gasses escape from the barrel. It essentially said that the small expansion chamber increased the dwell time of the barrel.
You are correct. Any enclosed chamber is in some respects an expansion chamber. Some comps and/or flashhiders are better then others. The Mod1 has a very small chamber, but it still tricks the weapon into thinking it has an inch longer barrel (after the gas port) than it does… Any increased dwell time is a benefit, especially for a 14.5" middy.
Thanks ESK. Is that feature found on both comps or just the Mod1?
Interesting. I did about 10 rounds with the A5 H4 buffer on the 14.5 middy I’m running an to my surprise, it cycled just fine.
I’m running the A5H2, Springco Green and LMT enhanced carrier. The he only issue I’ve had was with a few rounds of Tula, which was to be expected and is an ammo issue. The only failure was a failure to lock on empty. Same results with a standard BCM carrier. I’m undecided about the E carrier in the 14.5 midlength.
Just the Mod1 and the 762 Comp.
Looks like just the Mod1. I’m going to add one of these to my other 14.5 middy at some point.
A5H4 in my BCM 14.5" middy w/ Sprinco green… zero issues.
All I ever shoot is bulk xm193 though.
I’d love to pop the H4 back in and run the ELW on a full auto lower.
Like I’ve said in the past, my 14.5" BCM (with a Mod 1 comp) is by far my nicest shooting AR in my collection. I can’t even get myself to install an A5 on it because it shoots so well with just a standard spring & H2 buffer.
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That was my logic for using a Troy Claymore on my 10.5". After reading the BCM thread stating a 40% dwell increase for 11.5", I figured mine should gain a significant amount. Just a guess on my part as I understand the physics involved about as well as I do women.
Rogtac has a pretty nice 13.0 KMR package deal with BCG, Upper, and CH.
I was just about to post this same thing. There is something about my 14.5 middy with Mod 1, standard H2 and BCG. It is bar none my smoothest shooter and I’ve yet to have any hiccups from any specific type of ammo. Initially I didn’t expect the H2 to work in the system like it does but it hasn’t come out since I put it in. It is very comparable in hand to my 16 middy with A5H2 (which i’ll be trying a -3 on in the near future) but I still prefer the shooting characteristics of the 14.5 to it. Never really knew why, understand it a little better now. Dumb luck on my part.
On a related, yet still-off-topic note, I wonder if this is part of the reason that many brakes like the BC, AFAB mini, GA Flash Comp II, MAMS, etc. all have been reported as having a sharper recoil impulse? Possibly due to increased rearward BCG velocity from the added dwell time and gas volume afforded by what is apparently tantamount to an expansion chamber in each of these devices?
Yep, you are correct. Some of those mentioned comps have excessive expansion chambers, which trick the weapon into thinking it has a 2", 3" and 4+" longer barrel after the gas port. That’s the beauty about the AR platform, at least we can balance it out by adding more reciprocating mass, i.e. the A5 buffer system.
Thank you for replying. That’s very interesting.
How do you know what constitutes a properly sized expansion chamber for a given barrel length, gas port location/size, and ammo pressure range?
I’d assume that the size of the chamber (diameter and length), the shape, and the number/surface area of the exit holes would play a role in this calculation?
As I see it, you kinda have to work around what’s offered to you, meaning the barrels are a set specifications from the manufacturer. It’s not to often we can have a barrel made to our specifications. So, I usually work with what I have. There are many of time I’ve chopped barrels down, because A) the gas port is too big and B) there’s too much barrel after the gas port. I only install a expansion chamber type Comp/FH when the barrel is to short after the gas port. I like to run just FHs or non-expansion chambers Comps when running a proper length barrel. My biggest pet peeve with ventilated expansion chambers is the occasional fireball they produce every few rounds. I like my flash (or lack there of) as consistent as possible. The rest of the formula is working on adding or subtracting reciprocating mass, keeping it balanced around ammunition types.
Where in the hell are the rail covers??? GH