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87K views 46 replies 27 participants last post by  BugOutDude 
#1 ·
While researching the purchase of a new AR-15, I came across several forum topics on the M4 Carbine VS midlength debate.

It seems that the midlength rifle is a little more reliable then the M4, mainly due to pressures in gas system.

The question I have, in most of the debates people keep using the word "slightly". How much is slightly? Is a midlength 20% more reliable then the M4 gas system, 10% more reliable, 5% more reliable, 2% more reliable, .005% more reliable,,,,?

Surely there has been some kind of government, FBI or military study that shows the difference between the M4 and midlength systems?

The reason I am asking, I am down to the final line on a new AR purchase. At this time I am looking at a Spikes ST-15 midlength, or the M4 version. I like the looks of the M4 version, but I also want a full length 16 inch barrel + flash hider, and not a 14.5 inch barrel + flash hider.

It seems to me that some people try to break the AR15 into a science (correct me if I am wrong). I just want a rifle that works, and is compact enough to carry in my truck, in my boat, or on an ATV.

On the rifle I am hoping to add a Magul MOE grip + surefire tactical light. It seems to me that the M4 version would be easier to operate with everything so compact and close together.

I would like to hear from people who have combat experience with either the midlength of M4 versions. Which version do you prefer and why?

The intended purpose of the rifle is for home / property protection.

This is my Bushmaster Xm15 that was made during the assault rifle ban. I am leaning towards another M4 version so the parts can interchange easier.



 
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#3 ·
Both systems function reliably for me, don't have any percentages. The carbine system is a little harsher in function, nothing you couldn't cure with a heavier buffer if need be. The middie system probably saves a little wear and tear on the gun, but I doubt it is any real savings over the usable life of the weapon. I personally prefer the middie system, just personal opinion.
 
#4 ·
I would go with the collaspable stock. I had one on my M4 in the army and mine never jammed. That way you can adjust the stock into the postion that is most comfortable to you. If you are shooting in tight spaces, then you can collaspe it, or if you like the extended stock you can extend it. I prefer flexibility. For reliability I honestly dont know how it affects.
 
#5 ·
Kev,

You won't go wrong with an ST-15 (if you can find one in stock) There is a long wait period if you buy from Spikes website. They are backordered.

I own an ST-15 Mid-Length carbine. The biggest difference I can tell between a midlength vs a carbine length is the middy has smoother, softer recoil. The middy will be a bit heavier than the carbine length.

As you stated (in theory) the middy has higher longevity due to the length of the gas sytem. Not sure that there has ever been any actual testing to verify this but it makes sense to me. It will run cooler but when you are shooting 100's of rounds it's not really going to matter. Both guns are going to heat up.
 
#6 ·
my m4 has never jammed but then i've not submerged it in mud and !@#%ed in it either.

so can't say what it would do under those circumstances.

however a middy will be slightly heavier, but due to the weight will reduce muzzle rise and perceived recoil
 
#8 ·
however a middy will be slightly heavier, but due to the weight will reduce muzzle rise and perceived recoil
Why because it has 2 inches more of gas tube? Identically configured guns; one carbine gas and one a middy; and there will be virtually no weight difference. Now if they have different things on them (rail, stock, optics) then different story.


OP. I don't have actually figures in front of me but here's a small comparison. One AR is a DD, full 12 in Omega X rail, heavy ass ACS stock, gov't provile 16in barrel with carbine gas system. With optic and loaded mag it comes in at around 9-9 1/2 lbs. Second is a BCM with a 16in pencil barrel with middy gas, moe handguard, ctr stock. It's the lightweight training gun and with optics and mag probably comes it at 7 1/2 lbs. The heavier DD gun should absorb more of the recoil than the light gun but the middy is definitely a softer shooter.

I would say get the middy but if you get the carbine you will be perfectly fine as well (assuming bought from a quality mfg). The only issue I've seen with a middy was a 14.5" middy (with pinned FH to make legal) and it had some problems cycling the horribly underpowered wolf ammo. As long as you aren't shooting the cheapest ammo you can find and sticking with a 16" barrel, I think you will like the middy better. Pair it with a Vltor A5 kit and you're gold.
 
