Let's talk PDW's

[El Cid]

I think the sub-11.5" 556 thing is overblown. People on the internet hear something and take it and run. We use Daniel Defense Mk18s at work without issue. I've never witnessed a malfunction that wasn't immediately identified as a magazine failure. ETA: Correction, I saw one go down on the line for a gas key issue, which isn't isolated to Mk18s.

Regardless of everything I've read on the internet, our Daniel Defense Mk18s just plain work. "11.5" has 40% more dwell time". Okay. But ours still work just fine, and our duty ammo is still reliable performance out to 110 yards.

Personally I'd go 12.5" if I was choosing an unsuppressed duty rifle, because it's pure sex....but I think the statement that "going shorter than 11.5" in 5.56 isn't smart" is a bit exaggerated.

With that said, this is a PDW thread, and CQBRs are not PDWs....so maybe we should save this conversation for elsewhere.

I don’t think it’s overblown, and most of my information doesn’t come from the Internet. Mr Pannone actually brought it up in a class back in 2014. He commented on how “what’s old is new again” with regard to how agencies tried to go short and realized that 11.5” is the magic number. That of course was the length of the CAR-15 bbl like the one my dad was issued in Vietnam. In addition while I was on a Safe Streets TF the feebs started cutting their 14.5 rifles to 10.5. Suddenly the guns were having issues. Some worked with duty ammo but not training ammo. Some were the reverse. Some had issues with all their ammo. They realized if they cut them to 11.5 they worked much better across all ammo types. It’s also why they chose an 11.5” bbl when they bought/built new free floated rifles - the ones cloners love with the 10” Geissele Mk4 rail.

Doc and others have spoken about the better terminal ballistics so I won’t rehash all that. And you’re partly right that a 10.3 or 10.5 can be reliable but there are only a couple manufacturers I’d trust to do so. Daniel Defense is one of them. But those rifles need carefully tested gas ports and buffer weights/springs. For me it’s just not worth it to go an inch shorter. I see zero benefit in a 10.x bbl. If my agency didn’t give me the choice I’d make do, but otherwise I see no viable reason to go shorter than 11.5 with 5.56 rifles.

As a side note, some piston rifles seem to work reliably when going shorter but that brings other issues, not the least of which is cost.

[StraitR]

@StraitR, this is an important bit of data. Would be interesting to see a similar experiment run with .300 BLK with 5"-9" barrels.

A couple important things to remember here.

1- None of the tested 5.56 loads that day were designed to work in a 7” barrel, so they technically didn’t “fail a ballistics test”. I’m not aware of any mainstream duty loads made to do so.

2- There are 300blk cartridges designed to open at much lower velocities than 5.56, which enables them to function, as designed, in barrel lengths shorter than 10.5”.

3- A lot of bad people no longer walk this earth due to good guys doing God’s work with 10.5” barreled Mk18’s.

[psalms144.1]

I'll add that we had 16 Mk18s on my detail. Mine was NOT set up properly WRT gas, it had to be detail stripped and thoroughly cleaned every 200 rounds or so to avoid multiple failures. This was regardless of lube or lack thereof - just wouldn't go through a basic load without a cleaning. We had one other gun that was similar. We had two guns with catastrophic bolt failures. So, about 25% failure rate for the limited sample on my team. Full disclosure, these were older rifles that had been in service for quite some time, so they might have just been worn out. The four problem guns went back to Crane for depot maintenance and were never seen again - not sure if they were rebuilt and subsequently reissued to other end users, or if they were scrapped.

So, on the issue of 10.5ish inch ARs, my experience has led me to avoid them whenever possible. No doubt they can be made to work and work well, but I'm gun shy, pun intended.

[HeavyDuty]

So, what I need is an AR9 with LRBHO that feeds from Glock mags, and costs what a PSA gun does. I'll take mine in a 6-8" barrel, lightweight MLOC forend with top picatinny rail. Someone whip that up for me and I'll be the first in line to buy.

Start with this... I have a pistol built on one of their Uzi mag lowers, and it’s great. I wish I had built it with a Glock mag lower.

https://www.quartercircle10.com/rang...-receiver.html

[TGS]

@El Cid, people cut M4s down to 10.3" and found they had problems? Here's my surprised face. [sarcasm] That's obviously a sensible reason to cite as 10.3" barrels being problematic, because dontcha' know you can cut down the barrels to the gas port on every other AR15 variant and they'll still work fine[/sarcasm].

