Re: Subsonic Unsuppressed 300blk from 8.3" Barrel
Posted: Fri Aug 23, 2019 2:13 pm
All things 300 AAC BLACKOUT
http://www.300BlkTalk.com/forum/
I have a Ballistic Advantage "Hanson" profile barrel which does not have a removable gas block. It is a proprietary factory-installed gas block, so I hope that's not the problem.dellet wrote: ↑Fri Aug 23, 2019 11:29 am Lil'gun will make the problem worse, CFE BLK might be able to mask whatever the actual problem is enough to work.
Pull the gas block, make sure there is no leak or blockage. A leak will show up as a carbon track. Make sure the port is centered in a carbon ring and measure it while it's apart. That is the most likely area of failure. Also check the gas key on the carrier for leaks or being loose.
Unfortunately I don't have a chrono at the moment, so no data.
fancygunz wrote: ↑Thu Aug 22, 2019 11:33 am Hello all, this is my first post but I have been lurking for a long time. I have read probably 90% of all threads related to reloading subsonic 300blk, and none of the suggestions have been working for me.
I have an 8.3" unsuppressed barrel (muzzle brake) with a pistol-length gas system and a 0.0995" gas port (I think). I am using a normal carbine buffer and standard (read: cheap) BCG. Supersonic loads work very well.
I am reloading using the following recipe:
208gr Amax and 220gr ELD-X bullets
9.5gr up to 11.5gr Shooter's World Blackout powder (Lovex D063)
2.21" COAL
CCI #41 "Military" small rifle primers
No matter what I do, I can't get this to cycle properly (edit: not once has it actually fed the next round or locked back on empty). This powder comes highly recommended for this application (subsonic heavy bullets). Aside from increasing the gas port size or using a suppressor, is there anything else I can do to make this cycle? It seems others with similar setups are OK with this powder selection and loading.
Does anyone know the upper charge to stay subsonic with this powder in a short barrel? Most of the load data is with a 16" barrel.
So which is it?fancygunz wrote: ↑Mon Aug 26, 2019 11:08 pm Update: I stripped the rifle and thoroughly cleaned/lubed. I then went up to 11.5gr Shooter's World Blackout and...it cycled! Finally! I must have been on the edge with 11.0gr in a 8.3" barrel.
...however, as some other forum posts on this powder have mentioned, it left unburnt powder residue all over the inside of the gun and on the magazine feed ramps. It was also super smoky - not cool.
I bought a 1lb jug of CFE BLK and loaded it up with 11.5, 12.0, and 12.5gr, compressed loads. All cycled fine, and I could hear the supersonic crack at the 12.5 loading. Time to work down from 11.5gr.
I finally got a new chronograph and I'll test velocities soon.
Aha, you got me. My original post was a typo, I only went up to 11.0gr with SW Blackout. I doubt cleaning/lubing made too much difference, but I will make the borderline loads again and retest. I plan on testing velocities this weekend.dellet wrote: ↑Tue Aug 27, 2019 8:49 am So which is it?
Not trying to grind on the subject, but it’s actually important to know what actually solved the issue.
Was it more powder?
Did you miss something that you corrected in the assembly of the rifle?
Did it just need lube?
I would expect it to have full function down to at least 10.5 grains of Shooters World or 1680, but everything is different. Now that you know it works with 11.5 grains, I would work the load down some and try to understand exactly what the fix was.
Nice you have it working tho.
It reduces the velocity, but not the pressure needed to cycle. The reduced dwell time is a factor that is mitigated with port size.fancygunz wrote: ↑Tue Aug 27, 2019 11:26 amAha, you got me. My original post was a typo, I only went up to 11.0gr with SW Blackout. I doubt cleaning/lubing made too much difference, but I will make the borderline loads again and retest. I plan on testing velocities this weekend.dellet wrote: ↑Tue Aug 27, 2019 8:49 am So which is it?
Not trying to grind on the subject, but it’s actually important to know what actually solved the issue.
Was it more powder?
Did you miss something that you corrected in the assembly of the rifle?
Did it just need lube?
I would expect it to have full function down to at least 10.5 grains of Shooters World or 1680, but everything is different. Now that you know it works with 11.5 grains, I would work the load down some and try to understand exactly what the fix was.
Nice you have it working tho.
My thoughts are that the shorter barrel reduces velocities (vs 16" test barrels) so much that the minimum loads for cycling go up. I calculated a theoretical increase of about 18.5% more powder required to achieve the same velocity in an 8.3' barrel vs 16".
I was surprised how high CFE BLK velocities were out of the 8.3" barrel considering load data said 12.1gr should be 1060 fps out of a 16" barrel....??? This is the most difficult load development I have ever gone through!
If you have a load that will not cycle, but will lock back on the last round, you have a problem. The carrier has to travel farther to lock than to cycle. Carrier may be dragging on loaded rounds in the magazine, but something is wrong.fancygunz wrote: ↑Sun Sep 01, 2019 7:45 pm So here we go, my very strange results from the weekend at 50 yards. Extremely poor accuracy has been a recurring theme with this rifle, both handloads and factory. My most accurate subsonic load EVER is the 1.25 MOA load below. I am using a Primary Arms 6x scope.
I was surprised how high CFE BLK velocities were out of the 8.3" barrel considering load data said 12.1gr should be 1060 fps out of a 16" barrel....??? This is the most difficult load development I have ever gone through!
Shooter's World Blackout:
10.5gr - 2.200" - 927 fps - 2.0 MOA - did NOT cycle or lock back on empty, this was a repeat of a previous load with crimp this time.
11.0gr - 2.200" - 1035 fps - 2.5 MOA - did NOT cycle but locked back on empty. Added a crimp this time, which didn't help. This confirmed my pre-cleaning and lubing test of this load not working.
11.5gr - 2.252" - 1053 fps - 1.25 MOA - cycled and locked. Vertical stringing only so this load looks very promising (StDev 12.1)
CFE BLK:
11.6gr - 2.255" - 1096 fps - 2.5 MOA - cycled and locked
11.9gr - 2.260" - 1123 fps - 2.0 MOA - cycled and locked
12.2gr - 2.260" - 1142 fps - 3.6 MOA - cycled and locked, heard supersonic crack
Shot some factory loads to test my new chrono:
FACTORY Hornady "Black" 220gr - 1028 fps (box spec 1020 fps) - 2.5 MOA
FACTORY Remington UMB OTFB 208gr - 1031 fps (box spec 1015 fps) - 3.0 MOA
These seem a bit high considering I have an 8.3" barrel and factory speeds are usually out of 16", barrel length not specified on box.
2-3 MOA is not acceptable to me.
Dellet, thank you for taking the time to read my posts and reply. I greatly appreciate your feedback.dellet wrote: ↑Mon Sep 02, 2019 11:14 pm If you have a load that will not cycle, but will lock back on the last round, you have a problem. The carrier has to travel farther to lock than to cycle. Carrier may be dragging on loaded rounds in the magazine, but something is wrong.
CFE is being CFE, slightly unpredictable.
2 MOA with subs as a starting point is not uncommon. A 25 fps ES is probably worth close to an inch of vertical at 50.