300 Blackout Cycling

[petroid]

I am new to reloading 300 Blackout and am trying to develop a load for my AR15 pistol.
Barrel is a CMMG 12.5" 1:7 twist pistol gas port
Parkerized FA BCG
PSA LPK with standard buffer and spring

I am loading the Lee 230gr boolit cast from AC COWW
some PC'd with HF red, some Alox lubed
COL 2.25"

My first attempts were with Reloader 7
PC boolits
10.5 gr ejected did not cycle
11.0 gr ejected did not cycle
11.5 gr cycled, no LSHO - best group 1.5" at 25 yds

Alox lubed
10.5 gr ejected did not cycle
11.0 gr ejected did not cycle
11.5 gr cycled and LSHO - best group 1" at 25 yds
12.0 gr cycled and LSHO

Then I loaded and shot one round each with H110 and PC boolits starting at 9.5 and up to 10.5 gr
all ejected but wouldn't load the next round.

I didn't have a chrony so I don't know if they are subsonic, which is the goal.
I am thinking the loads that cycle the action are likely to be supersonic.

Does anyone have any advice?
Should I load higher charges of H110 and see what happens?
Should I change the buffer?
I don't know what size the gas port is but I'm wondering if it needs to be bigger.
I also am wondering if I just need to shoot some more to really break in the entire action. I shot one round and cleaned ten times with factory supersonic ammo prior to my cast boolit loads, but maybe it needs some more loosening up?

I appreciate any advice. Pete

[supersniper]

Pete,

So far, the best powder I've found for subsonic loading is AA1680.

With my 16'' CMMG pistol gas barrel I have an RL7 of 10.5 that cycles but no BHO and a IMR4227 load of 9.5 which does the same. Both are sub loads.

The AA1680 load of 9.5 and up cycles and has BHO - I have not tested lower charges than that.

H110 is best left for supersonic loads.

I have found that the lightest buffer (std.) is needed for sub loads.

Maybe an AR carrier would be lighter than your FA carrier?

Since you don't have a chrony, then you will have to listen for the "crack" if its supersonic.

[mrvmax]

Most of my feed problems were due to the magazines. Wilson Combat had some 300BO mags for sale that work great. In addition I think my all is about 2.12. There used to be a guy on 300 blackout.com thar sold some Wilson type loaded cartridge checkers that verify a loaded round is the correct size.

[petroid]

supersniper, I will continue trying the RL7 I guess since it seems to be working better than H110. I don't know the weight of the buffer, it is what came with the PSA LPK. I didn't think about the added mass of the FA carrier as opposed to the semi-auto version. Maybe a lighter buffer would help. listening for the crack is tough without a suppressor. My Form4 has been submitted, just waiting...

mrvmax, I don't seem to have trouble feeding when the load cycles, but do you think a different mag would help? I haven't tried my USGI mags yet, just a PMAG.

[DanWalker]

I used 10 grains of 2400 under that boolit, lubed with LLA. It cycled fine for me in my 300 BO. Mine is home built with an alexander arms upper receiver and a barrel bought off of Amazon.

[mrvmax]

I had four different mags that would each only work with 1 or two of my handloads. The D&H mags have a follower specifically for 300 AAC BO and it feeds every load of mine so far.
http://shopwilsoncombat.com/AR-Style-Magazine-300-Blackout-30-Round-DH/productinfo/TR-DHMAG30-300BLK/.
I a no expert and have not loaded for shorter barrels but try going to http://www.300blktalk.com/ and see if you can find some info there. There are a lot of problems/solutions posted.

[petroid]

I just tried some more test loads. Using the H110 and the Lee 230 PC with HF red. started at 10.5 and up to 12 gr when i saw pressure signs. nothing would hold bolt open on last shot. didn't test cycling just loaded one round and put in mag and shot. then i loaded up some reloader 7 at 11.5 and 12 grains with alox lubed boolit. neither would hold open on last shot like they both did at the range the other day.
Now, I don't have a place to shoot at my house, I have to drive 30 minutes to the range. I rigged up a bullet trap so i can test loads for function in my garage. 5 gallon bucket of sand with carpet lined bucket on top. Thus, i have to hold the gun with muzzle straight down. I am wondering if the angle is changing the burn characteristics of the powder and the physics of the action operating. the reloader 7 loads cycled and LSHO worked fine before.

Based on other posts I have read, I am leaning toward the gas port size as being the problem. All the loads I have tested so far should function fine and do in other people's guns, just not mine. I have heard that CMMG has small gas ports for 300 blackout. I don't have machinist's drill bits to measure mine or I would have before I put it together. I may have to get some bits and take it apart to check it. What would the optimal gas port size be for a 12.5" barrel? I have read that CMMG barrel are often .082" and that the "correct" size can be anywhere from .095" to .125" That's a pretty wide range! I really need to shoot some over a chrony so I know what powder charge nets a subsonic projectile and then I can work out the function issues.

[RP]

When I first got my 300 I was having the same kind of problems. I was at the upper plus load data for reloader 7 with a 247 noe boolit to get cycle and lock back. Now that I have fired several hundreds of rounds I have lowered my loads and everything is working nicely now. So get some range time in and let it settle in before you freak out over how its cycling. Well that's my two cents worth.

