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Love the MK18, but they require a lot of maintence because of the barrel length and high pressure issues...I'm looking to build an AR pistol. Can't decide whether to go with a PSA blemish 10.5" upper or a CBC blemish 7.5" . They are about the same price, I've heard that 7.5 is louder but is it that much of a difference? Any other considerations?
I went with BCM 11.5, kind of a pseudo MK18 Mod0 setupFor what it's worth, when I built my SBR I went 10.5.
The whole 10.3"/10.5" number came around because it is the shortest length barrel that can still use a standard FSB and carbine gas system, but they can be finicky. I won't go any shorter than 11.5" in 5.56 due to loss of velocity (terminal performance) and dwell time (operational performance). With a 11.5" vs 10.5" you get 4% increase in length of weapon with a 40% increase in dwell time, which translates to a very small increase in size vs a major increase in reliability.
I agree, but a 10.3/5 beats the heck out of the gun and that's why I chose the 11.5. Still rougher on the gun then longer options but I wanted something shorter that would work when and if I needed it.When you start at 7.5" and end up at 11.5", the idea of a "pistol" has faded away to a "little bit shorter than normal" rifle. But your points are valid. When I built my SBR, I wanted as compact as possible with still decent ballistics. Hence the 10.5.
That's where .300 BO comes in.When you start at 7.5" and end up at 11.5", the idea of a "pistol" has faded away to a "little bit shorter than normal" rifle. But your points are valid. When I built my SBR, I wanted as compact as possible with still decent ballistics. Hence the 10.5.
Agreed, 11.5 is the minimum I go with a .223.That's where .300 BO comes in.
A 12.5" is the happy spot for a 5.56 "pistol", IMO...
14.5 is the ideal length for that round... or so I have read...That's where .300 BO comes in.
A 12.5" is the happy spot for a 5.56 "pistol", IMO...
It is a pretty big difference over a 16", which most do to avoid the pinning thing. I built a GAU-5A 'ish pistol with a 12.5" and difference over a 16" is even more pronounced. I discovered a 12.5" barrel and a lower with a standard carbine buffer (I would normally use an A5 buffer) fully collapsed is a spot on equal match in overall component length. I'll probably add a 9" .300 BO for a more pistolesque alternative. I need to get some comparison pics together one of these days.So why are we even talking about pistols then? 12.5 is almost pointless for any real reason to build one.