#7 ·
I have a 20in on my ar. My next one will either be a 16-18 with the rifle gas system. One like said earlier a little easier recoil and two i want the greater distance for a better sight picture. I had a shorty and didnt like it. I love my rifle but to long for cleari.g the house. So im going with the 16 with full length rails and gas system. As far as reliable i never had problems with the m4 not preforming like it should.
 
#11 ·
I am kinda leaning towards a midlength AR-15.

Even though I already have a carbine version, it would be nice to have something different. At least then I can do side-by-side comparisons.

And, I really like the look of the rifle Getyershells posted in this thread - http://www.survivalistboards.com/showthread.php?t=211263
 
#12 ·
For proper function, there has to be a specific length of barrel in front of the gas port. The M4's gas port location was correct for the shorter military barrels. They just kept the same location when the 16 inch carbine length guns started hitting the civilian market. The mid length system slows the cyclic rate somewhat, which decreases the perceived recoil and helps reliability a bit.

What I especially appreciate about it is the increased sight radius. Personally, I think the dissipator concept over a mid length gas system is just about the perfect compromise.
 
#15 ·
My current AR was a built by me. I went down to a 14.5" barrel with a mid-length gas system. The muzzle device is pinned and welded in place to keep it legal. I used a low profile gas block and a free floating rifle length handguard. The front sight is on the end of the rifle length handguard for a nice long sight radius and plenty of room to get my hand WAY out for stability.

I love this combo. It shoots everything I feed it. It is more than accurate enough for a non-scoped rifle with iron sights or a red dot.

I HIGHLY suggest building your AR yourself. Its rather easy overall and you will get more rifle for your money.
 
#19 ·
I think these debates are all theoretical personally. I mean, I have a BCM 16" mid-length and it was harsh as hell, seemingly overgassed, and would recoil when the buffer hit the back of the tube too fast. I put in a spikes buffer and it calmed down quite a bit, but still, a mid-length gas system shouldn't need such a thing if you listen to what everybody says about them. I consider the Spikes buffer to be a band-aid and didn't like having to resort to that.

In contrast, you can watch the videos on a Daniel Defense M4 with a carbine gas system and they hardly move at all when you pull the trigger. According to the legend it should be the other way around, a heavy mid length should be crazy stable as compared to a light carbine but that doesn't seem to be the case.

In other words, it's all about how well the entire system is tuned. Spring rate, buffer weight, bolt weight, gas tube length, gas tube size, gas tube rear port size, barrel length... there's a whole bunch of things that need to work together.

If I were to do it over I'd get a Daniel Defense carbine system and be done with it. Also supposedly if you got a mid-length, the 14.5" barrels are supposedly actually smoother than the 16" like I got. I'm assuming that's because a 16" has another 1.5" that the bullet has to travel and more gas is pressing into the gas port during this time. A 14.5" should have slightly less gas pressure due to a smaller timeperiod that the gas can enter in other words. Of course this is due to BCM marketing too, but yeah supposedly a 14.5" mid-length is the smoothest shooting thing they offer.
 
#24 ·
I mean, I have a BCM 16" mid-length and it was harsh as hell, seemingly overgassed, and would recoil when the buffer hit the back of the tube too fast...

Also supposedly if you got a mid-length, the 14.5" barrels are supposedly actually smoother than the 16" like I got.
Sorry for the weird chopped up quote, typing on my phone. What lower was your 16" BCM mid on? Mine runs on a BCM lower with H buffer and it's smooth, again a softer shooter than my DD 16" carbine which is heavier. I would agree that the Spikes buffer is a bandAid however I also agree with you that it's a system and if the T2 buffer works for you then run with it. Having shot a variety of AR's I'd also say the balance to some degree affects the felt recoil, maybe not as much as gas system or weight but still some impact.

As far as the 14.5" middy I would agree that it may be the smoothest of the bunch. Based on my experience it's just not as forgiving of using underpowered .223 loads. If sticking with mid to high quality 5.56 it paired with an H or H2 buffer or an A5 kit might be the best choice. Obviously you just need to make your rail choice first and stick with it since the fh will be pinned (assuming you don't sbr it).

Edit: I saw someone above mention a piston. That's a whole other can of worms :) I will say though that I found the recoil impulse to be harsh. Sample size of 1 though.

