300 Blackout subsonic load data for bolt action w/7.5" barrel

[oaklandraider76]

I just acquired a new Christensen MPP bolt action with a 7.5" barrel (suppressed) and am getting ready to work up some subsonic loads using Hornady 190 gr Sub-X and Hornady 220 gr ELD-X bullets. I have been reoading 300 Blackout for a gas gun with a 16" barrel and have had good results with CFE BLK. I also have lots of Lil'Gun, Accurate #9, and other powders recommended for 300 BLK on hand. With the gas gun (suppressed) I have developed loads that consistently produce muzzle velocities in the 1050 range which is exactly where I want them. I would appreciate forum members thoughts and suggestions on working up loads for a bolt gun with a 7.5" barrel.. Thanks, Robert
*** barrel twist rate is 5:1"

 

[dellet]

Of the three powders you listed I would start around 8.2 grains #9 with the bullet seated a bit short and fine tune velocity with seated depth.

 

[oaklandraider76]

Of the three powders you listed I would start around 8.2 grains #9 with the bullet seated a bit short and fine tune velocity with seated depth.

Thanks dellet. Does this apply to the 190 gr Sub-x or the 220 gr eld-x bullets?

 

[Hoser]

Vhit N-110 is the most accurate powder I have tried with subs.

I mainly use Berger 230s and 215s.

 

[dellet]

Thanks dellet. Does this apply to the 190 gr Sub-x or the 220 gr eld-x bullets?

I have used it for both. Depending on seated depth you might have to adjust powder charge. The window in my AR is quite small for cycling, about 8-8.5 grains, but you won’t have to worry about that, so you can experiment a lot more for accuracy.

With 220 ELD, I’d start just odd the lands if possible, but that bullet is realLy jump tolerant. They both really are.

What is magazine length for your rifle?
I have my bolt actions set up to use AI pattern magazines so max length is around 2.4” depending on the magazine used. It completely changes the load dynamics if your not limited to 2.26”.

Hoser mentioned N110, absolutely worth getting a pound to try. N105 is also a great powder, but supposedly discontinued. It’s a bit faster than #9, but I like it much more.

 

[oaklandraider76]

I will measure the magazine when I get home. Thanks for all the good info.

 

[MisterHelix]

I run 190’s in a 10 inch tube over 9.5 grains or so of imr4227.

Not one of your listed powders, but it’s all I know.

 

[BobT]

If you have access, Shooters World Blackout is another good powder for subs although I never used either of the bullets you mention.

 

[WV Hitman]

I've had a .300 Whisper for 25+ years. JD Jones is a good friend & Tested bullets for him in the .300 for many years. I've never used the SubX bullets because I found 2 that work fantastic on game. The 220 gr. Sierra RN and 186 gr. Lehigh Controlled Fracturing are the only 2 bullets that dropped deer & other game in their tracks 98% of the time. Last year I took a very heavy 8 pt. in a driving rain storm. Dropped him at 240 yds. with the subsonic 220 Sierra. I've killed over 100 deer with these 2 bullets without any problems. The only powder I've ever used in my Whisper is WW296.
WARNING: when shooting a new gun with subsonic loads JD recommended shooting at least 25 supersonic rounds to smooth out the barrel. When loading for subsonic rounds he recommended starting higher than what you THINK you need and progressively load a few rounds with less powder until they are "quiet" when you shoot them.
For reliable use of subsonic rounds a mildot scope is mandatory for use since the bullets fly like a thrown rock. I did shoot a few Horn. SubX rounds in my Whisper. They shot so far off my regular loads that I would have to resight my gun.
JD developed the Whisper using Sierra 240 gr. HPBT Match bullets. They kill by tumbling. You get weird exit holes 7 ARE NOT 100% reliable in stopping game, but are very accurate. Surprisingly the 220 Sierras shoot the same as the 240s out to 250 yards. The 220RNs tumble & expand and are awesome in performance.

 

[mic2377]

I have had good experience with N110 as well. 8.2 - 8.5 grains are a reasonable starting point, and 8.2 grains is subsonic in my 16" barrel with the 190 Sub-x.

Lil'gun is also a good option. Similarly clean burning as N110.

 

[6Creed73]

I recently got a 300BLK bolt gun as well. I've been loading 300BLK for an AR for years, but the bolt gun opens up new possibilities.

No longer worried about cycling, I'll be experimenting with faster pistol powders to get really quiet and clean burning subs. I've heard people have had success with N320, so I'll probably start there. Should be fun.

 

[oaklandraider76]

Well, I took the Christensen MPP 300BLK to the range today and about 20% of the rounds chambered failed to detonate due to light primer strikes. Hmmm. I will be on the phone with tech support today but am not holding my breath. I can check firing pin protrusion and head spacing myself and plan to do this before I make that call. Frustrating, but I am happy with the performance of the rounds I did manage to send downrange. I loaded this ammo for an AR15 in 300BLK so I thought I'd just give it ago in the bolt gun.

Bullet: 208 grain Hornady HPBT match
Powder and charge: 11.9 gr CFE BLK
Primer: CCI small pistol
Case: Hornady
C.O.L. 2.25"
Suppressor: Banish 30

Average velocity (n=16) 944 fps
Extreme spread: 60 fps
STD: 18 fps

Also, the mags will feed cartridges as long as 2.5" so I've got plenty of room to maneuver.

