tribulations of subsonic 300 BLO reloading

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Precision
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tribulations of subsonic 300 BLO reloading

Post by Precision » Fri Oct 11, 2019 7:37 pm

I am supposed to be writing an article on the process of load development.

Pretty simple:
look up published data
do a ladder test start slightly high (slightly supersonic) and working down
check target for instability and to make sure the bullet left the barrel
run over chronograph for fps data
if a load cycles and stabilizes and is in the 1030-1080 range you likely have a winner

I ran out of imperial and grabbed Hornady one shot - case STUCK in the deprime / resizer die
No worries I have all that I need
Chrony won't work - 5 rounds later figured out the sensitivity needs adjusted, got that working
A 1680 shot over nonfunctioning chrony - sounded supersonic through all weights, hmmm
CFE BLK chrony works and get good subsonic readings
h110 chrony works and get solid readings of +2000 fps
recheck chart, my chart is correct from published data (Sierra)
reweigh 2 and reshoot - same thing
try again with A 1680 - same thing +2000 fps even at 1.8 gr lower than list for 1050 fps and one very bulging primer

checked Gem scale calibration weight is 20 grams shows as 19.993 grams or 308.64grains which reads as 308.54 grains. Seems like that is working well but who knows?
go to check throw weights with the balance beam scale. The helper who packed it for the move, did not pack the powder holder with the scale.
I guess Amazon prime balance beam scale order upcoming. And calling around for a loaner die or Amazon for the die too.


Wasted an entire day and 20+ $0.80 bullets to figure out not a damn thing
some days really just need to stop being so shitty.
"Those who hammer their guns into plows will plow for those who do not." ~Thomas Jefferson
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Netpackrat
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Re: tribulations of subsonic 300 BLO reloading

Post by Netpackrat » Fri Oct 11, 2019 11:50 pm

Something wrong with that picture. I can send you some info and possibly a spreadsheet with my velocity data, but I don't appear to have your email address any longer. What bullet and charge weight of 1680 are you using? I used the original sub load developed by AAC that used to be posted at 300blackout.com (had to use Internet Wayback Machine to find it again) as my starting point and tested 2 different bullets in 3 different rifles.

Also, CFE BLK powder is bad news... As documented on 300blktalk.com, there is a spike in its pressure curve, so it isn't really predictable.
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Precision
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Re: tribulations of subsonic 300 BLO reloading

Post by Precision » Sat Oct 12, 2019 1:52 am

Netpackrat wrote:
Fri Oct 11, 2019 11:50 pm
Something wrong with that picture. I can send you some info and possibly a spreadsheet with my velocity data, but I don't appear to have your email address any longer. What bullet and charge weight of 1680 are you using? I used the original sub load developed by AAC that used to be posted at 300blackout.com (had to use Internet Wayback Machine to find it again) as my starting point and tested 2 different bullets in 3 different rifles.

Also, CFE BLK powder is bad news... As documented on 300blktalk.com, there is a spike in its pressure curve, so it isn't really predictable.
Funny thing is CFE Black was the only one to give consistent subsonic.

CFE black was 11.2 - chrony error
... .... 10.8 - 1077
... .... 10.5 1018
both of which are in line with expectations

I dont have my paper handy, but 1680 started 0.3 gr lower than the Siera data for 1100 fps and I was getting +2000 fps one load was almost 2300 with a 200 gr pill. YIKES. Major primer issue on that one

h110 was 9.5, 9.2, 8.9 and 8.5 grains -- chrony didn't work on the first go round but did on the second and again +2000 fps

I am pretty sure it is my scale reading wrong, but the calibration weight seems to line up. Perhaps it is hinky at such low weights.
I have a new balance beam arriving on sunday so I can check the scale at low grain weights. If my "9.8 gr" is really 14.5 gr my results would make a lot more sense.

business email jbibby at fbagroupllc dot com
"Those who hammer their guns into plows will plow for those who do not." ~Thomas Jefferson
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Netpackrat
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Re: tribulations of subsonic 300 BLO reloading

Post by Netpackrat » Sat Oct 12, 2019 7:45 am

Spreadsheet sent. I settled on two loads using 1680 under 220 grain Matchkings and 220 grain Lapua Scenar. I am loading the Matchkings for my 16" rifles over 11.0 grains of 1680 and a CCI 450 primer, to an OAL of 2.120". Out of my Model 7 they averaged 988fps. You may note that this charge weight isn't shown on the spreadsheet I sent you; I decided to split the difference between my test loads of 11.2 and 10.8 grains of 1680, and the resulting velocity is less than you might otherwise expect because I tested the final load on a cooler day.

