I just purchased a 7.5" upper to try on my SBR.

It has a magpul handguard, so no front sight post, no top rail.

If I put a rail piece and front sight on the top handguard, will it be too tall to line up with the rear sight?
I am not concerned about cowitnessing with the red dot.
ar_pistol_magpul by redstone71, on Flickr

(NOTE: not my AR but the exact upper I am referencing.)

Honest question, nothing negative intended, what’s the mission of a sub 10” AR aside from fireballs and hearing damage? Other than… because you can.

If the front rail ends up being taller, you could maybe use a Troy micro in the front, and a regular-height rear sight. That front sight may not be super precise either, mounted on that plastic.

quote:

Originally posted by ah3:
Honest question, nothing negative intended, what’s the mission of a sub 10” AR aside from fireballs and hearing damage? Other than… because you can.

Just trying something new for a PDW. I have been running the 10.5" for a few years and I still have that setup.

It came with the magpul handguard, but I may go ahead and put a KAC rail on it.

quote:

Originally posted by redstone:

quote:

Originally posted by ah3:
Honest question, nothing negative intended, what’s the mission of a sub 10” AR aside from fireballs and hearing damage? Other than… because you can.

Just trying something new for a PDW. I have been running the 10.5" for a few years and I still have that setup.

It came with the magpul handguard, but I may go ahead and put a KAC rail on it.

In an AR firing .223/5.56 going shorter than 10.3" has been demonstrated to severely diminish ballistic capability, bullet performance, weapon reliability, part life, etc.

They make money into noise and can produce some big fireballs, but defensive use is generally not recommended.


Edit: Another curious question, why are you trying to put iron sights on this upper? Your photo example has a red dot, I would suggest the same. And if the PDW role is serious, a light and sling setup.

the iron sights are just a habit. I was trained to always have a BUIS, and roughly 1/2 my range time is on iron sights and half with the red dot.

As for the 7.5" it is just an experiment. The barrel was cheap enough. I have a 14.5 I can put on it. The thought was if I could reduce the overall length another 5" (3" from the barrel, 2" from the stock) I could fit it in a 'normal' backpack for work.

But I should have just done more research on the real short SBR/PDW builds. The general consensus seems to be 7.5 is bad, and screwing with a combo BCG-buffer to shorten the stock (Like the Troy M7A1 stock) is really bad.

I am thinking I will just put a standard M4 profile barrel on it, and call it.

This configuration is where the 300 blackout cartridge starts to shine. A supersonic load in a fast twist 7.5" doesn't have the same negative tradeoffs you see with a 5.56.

But yes, standard conventions are that a 20" barrel with rifle gas, rifle buffer is going to be the best setup for function, performance, and reliability for 5.56. As you continually go shorter you reach a point of diminishing returns.

That's not to say a 7.5" 5.56 AR can't work or won't work, but in this game of probabilities, planning, prepping, etc, well you know the conclusion.

Another option is to stick with 10.5" and add a folding stock adapter. The LAW folder is the only duty-rated choice for this application. Overall length is increased, balance of the gun is affected as it's not a light chunk of steel, but I've found it to be quite effective and the added length easily adjusted for in the stock position.

quote:

Originally posted by KSGM:
If the front rail ends up being taller, you could maybe use a Troy micro in the front, and a regular-height rear sight. That front sight may not be super precise either, mounted on that plastic.

Yep. Even if you could get such a front sight setup to line up properly with the rear sight, that plastic handguard is going to shift and flex, so you won't be able to maintain any sort of precise zero.

Mounting a front sight on a handguard is best left to free-floated metal handguards that are anchored securely to the upper receiver.

Would a 45 degree BUIS be an option? If the 2 o’ clock spot on the hand guard has MLOK slots, you could put a front sight there. An angled rail could be set up for a rear sight…just brainstorming.

My favorite AR is 5.56mm 7.5” suppressed PDW setup…it works very well, my only complaint is it only takes two 30rd mags to get the can scalding hot!

quote:

Originally posted by Creeping_Death:
Would a 45 degree BUIS be an option? If the 2 o’ clock spot on the hand guard has MLOK slots, you could put a front sight there.

Same issue as the top-mounted front sight, with handguard instability.

Regardless of where on the handguard you mount it, a plastic handguard held in place merely by the pressure of the delta ring is simply not stable enough for mounting a sight or an optic.

I have a similar pistol set up, I too wanted back up irons because training and habit. They were not feasible, I went with a micro laser mounted just in front of the red dot, not ideal but it is a back up

quote:

Originally posted by Rustpot:
...

Another option is to stick with 10.5" and add a folding stock adapter. The LAW folder is the only duty-rated choice for this application. Overall length is increased, balance of the gun is affected as it's not a light chunk of steel, but I've found it to be quite effective and the added length easily adjusted for in the stock position.

I am going to check this out a bit more. My number one issue is that my 5.11 bag still looks like an FBI agent trying to look normal. I have wanted to get my SBR overall length down to a size that could fit in my work back pack going to and from my car. This is what started the PDW stock and 7.5" barrel transition. I decided to start with the 7.5 because I wasnt sure it would work. Then I was going to start exploring various PDW stocks, but I do not like screwing with the BCG.

but the Law Tactical folding stock seems like a great option and I think it will give me the overall length I need. Time to get the tape measure out . . .