Velocities significantly higher than Load Data

[JamesM]

Hello, first time posting here. I recently started reloading after a 10 year hiatus because I want to be able to shoot subs through my 300 blackout MCX. I am using 208gr BTHPs, over CFEblk. I loaded up around 15 rounds from 10.2 gr up to the 11.6gr recommended in the available load data (load data is for A-max, but I cannot find specific data for this bullet to save my life.) Today I took them to the range to do some ladder testing and see what kind of velocities I'm getting. According to the book, velocities should be close to 1060 on the high end. Every round I shot was over 1400 fps. the 11.6 gr projectile was around 1465, and the 10.2 on the low end was 1423. Can anyone explain this discrepancy? I'm using an MCX with 9" 1/5 twist barrel so I'm even more baffled at the velocity increase.

 

[Adam in WI]

@dellet knows a bunch about the blackout. Maybe he can help you out

 

[Lone Hunter]

Checked your chronograph against another chronograph? That might explain the discrepancy. I have 2 chronographs for this very reason.

 

[Lone Hunter]

Hodgon shows 11.6 max with 1041 fps. 16” barrel on this data. Doesn’t show a starting load though. Doesn’t make sense using a 9 1/2” barrel your velocities are that high. Still would try another chronograph.

 

[JamesM]

Hodgon shows 11.6 max with 1041 fps. 16” barrel on this data. Doesn’t show a starting load though. Doesn’t make sense using a 9 1/2” barrel your velocities are that high. Still would try another chronograph.

I used a batch of factory rounds (super) prior and got around 1800 fps. Had the range guy shoot his PCC through it and it read right at around 1200 fps, so the velocities for everything else seemed to be right on the money, it was just the loads for the ladder test that were off.

 

[Lone Hunter]

Sierra 6th Edition shows 210 gr HPBT Match. This link from Hodgon shows subsonic loads in different cartridges.

https://hodgdon.com/wp-content/uploads/2020/07/subsonic-data-final.pdf

 

[JamesM]

I mean I followed everything I could find to the letter. 11.6 gr max, 2.25 coal +-.005in. I don't understand how it would be that much faster. I started thinking maybe because its a short stroke piston, but that shouldnt even have that much effect.

 

[dellet]

Using Hodgdon data will lead you down the wrong path.

How far out was the chronograph?
Less than 5 yards you might be picking up muzzle blast.

As for why other rounds seemed reasonable, CFE BLK burns so poorly that you might of had powder messing with the readings. The other rounds were burning clean. Just a thought.

It’s also prone to huge ES numbers with low density loads.

You’re no where near max load, based on pressure. Hodgdon and some others cut heavy bullet data off at 1050 fps, not max pressure. Here’s a different look at Sierra data.

I would start around 11 grains and seat the bullet as deep as possible, touching the powder if the bearing surface is still above the neck. The proper way to make that recommendation is the do a reverse ladder and just keep seating the bullet deeper starting at 2.220”

I looked up old data posted here for a 208 AMax https://www.300blktalk.com/forum/viewtopic.php?t=100097

11.2 grains at 2.225” had an ES over 100 fps with an average of 800 from an 8” barrel.

11.5 grains at 2.195” cut the ES in half and raised the velocity to around 1050 Fps. It also dropped the vertical stringing at 50 yards from about 4” to 1/2”.

If you can compress that powder, it works pretty well. It will cycle any thing sub sonic, but it’s dirty. Only powder I’ve ever used that I needed a gas mask.

Hope that helps.

 

[JamesM]

Using Hodgdon data will lead you down the wrong path.

How far out was the chronograph?
Less than 5 yards you might be picking up muzzle blast.

As for why other rounds seemed reasonable, CFE BLK burns so poorly that you might of had powder messing with the readings. The other rounds were burning clean. Just a thought.

It’s also prone to huge ES numbers with low density loads.

You’re no where near max load, based on pressure. Hodgdon and some others cut heavy bullet data off at 1050 fps, not max pressure. Here’s a different look at Sierra data.
View attachment 1375994
I would start around 11 grains and seat the bullet as deep as possible, touching the powder if the bearing surface is still above the neck. The proper way to make that recommendation is the do a reverse ladder and just keep seating the bullet deeper starting at 2.220”

I looked up old data posted here for a 208 AMax https://www.300blktalk.com/forum/viewtopic.php?t=100097

11.2 grains at 2.225” had an ES over 100 fps with an average of 800 from an 8” barrel.

11.5 grains at 2.195” cut the ES in half and raised the velocity to around 1050 Fps. It also dropped the vertical stringing at 50 yards from about 4” to 1/2”.

