300 blk load question

[wwiaftm]

Hey there, I have an Semi auto 10.5” 300 blk that I have just put my suppressor on. I am fairly new to rifle cartridges and try to follow my hornady book for info. Problem as others know we can’t find the desired components now. The only 220gr projectiles I could find were Everglades plated spire point. After tons of searching I think I’m going to start with a COL of 2.150. The question I have for y’all is about my charge. Only powder I have in that is in that range of burn rate is accurate number 9. I’m currently using it on my 150 gr super loads and it’s working great. My hornady book has 208gr and 225gr listings for #9. The 225gr is 7.5gr/1000, 8.3gr/1100. The 208gr is 7gr/1000, 8gr/1100. I was going to go try 7.4, 7.8, 8.2 and look for pressure but I ran into a few posts that say go as low as it will still cycle.

long story long, my question was when loading subs is it actually going low to keep velocity down for sound? Should I worry less about full case expansion to focus more on lower sound? These are plinking rounds shot at steel targets so accuracy is not the highest importance.

*note I do not have a chrono yet but I do have plenty of range time to use

 

[wedgy]

I haven't been doing the blackout thing for quite a while but I seem to recall with subs the lower end rounds being more danger and to load from the higher velocities down. Assuming they all cycle in your gun but you won't really know the velocity without a chrono. There are many things to play with as far as buffer spring, gas block, etc. to get them to cycle. Just be sure to avoid getting a bullets stuck in the barrel.

This is a good source ; http://www.300blktalk.com/forum/

 

[EOD Rob]

I haven't been doing the blackout thing for quite a while but I seem to recall with subs the lower end rounds being more danger and to load from the higher velocities down. Assuming they all cycle in your gun but you won't really know the velocity without a chrono. There are many things to play with as far as buffer spring, gas block, etc. to get them to cycle. Just be sure to avoid getting a bullets stuck in the barrel.

This is a good source ; http://www.300blktalk.com/forum/

I agree, been loading for sub 300bo for a while. From a reloading stand point, if you refer to them as reduced loads instead of sub sonic loads it will make more sense. As a reloaders, we are always told to start low and work up. However, in this case the rolls are reversed. You are not worried about high pressure with subs. Now you are worried about not cycling and getting a bullet stuck in the barrel. I try to keep mine right around 1050 FPS. this will keep you sub sonic at most elevations with little worry of getting a round stuck or cycling issues. Sound reduction is not going to change much once you get belong that point. Another thing I would recommend is the use of Magnum Primers if you can get them. With that little of powder in a big case, reliable ignition can be an issue. The mag primers are a bit hotter them standards and will help reduce that possible issue. I normally use Trailboss to also battle that issue. It has much larger grain size and help to full up the case with the same grain weight. Again, if you can find it. Hope this helps!
Rob

 

[EOD Rob]

After doing a little looking around, I would not go much below 8.2gr of accurate #9. A few places showed out of a 9" barrel, they were getting around 1021fps. This is were I would stop. I have, in the past loaded down into the 900fps range, but found no benefit to it.
Rob

 

[dellet]

300 Blackout is a silly little cartridge defies logic, and has its own set of rules that constantly shift.

Normally starting low and working up a load is because of safety issues with pressure. With sub sonic or highly reduced loads the danger of sticking one in the barrel or an unstable bullet causing a baffle strike is a bigger concern.

Then you throw a load combo like a 220 cast or plated bullet and a powder like #9, and rules change again.

It will likely be a short stubby bullet that will require a shorter COAL than most data you will find. So unless the manufacturer provides that, you need to find where’s it will hit the lands. It’s highly unlikely that you can load it to magazine length. Maybe your 2.150” is a good number, maybe not.

Because of the shorter seating depth, you have reduced case capacity. This will drive pressure and velocity up. Pressure is the red flag word.

With published data, predicted velocity will be from a 16” barrel, yours at 10.5 will lose 100 fps. The loss of velocity and fear of basically a squib load generally has people going to near max load and working down.

In this combination, that’s the wrong answer.

Most Blackout data for heavy bullets does not go past 1100 fps, instead of a pressure point. This is deceiving.

Hornady, one of the few that list that combination of weight and powder has a max load of 9 grains @ 1300 fps. That is a max pressure load. Not a subsonic max.

Because of all that. This is a combo that is best approached starting somewhat low. If 7.5 grains will exit a 16” barrel, it will certainly exit a 10.5”.

