Bi-metal Jacketing

[GeneFrenkle]

Ran across this interesting article about bi-metal bullets: http://www.uspsa.org/front-sight-magazi ... tal-Ammo-8

Apparently, the bi-metal refers to the jacketing where the jacket is actually steel with a thin copper coating. At least with the handguns used in the testing, the rifling scrapes through the copper into the steel.

I'm not sure how significant the exposure of the steel is to the rifling. Nonetheless, hope others find this interesting, too.

[MarcSpaz]

Sounds like a good way to wear the barrel out quick. Looks like a good idea, but I am a skeptic about the barrel life.

[M1A4ME]

Many military guns these days have chrome lined barrels.

You can buy AR15's with chrome lined barrels. An M1A with a surplus GI barrel is chrome lined.

There are other barrel "treatments" besides chrome lining that result in a very harder surface on the lands/grooves of the rifling in the barrel but I'm not really familiar with them, just read about there here and there.

In reality, how many rounds will you shoot through your barrel? There are folks who shoot hundreds of rounds, or even thousands of rounds through their rifles a year. I'm not one of them. For those folks, maybe this ammo, or lack of a chrome lined barrel will make a difference.

[gunderwood]

There was another thread with some testing on AR15s. Depends on how quickly you shoot, but rule of thumb is about half the barrel life.

[GeneFrenkle]

Yes, that was relating to the "cheap, steel cased" stuff (http://vagunforum.net/ammunition/brass- ... 16179.html). Slightly different, but definitely related. I just though tit was interesting how the bi-metal bullet was constructed and what may be happening with the lands which might be contributory to to luckygunner article results I posted. Certainly there's a lot more to it than just bi-metal bullet, "harsher" primer/powder, but there's also rate of fire, sustained fire through a "hot" barrel, chrome lining (as mentioned by M1A), etc.

[Chasbo00]

My problem with these bullets with respect to just pistol shooting is that lots of venues won't allow their use. Most indoor ranges will test ammo with a magnet and disallow any that's magnetic. Also, many ranges with steel targets are leery of these bullets because of their perceived capability to damage steel targets or result in bullet splatter that is more dangerous. I avoid the stuff for these reasons.

[gunderwood]

Yes, that was relating to the "cheap, steel cased" stuff (http://vagunforum.net/ammunition/brass- ... 16179.html). Slightly different, but definitely related. I just though tit was interesting how the bi-metal bullet was constructed and what may be happening with the lands which might be contributory to to luckygunner article results I posted. Certainly there's a lot more to it than just bi-metal bullet, "harsher" primer/powder, but there's also rate of fire, sustained fire through a "hot" barrel, chrome lining (as mentioned by M1A), etc.

It covered both and the barrel wearing out (relevant to the comment was the rifling which was caused by the bi-metal jacket that is used to keep the Russian ammo cheap, the cartridge case never touches the rifling). The wear on the throat and gas port is mostly a propellent function. Extractor and chamber wear are from the steel casings.

From your link:

There are two major types of centerfire rifle cartridges available on the market today:

Those which are loaded with steel, and
Those which are loaded with brass
This seemingly simple variation has caused a never ending stream of argument, discussion, speculation, and questioning from new and seasoned shooters alike. Complicating the conversation are other variables that typically get lumped into the argument without proper segmentation, such as:

The different coating options available on the steel-cased ammo (lacquer or polymer)
The different projectile loadings available (copper jacketed lead, the bi-metal coating that most Russian manufacturers use, etc)
The different propellant (gunpowder) burn rates.

...

We acquired 10,000 rounds each of the following ammunition (new production):
Federal 55gr – Brass-Cased – Copper Jacket
Wolf 55gr FMJ – Steel-Cased with Polymer Coating – Bi-Metal Jacket (steel and copper)
Tula 55gr FMJ – Steel-Cased with Polymer Coating – Bi-Metal Jacket (steel and copper)
Brown Bear 55gr FMJ – Steel-Cased with Lacquer Coating – Bi-Metal Jacket (steel and copper)

...

As indicated by accuracy testing, the steel cased/bimetal jacketed ammunition caused accelerated wear to the inside of their respective bores. While the barrel of the Federal carbine had plenty of life left, even after 10,000 rounds at extremely high rates of fire, the Wolf and Brown Bear barrels were subjected to the same rates of fire and were completely “shot out” by 6,000 rounds.

At the end of the test, the chrome lining of the Wolf and Brown Bear barrels was almost gone from the throat forward, and the barrels had effectively become smoothbores, with the rifling near the muzzles acting only as a mild suggestion on the projectiles. A throat erosion gauge could be dropped into the bore from the muzzle end with absolutely no resistance.

[GeneFrenkle]

> carbine’s gas tube and gas key were so fouled with carbon after 5,000 rounds that it would no longer function reliably. Nearly the same level of buildup was found on the replacement key and tube after they had seen just short of 5000 rounds

Yes, and it is unclear how contributory the fouling is in terms of abrasiveness in conjunction with the steel.

> As a company we would be excited if they did, but the use these rifles saw was far beyond what is likely to be encountered in the real world. So, for many consumers, this test will be justification that buying steel cased ammunition is a sensible decision. 

Still, I find this investigation and analysis kind of interesting, particularly when it came to the microscopy (couplea decades ago used to run a Hitachi TEM) as well as his suggestion that, given the cost difference on the bimetal stuff, you still are in the black in buying a new bbl, extractor and spring.

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