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Discussion Starter · #1 ·
Had an interesting debate today with some gunslingers... presumingly experienced riflemen (while searching for rifle stock) - and so my question to the forum. What happens when you fire a lower caliber shell in a higher caliber rifle (e.g. .270 shells into .30-06) or a .270 fired in a 7mm? Obviously the opposite could not occur - at least I don't think you could fit a 7mm into a .270 ... but the opposite is possible. Some guys suggested that the gun would "blow up" where as others (and I'm probably in that "others" school of thought) that the cartridge would fire (the bullet would travel down the barrel with little to no damage) and the cartridge would expand to the size of the chamber - and thats the real danger as brass shards and off-gassing would be looking for the easiest route of escape...possibly in both directions.

Any thoughts on who is correct and why?
 

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Part of the reason a gun fires is because the bullet is pushed into the rifling, sealing the chamber creating pressure. Depending on crimp and primer, some primers dislodge the projectile, in others the powder has to start burning first. Either way I figure that as soon as the projectile leaves the case instead of engaging rifling and creating a seal, that most of the gas would jet around the projectile and there wouldn't be as much pressure build. As for after that I don't know.

This video was neat, but it's not EXACTLY what you're looking for.

https://m.youtube.com/watch?v=sZaK7D4XVo8

-1911
 

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Hi 1911, TKS. Part of the reason I asked is because in my younger days I used to know a fellow who used to shoot a .270 cartridge in a 7mm Remington. When I asked why he explained that unless he packed his own loads, he could not find a 110, 120, or 130 grain 7mm cartridge...and the difference between the two cartridges is about .007. I think he was crazy. I didn't understand then and I still don't understand the reasoning ...why not purchase a 270 rifle. Maybe he couldn't afford two rifles? And even though it work ... what the heck does it do to barrel (just fouling, pitting, ???)?

I also saw this (
) which makes me wonder why the bullet doesn't bounce around inside the barrel...

Maybe in the cheaper barrels of 2016 you have all sorts of problems but in the older generation guns, i.e. Maluser 98, better steel equates to no issues?
 

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Like I said, beyond that I don't know, you would think that it would hit the rifling in your barrel but even then would significant damage occur? Copper and lead are both softer than steel, but things get fuzzy when that much energy is envolved. However, is that much energy really involved? There is a lot of jetting taking place. Does that effect bore erosion? Would the case expand into freebore? I would like to see how many rounds he put through his gun and see how many before accuracy falls out as compared to a 7mm and 270 of same barrel length. But such tests are expensive and hard to conduct. Sorry I don't have enough knowledge to say, but I hope I helped some. Good luck in your question!

-1911
 

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Hi 1911, TKS. Part of the reason I asked is because in my younger days I used to know a fellow who used to shoot a .270 cartridge in a 7mm Remington. When I asked why he explained that unless he packed his own loads, he could not find a 110, 120, or 130 grain 7mm cartridge...and the difference between the two cartridges is about .007. I think he was crazy. I didn't understand then and I still don't understand the reasoning ...why not purchase a 270 rifle. Maybe he couldn't afford two rifles? And even though it work ... what the heck does it do to barrel (just fouling, pitting, ???)?

I also saw this (
) which makes me wonder why the bullet doesn't bounce around inside the barrel...

Maybe in the cheaper barrels of 2016 you have all sorts of problems but in the older generation guns, i.e. Maluser 98, better steel equates to no issues?
He must have been shooting a 7 mm Express. My Dad was checking the zero on my new BAR 7mm Rem Mag the day before Deer Season opened and confirming his. A Rem 700 270Win. He mistakenly put a 270 round in the 7mm and evidently the recessed bolt head on the BAR centered the case and when the trigger was activated BOOM. Broke the forearm, the stock, and blew the trigger group and magazine out. Split case had to be driven out with a rod down the bore and I still have the target where the bullet went through it sideways. Thank God he didn't even get a scratch.
 

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When I fireform 6PPC from 220 Russian, I just load the 220 up as per normal and fire it a shot out 6PPC barrel that is a tight neck version and I get perfectly formed and expanded 6PPC fodder. All that remains is to expand the neck and turn it to dimension so the answer to your question, in this case is.............not a thing wrong. I would imagine if the spread between the 22 and 6 mm were much larger split brass could occur. Btw, this practice is hell on barrels [sending a 22 down a 6mm bore] so I only use a junker barrel for this forming operation. The distance from the base of the case to the datum line is the same for both cartridges so in this case it is not a headspace issue. For this operation the shoulder of the case must be in firm contact with the chamber or you must create a "false shoulder" when expanding brass in this manner.
 

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I actually did this today. I mistakenly put a 270 bullet in my 7mm mag. There was a big bang that sorta came back in my face. Different kinda sound then normal and the shell casing was split open. No damage to the rifle from what I can tell.
 

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I don't normally quote Larry the Cable Guy, BUT.... Lord I apologize for what I'm thinking... While it is true that most quality weapons are built to take varied ammo, only seasoned shooters should try to fire-form brass. Bad things can happen when the wrong ammo is fed into a firearm.... If the projectile doesn't actually exit the barrel during the first shot, the followup shot could be catastrophic. My hope is that a NUBE reads this and doesn't try other ammo than their weapon was designed for without an abundance of knowledge.
 

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I didn't do it on purpose but I thought that my gunsmith had replaced my worn out 7×57mm mauser barrel with a new one. I got it back without him saying one word about what he had done so I assumed that I could fire those 7×57mms which I did only to punch out stuck casings from muzzle end every shot after the first couple of shots. I realize that I those stuck casings were busted in the neck and crown area. I told my gunsmith what was happening and he replied that he forgot to tell me that he replaced that old 7×57mm mauser barrel with that of a .270. I ended up firing 12 rounds through the .270 barrel before contacting my gunsmith I know there's some difference between the 2 calibers but I don't think it was enough to hurt the .270 barrel since it shots good enough for me plus all my deer shots are less than 100yards
 
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