You really want to compare seated depth of the bullet in the data, and the one you are using. Not a big dea, just should be done. Remember that the bullets in the data, all have boat tails, you’re bullet will likely be flatbase, I am not familiar with it, that again takes case capacity and raises peak pressure.

As an example, in an 8” barrel 8.2 grains under a 190 Nosler CC, is 1020 fps. Same rifle, a 220 ELD is roughly 100 fps faster with 7.9 grains. The seated depth, bullet weight and profile cause that much more pressure/velocity by a much more efficient burn of the powder.

I would probably start around 8 grains, and watch the primer close for flattening even at that charge weight. 7.7 might not be a bad idea.

Make sure you see a bullet impact or check the barrel since you don’t have a chronograph.

Better to push a bullet out the barrel with a stick, than pull a bolt out of your face.

On a side note, you may not get that load to cycle without the added back pressure of the suppressor. If it at least cycles, the suppressor should do the rest when it’s attached.

Stay safe and ask questions if you have them. #9 is one of the few powders that will operate in the 40-55,000 psi range even as a sub.

 

[NZ_Fclass]

You may want to go and look at "Johnny's Reloading Bench" on You Tube. He has done a heap of videos on the 300BLK. He may not be a bench shooter, but the basics of reloading the cartridge are all there- and a variety of powders/bullets. You will get some good info out of it.

 

[P1ZombieKiller]

Listen to @dellet
I have learned alot about 300 BO. He posts on 300 blk talk also. much more good info over there about this little cartridge,

 

[wwiaftm]

300 Blackout is a silly little cartridge defies logic, and has its own set of rules that constantly shift.

Normally starting low and working up a load is because of safety issues with pressure. With sub sonic or highly reduced loads the danger of sticking one in the barrel or an unstable bullet causing a baffle strike is a bigger concern.

Then you throw a load combo like a 220 cast or plated bullet and a powder like #9, and rules change again.

It will likely be a short stubby bullet that will require a shorter COAL than most data you will find. So unless the manufacturer provides that, you need to find where’s it will hit the lands. It’s highly unlikely that you can load it to magazine length. Maybe your 2.150” is a good number, maybe not.

Because of the shorter seating depth, you have reduced case capacity. This will drive pressure and velocity up. Pressure is the red flag word.

With published data, predicted velocity will be from a 16” barrel, yours at 10.5 will lose 100 fps. The loss of velocity and fear of basically a squib load generally has people going to near max load and working down.

In this combination, that’s the wrong answer.

Most Blackout data for heavy bullets does not go past 1100 fps, instead of a pressure point. This is deceiving.

Hornady, one of the few that list that combination of weight and powder has a max load of 9 grains @ 1300 fps. That is a max pressure load. Not a subsonic max.

Because of all that. This is a combo that is best approached starting somewhat low. If 7.5 grains will exit a 16” barrel, it will certainly exit a 10.5”.

You really want to compare seated depth of the bullet in the data, and the one you are using. Not a big dea, just should be done. Remember that the bullets in the data, all have boat tails, you’re bullet will likely be flatbase, I am not familiar with it, that again takes case capacity and raises peak pressure.

As an example, in an 8” barrel 8.2 grains under a 190 Nosler CC, is 1020 fps. Same rifle, a 220 ELD is roughly 100 fps faster with 7.9 grains. The seated depth, bullet weight and profile cause that much more pressure/velocity by a much more efficient burn of the powder.

I would probably start around 8 grains, and watch the primer close for flattening even at that charge weight. 7.7 might not be a bad idea.

Make sure you see a bullet impact or check the barrel since you don’t have a chronograph.

Better to push a bullet out the barrel with a stick, than pull a bolt out of your face.

On a side note, you may not get that load to cycle without the added back pressure of the suppressor. If it at least cycles, the suppressor should do the rest when it’s attached.

Stay safe and ask questions if you have them. #9 is one of the few powders that will operate in the 40-55,000 psi range even as a sub.

Thanks everyone for all the information. I did find other flat tail 220gr's and they were listed to 2.150 thats why I went to that number. The Hornady data seemed to work very well with their 150 boat tails and accurate #9 so I am hoping for similar results here.

A friend of mine also told me to load for 1100 and back off until you hear "the crack" disappear. This seems like it might be an easy thing to explain but I am new to this round and the subsonic world. This morning I put together % of each 7.4, 7.8, and 8.2. I plan to test a few of my 150gr supers to listen for "the crack" and see the difference when I switch to the 7.4. I will watch each round carefully as suggested to make sure I don't have and stuck rounds before moving on. I was hoping that 8.2 and 7.8 would be on either side of the sonic crack and I could narrow in from there. I think I understand now what people are saying by working in reverse but with no load data on 220grs or flat tail projectiles I was afraid of over pressure. Now I can see that I am still probably under pressured but I will watch carefully for flat primers (probably not case damage).

