NATO ammunition: tombac bullets vs. barrel life

[DreadPirateMoyer]

Hey there guys,

I'm looking to purchase some European NATO ammunition and its FMJ is made of tombac, which I know to be copper alloyed with zinc. Does anyone know how this affects barrel life in an AR? Does it increase or decrease barrel life as compared to copper, or is it no different? I'd imagine it would at least lead to a slight decrease (isn't zinc alloyed in to make it harder?), but wasn't sure. Also, does anyone know if LC M855 is tombac-coated (is tombac specified for NATO specs, for example?), or is it pure copper?

I ask because I don't want my stockpile to be made up of ammo that will quickly wear out a barrel a la Tula/Wolf in that head-to-head test that was done with 4 Bushmasters. I'd like my stockpile ammo to be as easy on the barrel as possible.

P.S.: This may need to be in the ammo section, but since it was in relation to AR barrel life, I thought it would make sense here. If it would be better in the ammo section, feel free to move it and I apologize for the inconvenience.

[markm]

Wow. Never heard of it.

[DreadPirateMoyer]

Yeah, neither did I until I saw it's what the bullets were jacketed with!

I did a bit more research, and it seems everyone thinks "tombac" is copper either alloyed with mild steel or washed over mild steel like in Russian ammo, but it's not. Tombac is simply copper with zinc in it (and sometimes tin, arsenic, or lead). Really frustrating to find any information out there when all Google comes up with is people spewing about tombac "steel" jackets.

What I did find, and thought would be a good basis of comparison, would be tombac's hardness as compared to copper:

15% Zinc (http://www.robertlaminage.ch/de/produkte-und-dienstleistungen/datenblatter.html?download=373:cu-zn-15-tombac-technical-data-sheet&start=20): Vickers 55-145 (depending on temper)
10% Zinc (http://www.robertlaminage.ch/de/produkte-und-dienstleistungen/datenblatter.html?download=372:cu-zn-10-tombac-technical-data-sheet&start=20): Vickers 50-110 (depending on temper)
5% Zinc (http://www.robertlaminage.ch/de/produkte-und-dienstleistungen/datenblatter.html?download=383:cu-zn-5-tombac-technical-data-sheet&start=20): Vickers 45-110 (depending on temper)
Copper (http://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness#Hardness_.28Vickers.29): Vickers 77-99

It looks like tombac can actually be a lot softer than pure copper, which I guess would make sense since zinc is softer than copper (http://www.brownells.com/.aspx/bapid=129/ClientPage/Special-Orders) in the first place (though who knows how the chemistry actually works out). Seems to me like it's most likely a wash as compared to pure copper, if M855 is even pure copper in the first place?

[bp7178]

Copper and zinc is brass. The addition of arsenic is a concern...

I wonder if there would be issues with jacket separation in high twist barrels.

[DreadPirateMoyer]

Copper and zinc is indeed brass. Tombac is a form of brass, differentiated by its low zinc content and high copper content. As for arsenic, I doubt that the version used in bullet jackets has any, but who knows.

As for the speculation about separation, what makes you think that? Tombac has been used as a jacketing material for decades and I've never heard of it separating, so I don't think it would! Not to mention it's mostly copper anyway, and we know that doesn't separate out of 1-7 and 1-8 barrels with appropriate weight bullets.

I've just never heard of how tombac performs with regards to barrel life. Like I said, seems like it would be a wash as compared to copper. They look almost identical, if not actually a bit softer (better barrel life, I'd assume). However, I've never actually seen any data or had any experience with it myself, so I thought I'd ask to see if anyone knew. :)

[jstone]

It sound like tombac is European version of gilding metal. Most all jackets on us ammo is gilding metal not pure copper. I forget the percentages, but if you google it you should be able to find info on it. Gilding metal is copper and zinc. Its like 96% copper and 4% zinc iirc.

As long as you can verify that it has no steel it should be fine. If it is just copper and zinc practically qll the us ammunition you have shot has copper zinc alloy or gilding metal jackets.

[DreadPirateMoyer]

It sound like tombac is European version of gilding metal. Most all jackets on us ammo is gilding metal not pure copper. I forget the percentages, but if you google it you should be able to find info on it. Gilding metal is copper and zinc. Its like 96% copper and 4% zinc iirc.

As long as you can verify that it has no steel it should be fine. If it is just copper and zinc practically qll the us ammunition you have shot has copper zinc alloy or gilding metal jackets.

Ah, this is exactly what I was looking for. Thank you! Some of the information I read about the tombac jackets were that they were "gilding" tombac, generally ranging between 3 and 10% zinc content, so it sounds like US ammo and European NATO ammo use the same thing for the most part.

Phew. That makes me feel a lot better. I'll be pulling the trigger on this ammo very soon, most likely.