Choosing a powder...

[Sim G]

Keyboards and search engines..... Aparantly doesn't take long to become an expert. We've had our own few on here who've gone from "new boy" questions to sage advice in the matter of a few weeks.

[Sandgroper]

Well, I was wrong with my vague recollections - no surprise there!

What I remembered reading was a series of articles from Handloader magazine when Col. G.O. Ashley wrote an article that took the view that SEE was a myth. Dr Brownell disagreed and the result was the aforementioned series of articles in 'Handloader Magazine' of which Dr Brownell was the principal author.

I don't know where I got hold of them but Wolfe publishing apparently consolidated them into a book called Firearm Pressure Factors.

These articles could have been close to ground zero in regards to the SEE debate...then again maybe not.

[dromia]

I have Brownell's book Firearms Pressure Factors as well as the original Handloader articles and have referred to it here many times and recommended it as a must read, Brownell does indeed debunk Ashleys articles and confirms that there is a statistical probability off SEE with medium to slow rifle powders.

I have never said that SEE wasn't possible only that it wasn't so with fast powders.

Oh a little knowledge how treacherous it is.

[Sandgroper]

Oh a little knowledge how treacherous it is.

That's why I take on board what you have to say - I'm still learning and it always pays to to listen to your elders.

[Dougan]

All the stuff I have read on SEE relates to medium to slow rifle powders not to the faster powders.

Considering that there must be 100,000s of 38 special target rounds shot each year with fast pistol powders all having a loading density of way less than 50% then that must put the statistical significance of my own clubs continued use of 10s of thousands of rounds of less than 50% fast pistol powder loading density over the past couple of decades into the shade. Not to mention the work of Ed Harris based on Mattern's work of the 1930's, available on here in the library and many other sources why this fast powder "flash over" tale still exists.

I would like to see that article and ponder as to why it has credence after 5 decades of things being otherwise.

This has been discussed at length here previously but obviously to no avail.

I am still interested in Badgers source for this as he is new to handloading.

Not to no avail mate...I get it now - To be fair though, when you read up about 'flash over' the explanation about why it is not an issue with fast burning powders (being more to do with the chemical process and burn rate than volume), I found it a bit like quantum theory; in that you don't have to fully understand it to accept it...

...the way I see it, is that with low volume gallery or cast loads you just need to stick to the 'fast' powders quoted in the manual...or one with an equally fast burning rate.

As for the source of the flash over myth - I can't remember exactly where I heard it, but it is one of those things that people tell you when you start loading...I do remember though that it caused me unnecessary concern when I started loading for my lever action, and I messed about for a while with a 'bulkier' powder to fill up the .357 case before being put right.

[meles meles]

Our sources are twofold, the one we can lay our paws on most immediately being Speers Reloading Manual, 14th Edition, Page 48. It states that though SEE has been shown to occur in 20mm cannon ammunition, it has never been conclusively proven in small arms ammunition.

The second source was a printed article regarding subsonic loads. It urged caution, pointing out that a partially filled case lying on its side in a chamber has a much larger surface area for the primer to ignite than a filled case, thus the initial primer flash can start deflagration of a considerably greater quantity of powder than might otherwise have been anticipated and thus give an unexpected pressure spike. It seemed a logical explanation to us and hence our interest in Trailboss.

We thought it better to err on the side of caution and ask the question rather than blow our head off...

[Dougan]

*Puts down 'Speer no 14', picks up latest Lyman. Applies ice pack to frazzled brain.*

OK; as you have the Lyman manual I can highlight a couple of things that may help explain choice of powder and burning rate...

...If you look at the .303 loads on page 249 - Firstly look at the load for the 174gn Round Nose bullet - Now look at the 'burn rate chart' on page 458...the first thing you'll notice is that all the powders with a quoted load are similar in burn rate to each other; just with a a slightly higher starting load as the powder gets slightly slower...

...Now; say you only had a tub of Hodgdon H380 (number 86 on the chart) - The .303 data doesn't give a load for this powder, but it is very close in burning rate to IMR-4320 (number 85 on the chart)...so, all things being equal (bullet type, weight and seating depth), you can use the same starting load for the Hodgdon as the IMR.

Also, if you look at the 200gn cast boolit load - I wanted to work up a load for this boolit using Viht powder - The Lyman manual doesn't give a load with Viht powder, but if you look at the burn rate chart N120 is very close to IMR-4227...so I was able to use the IMR load data for N120; all be it starting a few grns lower to be sure.

[Dougan]

The second source was a printed article regarding subsonic loads. It urged caution, pointing out that a partially filled case lying on its side in a chamber has a much larger surface area for the primer to ignite than a filled case, thus the initial primer flash can start deflagration of a considerably greater quantity of powder than might otherwise have been anticipated and thus give an unexpected pressure spike. It seemed a logical explanation to us and hence our interest in Trailboss.

We thought it better to err on the side of caution and ask the question rather than blow our head off...

You're right to err on the side of caution, and what you've quoted can be true (though very little evidence of incidence) - But this refers to medium and slow burning powders; which is why I was concerned with going below the minimum load with a powder like N160...

...what Adam is saying is that there is very little risk of this happening with fast burning powders.

This needs understanding if you're going to try cast boolits - Most folk use a 174gn HPBT bullet with around 40gns of a powder equivalent in burning rate to N140 for milsurp .303 - This load fills the case right up to the shoulder and has no risk of flash over...

...but say you now want to try a cast boolit load for the same rifle - 40grns of N140 would be far too strong for a lead boolit (you'd be blowing a deformed mass of hot lead out)...but if you reduced the powder load to give a more appropriate velocity for a cast boolit then the volume would go below that that is safe for a slower powder in a large case like .303...

...so you have two choices - you can try to find a compromise using a harder boolit with a lower load and some filler...or the more popular approach is to switch to a faster powder where the low volume isn't a risk.

[meles meles]

Thanks squirrel, we're cottoning on to burn rates now. We're thinking that the Viht brews seem to be as good as starting point as any, in terms of performance and such things as availability & cost. We suspect we'll get a selection of VIHt and maybe a Ramshot or two to fill in any gaps as we progress. We'll start with just one cartridge and develop for that, then select a second...

[meles meles]

Why doesn't the risk increase with a partial fill of fast powder? That it doesn't seems counter-intuitive: a greater surface area of a faster burning powder seems a recipe for a pressure spike...