If you can compress that powder, it works pretty well. It will cycle any thing sub sonic, but it’s dirty. Only powder I’ve ever used that I needed a gas mask.

Hope that helps.

Thanks, I might have had the chrono just inside 5 yards. First time taking it out, so I may have just set it up wrong. I was just confused because the readings seemed fine for the other rounds, but the powder thing makes some sense. As far as powder goes the selection in my area is fairly limited. I believe they have H110 , so I may try that. Id just rather avoid hazmat charges. Is there anything you would reccommend? At the end of the day Im looking to make some subsonic target loads and when I can get my hands on it, some subsonic 190gr sub-x rounds.

 

[dellet]

I’m a huge fan of fast powders for subs, so I always shoot the fastest that will reliably cycle. It takes work and not where you want to start with the cartridge.

Big Vihtavouri fan, N120 works very well for subs, as does N110 in shorter barrels. Use data for 1200 fps and work down.

H110/296 is a good choice and will work both sub and super, but you have to be aware of the added back pressure a suppressor provides. Without one, there may be cycling issues. As the powder gets faster, and the bullets get lighter, the loads can take more effort.

1680, Shooters World Blackout, are all well known and good for subs. LT30 is easy to work with. 4227, 11FS are others that might be on the shelf longer than some other powders.

The big thing to remember is that if you treat the cartridge as 3 completely different cartridges, and a 4th that will throw some curves, you’ll have more success. Subs, with and without a suppressor will need a different load, maybe even a different powder.
Supers in a 9” 1/5 twist need to be kept below 2100 fps for a lot of bullets. Bullets spinning 300,000 rpm from a hot barrel have a habit of coming apart and 110 grain bullets can be pushed to 2300 in a 9”.

It can be a lot of fun, it can be extremely frustrating, it just takes a bit of thought and load experimenting.

 

[JamesM]

I’m a huge fan of fast powders for subs, so I always shoot the fastest that will reliably cycle. It takes work and not where you want to start with the cartridge.

Big Vihtavouri fan, N120 works very well for subs, as does N110 in shorter barrels. Use data for 1200 fps and work down.

H110/296 is a good choice and will work both sub and super, but you have to be aware of the added back pressure a suppressor provides. Without one, there may be cycling issues. As the powder gets faster, and the bullets get lighter, the loads can take more effort.

1680, Shooters World Blackout, are all well known and good for subs. LT30 is easy to work with. 4227, 11FS are others that might be on the shelf longer than some other powders.

The big thing to remember is that if you treat the cartridge as 3 completely different cartridges, and a 4th that will throw some curves, you’ll have more success. Subs, with and without a suppressor will need a different load, maybe even a different powder.
Supers in a 9” 1/5 twist need to be kept below 2100 fps for a lot of bullets. Bullets spinning 300,000 rpm from a hot barrel have a habit of coming apart and 110 grain bullets can be pushed to 2300 in a 9”.

It can be a lot of fun, it can be extremely frustrating, it just takes a bit of thought and load experimenting.

Thanks. I think my local store actually stocks n110, so I may look into grabbing that. Ive seen a lot of recommendations before I got the CFEblk, but they didnt have that so I went with the CFE as I wasnt sure about the N110.

As far as H110 goes do you think it would still cycle with larger bullets in a short stroke piston? I don't ever plan on going below 190 for subs. The MCX also has the adjustable gas regulator for suppressed and unsuppressed, so hopefully that will help a bit too.

I'll have to do some more research before I get into supers. ATM I can get access to factory supers for a decent price here, so I'm not as worried about reloading them, at least while I'm still tinkering with the subs. Ill keep the barrel twist in mind though when I do. I suppose I'll hold on to the CFE for when that time comes.

Thanks again. Hopefully that should be enough to see some more significant results next time I go to the range. Driving an hour to shoot a subsonic ladder that never went subsonic hurt my soul a bit.

 

[jcm800]

The easy button for supers.... h110/296 <150gr.
1680/ Blackout 150gr and over. Easy sub moa if your rifle is up to it.

 

[Ernest T]

I had a similar problem with 45 ACP, I expected mid 800s and got 12-1400 fps. I knew that was not possible so I looked at other sources of the discrepancy. I moved the chronograph back to 20' from 10-12' and the issue went away.

 

[JamesM]

I had a similar problem with 45 ACP, I expected mid 800s and got 12-1400 fps. I knew that was not possible so I looked at other sources of the discrepancy. I moved the chronograph back to 20' from 10-12' and the issue went away.

Thanks. Ill be setting up the chrono much further back next time around. Chalk it up to the learning curve. I literally got it in the night before I went to the range