Stop! Wrong Cartridge!

Back in November of 2021 had two different posts where I talked about how certain chamberings could fire multiple different cartridges safely. I stressed that this isn't always the case, however, and that care must be taken to stay on the safe side of cartridge combinations.

A friend recently shared an experience he  had at the range. A few benches over from him, some guys were shooting a very nice Weatherby rifle, and as is common on the gun range, he went over to chat. While there, he noticed their ejected brass looked odd. After a short conversation, he found out that while the rifle was chambered in .300 Weatherby Magnum, they were firing .300 Winchester Magnum.

As they told him, .300 Winchester Magnum was cheaper and easier to find, and it worked just fine in their rifle. With their permission he collected a couple of pieces of their fired brass. Later he sent me one of those fired cases, along with both .300 Weatherby Magnum and .300 Winchester magnum cases that had been fired in the correct rifles.

L-R: .300 Winchester Magnum; 

.300 Winchester Magnum fired in .300 Weatherby Magnum; 

.300 Weatherby Magnum

As can be seen, the cartridge fired in the wrong chamber has had its shoulder pushed forward, leaving a very short neck. If done intentionally, this is called fire forming and is part of the cartridge conversion process. In this situation, it was done out of false economy. While they saved some money on the ammunition, it was at risk of damaging or destroying a very expensive rifle:

• For example, the unsupported case of the shorter cartridge could have separated and lodged in the end of the chamber or further down the barrel, and the next round fired would have hit that obstruction; the ring just behind the shoulder on the middle casing may be a sign of incipient case separation. 
• Another possibility is the bullet of a fired round could hit the front of the chamber off-center, also potentially leading to an obstructed barrel.
• Even if these events don't happen, if a number of the shorter rounds are fired they will cause a buildup of carbon and other combustion residue at the end of the chamber. If left in place, this can cause damage to the neck of the chamber.
• Furthermore, if the correct ammunition is fired without the rifle being thoroughly cleaned beforehand, this ring of buildup can cause problems with extraction. Anyone who has experienced firing some rounds of .357 Magnum after a few cylinders of .38 Special is familiar with this experience.

L-R: .308 Winchester, 

.308 Winchester fired in .30-06 Springfield, 

and .30-06 Springfield

Due to the difference in overall case length, the middle .308 Winchester cartridge has been transformed into practically a straight-wall case with the neck blown almost all the way out. Looking closely, there's a slight curl at the very end of the case where the shoulder of the .30-06 Springfield cartridge would start; in fact, it looks almost like an all-brass, rimless .410 shotgun shell.

There are other examples of this concept, such as .40 Smith & Wesson or .357 SIG in a 10mm chamber, that aren't generally dangerous but can still cause problems. Of course, there are also potentially disastrous combinations, such as .30-06 Springfield in a .270 Winchester, .300 Blackout in a .223 Remington, .40 Smith & Wesson in a .357 SIG, and others. While these combinations shouldn't always be able to chamber, it has been known to happen, with the result usually being damage to the firearm and, all too often, to the shooter as well.

More details on these cartridges and many others can be found on the SAAMI (Sporting Arms & Ammunition Manufacturers Institute) website.

Always make sure that the ammunition being used is correct for the firearm. There's no need to take unnecessary chances in life; the necessary ones are bad enough.