I had several. Sold them off.

They really do need to be set up (like any AR) for the loads. Subs are going to have about half the gas volume of the supers. So, an adjustable gas block and a different buffer/spring combo is best.

Most of the uppers I built for customers, I set up for subs. Running a few supers, with faster powders and lower charge weights is doable in small numbers without damage or excess wear. Another way is to just have the gun tuned for subs with a fixed gas block and standard spring and buffer, then use a heavy buffer with a +25% recoil spring for the supers. Gets you close and it will be shootable in both cases. That is really the path when "buying" a factory gun since they will be set up to run subs and a steady diet of supers will eat gas rings and wear out bolts faster.

 

Ignorant question, but if I were to buy an off the shelf 300 blk, I should expect it to be set up for sub sonic ammunition? And if unknown, ant way to determine what ammo it's been set up for?

 

I’m fascinated by the 300 Blackout. But I keep hearing conflicting stories about switching from subsonic to supersonic ammo.

The manufacturers say their rifles will work with everything. But lots of posts say they need to be tweaked to work with one ammo or the other, you can’t just switch magazines.

1) If you do need to tweak an AR to work with different power levels of ammo, what’s the easiest way? Change out the buffer spring? Install an adjustable gas block?

2) If an AR is set up for subsonic, can you fire limited amounts of supersonic though it reliably?

3) I’m looking at a rifle, but any difference with an AR pistol?

I’m considering getting either a Ruger AR556 or a S&W M&P 15, so I don’t have $2k for a custom build. Or would a Mini 14 be better for switching between power levels?

Sir, I have 2 a Sig MCX Rattler, which is a short stroke piston and a Noveske which is a direct impingement.
The Sig has two gas settings ( Regular and Suppressed); while the Noveske is just the one setting….. it is not the switch block…..

The Noveske has the same point of impact at 25 yards regardless of whether it is firing supers or subs and regardless of whether it is wearing a suppressor or not. There is of course a vertical impact change @ 100 yards.
The Sig is more sensitive to bullet weight and whether it is wearing a suppressor.
Sig Rattler ….With a suppressor @ 25 yards :

My experience with the Sig Rattler , when zeroed @ 25 yards with 220 Grain S&B FMJ’s using a 2MoA Aimpoint will shift 3 inches high and 1&1/2 inches left when shooting 150 grain Super’s. The converse will also be true.
Subsonics through the Rattler and the AWC can are “Hollywood” quiet.

This is a long winded way of saying POI depends on the weapon and can combination and may also be affected by the can to gun mount (as with my Sig).
In terms of reliability and function not one problem from any bullet weight out of either weapon. Both shoot anything flawlessly without a hiccup.

 

In terms of reliability and function not one problem from any bullet weight out of either weapon. Both shoot anything flawlessly without a hiccup.

Do you have 10K, 20K, 30K through them? The reliability, in terms of broken and worn parts takes a while to manifest when shooting over gassed by a good margin.

 

I just shoot super thru mine. Never considered a suppressor. Mine are DI with no gas adjustments

 

I had one and dumped it. It ran everything great but the difference in POI/POA between subs and supers in my gun was 12" @ 25 yards.

 

Suppressed? Un-suppressed or both.

 

My Saint pistol in 300 Blackout runs great with both supers and subs. The trick, for me, is when running subs, use a suppressor. Subs don't function very well in mine without the suppressor. I don't see any reason to run subs without a suppressor.

 

I have a 300 Blackout with 8.5" barrel, and it is 100% reliable with 150g super. With 220g subsonic it wont cycle and is single shot only! Don't have a suppressor but told it would probably cycle subsonic fine with it attached due to higher back pressure.

 

I have a 13" upper that will cycle both super and subs without too much issue and I don't run a can. I will start getting short cycling when I get down to around 900fps with 220s but keeping it at 950fps and above I don't have issues. I run a pistol length direct impingement system with non adjusting gas block. I actually bought an adjustable gas block for it originally thinking I was going to have issues but I never had to use it.

 

I've played with it, but never with a can. I like the range of bullet weights and reloading options.