There's no "carefully tested" gas ports. There's a correct gas port sizes for various barrel lengths and gas systems. It's as simple as that. Use the correct size gas port for a 10.3 and it will be fine.

They all use a standard H1 buffer setup just like the M4A1 uppers mounted on the lower beforehand. Nothing special, nothing demanding extra care, attention or individual tuning. We're an agency that decided against issuing LAW folders agency-wide for general use because we're afraid of the lowest common denominator agent, FFS.

And, regardless of all the hoopla and drama you're citing.....ours still work fine.

On DD website it list that barrel as 10.3. At that length are you limited in ammo choices?

Not really "limited", there's plenty in that velocity range and all the best loads available work fine in that velocity range as well.....but you of course have more wiggle room with the extra velocity offered by a 11.5, and extend the range for a given load.

[El Cid]

@El Cid, people cut M4s down to 10.3" and found they had problems? Here's my surprised face. [sarcasm] That's obviously a sensible reason to cite as 10.3" barrels being problematic, because dontcha' know you can cut down the barrels to the gas port on every other AR15 variant and they'll still work fine[/sarcasm].

There's no "carefully tested" gas ports. There's a correct gas port sizes for various barrel lengths and gas systems. It's as simple as that. Use the correct size gas port for a 10.3 and it will be fine.

They all use a standard H1 buffer setup just like the M4A1 uppers mounted on the lower beforehand. Nothing special, nothing demanding extra care, attention or individual tuning. We're an agency that decided against issuing LAW folders agency-wide for general use because we're afraid of the lowest common denominator agent, FFS.

And, regardless of all the hoopla and drama you're citing.....ours still work fine.

Nah brother. No drama here. I’m simply saying the 11.5 has advantages over the 10.x and in my experience the 10.x guns offer no advantage. And that’s based on science as well as real world use by myself and others.

I generally like your posts and value your input. We can certainly disagree without being disrespectful. I suspect something is getting lost in having a virtual conversation.

[TGS]

11.5" has advantages, which I'm not denying. Like I said, I'd actually go for a 12.5" general purpose unsuppressed gun. There's nothing an 11.5" does that a 12.5" doesn't do better, but I would never assert that means there's a problem with the 11.5". An 11.5" works fine, but a 12.5" still has more advantages...just the same as a 10.3" gun works fine, but an 11.5" has advantages over it.

I'm just going after the assertion that "going shorter than 11.5" with 5.56 is not smart". That's untrue.

There's nothing disrespectful in my post, and I'm still of the opinion that most of the 11.5>10.3 stuff is taken out of context/misunderstood and overblown. It's no wonder that people who cut down 14.5" guns with .062" gas ports have reliability issues with their newly chopped 10"ers, but that's not reflective whatsoever, in any way possible, of a purpose built 10" gun with the correct .070" size gas port. Nor is it going to take any sort of special tuning and trial & error with various buffer setups to make a properly built gun work right.

The reason I used the sarcasm is to illustrate that. Would you take a 20" M16 and chop it to the FSB and expect it to work right? No, that's obviously not a good idea, though we have no doubts that a properly built 16" gun will work fine. So why would we think that chopping a 14.5" to 10.3" is going to work any better, and when it doesn't, use that as evidence that 10.3" guns don't work right? That dog don't hunt, plain and simple.

I'll add that we had 16 Mk18s on my detail.

We have twice that many on my last detail, and probably upwards of 5,000 inventory wide for the whole agency (if not more), and they work fine.

Do you know for sure if they were cut down 14.5"s or anything?

Because as of right now, the only thing I can tell is that a purpose built Mk18 runs fine, and a sawed off M4 doesn't....which shouldn't really come as a shock to anyone.

[Rex G]

So 11.5 vs 9. Thats only a two inch difference for comparable performance and the 5.56 is a lot more available in hd/sd/duty loadings. I am trying to figure out the draw for 300 BO. Can someone break it down for me?

I am certainly not one of the experts on this; I can only say why I went BLK, for an AR pistol, with a brace on a LAW-foldered buffer tube. One significant factor in my personal decision for 300 BLK was that it behaves one way as a heavy-bullet subsonic load, and completely differently as a supersonic light-bullet load. I might want to use it for nocturnal pest control with heavy subsonic, or antipersonnel with 125-grain supersonic.

Another thing is that my clumsy self keeps dropping .223/5.56, in ways that it rolls under things, or otherwise disappears. I rarely seem to fumble 300 BLK. I am serious; I was doing some spring cleaning, earlier today, and found several stray .223/5.56 rounds.

