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[dousan]

[kevman0154]

You dont need an adjustable gas block unless you are going to shoot suppressed. Which, assuming you live in CA, wont happen.

ARs with barrels from 10in-20 inch have been in use in conflict all over the world with fixed gas blocks for DECADES now. The issue with shorter barrels is the pressures and the gas going thru the gas tube to cycle the action. If you use ****ty steel cased, dont expect 100% reliability with a barrel shorter than 16 inches. If you are using brass cased ammo with milspec standards or better you will be fine.

Shorter barrels wont give you the best performance out of the 5.56/.223 but if you are just going to the range to plink at targets 250m> you wont even notice the diffrence.

[kevman0154]

Most of the ranges around me wont allow steel case so
Is there any reason I should go with 10" over 7-8"?

Yeah, reliability and shooting experience(Subjective). A 7-8 inch AR is going to be more than likely be less reliable with 5.56/.223. Also a 10 inch AR is loud af already, a 7inch AR is going to be louder with more concussive blast. TO ME , anything shorter than 10.3 in 5.56/.223 is a Meme. 9mm or 300 Blackout in barrels shorter than 10in. are perfect and almost preferred.

However if you think the 7-8 in barrel looks cooler or just dont care about sounds and percussion, go for the 7-8 inch and see if it runs. Worse case would be having to tune the entire system to get it to run or sell it on the marketplace and buy a longer barrel and swap it.

Also mentioned above, make sure you look at the buffer weight too. the military issued the MK18s (10.3 in) with an H3 buffer/standard buffer spring. You might need one of those to increase reliability. There are a ton of charts online that discuss buffer weights and types of buffer springs to use.

[ar15robert]

Have a 10.5 psa upper and it’s been great no issues.

[FeuerFrei]

Hello all,

I'm ppt'ing a pistol lower and the owner is keeping his upper. He mentioned that (pistol) under 10" barrels have finnicky gas port issues like failure to eject.

Since it will take a minimum of 10 days to receive the lower I figured I would order the upper online. On Palmetto I see lots of cheap complete uppers in 5.56 but it looks like they all have fixed gas blocks. I know my DD5V4 has an adjustable gas block.

Is it a matter of just order one, and if/when I have issues install an adjustable myself?

Also, palmetto takes weeks just to ship, is there anywhere else I should look for pistol length uppers?

I've done 7.5" AR pistols in piston and Stoner gas systems and both can be reliable with 223/556 ammo depending how much you know about the mechanicals involved.

Some oems run okay right out of the box w/223 because they're over gassed (large gas port/short dwell). When you switch to 556 it becomes over gassed and cycles the bolt faster than necessary. Sometimes fast enough to not strip a round out of the magazine and the bolt closes on an empty chamber and just goes "click" when you press the trigger.

I suggest shooting it first and see what you have. You can tune for reliability later and learn a lot. I do favor the use of adjustable gas blocks. Allows the use of 223 or 556 du jour.

Gas piston systems run great on shorties without knowing too much about tuning. Buffer weight swaps and actions spring swaps are usually enough.

[bohoki]

all i can tell ya is make sure the extractor spring is strong and you wont have any issues i got a bolt where i can move the extractor with my thumb pretty easy it works just fine in my a1 upper but in my pistol it fails to extract it so check your extractor if it causes pain to get it to move its strong enough for a pistol

[sigstroker]

Same here. It runs great with or without silencer. Horrendously loud with a flash hider, never fired it with the muzzle brake without the silencer.

The military did a lot of testing with the Mk18 (10.3 inches) and determined the 11.5 inch barrel was much better overall. Kevin Owen, famous SF guy, says he's killed people at 500 yards with an 11.5 inch.

[hitdank]

I have a psa 10.5 upper and it cycles perfectly even with bought 223 reloads. I used h buffer but i think regular should be fine.

[enorbit3]

Ive got a 10.5" aero upper with FSB. same as this one.

https://ar15discounts.com/products/aero-precision-ar-15-10-5-5-56-carbine-complete-upper-w-pinned-fsb-moe-carbine-fde/

Works flawlessly so far, but thats only a couple hundred rounds.

[SISKIN]

I am running a 7.5 aero upper and lower with a Geissele Super 42 braded spring with an H2 buffer. Works just fine . I did add a Aero adjustable gas block just because i could not pass it up. But it was working just fine without it

[G38xOC]

Definitely isolate the issue before spending money on it . Who knows problem could be something real stupid and cheap to fix .

[golfish]

I seem to recall opening up the gas ports a little on the AR pistols that I built. I didn't use a adjustable GB on them (I think)but I would if needed. Some ammo is better then others so a adjustable GB is a good idea...

PSA, doesn't always take weeks to ship. All of my orders from the last few years have shipped within a week.

[walmart_ar15]

Same here. It runs great with or without silencer. Horrendously loud with a flash hider, never fired it with the muzzle brake without the silencer.

The military did a lot of testing with the Mk18 (10.3 inches) and determined the 11.5 inch barrel was much better overall. Kevin Owen, famous SF guy, says he's killed people at 500 yards with an 11.5 inch.

This... Going below 11.5" would depend on the gas port, buffer weight, buffer spring, extractor strength, and sometimes even muzzle device. It can be tuned to work fine, but may take some trial and error.

The initial Colt Commando was 10.5" barrel. Military had enough issues with it that Colt engineers went with 11.5" later. But due to flash, they put a long flash can in front (ATF considered it as a suppressor). Back in the 70's.

Would recommend buying complete upper and ask the vendor what buffer weight and spring weight they recommend with their upper. Make sure your extractor has the black (?) O-ring, rubber insert to ensure good extraction. Supposedly, shorter barrel may not have sufficient dwell time for the empty case to fully contract, thus, still tight inside the chamber. Without a solid grip on the rim, the bolt can slip off and cause a jam.