Should I be testing these with the suppressor on or off? Will the crack be easily heard with and without the suppressor on?

Again thanks everyone for all of the info and links. I am trying to be safe and search for as much data as I can find.

 

[Oso]

Yes, You should definitely test with and without a suppressor. By screwing on a suppressor you increase the amount of back pressure (gas used to cycle the bolt). You want to test to make sure the load will reliably cycle your rifle so you take a few shots without the suppressor on the gun (lower level of gas to cycle bolt) to make certain that gun cycles properly (spent case gets ejected and also that bolt travels far enough back that it clears the rear of the magazine and on its return is able to pick up the next round off the magazine. A heavy bullet (+190gr) going near subsonic (1000fps) should have no problem functioning gun. Still double check, especially if you are also using an adjustable gas block.

The supersonic crack is easy to hear. The suppressor eliminates the Boom, but you still hear the high crack like a pressure release value venting air.

 

[dellet]

Using data for another bullet may or may not work out. Some photos may help.

Loaded to max length, where they hit the lands or magazine length. You should also get an idea of what the different bullets do to case capacity.

Hornady 220 round nose @ 2.220,
cast 245 @ 2.075”,
Hornady 250 A Tip @2.565” jam,
250 A Tip @ 2.260” mag length




What they would look like in the chamber,








Bullet weight and length means less than profile when case capacity/seated depth is concerned.

Hornady RN, 1.265”, @ 2.220” seated depth .410”
245 cast 1.330”, @ 2.075” seated depth .620”
Hornady 250 A Tip, 1.875” @ 2.565” seated depth, .675”
Hornady 250 A Tip, 1.875” @ 2.260” seated depth, .980”

Note the cast bullet has the shortest max COL. This is why knowing these two numbers are critical. Where it jams and how much bullet is in the case.

If you use Hornady data

208 AMax= 1.488” @ COL 2.250” seated depth is .603”
225 BTHP= 1.558” @ COL 2.250” seated depth is .673”

Finding your seated depth and jam is important for safety and function/cycling of the action. Seated depth is the biggest determining factor for pressure spikes in this application.

Finding subsonic by ear is mostly pointless. You have no idea if velocity is 700 or 1200. At 70 degrees speed of sound is basically 1130 fps. At 1200 fps at the muzzle, the bullet will drop to that speed at about 50 yards. Before the sonic crack can start it has to put run the muzzle blast, air moving faster than the bullet. That takes about 5-10 yards. So you have a sonic crack that lasts about 1/10 of a second.

Been fooled by that one more than once.

The other problem of subsonic by ear is bullet performance. A 50 fps mistake in velocity can mean inches to feet difference in drop at 200 yards. Then many subsonic designed bullets won’t expand under 1000 fps.

Make sure the bullets are stable, round holes in the target before attaching the suppressor. This is the most important thing in the process.

Doing subsonic right, is without a doubt more work than supers.

 

[wwiaftm]

Using data for another bullet may or may not work out. Some photos may help.

Loaded to max length, where they hit the lands or magazine length. You should also get an idea of what the different bullets do to case capacity.

Hornady 220 round nose @ 2.220,
cast 245 @ 2.075”,
Hornady 250 A Tip @2.565” jam,
250 A Tip @ 2.260” mag length


View attachment 1234633

What they would look like in the chamber,
View attachment 1234642

View attachment 1234641

View attachment 1234644

View attachment 1234643

Bullet weight and length means less than profile when case capacity/seated depth is concerned.

Hornady RN, 1.265”, @ 2.220” seated depth .410”
245 cast 1.330”, @ 2.075” seated depth .620”
Hornady 250 A Tip, 1.875” @ 2.565” seated depth, .675”
Hornady 250 A Tip, 1.875” @ 2.260” seated depth, .980”

Note the cast bullet has the shortest max COL. This is why knowing these two numbers are critical. Where it jams and how much bullet is in the case.

If you use Hornady data

208 AMax= 1.488” @ COL 2.250” seated depth is .603”
225 BTHP= 1.558” @ COL 2.250” seated depth is .673”

Finding your seated depth and jam is important for safety and function/cycling of the action. Seated depth is the biggest determining factor for pressure spikes in this application.

