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What is the most overbore cartridge YOU HAVE USED?

I built a lightweight sheep rifle in 6.5 STW about 25 years ago, everyone told me it would be a barrel burner, but I didn't much care since it was a purpose built hunting rifle not something I planed to shoot a lot.
This was before laser range finders were very capable so it helped me with range estimation errors quite a lot. It lasted me long enough to complete my grand slam and a few dozen other big game animals none of which made an escape dash of more than 10 yards, most fell straight down from shots taken from point blank to just under 600 yards.
That barrel lasted 1400 rounds before accuracy degraded to 1.5 MOA but the throat looked like a dry lake bed with cracks and fissures. JB was used extensively to smooth the throat to keep it shooting well.
I put a new 6.5-300 Weatherby chambered barrel on that rifle a while back and now have a little over 800 rounds on this one and it's time for a barrel change again. I wasn't as meticulous about polishing the throat on this barrel so perhaps that is why it didn't last as long but who knows. I'm planning on replacing it with a 257 Weatherby 7.5 twist throated specifically for the Berger 133 grain Elite Hunter bullet.
I know everyone says you need a heavier rifle for long range hunting but this Rifle with a 26" #2 contour barrel, titanium receiver, MCMillan edge hunter stock, blind magazine, and Leupold MK5 3-15X42 scope and custom rings comes in at 7 lbs 1oz ready to hunt and averages .5-.6 MOA for three five shot groups when the barrels were newer.
In the mean time I've been shooting a 30-378 and don't hate it, in fact it shoots really well and recoil is very manageable in a 10 lb rifle.
 
.375-50 BMG in State Arms shell holder bolt gun.
300 grain solid cooper's at 3800 fps 220 grains of WC 872 20mm powder, it was too fast, had to use fiber fill to fill the case and hold powder in place. This was 20 years ago, more powders are available now.
I also have dies and brass for the 50-20x103 Uniroyal. We thought we would chamber our 20 mm Lahti AT's in it, but never did.
 
.375-50 BMG in State Arms shell holder bolt gun.
300 grain solid cooper's at 3800 fps 220 grains of WC 872 20mm powder, it was too fast, had to use fiber fill to fill the case and hold powder in place. This was 20 years ago, more powders are available now.
I also have dies and brass for the 50-20x103 Uniroyal. We thought we would chamber our 20 mm Lahti AT's in it, but never did.
Winner Winner Chicken Dinner
 
Don't know if this goes here or on reloading forum, but figured I'd ask…

What is the most overbore cartridge you ACTUALLY have experience with? The craziest hot rod, the biggest case to bore ratio, the most ridiculous magnum, this worst barrel burner….

What have you learned from it? Would you do it again?

I know everyone on these threads makes jokes about a .17-50bmg or references the .22-378 eargesplittenloudenboomer experiment by ackley…I don't care about those. I don't know of a single person who has ever done such a thing in any serious effort. I'm trying to avoid that and learn about people's experiences and learning from actual field rifles in very overbore factory chamberings or more so truly impractical but still useful wildcats. I'm entertaining the thought of one myself.

@ButterBean @Fiftydriver @MagnumManiac i know you folks off the top of my head have played with some big cases pushing small bullets….
Have any of yall fooled with the 6.5/7 prc yet I can't help but believe it would be a hot rod
 
I didn't read all the replies, so this may have been covered already. When I do the accuracy qualification of our 300 WM rifles I use a load of 80.5gr of H1000 under a 180gr NBT. This usually yields a speed of around 3100-3150 depending on barrel length. The load I use for the 30-378 WBY is 100gr of H1000 under the same 180gr NBT. The speeds usually hover around 3250-3275, again, depending on barrel length. That's a pretty meager 100-125fps gain considering the huge powder, recoil, and muzzle flash increase with the Weatherby. To each their own, I guess.
 
I feel a bit inadequate after reading through this thread. I'm currently shooting fairly efficient cartridges, but after reviewing the list Feenix provided some may be considered overbore. I can't imagine hunting with a 30+ inch bull barrel. I'm actually looking to build a shorter barreled 7SAUM. I do enjoy reading the responses and performance from the wildcat crowd.
 
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