AR upper for subsonic rounds

[taliv]

i spent the morning working up subsonic 223 loads and I currently prefer that they don't actually cycle the action on my AR (16" barrel, midlength gas system) but i was wondering if I could actually make an upper that would cycle.

specifically, after reading the article bartholomew pinned in the rifle library about gas systems of various lengths and their effects on pressure and lock time, and after reading the threads about subsonic 223 loads...

i'm wondering if i got a full-length barrel (20 or 24 inches with a 1-in-6.5 twist and put the shortest gas-system i could find on it, with a barely subsonic load using a 69g or 75g bullet, if i could actually get it to cycle. (i don't want to go so far as swapping the recoil buffer springs or using a lighter material in the BCG)

anyone ever tried a long barrel with a short gas system?

 

[knoxx45]

If you don't mind...

Why do you want a sub-sonic AR? Suppressor??? If that is the case give DL Sports a call they specialize in suppressed weapon systems, and might be able to help.

 

[HorseSoldier]

A Mk 12 SPR (18" barrel) with suppressor fitted and subsonic loads will not cycle, from firsthand experience. I'm not sure on the particulars of the subsonic load in question, however, and not sure how close they approximate what you're talking about on the handloading side of things.

 

[redneck2]

If you want a subsonic, consider the Colibri .22 subsonic. It's 60 grains at slightly less than speed of sound. 60 grains are 60 grains regardless of the platform.

If you want something with "whack", you might want to look at the Whisper series. Big, heavy bullets at subsonic speeds. HTH

 

[taliv]

thanks for the replies, guys. i've already played with the whisper stuff, and shot tons of subsonic 22. (and i think you're thinking of the aguila super sniper subsonic stuff that's 60g. the colibri and super colibri are just 20 grains i think, sans powder).



all i want to know is if a short gas system on a long barrel will provide sufficient gas from a low-pressure round to cycle a normal AR carrier.

 

[beerslurpy]

45 acp is the answer you are looking for.


cav arms lower plus oly arms upper is the way to go for a subsonic AR. And best of all it has no gas system.

 

[444]

To actually attempt to answer your question, no, I wouldn't think you could get it to cycle. That is just my guess. I don't know of anyone that is offering a wide variety of recoil springs for the AR15 and I don't think you can get enough gas to cycle the standard spring.

As far as the subsonic loads, have you tried Trail Boss powder yet ? I made a post on www.silencertests.com about my experience using Trail Boss and 77 grain Sierra Match King bullets. It is in the ammo section of that board. VERY quiet and very good accuracy out of my 1:7 barrel and AAC M4-2000 suppressor. These loads are truely Hollywood quiet and Trail Boss gives you over 50% of the case filled. I am going to play around with 100 grain bullets when I get the chance. I bought the bullets but haven't had the time. Working WAY too much.
What loads are you playing with ? If you are of a mind, post your experiences over on that silencer board, ammo section.

 

[taliv]

i will, thanks, 444. I haven't read silencertests in a while.

I was using solo 1250 and H 38. I wanted to use solo 1250, but I can't get the stuff to meter worth a #@$(*%@ in my harrell culver. it's got flakes the size of pancakes. so i tried H38. I started with 55g FMJBT and am working my way through 69g and 80g. I was assuming I'd never get the 80s to stabilize though in my 1:7. If I do, I'll start working on the 90g I was not aware anyone made a 100g .224 bullet.

i am getting hollywood quiet out of these loads. in fact, all the loads i've tried so far have made much less noise than the aforementioned 60g subsonic .22LR ammo shot through a ceiner conversion. they're actually on par sound-wise with the super colibri.

however, trailboss sounds really cool. current loads are about 15% case capacity. 50% would rock.

 

[444]

There is a thread on that board about the 100 grain bullets. No real information about load data or performance, just idle speculation. But the thread does contain the info to buy the bullets from Lock Stock & Barrel.

The 77 grain bullets stablize fine through my 1:7. They are very accurate with that load. BUT, past about 75 yards the wind is murder.

Trail Boss doesn't meter much better than anything else. I have been trickling the charges. But, I am not shooting a whole lot of these subsonic loads anyway. I am eventually just going to load a few hundred up and keep them in AR magazines identified with an orange Mag-Pul.

I am trying to get this load testing done right now while the weather is hot. If these loads are subsonic now, they will be subsonic anytime. All of that load testing with the 77 grain SMKs was done at over 105 degrees.

 

[taliv]

hey, 444, i tried trailboss, finally, this weekend.

i tried 5 rounds of 55g win fmj over 4.7g of TB in a 16" barrel, and avged 1130 fps with a 3.8 SD and 10fps ES. accuracy was fine. couldn't be happier with that. except that they were just barely supersonic. i'll drop the load maybe .3g and work on heavier bullets next time.

 

[MisterPX]

You could also try a lighter buffer, and lightening the carrier.

 

[wdlsguy]

You might contact Fulton Armory to see if an Adjustable Gas Tube would work in your situation.

 

[taliv]

hey 444

i know you were reporting over on silencertests, but i'd rather talk about it here...

iirc, you said your tests with the 100g bullet didn't go well at all. i just got mine this morning from LS&B and I'm a little disappointed.

Did you get the "blemished" bullets?

The only 100g .224 bullets they had were generics in the "blemished" section and they had 3000 of them left (2000 now, i guess) and only came in 1000ct boxes.

Are we talking about the same bullets here?

I was told the "blemish" was "discoloration".

see if you can guess from these pictures what *I* think the "blemish" is.

these were sold as "hollow points" and that would be a fair assessment of about half of them.

anyways, 444, i'm wondering if yours were like this, or if that might explain the inconsistency of which you spoke on silencertests. i'm taking some to the range tomorrow for some quick chronograph work.

the only reason i'm not very disappointed is that for what I'm doing with these, the "blemish" might actually help terminal balistics.

 

[Bartholomew Roberts]

I don't think the method you mentioned would work because even though the dwell time is long, the gas volume isn't very much. However, you might get some success using a longer barrel, short gas port and a suppressor that bleeds gas off the round so it exits at subsonic speeds. Load to sonic, cycle the action as the bullet passes the gas port and then slow it back down by bleeding off gas with holes in the barrel venting into the suppressor.

Probably be pretty temperature/environment sensitive if it did work...

 

[rustymaggot]

aguilla sss .22lr is what you want to go with. get a 22 kit for yor ar. as redneck2 said, 60 granis is 60 grains.

 

[taliv]

bartholomew, thanks. i hadn't thought of that, but i didn't actually expect my idea to work either. so no big deal.

rusty, the 60g agila subsonics were mentioned in post #5. i've been shooting them out of my ceiner conversion for a long time. that's NOT actually what i was looking for, but thanks. (btw, not all bullets of a given weight are equal. different constructions and shapes have different BCs and terminal ballistics, etc)

 

[PAC 762]

Not sure if it would work with a .223 subsonic, but AK guys are building pistol caliber carbines by converting to straight blow-back. They just mill out the bolt carrier and weld the bolt back in the "fire" position, but in the position where the lugs are unlocked.

If you rounds are low-pressure enough to be safe with this, I dont see why it won't work. Just make sure you never run regular ammo through it.

 

[taliv]

btw, here's what 100g .224 bullets look like when they keyhole at 50yrds.

pay no attention to group size, i was intentionally aiming at different places on the paper so none of the holes would touch. however, there were 5 shots fired, and i'm fairly certain i didn't entirely miss the paper. so i dunno where the missing bullet went.