I've got a 10.3" factory Colt M5 CQC and a 11.5" Colt 6933 with MI Ultralightweight rail (ADCO shaved FSB).
Obviously, the 6933 is a little over 1" longer, but (similarly equipped) the CQC is actually about .5lb heavier.

Either one would be dedicated for a HD SBR. The other I would get rid of.

Which would you keep?



CQC in foreground
6933 on black stand (ignore bipod, used for range zeroing)
6720 in background

5.56?  
11.5" easy.  (12.5" would be mo betta)

Honestly, I'm the one guy in the room who prefers the 10.5 (or 10.3).   I will absolutely agree that the 11.5 is notably more performance, for just 1".  In my case, it's also just notably bulkier, even with that just 1".

At 11,000 rounds I wore out my 10.5" BBL and PSA warrentee replaced it for free.  Per my request, based on lots of folks input here, I asked for an 11.5", which they did.  (and by the way - just holy crap mad-props to PSA on all of that; barrel life durability, and the customer support - just wow).

I don't run supressed, and actually consider the flash-bang a feature (again, I'm the only guy in the room who thinks this way, so don't read too much into just my answers).  Because I have ear pro.  If I have time to grab a two handed weapon system, I have time to done electronic ear muffs.  Since I live in those 8 hrs a week, I can use them just fine.  Now if I shoot, whatever I shot it is FlashBanged, while I'm fine.

So Ok, anyway, back to size differences, here's my 10.5", vs the 11.5".   The 11.5 is just bigger and heavier.  Not ouchies, but it is.


vs 11.5






if the goal is performance, well - 17" beats 11.5" by quite a bit, and in a pckage that's even shorter




If I had to do it over again, I would have run the 10.5 again, despite the velocity and impact losses.  Personally.  

HD?  10.5”

I own and use both, plus 12.5”.  The additional barrel length isn’t buying you much at short ranges.

10.5” + 12.5”:
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11.5”:
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I have and use both, but if I could just keep one it would definitely be the 11.5.

Dedicated HD is as short as possible. In 5.56 that's 10.3" in my book. 11.5" will full length rail feels noticeably longer and heavier to me even if it isn't much difference on paper.

I think supressors make a big impact on the selection choice.  You can feel the difference in manuvering and handling a bare10.5 vs an 11.5.  That's how I run, and A2 FH dimensions are the maximum size dimensions I'll run as a muzzle device, if bare (which BCM Warfighter is).  But once you put a can on it, then now the system is 6" longer, with a big bulb of metal on the end.  So now it's the practical difference of a 16.5 vs a 17.5" system, and are you really going to notice that as being that much of a difference?  Probably not.  And those who run supressed tend to run 2-3" long bayonette looking flashhider things when "bare", which also will have the same effect even when "bare", since the % barrel length difference between 10.5 and 11.5 is less with that on the end of each.

If you are going supressed, I don't think it matters - since you're already running a 16" rifle length weapon system now anyway.

personally, If I'm willing to run 16" weapon system, I want 16" ballistics.  If I'm in an assault squad that needs coms and at risk of Flash-Banging each other on the team, THEN I will want a supressor.  JMHO, and this is fighting words I know, but to me, most civilian supressor usage is for convenience and comfort, more than tactical.  If I'm going short, its because I want the tactical capability of going short.  If I'm willing to go 16" total barrel length (+jewelry), then I want the ballistics from that first.  A 16" barrel system with the ballistics of a 10.5" BBL, is a trade-off I'm not making for comfort, when that same comfort is achieved with ear-pro and now I have the performance too.  It is a tradeoff that makes sense in military squad applications where your shots and actions affect the rest of the team in indoor encounters.  And can have impact on the other hundred badguys finding you in an open combat military engagement.  I'm not on an indoor assault team and don't engage with hundreds of dispersed enemy combatants.

Again though, I'm not the typical guy - most people won't give my answer on that, so discard that take as you will.

I prefer my 11.5” over my 10.5s.

More barrel isn’t a bad idea for 5.56.

My opinion is I don't really notice any size/weight/handling difference between them (suppressed or not) but the 11.5 runs smoother with the longer dwell time, is generally less high strung and doesn't beat up the suppressor quite as hard.  And obviously you get a bit more velocity.
My two points of reference are Geissele Super Duty 11.5 and DD MK18, so maybe it isn't straight apples to apples, but I feel like it's pretty close.

I have so many sizes it's funny. preferences for use in order: 11.5 , 12.5, 7.5, 10.3.

The 11.5 and 12.5 have so much gain for that extra little length. The 7.5 is next because if I am going short, Fuck it. Go short and take the hit for length. Then maybe the 10.3

If you really need to keep only one, then I'd say the 11.5".

This coming from a guy that loves 10"+ ARs.

Lots of good feedback. A couple of other data points...

-- Looking to fill a PDW gap (could become my HD weapon?)
-- I'm building a 10.3" A2. Wasn't intending this to be a HD weapon or PDW, but maybe???

PDW generally refers to a very compact weapon capable of being surreptitiously carried/concealed.  You could certainly do that with a 10.5”-11.5” AR, but I’d be looking at something smaller than that if your needs/requirements actually call for a true “PDW.”

