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powder burn/pressure rates

John A.

John A.

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I was looking at some load data, trying to determine which would be the most ideal for my purpose.

In this case, I'm going after the quietest 300 blackout round that I can make. Because while commercial offerings are alright I guess, there is probably always room for improvement by paying attention to the little details.

And in as much, I am on the hunt for the best powder choice for that. I have looked at many different brands and different powders in their lineup the last couple of days that have published data and I keep coming back to hogdon.

Below are snips of their load data for 208 gr.

208 gr 300 blackout load data.PNG

I ordered a pound of H4198 because it looks like it has the least pressure of the bunch. I also understand that CUP and PSI are not the same thing.

Nevertheless, less pressure should (I HOPE) be easier for the suppressor to make it more quiet if comparing apples and extend brass life. Further, I will likely downgrade the charge to about 10.8 - 11.0 gr because I prefer to be closer to ~1025 fps due to my elevation and to give a little wiggle room in hot weather and I think 10.8 will probably get me there.

If there is anyone here who can convert CUP to PSI, I would be interested in hearing roughly what the PSI of these would be.
 
I have never been able to consistently convert C.U.P to P.S.I>>>>>

The Quietest .300 Blackout sounds pretty kewl.

I really want a 6.8 SPC upper/bolt/mag and damn the little bit of noise over a suppressed .300 BO.

Anyone want to contribute to my gofundme to get this done?


OHHHH WAIT.....

This is a thread which John A. started~ forget what I just said ..........

;) ;) ;)
 
I had a 6.8 spc II years ago. It was an OK round. 2400'ish fps.

I was a little put back when I shot a young buck at about 25 yards and found fragments under the hide on the far side (meaning, incomplete pass through, even with bonded bullets).

Still, I can't really argue with dead on the spot. The deer fell where it stood. Heart and lungs looked like slush puppy when I field dressed it. Dumped all of its' energy on target.

Kind of like a hornady varmint vmax, but on a larger scale.
 
running a bolt gun I can see your thought process
Running a gas gun, it doesn't make much since to me to cut pressure, unless you don't mind a single shot
I guess find the threshold of failing to cycle and go from there
Dont know anything about the powder you bought for 300 though, it is super sloooooow burning.....I know people like it for X39
It will be the first time I have seen anyone load rifle powder for a BLK.......but its in the data so whatever I guess
 
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I understand your point Oli.

And I agree and will be watching.

But I think it's worth a shot, because when adding a suppressor, that adds to backpressure.

That added backpressure will (should) help cycle the bolt.

And if there is less pressure involved getting it to speed, should be less pressure for the suppressor to have to deal with, (theoretically) making it more quiet too.

On a little different note, the buffer spring I am running in the gun is a full length tubbs flat coil C/S spring which are notably heavier and longer than a standard short carbine spring and also has an H1 buffer in it and if it has cycling issues, I can always swap springs and buffer for a lighter one if need be.

I don't think it'll turn it into a single shot though.

But then again, I am new to rifle cartridge reloading, and very new to the 300 so it may all look good in my head, but be terrible in person.

I also found a few references to folks using it OK.

"Try H4198 with the 208 amax. I have mine cycling and locking the bolt back without a suppressor. I can't remember my exact load. I believe it is posted in the loads thread. I'm thinking about increasing the charge a little. I'm using an AAC 9" upper with spikes buffer. OAL is a tad shorter than posted for the 220 gr"
--------------------
"I have 100% lock back with Subsonic 200, & 208 gr. with & without a suppressor using both A1680 & H4198 in my DI AR. and that is with a Spikes ST-T3 Heavy buffer.

Sierra 200 gr. GK__11.4 H4198*__COL 2.24" __1035 fps @ 48 deg. F.
"____________" ___10.9 A1680 __"_______" __1038 fps @ 49 "____"
Hor. 208 gr. AM ___10.8 H4198*__ COL 2.22"__1033 fps @ 51 "____"
"____________" ___ 11.0 A1680 __"_______"__1036 fps @ 50 "____"
*H4198 is my preferred powder for 300 Blk subs. It's less sensitive to temp. change, it runs a little cleaner & produces a better SD which are all inherent to better accuracy!"
---------------------------------
"
Don't fret about H4198 being cylindrical.., it's a very fine extrusion w/short kernels, it meters well!!
Not sure about max COL, but 2.22" is what I have settled on for the 208 Amax.
I use un-modified 20 rd. P-Mags for subs."
-----------------------------------
"He last time I took Robert's advice he was wrong and I had to go back and correct that information after having tested it and discovered the problem.

