300BLK: where do I go from here?

[benvigil]

In classic fashion, I decided to dive into the reloading "deep end" with a with a 6" pistol gas 300BLK AR-15. Why do something easy like 9mm (to be fair, I did that too, but I digress)? Before I got the suppressor, supers ran quite well and sub were largely a bust. With the suppressor, subs are on the edge of reliability, depending on load, depending on how clean the barrel is, depending on day of the week. It feeds most of the time, locks back only occasionally. I haven't seen any keyholes, probably thanks to the Faxon 1:5 barrel twist.

My use case for this rifle: suppressed, reliable & quiet for self-defense. Don't need supers and I don't need 1 MOA at 200 yards. AAC ammo was garbage and I had no interest in paying $2.25/round for good subs.

Enter... reloading. Obviously.

The 3 loads I'm developing are:

• Berry's 220gr FMJBT over 11.0gr N120 @ 2.100" OAL
• Hornady 190gr SUB-X over 11.2gr N120 @ 2.050" OAL
• Lehigh 198gr CF over 10.9gr N120 @ 2.225" OAL

If I could do it over again, I'd just invest in the Lehigh (versus Hornady) projectiles, but for now, I have a few hundred of the Hornady's that are good for testing.

Thought 1: Increasingly, the cases are coming out covered in soot and the barrel is getting so dirty that malfunctions starting occuring after 50-70 rounds. I've concluded the most likely culprit is brass hardening (these are 2x fired cases on the 3rd firing) preventing a proper case/chamber seal. First, I have some new Starline brass I'm going to test next time I'm at the range to see if that theory bears out. Second, I'm looking at an induction annealer to test that theory with the existing brass. I feel like a proper chamber seal will also tighten up the velocity swings I'm seeing. Segue...

Thought 2: My velocities seem to be consistently 10-15% lower than what others are reporting for the same loads, and what I should be seeing based on the predictions from GRT. Does an inadequate chamber seal typically result in that big of a velocity drop?

Thought 3: the barrel has a 0.125 gas port, so if the gas is there, it oughta be working. That said, with a 6" barrel, the dwell time is minuscule and 11gr of N120 might be too low pressure, thus exaggerating the seal problem above, and TOO slow burning to build enough pressure during that precious little dwell+suppressor time to cycle adequately. Too much gas and unburnt powder is being lost in the chamber and out the front of the rifle.

Thought 4: N120 seems to have a great reputation but I'm also seeing that most people who love it are running 8"-10.3" barrels. In the earlier days of 300BLK talk a lot of people were trying, with some success, other powders like N110, N105, and Accurate #9. I like the idea of A#9 because it's locally available to me and that'd be ideal. I'm wondering if a load that is faster burning will help with chamber pressure, but still be slow enough at the right charge that burnout takes place fairly close to the barrel length. This might increase the percentage of gas available to cycle the action with less wasted energy.

Thought 5: Maybe I should just cut bait and put an 8" barrel on here? I don't like to fail.

What are your thoughts?

 

[FROGO207]

I have one in 10.5 inch and running it without a suppressor. I have found that the speed of the propellant does make a marked difference for me. I would think a faster propellant and work up to the speed you want would seal better and burn cleaner. I would treat it more like a regular pistol with delayed unlocking as opposed to a rifle round. Its all about the dwell time and resulting gas returned to the action.

 

[mcb]

I am running a 5-inch gun that I run exclusively with sub sonic ammo. I have a somewhat smaller gas port at only .081. With the 220 gr Barry spire point plated bullet iam using 4227. For hunting I am using the 220 gr Maker REX all copper bullets and pushing them with Accurate 1680. I liked the 4227 since it was noticable quieter than many other powder I tried but it would not cycle reliably with the Maker bullets so I switched to the 1680. What velocities are you getting with your loads?

 

[small town life]

Does it have a micro gas system rather than pistol gas? Soot is an early unlock (bolt push back) issue. What recoil system are you using? You say 6" pistol gas, but what is barrel length? I have two 8.5" barrels from aero that run great (ilk need to check gas length), but don't have a suppressor. I believe both are an 8 twist.

 

[mcb]

Pistol length gas systems are pretty normal on 300 BO of nearly any length. My 9-inch and even my 16-inch 300 BO have standard pistol length gas systems. My 5-inch gun has a shorter than pistol length gas system simply due to the extremely short barrel. Short gas systems and 300 BO usually behave very well together. My 16 inch will run supers and subs both with or without my suppressor all with equal reliability. My 9-inch gun get a bit touchy with some subs unsuppressed, it does not lock back all the time without the suppressor. My 5-inch gun only gets subs and runs them very reliably with or without the suppressor but why would you want to run a gun that short without the suppressor? My fingers fear that super short barrel without the suppressor mounted.

 

[Lennyjoe]

I use 1680 for my 190 gr Sub X and 208 gr BTHP subs with a suppressor and definitely use an adjustable gas block to control cycling.