Below 10.3 is absolutely 100% 300blk territory for me.
It is much better in every way at those lengths.

10.3 is noticeablely handier but the 11.5 is a better do it all rifle IMHO.

I have both, vastly prefer the 11.5, it is slightly better in every respect to the 10.3.

Why not keep both?

Keep both.  Get dedicated cans for each.  Use either.

I need to rationalize what I own. Getting rid of anything/everything that I don't have a hard need for.

One for each hand, Tom Cruise style?

But you're also considering building another 10.3" in A2 flavor?  

How would that be better than your first two 10.3" and 11.5" choices?

I'd say that the 10.3 in a Colt is going to be worth more, and have more sentimental value. If you're selling it for the money, that would fetch a better price, due to the whole MK18 craze.

I have a PSA 10.5, which I SBR'ed before free tax stamps became a thing. I did it for sentimental reasons, because of the whole pistol thing. But I like and trust that gun. IMO, the 10.3 is built more for duty than the 11.5. Heavier barrel, and you can get the cool guy stuff for it later and dress it out, which will make others here drool over your wish they owned it gun.

Realistically, keep the one that shoots better.

I would have kept the Colt M5 because it's a factory upper that would likely retain value better over time.

On the flipside perhaps thats a better reason to sell it.

In the end, this trumps most everything.  Heck, "keep the one you like better", is really the correct answer.  The day where you shake-fist-at-sky bemoaning you kept the wrong one of the two, is never going to come

Yeah, I'm in the middle of a few projects that I'll likely turn around and just sell.

Laws are not getting more lax to own scary assault rifles.

How's that one?

Valid point. You can always reconfigure them, but if another ban hits, starting a new one with be a pain in the ass and expensive.

I have a Colt 6945 that has the same issue as an M5, it has a proprietary barrel nut that needs a proprietary tool to remove the barrel. So, replacing a barrel on that upper will be more expensive and few places will be able to do it.

But I agree with everyone else, the Colt will hold its value.

I would not sell any if I were you. You never know if you will be able to re-purchase anything in the future.

Shoot both for accuracy and keep the more accurate one.

My take is this...

The 10.3" is a little bit handier due to length. That's it. Normally, one inch of barrel means about an ounce or so added to the gun. In this case, the 11.5" is lighter due to the 10.3" being heavy profile. And not by just an ounce or two.

The 11.5" has a smaller gas port and beats up the bolt a little less, it will be a tiny bit more reliable, it has a tiny bit less concussion, a tiny bit less recoil, it has more velocity for outdoor distances to keep the projectile in its performance window. Basically, it is just better in every single way but one.

You are more likely to screw up handling by getting too long or heavy of a suppressor... or too big of a stock to fit with body armor. Or to have too heavy or long of an optic. Or too heavy of LAM or weaponlight.

I have been reading this thread and avoiding commenting but I just do not understand all of OP's rational.  Why get rid of either?  Are you just not allowed to have stuff for fun or because you want?  I get that we all have a go to rifle in the event that the world is coming to an end but what fun is it if that is all you focus on?  The gun hobby is more than preparing 100% of the time for a scenario that more than likely will never come.  Have some fun and lighten up!  Buy some guns because they look cool or have no purpose other than they are fun to shoot or own.

That sounds like some communist thinking.

Been there; done that. Have a few t-shirts. Time for new hobbies.

Well this discussion took an unexpected turn. Hmmm.

don't know i can see the point of not having redundancy too much.  Anyways for me 11.5" ,  i have two but ones a Criterion with a MI ultralight the other a xm177ish with a older .625 spikes fn barrel. If i go any shorter I think i'll just build a .300 blk and go full steam.

You wanted justification to keep both...

I just rebarreled my only 10.3” to an 11.5”. It’s handy and it looks great with a can, but it just seems like it went through wear parts much more than any of my AR’s, plus it was still gassy even with a reduced size ‘crane spec’ gas port.

10” ARs just seem like a niche gun for when you need a compact PDW for within 100-150 yards, and a pistol cartridge isn’t enough.

Yup, I actually replaced my 10.5" 5.56 with 300blk (7.5", 8.3", 8.5", 9" and 10.5"), along with a 12.5" 5.56.

I’m a keep both kind of guy, but I would say go to the range and see how they shoot. Run various drills and try to have both guns set up the same as see which one you are better with. And after that roll through your house as the gun would be set up clearing it out looking for a burglar and see which one feels best.

I have a 10.5 (FN barrel) that has been flawless. Hell i've won local club matches with it. Doing it over, i would go 11.5.

I truly believe to go as short as you can and still make all the suppressor min bbl length requirements for warranty. Those numbers have changed since i built this SBR. Back then it was 10.3. With the jump in velocity, 11.5 would be nice.

Decided to part with the CQC. I'll hang with the 11.5" until I can source a SIG Rattler LT upper in 300BO.

The 6520 will scratch my itch for a 10.3" and retro at the same time.

Thanks for the discussion. Have a happy 4/20.

The price of 300 BO ammo is too high IMO. That keeps me away

Longer is always better. Ask any girl.

lol. Should have seen the commentary I generated about shifting to 5.7. Expensive AND unobtainable.

That's part of why I got rid of my Rock 5.7 & PS90