 

[nakneker]

Well, I took the Christensen MPP 300BLK to the ranged today and about 20% of the rounds chambered failed to detonate due to light primer strikes. Hmmm. I will be on the phone with tech support today but am not holding my breath. I can check firing pin protrusion and head spacing myself and plan to do this before I make that call. Frustrating, but I am happy with the performance of the rounds I did manage to send downrange. I loaded this ammo for an AR15 in 300BLK so I thought I'd just give it ago in the bolt gun.

Bullet: 208 grain Hornady HPBT match
Powder and charge: 11.9 gr CFE BLK
Primer: CCI small pistol
Case: Hornady
C.O.L. 2.25"
Suppressor: Banish 30

Average velocity (n=16) 944 fps
Extreme spread: 60 fps
STD: 18 fps

Also, the mags will feed cartridges as long as 2.5" so I've got plenty of room to maneuver.

What kind of accuracy did you get with the round that did ignite. Been looking at one of their bolt 300 blackouts.

 

[oaklandraider76]

What kind of accuracy did you get with the round that did ignite. Been looking at one of their 300 blackouts.

Very good accuracy. I didn't measure the groups but I am very pleased with what I got shooting at a 50 yard target through an EOTech XPS3-0 without magnification. All 16 rounds within a circle about the size of a half-dollar.

 

[Tesoro]

What kind of accuracy did you get with the round that did ignite. Been looking at one of their 300 blackouts.

Why dont you just build your own out of quality components? I dont know anything about Christensen AR's but if they are anything like their bolt brothers then it is a crapshoot on quality control and barrels.

 

[oaklandraider76]

Got this in a trade.

 

[dellet]

Light primer strikes is a pretty common problem in bolt action 300 BLK. The problem is the brass. A lot of commercial brass is at or below minimum base to shoulder length. Not uncommon for dies set up touching the shell holder and a 1/4 turn to do the same. AR’s are much more forgiving so not a lot people notice.

This is compounded with low pressure loads and powder like CFE BLK. You never get enough pressure for the brass to completely form. You need high pressure loads to establish headspace clearance.

It’s tough to get a sub load over 40,000 psi. Powders like N110 still don’t have enough pressure in a sub with a heavy bullet. Best to just shoot some full power supers to fire form.

If you load CFE again, get the bullet down into the powder, your ES number and group size should be reduced to at least half what you have now.

Here’s the difference if made when I tested the powder a couple years ago at 50 yards.

There are so many good powders for bolt guns, CFE is not worth the effort. Accurate #2 and 5 are also excellent choices.

 

[nakneker]

Light primer strikes is a pretty common problem in bolt action 300 BLK. The problem is the brass. A lot of commercial brass is at or below minimum base to shoulder length. Not uncommon for dies set up touching the shell holder and a 1/4 turn to do the same. AR’s are much more forgiving so not a lot people notice.

This is compounded with low pressure loads and powder like CFE BLK. You never get enough pressure for the brass to completely form. You need high pressure loads to establish headspace clearance.

It’s tough to get a sub load over 40,000 psi. Powders like N110 still don’t have enough pressure in a sub with a heavy bullet. Best to just shoot some full power supers to fire form.

If you load CFE again, get the bullet down into the powder, your ES number and group size should be reduced to at least half what you have now.

Here’s the difference if made when I tested the powder a couple years ago at 50 yards.

There are so many good powders for bolt guns, CFE is not worth the effort. Accurate #2 and 5 are also excellent choices.

Good info

 

[oaklandraider76]

Light primer strikes is a pretty common problem in bolt action 300 BLK. The problem is the brass. A lot of commercial brass is at or below minimum base to shoulder length. Not uncommon for dies set up touching the shell holder and a 1/4 turn to do the same. AR’s are much more forgiving so not a lot people notice.

This is compounded with low pressure loads and powder like CFE BLK. You never get enough pressure for the brass to completely form. You need high pressure loads to establish headspace clearance.

It’s tough to get a sub load over 40,000 psi. Powders like N110 still don’t have enough pressure in a sub with a heavy bullet. Best to just shoot some full power supers to fire form.

If you load CFE again, get the bullet down into the powder, your ES number and group size should be reduced to at least half what you have now.

Here’s the difference if made when I tested the powder a couple years ago at 50 yards.

There are so many good powders for bolt guns, CFE is not worth the effort. Accurate #2 and 5 are also excellent choices.

Dellet. Thanks for that - it makes perfect sense. Your experience is showing. Anyway, I love unravelling this type of problem but I'm obviously not as knowledgable as you and other members of this forum - sure glad I found you guys. Can you suggest a safe high-pressure load that I can use to fire from some brass? After that, should I neck size the cases, load subsonic, and try again? Also, I do have other powders besides CFE BLK, just haven't gotten around to loading anything up for the bolt gun so I'm using rounds I loaded for the gas gun. -Robert

 

[dellet]

If you dig around the forum here, and look at why the big kids are doing to prepare to shoot 1000 yards, and load your subs with the same care, MOA at a couple hundred yards is well within reach. Quality bullets, consistent brass, tight tolerances. Go a long way.

Your load may only have 8 grains of powder. Some people with high capacity cartridges may shoot a ladder wider than that. 1/10 of a grain change or less can make a huge difference. That’s why I use seated depth to fine tune. It’s all about case capacity changes and percentages. .005” change in bullet depth can be a huge movement on target.

When you start shooting faster powders, there’s a good chance you will become a noise snob. When your rifle makes less noise than an air rifle. It becomes hard to not to.

You probably noticed a big difference in the same rounds just from firing them in the bolt action. A powder change will drop the noise level even more.

Look forward to seeing some progress.

What other powders?