300 blk pressure problems

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NoName47

NoName47

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I am new to 300 blk. Just built a 9in pistol with ballistic advantage premium series barrel. I am using converted LC brass with a cci 400 primer and 15.0 grains of h110. Hornady 150gr fmj loaded to 2.090in. Major pressure signs, flat primers and ejector marks. Tried 2 different bolts and same results. Hornady book max is 15.7gr and hornady book is known to be conservative. Any ideas or advice is much appreciated.
 
Grabbed 10 random and all measured .330 or .331. I use cci 400 in all my 223 loads without any high pressure signs.
 
Standard seating depth is usually around 2.20 and higher. You may well be seating very deep making the charge effectively over max.

I regularly seat my Blackout bullets much deeper than what the book calls for to get them to fit in my mags, but at the same time I don't combine that with anything near max data.
 
Havok7416 said:
Standard seating depth is usually around 2.20 and higher. You may well be seating very deep making the charge effectively over max.

I regularly seat my Blackout bullets much deeper than what the book calls for to get them to fit in my mags, but at the same time I don't combine that with anything near max data.
Click to expand...
2.090 is barely to the cannelure and is what hornady has in their book
 
Who's to say the cannelure is in the right spot? Nevermind that sesting depth isn't necessarily tied to that point of the bullet.

I have a One Load book for Blackout, although I don't have it in front of me this very minute. The OALs listed in the various sections are overwhelmingly longer than what you list (the book does include Hornady data which I will verify for you as soon as I can). The bottom line when it comes to the signs you have mentioned is either too much powder or not enough case volume for the amount/type of powder in the case. I ignore the OAL when I load Blackout to allow my bullets to fit in my mags and I routinely shoot everything from 147gr to 265gr.

I have done some load development with Blackout using H110. I wasn't happy with the powder and quickly replaced it with more stable options. Hopefully you have a way to verify the accuracy of your scale.
 
https://www.thehighroad.org/index.php?media/albums/high-pressure-signs.148/

The ejector hole may have a burr?
Light ejector makes on the case head may be seen in some factory loads. But i have not seen any 300 brass laying around to check.
Is there any damage to the rim? This happens when brass sticks in the chamber from high pressure.

Hodgdon data showes longer COL for heavy bullets.

Not all brass has the same volume. Less volume, more pressure. What brass are you using?
 
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Havok7416 said:
Who's to say the cannelure is in the right spot? Nevermind that sesting depth isn't necessarily tied to that point of the bullet.
Click to expand...

2.090 is the oal in the hornday 10th manuel. My guess for this length is so the bullet has full contact with the length of neck to the shoulder.
 
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Havok7416 said:
I ignore the OAL when I load Blackout to allow my bullets to fit in my mags and I routinely shoot everything from 147gr to 265gr.
Click to expand...
I am guessing the 147s are m80 pull downs. What oal do you use, if you have the number handy
 
I went to 15.0 Grs N-110 (1875ish FPS), 16.0 Grs of AA #9 (1900ish FPS), and 14.5 Grs 2400 (1850ish FPS) with pulled 147s @ 2.144 OAL

Good plinker loads.

Do not have any H-110.

Use these loads at your own risk, they did not come out of manuals.
 
Just measured my 147gr rounds. They come to 2.18 to 2.19 OAL. Furthermore, my One Load book has Hornady data in it showing OAL for all 150 to 155gr projectiles at 2.22 (see below). 15615502235078979066699922421493.jpg
 
Havok7416 said:
my One Load book has Hornady data in it showing OAL for all 150 to 155gr projectiles at 2.22
Click to expand...
This is my load book, very different for oal lengths.
20190626_082625.jpg
Sorry for the glare
This is the bullet at 2.20. I would not feel comfortable using this length in an ar due to lack of contact between bullet and neck of case
20190626_082640.jpg
 
My guess is Hornady changed the OAL to address magazine fit issues but didn't retest the data. This would put your charge/OAL combination over max values. It certainly would explain your issues. If you must seat the bullet deeper I would recommend dropping the charge by a grain or so. H110 doesn't produce the highest velocities in Blackout anyway, so backing the charge won't hurt anything.

FWIW I wouldn't hesitate to shoot those bullets seated to 2.18-2.19. There's plenty of neck support (IMO). I actually have a bunch of .308 rounds that have the cannelure in almost the exact same spot when seated in the case.
 
Havok7416 said:
FWIW I wouldn't hesitate to shoot those bullets seated to 2.18-2.19. There's plenty of neck support (IMO). I actually have a bunch of .308 rounds that have the cannelure in almost the exact same spot when seated in the case.
Click to expand...
Would you use a heavy crimp then to avoid bullet setback or just use my regular light crimp
 
I lightly roll crimped into the crimp groove on these, and later on the cannelure on the factory seconds (14.5 Grs 2400 & 2.057 OAL) that looked like Hornady bullets.

Use this load at your own risk, they did not come out of manuals.
 

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NoName47 said:
Would you use a heavy crimp then to avoid bullet setback or just use my regular light crimp
Click to expand...
Bullet setback is prevented by neck tension, not crimp. Blackout is a difficult cartridge in that it can (and often does) use brass converted from other calibers. This can result in the brass at the neck being thicker (or thinner) than what it should be. This correlates to better or worse neck tension of course.

What I use is the Lee FCD. It doesn't crimp heavily on rifle rounds. Usually it just removes the flare (sometimes needed on Blackout to get the bigger bullets to properly seat).

In short, I wouldn't change how much crimp you are applying but I would function check the loaded ammo in the gun you intend to shoot them from. Cycle a few rounds of ammo randomly picked from your completed rounds and check them for setback if need be. I have struggled with Blackout, particularly in keeping the larger bullets from jamming into the lands on 2 different rifles (soon to be 3). As a result I have been doing these very things over and over trying to find a suitable load.
 
Havok7416 said:
Bullet setback is prevented by neck tension, not crimp.
Click to expand...
With an auto caliber with a taper crimp I agree, but with the 300 BLK with a bullet with a good crimp groove or cannelure a crimp can help prevent setback.
 
Try a longer OAL or reduce the powder charge. If you're getting high pressure signs those are the most logical steps. Test for neck tension on the load rounds with the longer OAL and see what happens. When encountering problems like this it takes some trial and error to figure out what works best between your brass, your dies, your bullets, and your gun.
 
I do not load 300 BO. Open question for those who are smart - does the Lake City brass have a reduced internal volume due to a thicker case wall? Would this drive pressures up compared to commercial brass in the same load?
 
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