Did it ever occur that as the manufacturer's rep he may have a vested interest in that particular bit of "information" you are parroting back?

Stop being a following like a puppydog and learn to think for yourself. I have done extensive work on subsonics of all kinds of different weights and configurations using standard buffers and springs and have had no problems getting different stuff to work.

The suggestion that only the heaviest bullets will work reliably is pure bunk. The 300 Whisper has been around for nearly 25 years now. If the bullet weight issue was real don't you think we'd have heard of it long before Remington started making subsonic ammo using a 220 gr bullet?"
 
You mentioned burn rates earlier.

Looks like the Hogdon 4198 and the IMR 4198 powder are smack dab in the middle of the burn rate chart.

#73 out of 150 (from fastest to slowest).
 
John A. said:
You mentioned burn rates earlier.

Looks like the Hogdon 4198 and the IMR 4198 powder are smack dab in the middle of the burn rate chart.

#73 out of 150 (from fastest to slowest).
Click to expand...
yes in general its in the middle.....300 is very unique.
I would say follow more pistol loading thought on burn rates.
The cartridge was designed using pistol powder, magnum pistol powder is the slowest reliable powder to use.
You are using a fast rifle powder....slower than a slow magnum powder
Just the fact that the conversations you quoted were taking place is evidence that there are problems
You are new to reloading, new to the cartridge, new build.......at least load with something fool proof till you get it all figured out.....or not lol

also 4198 is extruded and in stick form, hard to meter if you are on the .5 grain thing needing to make or cut speed to get quieter
H110 and others are a spherical, making fine tuning a breeze

if you can get with in a couple Dbs of a powder that is more reliable, easier to work with why mess with it
 
Very good points.

On all accounts.
 
but then again, you need to cross this bridge sooner or later .....I know ....I am not any help lol.
You'll get it either way I just want to try to save you from beating your head on the wall
 
Also worth noting, the primers are a little hotter than a cci 400 too. Federal 7 1/2's (which are more like cci 41's I believe). If that makes any difference.

I know I have a big learning curve and am really green at this. And I appreciate you guys that have been doing this for a long time watching out for me and pointing me in the right direction.

I'll be in experimentation mode for a long time until I find the recipe that gives me the best performance downrange with the most quiet report. I have no doubt. And there will certainly be other loads coming up in the future to try out.

I think Remington/AAC has said that 1680 was one of (if not) their favorite powder for subsonics. Not entirely sure if there's a lot of hidden reasons why. But looking at my chart, 1680 is number #69 on the burn rate chart, compared to #73 for the H4198. Not a huge difference there.

But if you know of a proven subsonic recipe for 220 Sierra match boat tips that'll do around 1020'ish fps that you think would get full burn in an 8 1/2 to 9 inches of barrel and keep pressure relatively low at the same time, I'm more than willing to listen. Bonus points for a powder/bullet combo that is in stock.

One link you guys may be interested in:
http://www.300blktalk.com/forum/viewtopic.php?t=86656
 
Federal calls their 7.5 a benchrest primer.
not sure on cup hardness but I think they are on the warmer side like a CCI450. I know 450's have a hard cup because if I am working up loads and start tp pierce 400's as I am getting close I will switch to 450's and back off a little. I end up working past the spot where I was piercing primers on 400's and getting to the speed I require for distance shots.
#41 is a harder yet cup , I imagine they are as hot as it gets because they have to touch off a ton of spherical.....close to 28gr of WC855 (H335)

If anyone is playing with those JP light hammer springs......time to quit when in the harder cup......for reliability

The CMC rocket wire actually hits harder than Milspec
 
Used lots of JP Reduced power springs in the past.

This gun does have the CMC trigger in it ;)

(still thanking you for talking me into that)
 
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the geometry of the trigger is really cool, allowing a nice light pull and more striking power......there is not a primer it wont pop, it will really grow on you. You will get used to it and you will not have issue using it defensively.......it will be awesome though when others shoot it for the first time, awesome for you to watch their face, everyone will comment if they shoot at all
 
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