So I was at the range yesterday getting ready for rifle season. Was alternating between a 300 Savage and a .308, a lapse in attention resulted in firing a 300 savage round in my .308. Fortunately I was single loading and only did it once. And, fortunately, it wasn't the other way around.
Ended up with a "flyer" about three inches low, and a 300 case trying to do an imitation of a 308 thru fireforming. Primer backed out slightly.
Not a smart or recommended test, but probably just about the most harmless cartridge/chamber mismatch.

did that once with my Marlins, fired a .30-30 in my .45-70.

Ended up with a reverse bottleneck case. From the mouth back a little over an inch the case was fireformed to the chamber, i.e. .45 caliber. The rest of the case looked normal.

No idea where the bullet went. All I heard at the time was the 'clack' of the hammer dropping.

{Edited to add photo}

"Not a smart or recommended test, but probably just about the most harmless cartridge/chamber mismatch."

I was shooting some Winchester 180 gr. Powerpoints althernating between a .308 and 30-06. Was doing a run with the 06, single loading from the box with a very decent groupxs considering some older factory ammo. I wish I could have seen the look on my face when I picked up the brass. I'd shot two rounds of that .308 brass and the group was just great. Three rounds of 06 and two of .308 in a groups slightly over an inch. No problems whatsoever. Guess I must have had myhead in it's usual resting place.
Paul B.

A, um, 'friend' of mine, may or may not have a strange looking piece of 7 rem mag brass pulled from his 7STW chamber.

Last season on our indoor rifle range I noticed a rather odd looking piece of brass in the brass bucket. I pulled it out and it was a .300 Win that had clearly been fired in a .300 Wby, the shoulder fully blown out straight with the case mouth nicely rounded where the Weatherby venturi shoulder was. I dug around and pulled out 20 pieces. The Einstein had fired a full box of the wrong ammo in his rifle and was probably scratching his noggin trying to figure out why he couldn't hit the same spot twice. I carried the brass back into the store and told one of my co-workers that I had developed a new wildcat, the
.300 No-Neck Magnum.

Fire-formed a 25-06 in my 30-06 once.

You wouldn't be able to close the bolt on a .308 in a .300 chamber. Worst that could happen is to need a rod to knock out the cartridge. My only miscue like that was going hunting with my .25-06, but accidentally taking .30-06 ammo with me. I tried to chamber the cartridge and it jammed in the rifling. No leaning rod handy, so I got to sit in the truck while my brother hunted until dark. The source of the problem was that back them I formed .25-06 cases from .30-06. After that, I started forming them from .270s so I would have different head stamps. The .270 cases were given to me by friends and family who did not load.

That is the reason I chambered my 6.5-06 in the AI variety. I fireform using .25-06 brass and even though I don't own a .25-06 today, who knows what the future holds? No waas a 6.5-06AI will chamber in a .25-06 chamber.

Only mismatch that I have experienced was shooting .22lr in a .22 Magnum cylinder and wondering why the cases were coming out with cracks in them.

Similar thing happened to me but I didn't do it. I was shooting my 30-06 and my .308 and my buddy grabbed a .308 cartridge, chambered it in the 30-06, and fired it. It hit the target but it was off. The first clue was the bolt was very hard to open. The .308 case came out fireformed to the 30-06 chamber.

I still give him crap about it.

I have seen a few nearly straight walled 308 cases left at the range before. I wondered how often that happens.

did with a 270 in a 30-0 6 a few weeks ago......

Lesson learned even though I should have checked first.

My elderly uncle used to shoot Redwing Blackbirds in our corn patch with 16 ga. shells in a 12 ga. Model 12. Actually seemed to work okay but the brass would split on the old paper shells. He didn't do this on purpose but some would would get mixed in with the 12's. Fortunately he didn't have a 20 ga.

I saw a guy in hunting camp with a .338 WM in his shell belt. He carries a .300 H&H. I told him about it and he had no idea how the .338 got into his belt.

