Some general ammunition design/specification questions...

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Now that I've been shooting awhile, I'm getting to find ammo to be nearly as interesting as guns themselves. However, I think I understand the issues poorly. I'm wondering if someone could either tell me, or direct me to a good website, some general principles about cartridge design. Needless to say, I'm not a reloader - lack of time, space, etc., at the moment, but it's by no means out of the question in the future.

1. Obviously there is more to cartridge performance than the raw volume of the case. Fast powders...slow powders...primers...etc. I could borrow someone's reloading kit, breeze through the manual, and crank out feeble and ineffective 9mm rounds that were nonertheless over-pressured and extremely dangerous chamber bombs. On the other hand, Double Tap, for example, produces safe and reliable 9x19 rounds that get into .357SIG and .40SW territory, performance-wise. Some magical mix of different powders, etc.? Is there a lot of complex but fascinating stuff about the processes that occur within a cartridge case when the firing pit hits the primer?

2. On a related note, there is the topic of the materials and shape of the case itself. Is .40SW more prone to pressure-related failures than other common defense calibers (whether in GLOCKs or any other kind of pistol)? If so, why is this? I've read some interesting stuff about the "case web" of .40SW, 10mm, .45ACP, and .45GAP ammunition, and it has made me wonder about case wall thicknesses, thicknesses in critical places, and the effect of the shape (straight-walled, tapered, necked-down, etc.) on how the powder burns.

Anyhow, I realize it's a broad subject and I expect people have better things to do than give me a detailed primer on the finer points of cartridge design and specification, but I'd be grateful for a link to a good source of information on this. Thanks!

 

[asknight]

I'll touch briefly (because I'm no expert by any means) on what makes companies like Double Tap, Cor-Bon, etc. worth their weight in the marketplace. They have taken the genuine scientific art of gunpowder to it's highest level. Most commercial manufacturers just select a cannister powder, or one of similiar properties, to load their ammunition with that will give acceptable velocity and accuracy, without excessive pressures.

Sure, the big companies measure things such as pressure curve and burn speed, but they don't go as far as boutique manufacturers do in developing the most efficient cartridge developing the most power and accuracy while not developing dangerous pressures. The smaller guys spend time with many different facets of loading, but one being the experimenting on a wider scale with blended powders. Otherwise altering a powder's burn qualities, speed, flame shape and travel, etc to find the right charge, of the right powder, for the right projectile, in the right case... sometimes in the right gun.

Example: Only from the smaller manufacturers will you find loads developed and optimized for certain lengths of barrels. Only from the smaller manufacturers do you even have a chance of getting an answer of what specific guns and barrels they utilized in the development of a specific loading.

It's the same no matter what industry you discuss. Innovation occurs by the smaller companies. The bigger companies have stockholders, consultants, and accountants to pay, so they're looking for a product with a higher profit margin that they can mass produce and widely distribute as fast as possible.

I'll subscribe to this thread, because I'm curious about what the guys closer to the manufacturers will say. Am I at least partly correct in my thoughts?

 

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Good points, asknight, just the sort of stuff I'm looking for. I hadn't even thought of the barrel length issue when I posed the question. Thanks for the reply.

 

[Creeping Incrementalism]

Regarding #2, shorter, fatter cartridges tend to have the most efficient and consistent powder burn. That's why the new Winchester short magnums are the way they are, and why short, fat brass like the 6mm PPC do well in benchrest accuracy. However, the short fat case geometery can be less reliable to feed.

Have you heard of "forward ignition"? You can more get consistent powder burn when it starts from the bullet end of the case, as more of the powder is burned in the confines of the casing, and less is blown down the barrel before burning. However, you need a sort of tube going from the end of the brass to the front for this to work, and its expensive, so its rarely used for rifles. I think it is more common with artillery rounds, because it becomes more economical and worthwhile at that point.

The question of what cartridges are more prone to case failures is, I think, only supported by anecdotes, and not statistics or the opinions of engineers.

Something I've been wondering lately is--how long does powder last? Does it slowly degrade over time? How does 30+ year old pulldown 4895 compare to modern stuff?

I personally find bullet design more interesting than powder burn. Check out http://www.ammo-oracle.com/ and www.firearmstactical.com

 

[Nashmack]

I would think that theoretically, Boxer primed cases could be readily adapted to forward ignition, if one had the correct primer for it...

 

[HankB]

Have you heard of "forward ignition"? You can more get consistent powder burn when it starts from the bullet end of the case,

IIRC, many years ago old Elmer Keith wrote about his experiments along these lines when he was working for Army Ordnance . . . though only one powder was used, for some reason he referred to these as "duplex" loads. He claimed 202 ft/sec more velocity with normal pressures, but claimed that an oversize chamber would cause problems. (He may have been working with .50 BMG . . . it's been quite a while since I read the original article.)

I've found there's a pretty simple rule of thumb to get maximum velocity: Use whichever double-base powder requires the heaviest powder charge to achieve maximum safe chamber pressure. (Of course, this "rule" isn't absolute, given the powder choices available, and doesn't consider things like accuracy, temperature stability, or port pressure, so common sense is required in its application.)

 

[unspellable]

Ammo design

This question requires a book to properly answer it so I'm only going to touch on one point here. And that one at the risk of being accused of over simplifying.

The point of having powders with varying degrees of quickness is that peak pressure is limited by the strength of the case/gun combination. But velocity is determined by something like the average pressure, not the peak pressure. Given a slower powder you can use more of it and maintain reletively high pressure longer without exceeding the peak pressure limit. Suppose you graph pressure vs time. You will have a curve. The failure point of the gun limits the height of the peak point on the curve. But the velocity is related to the AREA under the curve.

 

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Thank you for the replies, folks. As I said, I'm not looking for a comprehensive analysis, but just some basic ideas to form a crude understanding of the topic before looking into it more deeply, and finding some great points to ponder here. Thanks again!