And the more thinking about the 14.5" I do, I think come tax time a new upper in 300 Blackout might just be on the menu.
 
#21 ·
I have all three gas systems (carbine, rifle, midlength).
I have a soft spot for my 20" rifle length system, but the middie is a close second. The carbine is fine too, not that big a difference, though I have an H2 buffer in it.
MikeK hit it, the real difference is to optimize pressures and dwell time for the civilian required 16" barrel. Mil barrels are 14.5 inches, which you can only get on the civ market as an SBR or with a permanently pinned flash hider. So a midlength gas system is considered 'optimal' with a 16" barrel.
Is it necessary? No, but I like the extra handguard length and also the longer sight radius. You might also.

Of course, you could get a piston system and really throw everything out the window! ;)
 
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#22 ·
M4 feedramps are supposed to eliminate most reliability issues with the carbine gas system. That being said I went with midlength for a few reasons.

1. Reliabilty. The theory is that the action cycles slightly slower than a carbine gas system, which increases reliability.

2. Lower recoil=easier to stay on target, faster follow up shots.

3. Reduced wear and tear. Midlength gas systems operate at lower pressure than carbine systems. Less pressure means less wear. Gas port erosion is also reduced.

4. More space to put "stuff" if railed handguards are your thing, or more space to put your hands if you find the carbine system too confining, or if you have long arms.

5. Longer sight radius= possibility of slightly better accuracy.

6. This is also theory, but some people say the midlength system isn't as dirty as carbine. A cleaner bolt is always a good thing with an AR.
 
#23 ·
Going out of my way to assume you'd like this rifle for practical purposes too, considering this is a survivalist forum...

16'' not only gives you a smoother operating gas system over 14.5, but increases velocity of the rounds, too. And after all, that's the big deal with 5.56. With ammunition like the M193, you have a round (with a good, deep cantilure) that will yaw inside soft targets, and then break apart into small pieces, which makes a once temporary cavity, a perminant one. But the round will only yaw if it's traveling at 2600-2700+ FPS. Depending on the exact round and other factors, you have about 150 yards or less to accomplish this. Essentially, you lessen your ''maximum effictive range'' by using a shorter barrel.
 
#28 ·
I bought a 16" BCM middy upper about a year ago, the only noticeable difference, is the sight radius (the distance between the front and rear sight), and the longer handguards, all functions are identical to my 14.5 LMT providing I use the same weight buffer.

My middy has the hammer forged barrel so it's heavier, and with the Tango Down bipod it's not something I want to carry for long, thankfully it's not my 'patrol' AR, it's the 'base' model.

To the guy that said his buffer was slamming into the back of the tube. Buy a heavier buffer, an H2 or H3 should make a difference. I run a 9MM buffer in my LMT and the recoil was reduced a little and because of the heavier weight it throws the brass backwards and to the side, not forward as most standard buffers do. (in case that matters)

Good luck with your search. :thumb:

 
#39 ·
build you own

I would try building you own. I built ar-15 so I would have a clear understanding of the rifle. Also so I would clearly understand that inter-workings on the rifle, and could repair most issues that would arise. I chose that mid-length for the reason that it was claimed to be more durable and it was a little more comfortable to me due to arm length. Kev if you have any question P.M me I am in your area about every other week or so.
 
#47 ·
I live in the great commie state of New York so my muzzle device is going to be non-removable no matter how long the barrel is. I really really gotta move!


My last four AR's have been 14.5" mid-lengths. Zero issues with thousands of rounds downrange. The thing I like about the 14.5" is they make a noticeable difference doing house clearing drills (easier to maneuver) compared to the 16" and still they perform well out to 200 yards.

That's kinda what I was thinking. I want a more maneuverable gun that could be used in house clearing if need be. If it can shoot well out past 200 yards, that's good enough for me. I'll probably put a 12" rail on it for more real estate.
 
#46 ·
I wasn't trolling, and I am not really an AK fan. I just wanted to make sure Kev understood that a SHTF rifle should be effective out past 300 yards, thus he might want to consider the 16" barrel at minimum. SBR's are great in close quarters combat but SHTF out where he lives is rarely close quarters. Sorry for the confusion.
 
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