I've always figured I saved that guy some expensive surgery, because I'm pretty sure that .338 would have chambered in his .300

And judging from the guy's history, he would have dropped the pin on that shell sooner or later in a barrage to drop some sort of critter.

My father in law gave me a .35 Brown-Whelen in a 1917 Enfield action. It's a .35 Whelen AI with the shoulder pushed forward, neat looking round. I asked about fireforming, and he told me he just shot .30-06 in the chamber and fireformed them. I asked him haw many firings he got before head separation, and he just looked at me funny. I later started necking brass up to .375, necking back to .35, and jamming a .35 bullet into the lands in fireforming loads. Worked well with no case loss, and no headspace issues. For giggles, I did it his way once. It worked, but I'm not sure where that bullet went.

Hmm........I once fired a .308 through a 25-06.

Mic McPherson's Metallic Cartridge Handloading has a fair few photos showing this sort of thing from a large range of cartridges

My BIL managed to touch off a .338 Federal round in a Model 700 chambered for 7 mm Rem Mag earlier this week and somehow walked away unscathed. Apparently the gun is toast though as he had to interrupt his elk hunt to go buy a new gun. It's a shame as it was one of the blued stainless barrels that Remington produced back in the 70's I think and was a heck of a nice shooting rifle.

I didn't know that a .338 projectile would squeeze through a .284 hole without causing a whole lotta ruckus on the action end but apparently he nearly hit a coyote with a really long & newly sized 7mm projectile!

A good reminder to clean out the pockets of your jacket, vest etc. if you tend to shoot multiple chamberings on the same hunting trip!

I zipped a 270 WSM round through a 300 WSM at the bench by accident once. Other than making a strange sound and producing a different recoil signature it was pretty uneventful. I make a habit of double checking headstamps when firing multiple guns from the bench now.

Being human is a bidtch. I recently was wolf hunting in Idaho. Prior to the trip I got a great deal on 200 rds of 308 168gr. tsx rem. factory ammo. I took some to the range and they shot very well in my Tikka T3, as does everything else. The seller also threw in 20 rounds of 30-30 tsx hoghammers.

My rifle case has a pocket w/ loops for 10 rounds of ammo which I loaded w/ 30-30. As soon as I cleared town I loaded the mag for targets of opportunity. At the end of our 2nd hunting day after getting rained on all day I tried to strip the ammo from the mag to clean and dry it and after putting on my glasses I discovered I had managed to stuff it w/ 30-30.

I would have been seriously miffed if I had actually seen a wolf and tried to chamber a round in my 308.

mike r

Try a 30 cal. through a .25.........Savage makes a strong action. Barrel looked fine as well.

This summer I jammed a 243 round into a 270.....for some still unknown reason it hung up in the chamber and I had to "pop" it out with the cleaning rod.

Not 30 seconds earlier I had been preaching to my 15 year old son the virtues of firearm safety at the range..............sheesh.

Casey

A guy at the range was shooting a few table down from me one day.

He opened his bolt and said something about that felt strange. He had 2 rifles with him. Come to find out he fired a 257 Wby cartridge in a 300 Wby gun.

I can't believe some of your can leave the house without a note pinned to your shirt.

Laffin!

A buddy and I were strafing sqeekers from a hay bale rest one day.
Both right handers, I lay some .243 rounds on the bale to the right of my rig - and he put his 22-250's next to them at some point. I reached over and scooped a round and threw in in the chamber....no bangy when I squeezed off the shot?! I had to bump the rifle butt to get the cartridge to drop out.
We got our chit together right quick and separated the ammo!

I've found .243 cases blown out in a .308 chamber at my private range, but none of my friends will own up to shooting them...

Public sight in days at the range were always a bit of a hoot. After about 3 incidents of wrong ammo in a rifle on the same day, the next year they mandated that all ammo and rifles would be verified by a member before firing.

My brother once had brass pulled out of his eyeball after shooting a 270 round out of a 7mm Mag, a friend had laid down ammo for a different gun when my brother wasn't looking. No damage to his eye, amazingly, just little pieces of brass half-embedded in the outermost layer of the eye. Makes me shudder to even think of it.