7.5" vs 10.5" AR pistol

[Hardcore_rucke]

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?

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[Kruel J]

I'd stick with 10.5, I've owned both. The 7.5 will be louder and the shorter barrel will neuter the round's performance quite a bit. Like half.

 

[RobMa]

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?

Love the MK18, but they require a lot of maintence because of the barrel length and high pressure issues...

 

[clanhanson]

Neither are great for 5.56. Get a 5.7x28 if you want that level of ballistic performance. At least then you won't have massive concussion, blinding muzzle flash, and permanent hearing loss.

 

[CountryGent]

I'd stick with 10½" on 5.56㎜. I have an SBR with said and it is real loud with out a can in place. Even with the silencer, it is pretty noisy.

 

[Kruel J]

Rough numbers here:

7.5" barrel: around 1700 FPS
10.5" barrel: around 2300 FPS

Don't forget the increased wear and tear from a 7.5" barrel too.

Bottom line, my first pistol I built was a 7.5". It ran just fine. Spit huge fireballs and was quite compact. All that fun aside, the performance of the projectile along with reliability and wear/tear should be more important to most.

For what it's worth, when I built my SBR I went 10.5.

 

[RobMa]

For what it's worth, when I built my SBR I went 10.5.

I went with BCM 11.5, kind of a pseudo MK18 Mod0 setup

 

[titsonritz]

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.

 

[nwslopoke]

As mentioned, the 7.5 is more of novelty in 5.56. Go 11.5 if possible. I have a 10.5 and 11.5 set up different and bought several years apart. Out to 100 yards not much difference. I just know the 11.5 has more velocity.

 

[Kruel J]

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.

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.

 

[RobMa]

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.

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.

 

[titsonritz]

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.

A 12.5" is the happy spot for a 5.56 "pistol", IMO...

 

[DLS]

If you look at the terminal ballistics of a 7.5 inch .223 and compared that to a PCC the PCC makes a lot of sense.

Far FAR less muzzle flash and blast ... less recoil / perceived recoil, longer firearm life, etc.

A .223 is drastically neutered with a barrel of that length.

 

[DLS]

Agreed, 11.5 is the absolute minimum I go with a .223 for all the reasons mentioned.

 

[DLS]

That's where .300 BO comes in.

A 12.5" is the happy spot for a 5.56 "pistol", IMO...

Agreed, 11.5 is the minimum I go with a .223.

 

[RobMa]

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...

 

[Kruel J]

So why are we even talking about pistols then? 12.5 is almost pointless for any real reason to build one.

 

[titsonritz]

So why are we even talking about pistols then? 12.5 is almost pointless for any real reason to build one.

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.

 

[Member 34319]

Clearly 4.75" is the answer. Has way more better good ballistics.


7.5 556 > 22lr

Personally my shorties are all 11.5". Though I've built at least one 7.5". It was a fun little thing. Get the right blast forwarder and tune the buffer/spring right, they can be a decent weapon.

 

[Member 53328]

My personal choice is a 10.5 or 11.5 Do an SBR not pistol. And who cares about ballistics….. you're not building an SBR/pistol to reach out and touch something. It's for compact/CQB aka combat/self defense. If you can neutralize a threat inside a building or within a close distance, I think you will be ok. Good luck with whatever you choose though. Like others have said you may want to invest in a can, or quality ear protection. You can't buy more hearing and Lord knows they are louder the shorter you go.