Finding subsonic by ear is mostly pointless. You have no idea if velocity is 700 or 1200. At 70 degrees speed of sound is basically 1130 fps. At 1200 fps at the muzzle, the bullet will drop to that speed at about 50 yards. Before the sonic crack can start it has to put run the muzzle blast, air moving faster than the bullet. That takes about 5-10 yards. So you have a sonic crack that lasts about 1/10 of a second.

Been fooled by that one more than once.

The other problem of subsonic by ear is bullet performance. A 50 fps mistake in velocity can mean inches to feet difference in drop at 200 yards. Then many subsonic designed bullets won’t expand under 1000 fps.

Make sure the bullets are stable, round holes in the target before attaching the suppressor. This is the most important thing in the process.

Doing subsonic right, is without a doubt more work than supers.

I have an OAL gauge but have not been able to get a 300 blk modified case yet.

Everglades plated 220gr 1.360


Finished OAL 2.15


*Seated depth .57, does this seam way out of line?

Ogive 1.581


I understand this isn't a great measurement its only used when I read it from the OAL gauge in the rifle so its just here for reference.

I think this is going to be the push I need to go out and get a chrono. The main idea here is to minimize the length the bullet needs to travel before making contact right? So seating a round nose (I have no experience with this) should be calculated by the ogive the same as a point. That is the reasoning for the difference in seating depth.

 

[dellet]

As long as at that length, is less than max for the chamber, you’re in great shape. You could even seat it a bit deeper if you wanted to closer match the Hornady data. You’re still .030” less bullet in the case, the boat tail taper will take some of that, but you’re a good starting point.
Your case length is .1.360” based on the numbers you show.

A chronograph saves a lot of time and components. If you load 8 grains, and have a velocity of 1200 fps, and the gun does not cycle. You’re finished. That powder and bullet combination will require work to gun. 2-3 shots and it’s over.

Well worth the investment.

 

[Barman54]

Post for Reference
Barman54
Out

 

[wwiaftm]

Got the chronograph hooked up and worked up a couple loads ending on 8.4gr. This seemed to keep me in the area I wanted to be 1074, 1089, 1074, 1063 fps. With the supers everything cycled perfectly with the subs I am getting bolt over brass failure. I was thinking the bolt was short cycling but a friend of mine told me it might be cycling too fast. When I got home I read that I should shoot one round to see if it locks back on the mag for a full cycle. Im thinking probably need a lighter buffer spring. So far I have standard carbine spring, H1 buffer, I tried a standard carbine buffer and it seemed to improve a little. Any other suggestions from the pros?

 

[dellet]

Was that with or without the suppressor?

If without, the back pressure from the suppressor will probably push that over the edge and cycle, probably lock back. That's the good news.

Bad news is that it might raise the velocity 15-20 fps if that matters to you. You won't know until you actually test.

What were the other loads, and did they cycle?

Stay at 8.4 grains and if the chamber will allow, move the bullet out, .015-.020". .010" might be enough if that's all you can get.

Moving the bullet out, decreases peak pressure, increases muzzle pressure. Muzzle pressure is what moves the bolt. It will also slightly drop velocity do to the change of burn rate of the powder.

There is a balance between having enough powder to create enough gas volume and pressure to cycle the action, and keeping the pressure level low enough that the charge burns out too quickly.

Here is why the chronograph is so important. If you note the velocity drop by moving the bullet out, and still do not have enough bolt travel to cycle, add .1 grain of powder. Monitor velocity to stay in the window you want. Without the chronograph it's impossible to see the difference these small changes make.

If you can keep from resorting to lighter buffers and bigger gas ports, the switch from sub to super is much easier. You won't be so over gassed and will have less recoil with supers.

 

[LVLAaron]

For what it's worth, CFE BLK has been readily available from many places lately, and it's the best powder for what you're doing.

 

[dellet]

For what it's worth, CFE BLK has been readily available from many places lately, and it's the best powder for what you're doing.

I'll argue that pretty aggressively.

It's comparatively loud, dirty and throws inconsistent velocities to the point of triple digit ES numbers, unless loaded to high densities or even better when compressed. Not really the qualities you want for subsonic shooting.

On the good side it will cycle anything no matter how poorly put together,......
until there is so much un-burned powder in the fire control group that the trigger won't set or it requires the forward assist to chamber a round.

It can be very accurate with supers, but the trade off is a 5-10% loss in velocity.

 

[LVLAaron]

> but have not been able to get a 300 blk modified case yet.

Send me a fired case and I'll make you one.