How Much Compression Is Too Much?

[Cosmoline]

I'm loading .50-70 rounds with 2F Goex. I put together a nice long drop tube using some copper tube and a spare piece of wood (see attached). Works great and does pack the powder in well. But loading 500+ grain slugs into that fairly small case I still have to compress quite a bit after packing. I use a thin wad on top and the compression insert for the die. The good news is 70 grains 2F can indeed scrunch down enough to permit seating of a 515 grain FN within the OAL of the cartridge.

I'm wondering, though if there's a limit to how far you should compress a load. I've looked on line and in the books and found none, though most are not compressed this far. I also found references to .50-70-500 loadings and they had to have done it to fit the bullet.

Is there a danger of a pressure-caused KB while using the die to compress the powder under the wad?

 

[mykeal]

Real black powder is very stable under compression. I'm not aware of any incidents of ignition while compressing it in a cartridge.

 

[col.lemat]

How much

When the case splits or starts to bulge thats too much compression. I had to throw away a half a dozen 45/70's that would not chamber in my Remmington

 

[SAA]

When the powder crushes enough to change the granulation, that is excessive.

 

[Foto Joe]

Keep in mind that the original 50-70 balloon head brass had a higher interior volume than the brass we use today. As far as how much compression is too much compression, I think the real question should be "what powder load achieves the best accuracy".

I've mashed period correct powder charges into 45 Colt and 44-40 and the boom is impressive but the accuracy increased with a lighter load, your mileage may vary.

 

[Cosmoline]

I think you're right about that. In testing yesterday accuracy with the highly compressed 50 grains 2F was OK but not great. I'm sure this Rolling Block can do better. And there was a lot of impressive burning powder in the muzzle blast. Looks cool but probably not a great sign. I'm also switching to magnum rifle primers for better ignition.

I'll experiment with a 45 grain charge next time, which I've seen in some writeups on this cartridge.

 

[Foto Joe]

I'm also switching to magnum rifle primers for better ignition.

Keep in mind that Magnum primers are for smokeless powder. You're not going to hurt anything by using them but you may or may not notice any difference. The speed at which smokeless burns is a product of ambient pressure. As the pressure increases the speed of combustion increases, increasing pressure, increasing the rate of ignition, ad infininum until A: the pressure releases or B: you run out of fuel or in the case of cartridge ammunition the two basically happening around the same time.

I'm not an expert in this area but my take on it is this (and I could be wrong, again): The magnum primer for smokeless gives an initial high pressure ignition that exceeds what a normal primer would provide. This would result in a faster burn of the smokeless powder and increased pressures providing higher muzzle velocities which is one of the hallmarks of magnum ammunition.

Black Powder on the other hand burns at the same rate no matter the ambient pressure. An initial increase in pressure from a magnum primer therefore would hold little if any benefit and by my flawed reasoning might also lead to the powder charge being ejected faster and possibly not completely burned thereby even having a negative impact.

Keep in mind that igniting Black Powder is expotentially easier than igniting smokeless. Getting the stuff lit is the least of your worries.

Here's something that a LOT of us would be interested in knowing. Let's say you use the magnum primers and a specific charge with a specific bullet. Test a dozen of these for accuracy then do the same with regular rifle primers. Then...chronograph both and see if you have any difference in muzzle velocity.

I've used magnum caps on my Navy when I goofed and grabbed the wrong tin. I felt no difference whatsoever in recoil and noticed no accuracy change. On the other hand, I've never been able to figure out "why" there is such a thing as a magnam percussion cap. I understand that they burn longer than standard caps and maybe they would have a use when shooting Pyrodex. I really don't think that there is a correlation between magnum percussion caps and magnum cartridge primers.

I understand that you are using wads. Are they lubed wads, dry fiber wads like you would use in a CB pistol or are they something like a Walters Wad of say .030 or .060 thickness? Also what type of bullets are you using, size and lube?

 

[Cosmoline]

I was using a supply of 515 grain mystery slugs that came with the rifle. I've got some lighter ones on order. My wadding was lightly lubed buttons torn in half. It's all I had on hand.

The magnum primers were suggested in some on-line sources, but I'm not sure how much of a difference they'll make either. I strongly suspect that dropping five grains fewer will have the biggest impact of all. I can see from film of the muzzle blast that there's a lot of powder still burning.

I just got my copy of Barker's book on the 50-70 so I'll be going through that for additional pointers. Right off the bat I see his suggestion for 2F under a 520 grainer is just 63 grains. So I think I was way over-packing this stuff and consequently not getting an efficient burn. But then again he packs 71 grains under a 600 grain bullet!

Part of the issue is I'm still measuring by volume as I do with my muzzleloaders. I believe this is not precise enough for cartridges and will switch to weighed charges for the next batch. I also see that Barker's book emphasizes measuring the uncompressed powder, which I hadn't been doing.

As far as the bullet making--lordy! I've cast roundballs, but the cartridge boys are WAY more precise than the smoke pole crowd.

The book is advocating magnum primers FWIW. Apparently there's an issue in trying to get as much flame to as much powder as possible while the bullet is still in the chamber.

 

[mykeal]

Magnum percussion caps are intended for use with substitute, or synthetic, black powders. Those powders have a higher ignition temperature requirement than real black powder; magnum percussion caps produce more and hotter gas than regular percussion caps.

All of which has nothing to do with whether you actually NEED magnum caps with substitute black powders. It's just the explanation for why they exist.

I came across the following on the internet some time ago; it may be useful here:
On page 83 of DaveEhrig's book "Muzzleloading for Deer & Turkey", he lists some information on percussion caps and primers.
#11 standard cap - 6.53 cc of gas at 3,024 degrees F when fired.
#11 magnum cap - 7.59 cc of gas at 3,717 degrees F when fired.
U.S. #2 musket cap - 14.36 cc of gas at 3,717 degrees F when fired.
#209 shotgun primer - 21.98 cc of gas at 3,024 degrees F when fired.
#200 rifle primer - 11.68 cc of gas at 3,024 degrees F when fired.

 

[Jaymo]

So a standard percussion cap burns as hot as a shotgun or rifle primer, and a magnum or musket cap burns even hotter.
Did NOT know that.
Thanks, mykeal.
I've thought about replacing my #11 nipples with musket nipples on my TC sidelocks and inline, and on my Pedersoli Howdah.
Same temp as a mag cap, but nearly twice the gas volume.
Should be great for igniting Pyro, 777, and white powder.

 

[mykeal]

Same temp as a mag cap, but nearly twice the gas volume.
Should be great for igniting Pyro, 777, and white powder.

Pyrodex and 777 have higher ignition temperatures than black powder (not sure about white powder). I would think you'd prefer the higher temperature caps; I don't see how a greater volume of gas will help any.

 

[cogburn]

some other places to look

You would do well to visit the "Shiloh Rifle forums" just look on the Shiloh Rifles web page and go to the forums

The other place for BPCR info and casting is "Castboolits.com"

You can spend days researching and discuss real time solutions with real time BPCR shooters

i think all you questions and thoughts will find answers in these fine forums

Dave