What burn rate needs to concern flashover?

[someguy2800]

In this case being a break action it's easy to set headspace so I adjust the dies to give .001" headspace measured across the back of the barrel. I don't have the notes from that charge but it would have been around 20 grains or so in a LC 5.56 case so that would be about 60-70% load density. The load I have in my notes for that gun which I found to be safe was 24 grains of benchmark for a 55 gr hornady sp and later went to 26 for a 40 grain varmageddon, both of which gave no pressure signs with the same lot of powder and primers and brass headstamp. I've shot quite a few pounds of benchmark in my savage and it my favorite powder. I honestly don't know why that load was so overpressure. I guess if there is another factor involved besides charge weight I don't know what it was. I loaded more the same day back up at the starting load and up and it was happy again.

 

[someguy2800]

But some powders don't download well, you have to be careful when downloading.

I'm with GooseGestapo on this one.

I hear ya, that's why I was careful in how I approached it by working down from starting load and stopped when the components told me they were unhappy. Just wanted to share my experience so others can watch for the same thing.

 

[HankC]

Just want to give an update. 123 gr PC cast bullet with 16 gr 4227 in 7.62x39 does not group well! Burned clean but gave me a 5" pattern at 50 yds, Worse than Trail Boss (8.8 gr) and 4895 (25 gr) I tried. I guess low fill rate has an effect on 4227. 8.8 gr Trail Boss (max fill) gave vertical string, 25 gr H4895 grouped OK but still had unburned powder, too fast and cooked the polymer coating. I can try the 123 gr cast in 308 with trail boss or 700X. The old Lyman Cast Bullet HDBK has 123 gr cast bullet (311576) 308 load data with 700X, 9.0 gr (1508 fps) -12.3 gr (1845 fps). Maybe the 9gr 700X works in 7.62x39! I have 700X.

 

[stoky]

go figure.............
Could be why the manufacturer says 4227 is a Magnum Pistol powder.

 

[Walkalong]

And works well for it too. Fast for rifle, slow for pistol.

 

[stoky]

I'm still trying to figure out why download the 7.62x39?
Are we after a commie 300 BLK.?

 

[Sunray]

"...4227 is a medium burn rate powder..." It's considered to be a fast burner. Used in magnum handgun rounds, .30 Carbine(where it shines in compressed loads), et al. Isn't normally used with cast bullets though. Where'd you find the cast data? Just curious.
Anyway, you really don't need to worry about whatever 'flashover' is.
That Barnes 108 is as light as you'll get. It's a frangible bullet(powdered-metal copper-tin core inside a guilding metal jacket) made for training. I'd bet they do amazing things to a varmint.
It's the burning powder that creates the pressure. Pressure doesn't cause anything to burn or not burn.

 

[Walkalong]

Burning powder creates pressure, and that pressure affects how the powder burns and how fast it burns. It's why some powders do better at higher pressures and do not download well.

 

[HankC]

Isn't normally used with cast bullets though. Where'd you find the cast data? Just curious.

Actually I just found Lyman Reloading HDBK 48th Ed lists 4227 17.5 gr (1883 fps) - 19.5 gr (2097 fps) for 130 gr cast bullet (311410 #2 alloy) for 7.62x39. Lyman also shows 115 gr cast bullet (311359, #2 alloy) with 17.0 - 19.5 gr 4227 flying 1906-2142 fps.

 

[Varminterror]

In black powder revolvers, it's more cylinders firing than the one lined up with the barrel.
guess that's not what we're talking about

I've heard that phenomenon called "flash over," but more often called "chain fire."

 

[DukeConnor]

You say flashover but I think what you really mean is a secondary pressure event. Some thing like this:

Graphics from the fine folks at RSI

I have absolutely no need for this device,but, I find myself wanting one.

 

[Orcon]

No kidding, Duke. Some friends and I were going in on one together but most of them backed out on it. I'm still saving my allowance though, I will own one of these.

 

[ants]

I think Hank C has read about super explosive combustion they used to talk about (theoretically) 3 or 4 decades ago at gun counters and some gun rags, postulating that it would go thermonuclear and blow up the known universe, causing injury or death to the shooter. They don't talk about it much anymore. I suspect he's calling it flashover, although that term may be related to backdraft like in the movie Backdraft.



For our buddy Someguy 2800 -- many many years ago we saw a nice conversation between Walkalong and some other senior members on low powder charge. When powder charges get too low, the initiation of combustion first pushes the primer part way out until it hits the bolt face or breach face. Then the cartridge case pushes back against the primer and reseats it. In some instances, it actually smashes it.

I don't suspect you got overpressure from a reduced powder charge. I suspect you got smashed primer from an undercharge.

If you have a revolver, put a primer in an empty case and pop it in the gun. It often backs out under its own pressure, even with no bullet or powder.

 

[someguy2800]

For our buddy Someguy 2800 -- many many years ago we saw a nice conversation between Walkalong and some other senior members on low powder charge. When powder charges get too low, the initiation of combustion first pushes the primer part way out until it hits the bolt face or breach face. Then the cartridge case pushes back against the primer and reseats it. In some instances, it actually smashes it.

I don't suspect you got overpressure from a reduced powder charge. I suspect you got smashed primer from an undercharge.

If you have a revolver, put a primer in an empty case and pop it in the gun. It often backs out under its own pressure, even with no bullet or powder.

Not to belabor the point but again the gun I was talking about is a break action single shot so the headspace was adjusted with the dies to .001". So its not really possible for that to happen. It also does not explain why the brass was sticking in the chamber at the lower charge weight as apposed to the higher charges that extract very easily. I don't know the answer either, I just know I won't download that powder again.

 

[Walkalong]

Break action single shots can have a lot of flex. Don't know if that is relevant here, but I doubt you were getting "flashover" or SEE.