The Lapuas are loaded over 10.4 grains of 1680 at 2.160", and averaged 990fps out of my 10" SBR. The Lapuas gave higher velocity than the SMKs due to their being much longer than the Sierras and leaving less powder space in the case. As it was I had to seat them out farther; the OAL used still fits in the Lancer mags I am using and functions through both of my ARs perfectly. Even the lightest of the loads I tested (10.4gr 1680) still functioned both ARs perfectly and locked the bolts back on the empty mag.

I could probably get a little more velocity and still stay subsonic most of the time, but a lot of my shooting is done during the winter when the speed of sound is lower, and it's really annoying to get a crack when you were intending to stay quiet.

FWIW here is the suggested load that AAC developed originally, which I used as my starting point:

-RP 300 AAC Blackout brass
-Remington 7.5 primers
-11.2 grains of A1680
-Case length 1.368 +0.000" -0.020"
-Sierra 220 Matchking @2.120" OAL
-Chamber Pressure 21,100psi
Last edited by Netpackrat on Sat Oct 12, 2019 3:06 pm, edited 1 time in total.
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HTRN
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Re: tribulations of subsonic 300 BLO reloading

Post by HTRN » Sat Oct 12, 2019 10:51 am

Are you using kapok as filler? Because you have to keep the powder over the primer for optimal ignition.

Have you tried the various slow volumetric powders like sr4759 or aa5744? Theyll completly fill the case and give very modest velocities.
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Netpackrat
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Re: tribulations of subsonic 300 BLO reloading

Post by Netpackrat » Sat Oct 12, 2019 3:03 pm

HTRN wrote:
Sat Oct 12, 2019 10:51 am
Are you using kapok as filler? Because you have to keep the powder over the primer for optimal ignition.

Have you tried the various slow volumetric powders like sr4759 or aa5744? Theyll completly fill the case and give very modest velocities.
With the long, heavy bullets generally used for subs in 300 blackout, he shouldn't need any filler. There's more to loading blackout subs than just achieving the desired velocity, otherwise lots of powders would do, and in fact WILL if you are loading ammo to be used exclusively in a bolt (or other manually operated) action. But getting a gas operated gun to run reliably with subsonic ammo is non-trivial, and that's what most people shooting blackout want. The reason A1680 is so commonly used for Blk is that it provides plenty of gas to cycle the action at subsonic velocities. Downsides are it is pretty filthy at those velocities, and because it makes plenty of gas it isn't as quiet as other powders.
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Rich Jordan
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Re: tribulations of subsonic 300 BLO reloading

Post by Rich Jordan » Wed Oct 16, 2019 12:54 am

I've only loaded a few subsonic .300BLKs, and they were with the plated Berry's 220gr bullets. I had enough trouble getting them to feed (the rifle feeds every commercial load I've tried including 220gr subsonic) that they're on hold and I'm playing with supersonics for now. Its a tack driver with 125gr SSTs.

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Netpackrat
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Re: tribulations of subsonic 300 BLO reloading

Post by Netpackrat » Wed Oct 16, 2019 2:47 am

Rich Jordan wrote:
Wed Oct 16, 2019 12:54 am
I've only loaded a few subsonic .300BLKs, and they were with the plated Berry's 220gr bullets. I had enough trouble getting them to feed (the rifle feeds every commercial load I've tried including 220gr subsonic) that they're on hold and I'm playing with supersonics for now. Its a tack driver with 125gr SSTs.
Thanks for the report. Have not heard much good about the Berrys from people who have actually used them. I had hoped they would have been the answer.
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BDK
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Re: tribulations of subsonic 300 BLO reloading

Post by BDK » Wed Oct 16, 2019 5:01 am

Lots of folks liked them in US PSA but totally different than rifle

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Netpackrat
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Re: tribulations of subsonic 300 BLO reloading

Post by Netpackrat » Wed Oct 16, 2019 5:12 am

Yeah I was speaking only of their 220 grain 30 caliber bullets for subsonic blackout. I use lots of their bullets for pistol cartridges and don't have any complaints.
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