Store-bought subsonic was much tougher to get to cycle reliably. Some store-bought ammo was more reliable than others (sorry, don't recall which at the moment). If you reload, AA1680 powder is pretty good.

I like the reloading challenge. I also have a bolt rifle in 300BLK so no ammo goes to waste if it does not cycle AR well

Good 300BLK site: 300BlkTalk -Index page

Poster Dellet is very knowledgeable.

 

My suppressed 10.5" LWRCs handle both with no tweaking, but they're set up for subs and the supers pound the **** out of the gun.

The whole point of 7.62x35, for me, is subsonic shooting. If I want a 7.62 going at supersonic speeds I just use a 7.62x51...

 

My suppressed 10.5" LWRCs handle both with no tweaking, but they're set up for subs and the supers pound the **** out of the gun.

The whole point of 7.62x35, for me, is subsonic shooting. If I want a 7.62 going at supersonic speeds I just use a 7.62x51...

But then you gotta haul a large frame around. Fine if you need the extra oomph, but more fatiguing

 

I’ve not found any of the 12 300’s I built (12.5 inch, 18 inch that are mine, and 10 16 inch guns for pig hunting when I was a part of a pig hunting business) to be terribly hard to get to cycle with either.


Brand new, they sometimes took a little breaking in, but after 100-150 rounds they should all reliably run both.



My one took some extra tweaking because I wanted a specialty gun (aka 18 inch Mk-12 clone capable of shooting either sub or super suppressed for an ultra quiet pig gun used to drop lone pigs while approaching sounders, but able to fire supers once the whole group went live ). But it was doable, just took some experimentation. It’s also kind of unique because I built the suppressor just for it, because I wanted to avoid adjustable gas blocks.



We only ran the 300’s for about a year-year and a half before we moved to the 6’s so they only had maybe 3-5K through them at most. Mine are probably approaching 7 ish now. Haven’t had any issues with accelerated breakage but ymmv.

 

I’m fascinated by the 300 Blackout. But I keep hearing conflicting stories about switching from subsonic to supersonic ammo.

The manufacturers say their rifles will work with everything. But lots of posts say they need to be tweaked to work with one ammo or the other, you can’t just switch magazines.

1) If you do need to tweak an AR to work with different power levels of ammo, what’s the easiest way? Change out the buffer spring? Install an adjustable gas block?

2) If an AR is set up for subsonic, can you fire limited amounts of supersonic though it reliably?

3) I’m looking at a rifle, but any difference with an AR pistol?

I’m considering getting either a Ruger AR556 or a S&W M&P 15, so I don’t have $2k for a custom build. Or would a Mini 14 be better for switching between power levels?

I read years ago (don't know if it's true and probably couldn't find the article if I had to) that the blackout was designed to be run subsonic-suppressed or supersonic-unsuppressed. That takes care of the gas volume issue.

Mine has a 10.5" barrel and a SureFire SOCOM300-SPS. I run almost exclusively subsonics through it. I use an adjustable gas block and found that going to a heavier spring and heavier buffer made tuning with the gas block easier. Without the heavy spring and buffer, I was on the last "click" for the gas block. It worked but was still overgassed a bit - brass would hit the front of the port.

I can run supersonics through mine by taking off the suppressor. I've not tried to shoot supersonic suppressed. You could probably get there with enough tuning, but I don't know.

I'm not a big fan of pistols - I don't like the braces. I would rather run an SBR with an adjustable stock. I find a rifle (16+ inch barrel) to be a pain with a suppressor. Not something I'd want to be swinging around in a hallway.

I like the SLR gas blocks. They are adjustable and you can get a rebuild kit for it for when it breaks - and it will break eventually. I also run JP Rifles silent captured spring. Works very well.

 

The platform just was ho hum for me. Ammo shortage hits and I am out. I will say 220 gr subsonic suppressed was scary quiet!

 

I like shooting subs to 100 yards

but when switching to supers at 150 yards and greater, the point of impact is so dramatic you have to rezero your optic for supers.

Any manufacturers make a red dot with two different zero settings that can be switched on the fly?

If not, I think I am better off shooting PCC's. Since the ammo is dramatically cheaper