 

[benvigil]

I am running a 5-inch gun that I run exclusively with sub sonic ammo. I have a somewhat smaller gas port at only .081. With the 220 gr Barry spire point plated bullet iam using 4227. For hunting I am using the 220 gr Maker REX all copper bullets and pushing them with Accurate 1680. I liked the 4227 since it was noticable quieter than many other powder I tried but it would not cycle reliably with the Maker bullets so I switched to the 1680. What velocities are you getting with your loads?

This is exactly my use case.

It seems a LOT of shooters have used Accurate 1680 and moved away from it due to it being so dirty. Has that been your experience, gas-wise?

4227 and 1680 are both in that in-between N120/N110 range along with a lot of other commonly used [for 300BLK] powders like CFE and H110.

 

[benvigil]

I would think a faster propellant and work up to the speed you want would seal better and burn cleaner.

That was my thinking. That's part of the reason so many use N120... it's one of the cleanest burning, but is gassy enough to cycle these shorter barrels and gas systems.

 

[mcb]

This is exactly my use case.

It seems a LOT of shooters have used Accurate 1680 and moved away from it due to it being so dirty. Has that been your experience, gas-wise?

4227 and 1680 are both in that in-between N120/N110 range along with a lot of other commonly used [for 300BLK] powders like CFE and H110.

Not dirty enough to stop me from using it so far but I do shoot a lot more of the 4227/Barry's load than the 1680/Maker loads simply due to the cost of the Maker REX bullets. I do have a pound of CFE Black that I am going to try I don't see any reason to stop using 1680 yet.

 

[benvigil]

Does it have a micro gas system rather than pistol gas? Soot is an early unlock (bolt push back) issue. What recoil system are you using? You say 6" pistol gas, but what is barrel length? I have two 8.5" barrels from aero that run great (ilk need to check gas length), but don't have a suppressor. I believe both are an 8 twist.

6" IS the barrel length. It's a Faxon Match Series 6" Gunner 300 BLK, 1:5T Pistol length, 0.125 gas port. I've tried this with Carbine, H1, H2, H3 buffers with little difference between them. I've tried carbine spring and yellow SpringCo.

This gun has run a variety of supers just fine with or without the suppressor.

 

[benvigil]

Not dirty enough to stop me from using it so far but I do shoot a lot more of the 4227/Barry's load than the 1680/Maker loads simply due to the cost of the Maker REX bullets. I do have a pound of CFE Black that I am going to try I don't see any reason to stop using 1680 yet.

That's interesting that the 4227 wouldn't push the Maker loads, since they are the same grain weight. Are the two different enough that the seating depth difference affects the performance or gassiness?

Developing a good load for 5" or 6" barrels in 300BLK seems like I'm threading a needle here!

 

[benvigil]

My 5-inch gun has a shorter than pistol length gas system simply due to the extremely short barrel.

Okay, so micro. I didn't catch this first time through. That would increase your dwell time a little bit (0.52") and help you out. It's ironic that your 5" has a better dwell time than my 6" has with a regular pistol length gas.

Short gas systems and 300 BO usually behave very well together. My 16 inch will run supers and subs both with or without my suppressor all with equal reliability. My 9-inch gun get a bit touchy with some subs unsuppressed, it does not lock back all the time without the suppressor. My 5-inch gun only gets subs and runs them very reliably with or without the suppressor but why would you want to run a gun that short without the suppressor? My fingers fear that super short barrel without the suppressor mounted.

Yup. That's basically my experience and use case for the 6" --- suppressed subs. But I spent a year waiting for the suppressor and dabbled in supers during that time.

 

[mcb]

That's interesting that the 4227 wouldn't push the Maker loads, since they are the same grain weight. Are the two different enough that the seating depth difference affects the performance or gassiness?

Developing a good load for 5" or 6" barrels in 300BLK seems like I'm threading a needle here!

Remember the Barry spire point is a thin copper plating on a fairly soft lead core and the the Maker REX is a monolithic all copper bullet. My guess is something about the increased force required to drive the bullet into the rifling and down the barrel somehow influences the pressure at the gas port.


Left: Maker REX Right: Barry's 220gr Spire Point

I guess I got lucky. I worked my current loads up from my 16-inch carbine and have been using them in my 9-inch and 5 inch gun without issue. I definitely loose some velocity but so far both loads cycle great in all three uppers. I do plan to work up loads specific to each barrel length to get the velocity from the shorter guns back up closer to 1050 fps that the loads were originally made to do in my 16-inch gun.

Okay, so micro. I didn't catch this first time through. That would increase your dwell time a little bit (0.52") and help you out. It's ironic that your 5" has a better dwell time than my 6" has with a regular pistol length gas.


Yup. That's basically my experience and use case for the 6" --- suppressed subs. But I spent a year waiting for the suppressor and dabbled in supers during that time.

I don't think there is a standard micro length gas system. Most of the one I have see use a 5.25 inch length gas tube. My gas system is actually shorter than many Micro, a 4.775


The gas port is all most directly over the tip of the bullet when a cartridge is chambered.

