300 blackout reduced COAL 220 gr Berry’s

[Agbrownmc]

I have a few different powders that I have been working up for light weight subs and heavy subs for my 8” 1:8 pistol AR.
I have gotten several different loads to work just fine with CFE, H110 and now I’m working IMR4227. I just got a nice 150gr FMJ load done and I had it seated to 2.015 OAL. Stupid quiet and cycled great. Anyways, I started on the 220 gr Berry’s and forgot to change the seating height and seated the 220 to 2.015 which is short for a heavy. I have been seating to 2.23 for the previous CFE and H110 loads. Anyways, it seated with no issue and with 10.0 grains of 4227 it just barely went supersonic at 1090 FPS. So I brought it down to 9.5 and it was subsonic at 1026 and then to get a little quieter I went to 9.3 grains. I didn’t shoot for groups, I am going to do that in The morning, but my question is, is there anything wrong with seating to 2.015 when it fits, uncompressed and it shoots good? I guess it’s possible I will see a bad grouping tomorrow, but it cycled good and sounded good. Im guessing that someone may say that there is increased pressure with reduced COAL but I had zero signs of that.
Thanks for any input.

[bangbangping]

It probably would have been better to ask this question before shooting them.

The 300 BLK case is so small that changes in seating depth can cause big changes in pressure. This is especially true with near-max super loads, but you can also get into trouble with subs. If you don't have the experience and/or the references to know what's going to happen, it's always best to stay with book values.

In this particular case, changing the OAL from 2.23 to 2.015 increases the chamber pressure on the order of 50%. But with 4227 the initial (book) pressure was low enough that you're still well inside safe territory. As you mentioned, accuracy may suffer if the bullet doesn't like the long jump. On the other hand, the higher load density and resulting pressure will likely make the load more consistent, so it may shoot better at distance.

Welcome to the forum, and be safe.

[Agbrownmc]

@bangbangping
You are 100% correct. Probably shouldn’t have shot it, but with such a small load and small change in the OAL I thought it would be ok. I had no idea it was a 50% change in pressure. That’s crazy. Again, I probably shouldn’t have. I was hoping that having it seated lower would help the case fill problem with the subsonic loads and the powder position problems. I was hoping that it would help the consistency like you said. Is there a resource that I can use in the future that shows seating depth vs pressure? And where do find the max pressures? I have seen some load data highlighted “max loads” and I have seen some that show the pressures, but I haven’t seen any discussion of max pressures for subsonic loads. That’s why I thought it would be ok. I thought max pressures were more for loading super Sonics.
Thanks for your reply !

[Agbrownmc]

The results are in!
Very very consistent velocities
100% function in AR
The group wasn’t great, but good enough for shooting steel in the back yard. I didn’t measure it but I’m guessing 3” group with the majority in the 2” size at 35 yards. I have a picture of the target but can’t figure out how to upload pics.

Created: 12/15/21 15:12
Description: 2.015-2.017 OAL
Notes 1: 220 gr Berrys
Notes 2: 9.3 gr IMR 4227
Distance to Chromo(FT): 10.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 220.00
Temp: 30 °F
BP: 1008.40 inHg
Altitude: 2500.00
# FPS FT-LBS PF
5 1029 517.33 226.38
4 1024 512.32 225.28
3 1032 520.35 227.04
2 1034 522.37 227.48
1 1041 529.47 229.02
Average: 1032.0 FPS
SD: 6.3 FPS
Min: 1024 FPS
Max: 1041 FPS
Spread: 17 FPS
Shot/sec: 0.3
True MV: 1032 FPS
Group Size (in): 0.00


Bullet Weight(gr): 220.00
Temp: 30°F
BP: 1008.40 inHg
Altitude: 2500.00
# FPS FT-LBS PF
6 1022 510.32 224.84
5 1038 526.42 228.36
4 1031 519.34 226.82
3 1004 492.50 220.88
2 1022 510.32 224.84
1 1041 529.47 229.02
Average: 1026.3 FPS
SD: 13.5 FPS
Min: 1004 FPS
Max: 1041 FPS
Spread: 37 FPS
Shot/sec: 0.2
True MV: 1026 FPS
Group Size (in): 0.00

[bangbangping]

@bangbangping
You are 100% correct. Probably shouldn’t have shot it, but with such a small load and small change in the OAL I thought it would be ok. I had no idea it was a 50% change in pressure. That’s crazy. Again, I probably shouldn’t have. I was hoping that having it seated lower would help the case fill problem with the subsonic loads and the powder position problems. I was hoping that it would help the consistency like you said. Is there a resource that I can use in the future that shows seating depth vs pressure? And where do find the max pressures? I have seen some load data highlighted “max loads” and I have seen some that show the pressures, but I haven’t seen any discussion of max pressures for subsonic loads. That’s why I thought it would be ok. I thought max pressures were more for loading super Sonics.
Thanks for your reply !