[Jupiter7]

.095 would be minimum for a pistol length gas system. The h110 loads at about 10grs were supersonic, also is is advised not to download h110 as it is position sensitive and known to pressure spike when downloaded, best at near max load density. 300blk was designed to run carbine buffer and spring, gas port would be where I would concentrate my efforts. Cant help ya with rl7, haven't used it. As above aa1680 is really easy to get function. I use lil gun with good success in both sub and super loads, jacketed and cast.

[petroid]

Thanks to all for the input. In addition to some more range time, I think I'm going to get some drill bits and pull the rail and gas block off to measure the gas port. I feel like I should know what size it is regardless. Hoping some more shooting will help loosen things up a bit and make things work.

[Jailer]

Make sure with a new gun that you are running pretty wet. Get liberal with the lube until it's worked in a bit.

Before you go hogging out the gas port check gas block aligment and rule that out as a possible problem.

Might try some 4198 too if you've got some and see how that works out for ya.

[wlc]

If the upper is new, before drilling out the gas port etc, lube it up really well and hand cycle the action a couple of hundred times. I did have to change out a F/A carrier for an AR carrier on my 16in upper though. H110 is best left for supersonics as has already been said. 1680 is the "best" for subs that will cycle the action. I've has decent luck with RL7, but not as good as 1680.

[petroid]

I plan on doing more shooting to break everything in before I resort to modifications. Just have to find time to go shooting. Thanks for all the advice

[petroid]

Well I loaded some more reloader 7 rounds down to 10.8 and it would cycle. this time i held the buffer against my shoulder like a rifle. I think holding it with an outstretched arm and pointed down into my bullet trap was not giving it the support it needed for the bolt to cycle. still no LSHO with lower charges but im getting there. didn't try any more H110 because I didn't like using it in my Lee Perfect Powder Measure. Granules were so tiny they leaked through every tiny orifice and were making a mess and jamming up the measure. I'll try some more eventually using a dipper and funnel. If it works, I'll try it in my turret press with auto disk measure. Hopefully that works better.

[petroid]

Buddy scored some H110 for me. Started at 9 grains and worked down. Full function including LSHO down to 8.5 gr. 8.2 would cycle but not hold bolt open. Accuracy was so-so, 4" group at 50 yards. I assume this load to be subsonic but didn't have a chrono. My Hornady manual lists 9 gr. at 110 fps with 230 gr jwords so I should be just below the threshold.

[guywitha3006]

OP, just a friendly reminder/heads, most 300 blackout barrels list in the specs/descriptions that they are designed to work with supersonic rounds unsuppressed or suppressed but most say they may or may not work with subsonic ammo without a suppressor. You never mentioned if you have/plan to use a suppressor, if you have a .30 caliber can that should help out. I am hoping it will be reliable either way for you. I know I have my fingers crossed that I won't have to buy a $150 AAC brake right away to get my new 10.5" pistol (some assembly required yet) to run subsonic ammo...Lead is plentiful and easy to get...powder not so much.

My load with the lee 230, COWW, Winchester Small Rifle primers, and H110 is right around 9.5 grains (use at your own risk). This load is subsonic in my 16" Noveske with or without my suppressor. I get LSHO and decent accuracy with it, have not tried R7 so I can't help there.

Good luck,
Guywitha3006

ETA I use either the 45/45/10 Alox lube for ammo I don't plan to shoot through the suppressor or ESPC Harbor Freight Black for the ones destined to go through the can.

[Poppa-64]

8.5 barrel through a Thunder Beast 30PS chronys at 1022 fps with 11.6g 1680 shooting the 230g Lee. I use WW with added tin measures 13.9bhn with my Lee tester. COL is 2.25.
Google SEE (secondary explosive effect) to see what happens when you reduce charge below safe levels.

http://members.shaw.ca/cronhelm/DevelopSubsonic.html great site with common sense rules for playing the slow game.

My load may or may not work for you and may actually cause serious harm or death. Use at own risk.

[FLHTC]

I am new to reloading 300 Blackout and am trying to develop a load for my AR15 pistol.
Barrel is a CMMG 12.5" 1:7 twist pistol gas port
Parkerized FA BCG
PSA LPK with standard buffer and spring

I am loading the Lee 230gr boolit cast from AC COWW
some PC'd with HF red, some Alox lubed
COL 2.25"

My first attempts were with Reloader 7
PC boolits
10.5 gr ejected did not cycle
11.0 gr ejected did not cycle
11.5 gr cycled, no LSHO - best group 1.5" at 25 yds

Alox lubed
10.5 gr ejected did not cycle
11.0 gr ejected did not cycle
11.5 gr cycled and LSHO - best group 1" at 25 yds
12.0 gr cycled and LSHO

Then I loaded and shot one round each with H110 and PC boolits starting at 9.5 and up to 10.5 gr
all ejected but wouldn't load the next round.

I didn't have a chrony so I don't know if they are subsonic, which is the goal.
I am thinking the loads that cycle the action are likely to be supersonic.

Does anyone have any advice?
Should I load higher charges of H110 and see what happens?
Should I change the buffer?
I don't know what size the gas port is but I'm wondering if it needs to be bigger.
I also am wondering if I just need to shoot some more to really break in the entire action. I shot one round and cleaned ten times with factory supersonic ammo prior to my cast boolit loads, but maybe it needs some more loosening up?

I appreciate any advice. Pete

you should be up around 14 to 15 grains. I shoot 18 grains with a 170 grain gas checked bullet