Choosing a powder...

[Dougan]

You're welcome mate - As a relatively new loader myself I'm aware of how confusing it can be in the beginning...

...let us know how you get on, and keep the questions coming...you can't possibly ask any dafter questions than I already have on the forum razz

[dromia]

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...

As to your second source which seems to be the one you have followed, context is everything and I am sure that this advice is in the context of trying for subsonic loads with medium to slow rifle powders with jacketed bullets, the reduced part is in relation to reducing the charge with these powders not in the context of faster powders.

The articles explanation of SEE, secondary explosion effect which is what we are talking about here is not correct. SEE is when the load density is less than 50% with medium to slow rifle powders, the ignition flash going over the powder can cause an incomplete or delayed burn however the primers flash is enough to drive the bullet out of the case and jam it in the rifling, the slow burning powder finally combusts and starts building pressure however the bullet is no longer part of the cartridge and has become a blockage in the barrel requiring greater pressure to move, the combustion of smokeless powder is dependant on the volume of the space it is burning in, usually this volume is increasing as the bullet travels down the barrel thus managing powder burn and pressure level, when this doesn't happen as with a jammed bullet that is when the chamber pressures can go through the roof.

Regarding the surface area bit I'm not sure about that as I imagine with a case full of powder there would be even more surface area of powder exposed to the primer flash as it goes through the powder and the quantity of powder is the quantity of powder, ignition doesn't start at the bottom and work up, you want the powder to ignite as instantaneously as possible so I cannot see the logic of that at all.

This why I have been emphasising understanding burning rate before starting to think about powder selection.

[dromia]

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...

It isn't counter intuitive at all, if you understand burning rates. Also the surface area argument doesn't stack up see previous post. I would appreciate a link to or a copy of this article.

Fast powder is just that it ignites easily and burns quickly, like the differences between petrol and diesel, so with low density loading of fast powder the primer flash will ignite the powder instantly and it will reach pressure very quickly (fast) so there is no chance of a partial or delayed burn as with slower powders and a bullet jam leading to SEE, there is no chance of a secondary explosion because it is a fast powder.

This why I have been emphasising understanding burning rate before starting to think about powder selection.

[dromia]

- 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.

"- 40grns of N140 would be far too strong for a lead boolit (you'd be blowing a deformed mass of hot lead out)"

No, I use N140 and slower with cast bullets at jacketed velocities.

"so you have two choices - you can try to find a compromise using a harder boolit with a lower load and some filler"

Not really an option, filler with smokeless in bottleneck cases is definitely uncharted territory. Some swear by it and others have had proven ringing or worse, it is far less well researched area than the dreaded SEE, not somewhere I would personally go as the chance of the filler becoming a wad, the cause of ringing, is too much of a risk for me.

For higher velocities it is a tougher not a harder bullet you need.

For me for the lower velocities up to around 2000 fps the pistol and fast rifle powders are indeed the way to go.

[meles meles]

Hmmm, maybe we'd better drop a line to Nicola Tesla and see how the rail guns are coming along...

[meles meles]

So, let's see. Check our working out, oomans, (and squirrel).

We have some N560 and a load for it that works well with hefty Match Kings in 7mm Rem Mag.

Our next task may be to paw load for our various 6.5x55 Swedes. We have a mould for making some 163 gn cast boolits (NOE 269). According to the Viht manual, N 560 is a slow burning powder, and it seems that pushing a hefty bullet up a long thin barrel is a good application for slow burning powders. Lyman suggest that 41.5 gn of N560 is a good starting load for a 160 gn bullet so that seems a reasonable place to begin. If we cross reference to burning rate tables, N560 is considered similar to Reloder 22 and Hodgdon 4831 and, lo and behold, Lyman quotes very similar loads (and resultant velocities) for those two powders too. We can thus either use N560, or if that isn't available, we could try Reloder 22 and Hodgdon 4831? So far, so good?

[dromia]

You have got your powders right for 6.5 Swedish at jacketed velocities, however you have probably chosen the most difficult calibre to shoot cast in at such velocities.

However if 1600 fps is suitable for your application then Vihtavuori N110 and N120 would be a good place to start.

If not then use jacketed with the powders you have selected.

Personally for jacketed in the 6.5 N160 is my powder of choice, N560 will no doubt work as well but I don't like using hot powders like N560 in my Swedes.

Loading for and shooting cast boolits needs a totally different approach to doing so for jacketed. Loads for bullet weight are transferable but to get success from cast requires different case prep, loading techniques, a tougher alloy, high quality casting and quality control. Especially in the 6.5 which has a fast twist rate with easily deformed, long, skinny, high BC boolits.

[meles meles]

Loading for and shooting cast boolits needs a totally different approach to doing so for jacketed. Loads for bullet weight are transferable but to get success from cast requires different case prep, loading techniques, a tougher alloy, high quality casting and quality control. Especially in the 6.5 which has a fast twist rate with easily deformed, long, skinny, high BC boolits.

oooh, 'eck ! Just when we thought we had grasped it...

So, for a cast 163 gn boolit in 6.5x55, what do we do ? Say just for 300 and 600 mards ...

[dromia]

N120 works for me.

[meles meles]

Now, N120 is a fast burning powder. So it generates a lot of gas quickly and presumably gives the cast boolit a good 'ard kick up the base to get it moving up the bore, pronto.


Roger so far ?