What are the advantages/disadvantages of the mid-length uppers vs the M4 uppers??? I am trying to decide between the BCM Middy and M4. I already have an M4 and need a backup rifle for training. I am reading up on this, but I always find such expert opinions here.
Thanks.
someone hasn’t been eating his technical stickies…
midlengths extend the gas system. the longer the “dwell time,” or length of time the projectile stays in the barrel after passing the gas port, the harder the weapon will cycle. the carbine system was designed for SBR barrels- 10.5-14.5"- not 16", which is really way too long for it. so the “mid-length” system moves the gas port out farther, reducing dwell time. smooths recoil, less rough on the gun.
Thank you BKB, I never understtod it clearly. From reading your post and a post last week… I became enlightened. Now I am beginning to understand the concept of timing, or time before the gas port that all pressure is for bullet pushing and time after the gas port that still pushes the bullet but splits into the DI chamber as well.
So when you buy an AR-15 “carbine”, is it a true carbine system, or do some companies use that as a catch phrase to sale the rifle? Now I want to learn what the different gas tube sizes are so I can see how long mine are and determine what ones are carbines versus mids versus rifle.
technically, mids are carbines too. Anything shorter than a full length rifle= carbine.
i think literally speaking, “carbine” means any weapon shorter than 20", since the original ar15 was 20. carbine just means short rifle. but the original short version of the ar15/m16 was the 14.5, so that became THE carbine version of the platform. since the 7.5" gas system was designed for the “carbine (14.5),” any 7.5 gas system- regardless of the length of the barrel it’s on- is refered to a carbine gas.
There are a lot of terms used for the different versions of the platform… CQB for 10.5, carbine for 14.5, and then there’s specialized weapons like Recces and SPRs that are 16 and 18" respectively, but not all 16 and 18" weapons are Recces or SPRs… further confusing the mix.
Furthermore, in addition to carbine, middy, and rifle length gas systems, there’s the “intermediate” gas system, as used by a couple of manufacturers- noveske and, IIRC, KAC, used for SPRs.
Just remember that “carbine” is for weapons 10.5-14.5, middy is for 14.5-16.1, intermediate is for 18", and rifle is for 20"+
I found this:
Standard rifle gas system is with the gas port located at 13.0" and having a 20" barrel… the standard carbine system is with the port at 7.5" and a barrel of 14.5"
This is a very small SNIP of a huge tech read that went buzzing directly over my head, it was located at the TheHighRoad.org here:
http://www.thehighroad.org/showthread.php?t=199626
That is getting into some deep shit right there fellows. Albert E. would understand that… not Larry M.
Also there is the advantage of a longer handguard (without the use of a rail) for those who shoot with their off hand around the handguard. When using irons you have a longer sight radius.
-I bought one last week (middy from Grant). It does shoot smoother than my CAR gas systems.
Thanks for bringing this up. All these middys are making my change my direction of my build. I’m not ready to build a SBR right now. The middy sounds like it will not beat up the rifle as much.
not to seem like a condescending or pompous assjack- but this is pretty basic stuff. i didn’t read the whole thread, but there’s a little unfounded speculation and outright falseness going on in that thread, as well.
If I understand the progression correctly, the carbine length gas system was originally designed for an approx. 11" barrel, but was then (also) subsequently “applied” to an almost 15" bbl … perhaps without much thought being given to the pairing.
And although the bugs have essentially been worked out of that combo at this point, it seems that that wasn’t necessarily the case in the beginning.
IMHO, the 14.5" bbl./carbine gas system is technically a mis-match, and a 16" bbl./carbine gas system is an even worse mis-match.
However, according to some industry professionals, the midlength gas system provides an excellent solution for a 16" bbl, and I believe there are others would also argue that the MLGS is actually a better system (i.e. a more appropriate match) for a 14.5" bbl vs. a carbine length system.
One difference is a standard CAR 16" CVM barrel is relatively easy to find.
A CVM 14.5 or 16" CVM Mid length, not so much.
There seems to be a trend toward SS, which I am unsure is a good thing.
Eh? there’s a lot of 14.5 CMV barrels… LMT, BCM, Colt, Sabre, Noveske, CMMG, AFM, to name a few off the top of my head.
SS has definately come into it’s own- but they’re certainly not taking over or anything. the only main-streamed SS 14.5 i can think of is NRW’s
I should have said one in stock.
+1 I have been looking for a mid length and can’t find much other than ss.
I understand the concept of the gas port (carbine length) being designed for a specific barrel length/dwell time, and how the 14.5/16" lengths cause more pressure back into the receiver, increasing wear. Anyone have any experience as to how much, or is it a fairly subjective thing? For instance, should you replace the action spring sooner, wear on the bolt, etc? And would a heavier buffer and/or action spring help dampen some of the energy and extra wear? I have a MGI rate reducing buffer in both of my AR’s (14.5" carbine length gas sytems). They have both been very reliable and the buffer smooths them out without a doubt. Help and advice would be appreciated as I am thinking about putting a 16" carbine lengthupper on one of them.
the middy system is the new system, so any existing PM schedule is gonna be based on a carbine system. therefor, “sooner,” doesn’t really apply. the heavier the buffer, the slower the action, the lighter the carrier bangs around inside the receiver, but i don’t think the spring is going to be effected. i dont think the speed at which a spring compresses has any effect on spring set. once the spring bottoms out, it cant go any further. i cant even really see wear against the receiver extension changing.
Grant has BCM middies in stock, at least he did when he shipped mine off today. Now my BCM carbine upper needs a home …
Just less bolt lug breakage then? Maybe better extraction since some say that the extractor O-ring is not really required on the middy’s?
That makes sense on the spring, thanks for the reply. I guess I was wondering what you meant by “less rough on the gun”. Is it a wear issue or just recoil?
middys are definately easier on bolt assemblies