I do have a 5.56 BCM Lightweight Middy carbine, so am not irrevocably committed to BLK, but it is the BCM carbine that is unloaded, and put away, indefinitely, in the safe. I might not have bought the Lightweight Middy, except that I almost re-joined the patrol rifle program, at work, several years before I retired, but now that I have it, I’ll keep it, ‘cause ‘Merica, and all that.

For me, realistic HD is done with handguns, and Benelli M2 shotguns, so 5.56-vs.-300 BLK was not part of that equation. Packable away-from-home SD is where the carbine/PDW enters the picture, and I am not yet ready to commit to the braced AR pistol. (The main competition, that the braced AR pistol has to overcome, in my case, are 4” to 6” Ruger .357 Magnum revolvers.)

To be clear, these are my reasons. I am not trying to convince or convert anyone.

[Wake27]

@El Cid, people cut M4s down to 10.3" and found they had problems? Here's my surprised face. [sarcasm] That's obviously a sensible reason to cite as 10.3" barrels being problematic, because dontcha' know you can cut down the barrels to the gas port on every other AR15 variant and they'll still work fine[/sarcasm].

There's no "carefully tested" gas ports. There's a correct gas port sizes for various barrel lengths and gas systems. It's as simple as that. Use the correct size gas port for a 10.3 and it will be fine.

They all use a standard H1 buffer setup just like the M4A1 uppers mounted on the lower beforehand. Nothing special, nothing demanding extra care, attention or individual tuning. We're an agency that decided against issuing LAW folders agency-wide for general use because we're afraid of the lowest common denominator agent, FFS.

And, regardless of all the hoopla and drama you're citing.....ours still work fine.



Not really "limited", there's plenty in that velocity range and all the best loads available work fine in that velocity range as well.....but you of course have more wiggle room with the extra velocity offered by a 11.5, and extend the range for a given load.

What’s the concern over with the LAW, that they’ll be fired while folded?


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[Wake27]

Back before electricity when I was doing protection, our long gun options were MP5KN or Mk18. The MP5, while possibly my favorite shoulder fired weapon of all time, doesn't do very much except allow for exceptional accuracy with pistol rounds, and the ability to make a very happy shooter when you mag dump. The Mk18 couldn't be carried ready to fire in anything short of a mountaineering rucksack - on our trips to Pakistan where we were not officially armed, it was pretty obvious to everyone in the grid zone that we were - not just because of the HUGE rucks we were all carrying in urban settings, but the fact that rifle plates over soft armor under an untucked "casual" shirt doesn't conceal all that well. That and the ear pieces - and the cool guy shades Oakley shades, of course. The alternative to the Yuge ruck was carrying the rifle in two parts in a backpack - not best choice for quick deployment.

When we got the Mk16 (SCAR-L), I thought I was in heaven. They could be carried (and fired) in the stock folded position, so they'd fit into a 3-day pack - MUCH lower profile. And ours were accurate, reliable, and durable - but we didn't set out to break them like some end users did to "prove a point."

To me, I think of the PDW as the modern equivalent of the M1 Carbine - a smaller, lighter, still capable shoulder fired weapon that REMFs who can't handle an M4 can carry without whining. I think the current crop of 7-9" 300 BOs pistols/SBRs meet this requirement nicely - with the down side of a logistics tail for a unique caliber. Going to an AR9 platform simplifies logistics, but you're back to having an accurate but large pistol - basically a 100 yard gun against unarmored targets only. Honestly, for today's environment in the US, I think that will handle 99% of what non-LE/.mil folks need when you say "PDW."

I'd love to pick up a Scorpion, if only they could be adopted to Glock magazines (of which I have an actual metric ass ton). I keep putting PSA AR9s in my shopping cart then NOT buying them because of the lack of a last round bolt hold open - it's not a show-stopper from a manual of arms perspective (I deal with it all the time with my MP5), but it's different enough from the AR that it takes something away from the "muscle memory" piece of an AR-platform 9mm.

So, what I need is an AR9 with LRBHO that feeds from Glock mags, and costs what a PSA gun does. I'll take mine in a 6-8" barrel, lightweight MLOC forend with top picatinny rail. Someone whip that up for me and I'll be the first in line to buy.

While there are some significant cultural l problems with personnel in support roles, I’ve never actually heard a single one whine about the M4 being too much.


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