 

[Gordon]

I sure hope you have a 1/7" twist in that 6" barrel to save the baffles in your suppressor with 220 grain subsonics , those extra short barrel with 1/8" twist are famous for tipping an occasional 220 grain subsonic load thru the suppressor. The shortest barrels I've shot with is an AR 8.5" pistol and I prefer a 10" or so , all with Pistol length gas tubes. (and 1-7" twist) . In the short barrels my son and I use Berry's 220 grain with 11.5 Grains of CFEBLK and get 970-1030 fps depending on the barrel exiting the suppressor. On our 16" .300 Black guns, usually reserved for supersonics, it gets just 1070 FPS but that does give a slight down range echo. We have also used 4227 and like it with around 10.5 grains but we only run carbine springs in.300 BLK and all are pistol length gas tubes, the heavier subsonics seem more reliable function wise. We seat those Bullets to 2.250" and use magnum primers if we can get them.

 

[benvigil]

I don't think there is a standard micro length gas system. Most of the one I have see use a 5.25 inch length gas tube. My gas system is actually shorter than many Micro, a 4.775

View attachment 1192607
The gas port is all most directly over the tip of the bullet when a cartridge is chambered.

I've seen 2.78" as standard for micro length on various sites, such as. But yours definitely looks shorter than micro for sure. That would help your dwell time even more.

 

[benvigil]

I sure hope you have a 1/7" twist in that 6" barrel to save the baffles in your suppressor with 220 grain subsonics , those extra short barrel with 1/8" twist are famous for tipping an occasional 220 grain subsonic load thru the suppressor. The shortest barrels I've shot with is an AR 8.5" pistol and I prefer a 10" or so , all with Pistol length gas tubes. (and 1-7" twist) . In the short barrels my son and I use Berry's 220 grain with 11.5 Grains of CFEBLK and get 970-1030 fps depending on the barrel exiting the suppressor. On our 16" .300 Black guns, usually reserved for supersonics, it gets just 1070 FPS but that does give a slight down range echo. We have also used 4227 and like it with around 10.5 grains but we only run carbine springs in.300 BLK and all are pistol length gas tubes, the heavier subsonics seem more reliable function wise. We seat those Bullets to 2.250" and use magnum primers if we can get them.

This Faxon 6" is a 1:5 twist. 300-400 rounds I've put through it and not a single key hole. At 7.5" or under, barrel makers have a mix of 1:5 and 1:7, but pretty much all of them are 1:7T once you get to 8" barrels. Projectiles coming apart is too great a risk at 8"+ with supersonics if they were 1:5T.

 

[Gordon]

This Faxon 6" is a 1:5 twist. 300-400 rounds I've put through it and not a single key hole. At 7.5" or under, barrel makers have a mix of 1:5 and 1:7, but pretty much all of them are 1:7T once you get to 8" barrels. Projectiles coming apart is too great a risk at 8"+ with supersonics if they were 1:5T.

Excellent ! And Faxons are great barrels IMHO

 

[small town life]

6" IS the barrel length. It's a Faxon Match Series 6" Gunner 300 BLK, 1:5T Pistol length, 0.125 gas port. I've tried this with Carbine, H1, H2, H3 buffers with little difference between them. I've tried carbine spring and yellow SpringCo.

This gun has run a variety of supers just fine with or without the suppressor.

So you use carbine tube/sbr setup?

 

[small town life]

Doesn't seem like enough dwell time with a pistol length gas vs micro gas for a 6" barrel? I think it's 1.7" of dwell.

 

[mcb]

Doesn't seem like enough dwell time with a pistol length gas vs micro gas for a 6" barrel? I think it's 1.7" of dwell.

You can always beat dwell time with port pressure and volume. If you look closely the bullet is sticking out of the end of the barrel and yet the gun cycles.

 

[Walkalong]

That’s crazy! Very interesting

 

[benvigil]

So you use carbine tube/sbr setup?

Yup.

 

[benvigil]

Doesn't seem like enough dwell time with a pistol length gas vs micro gas for a 6" barrel? I think it's 1.7" of dwell.

I need to try a few more things (fresh annealed brass, couple other powders, etc.), but yeah, it's uhm .... annoying that a 7.5" would give me better dwell time (obviously) and a 5" or 5.5" with micro gas would also give me more dwell time.

 

[benvigil]

You can always beat dwell time with port pressure and volume. If you look closely the bullet is sticking out of the end of the barrel and yet the gun cycles.

What did I just watch???

At some point, when the ATF comes after you for an unregistered SBR, you just respond "Sorry sir, but it doesn't HAVE a barrel."

 

[mcb]

What did I just watch???

At some point, when the ATF comes after you for an unregistered SBR, you just respond "Sorry sir, but it doesn't HAVE a barrel."

Or is it a short barrel shotgun? I wonder how much of the rifling is present in that barrel given given you can see the tip of the bullet beyond the muzzle.