There are lots of ways to get into trouble with subs, especially when using fast pistol powders. The only reference I'm aware of is a program called QuickLOAD. You can play "what if" with just about any cartridge/barrel length/powder/bullet combination you can imagine. Not cheap, about $150, but these days that's only a couple of boxes of ammo. QuickLOAD

[dellet]

I will just throw this out there for perspective of pressure differences related to seated depth and bullet weight. How it can be manipulated to your advantage.

My sub load for for 125 SST’s is 11.2 grains at 1010 fps. In an 8” barrel.

[Agbrownmc]

@dellet
You didn’t say powder type or COAL.
11+ grains seems on the high side, so I’m guessing 1680 or TB.
And I don’t 100% understand your comment.

[dellet]

@dellet
You didn’t say powder type or COAL.
11+ grains seems on the high side, so I’m guessing 1680 or TB.
And I don’t 100% understand your comment.

125 SST
4227, 11.2 grains
2.10 COL
1010 FPS, 8” barrel
Full function

Smokeless powder needs pressure to work, it’s a time and space relationship. If you increase pressure, it burns faster, and that creates more pressure. The faster that pressure builds, the higher it peaks, the faster it drops.

Smaller space, heavier bullet, more pressure, more efficient burn, higher velocity.

So moving the bullet in and out, changes the pressure curve. The height of the peak, length of the downward slope and ultimately the muzzle pressure. You use that information to tune your load, effecting cycling reliability, noise/muzzle blast as well as velocity.

That’s the advantage of something like Quickload, you can map or graph pressure curve and load efficiency.

[Ryno785]

@dellet
You didn’t say powder type or COAL.
11+ grains seems on the high side, so I’m guessing 1680 or TB.
And I don’t 100% understand your comment.

125 SST
4227, 11.2 grains
2.10 COL
1010 FPS, 8” barrel
Full function

Smokeless powder needs pressure to work, it’s a time and space relationship. If you increase pressure, it burns faster, and that creates more pressure. The faster that pressure builds, the higher it peaks, the faster it drops.

Smaller space, heavier bullet, more pressure, more efficient burn, higher velocity.

So moving the bullet in and out, changes the pressure curve. The height of the peak, length of the downward slope and ultimately the muzzle pressure. You use that information to tune your load, effecting cycling reliability, noise/muzzle blast as well as velocity.

That’s the advantage of something like Quickload, you can map or graph pressure curve and load efficiency.

125 grain subs huh? What buffer are you running and any idea what size your gas port is? Also, assuming you are running suppressed?

[dellet]

@dellet
You didn’t say powder type or COAL.
11+ grains seems on the high side, so I’m guessing 1680 or TB.
And I don’t 100% understand your comment.

125 SST
4227, 11.2 grains
2.10 COL
1010 FPS, 8” barrel
Full function

Smokeless powder needs pressure to work, it’s a time and space relationship. If you increase pressure, it burns faster, and that creates more pressure. The faster that pressure builds, the higher it peaks, the faster it drops.

Smaller space, heavier bullet, more pressure, more efficient burn, higher velocity.

So moving the bullet in and out, changes the pressure curve. The height of the peak, length of the downward slope and ultimately the muzzle pressure. You use that information to tune your load, effecting cycling reliability, noise/muzzle blast as well as velocity.

That’s the advantage of something like Quickload, you can map or graph pressure curve and load efficiency.

125 grain subs huh? What buffer are you running and any idea what size your gas port is? Also, assuming you are running suppressed?

Suppressed, What would be the equivalent to an H2 buffer, but it’s a JP captured tungsten, port is .102”, SLR adjustable 3 clicks from wide open.