11.5" Carbine vs. 12.5" Mid-length Unsuppressed

[PrivateCitizen]

For what it's worth I tried this before it was derailed by a vendor pushing his own wares …

https://www.m4carbine.net/showthread...put&highlight=

The gist seemed to be the 12.5 mid is pretty mild shooter once dialed in and, in the realm of compromises, doesn't give up too much in any particular direction. Longer and handling/weight start to be a con, shorter and recoil/gas become areas of concern.

I have one now, a Faxon 12.5 I got on trade, and it is not my favorite. My intent was to step into the Centurion, but …

Honestly, my only dig on the 12.5 overall as a platform is none of *my* preferred handguard makers (BCM, KAC, Geissele, DD) have an optimal length (11.5 ish) … I like it as far out as it can go.

My dilemma came to an impasse and I ordered a Sionics 111.5 RGP as suppressed was a high factor and it should be here this week… The Centurion mid will be my next and I'll probably put a Larue LAT 11" or URX4 10.75" on it (or not as there was a ton of gushing over the Sionics and maybe it will be my Nirvana).

TLDR; Suppressed 11.5, Un-suppressed 12.5. YMMV.

[themonk]

For a do all rifle I would do 12.5 but with carbine gas. If it must be between a 12.5 mid length gas I would the 11.5 route.

[Steve-0-]

12.5" middies need jenna sized ports to run as smooth and reliably as a good 11.5" carbine. Go 11.5" and dont look back unless you want a Kino config which isnt really a middy.

[sdacbob]

Here is a good comparison done by Garand Thumb. Pretty interesting! https://www.youtube.com/watch?v=Mxwi9fAe4s8

[prepare]

Here is a good comparison done by Garand Thumb. Pretty interesting! https://www.youtube.com/watch?v=Mxwi9fAe4s8

I think this is pretty solid.

[titsonritz]

Here is a good comparison done by Garand Thumb. Pretty interesting! https://www.youtube.com/watch?v=Mxwi9fAe4s8

He's talking about a 12.5" carbine upper rather than a middy. Good basic info though.

[Clint]

Finally found the reference to a very good previous discussion on the 12.5" MID configuration.
https://www.m4carbine.net/showthread...arrel-Feedback

Here are a couple highlights from some very experienced members.

I would tend not to use a mid length gas 5.56 11.5" without a can, but it would need dedicated porting for that.
To get one to run fairly reliably without a can, you're talking about a fairly large gas port.
If you add a can to that large port, you are aggressively over gassed, more than what you can control easily with buffer swaps.
The port size for dedicated suppressed is much smaller, there really isn't any overlap between the two.
If you are setting it up for use without a can only, you can run into issues much faster in cyclic rate than with a more conventional carbine length gas system.
Just seems to add too many issues for my taste unless it's suppressed only with dedicated porting for that.

The 12.5" mid length gas 5.56 fares only a little better than its 11.5" counterpart, still not really a good place to be for function.
You really don't begin to get into an good overlap in function until you stretch out the barrel to about 13.5" for the mid gas.
With a 13.5" 5.56 mid length gas with proper porting, you can handle a can well with a simple buffer swap.
I have not yet found an existing 13.5" mid gas barrel with porting that I prefer.
To get them where I want them, I normally just cut down a longer barrel, like a 16" mid length gas barrel.

It will have to be ported aggressively to run without a can and likely over gassed worse than a carbine gas 12.5".

I would question the OP as to what gain you think possible with a midlength gas system on a 12.5", as opposed to a carbine length system?
There are a bunch of companies making things because items are different, but not always because there is a gain or improvement.
I'm not going to cry about it, and I understand the concept of lengthening the tube to smooth things out overall, but I know that my 12.5s use a carbine gas system, and will continue to do so.

[BoringGuy45]

The 12.5" barrel is, in my opinion, the best overall length and it should become the standard. I don't know why it's still a bit of a unicorn. It's a great compromise of the maneuverability of the 11.5 and the velocity of the 14.5.

[1168]

The 12.5" barrel is, in my opinion, the best overall length and it should become the standard. I don't know why it's still a bit of a unicorn.

I’ve actually put a lot of thought into this over the years. I think the reason has to do with the legacy handguard lengths.

10.x” barrels are popular because of the MK18, being the shortest you can go with a FSB, and stayed popular because its the shortest barrel that will work with a free float ~9” “midlength”.

But, people have had mixed experience with reliability with 10.5” barrels. And we’re really getting into the margins of terminal performance here. BCM, Colt, KAC, and Sionics had the half century old cure: just a little longer. 11.5”. Since this is the shortest barrel length that can function properly with a wide range of ammo and a reasonable gas port, it has exploded in popularity, alongside pistol braces. Therefore, everybody and their brother makes 10”-10.75” handguards, so the 11.5” is pretty much locked in as a popular and widely available option.

13.5-13.7” developed a cult following because its as short as you can go with a rifle length free float, and retains good velocity also. Because rifle length free floats aren’t going away, 13.x” barrels also won’t go away.

14.5” is popular due to .mil association, and pin/weld reasons. So, of course, when the handguard all the way to the muzzle fad came along, everyone made ~13” rails for the 14.5” barrels. The legacy 12.25” rifle length handguards work well, also.

16” is super common due to NFA, so 14.5-15” handguards became widely available at the same time the handguard-to-muzzle and c-clamp hold fad hit the interwebz.

TL;DR? The 12.3 and 12.5 barrels exist in a nether region between 11.5 and 13.5, despite being an awesome barrel length that is compact, but compromises very little in velocity. Most handguards suitable for the 12.5” barrels are really made for 11.5” guns, but they work just fine. I’ve got one in a KAC 10.75 URX4 and another in a SLR 11.7.

[JediGuy]

I was disappointed when ALG discontinued their 12” handguards. I missed out on buying one on clearance. Seemed like the perfect length for a 12.5” barrel.