What is the most overbore cartridge YOU HAVE USED?

[Ronald W Schaefer]

I wonder if 6.5 PRC or 6.8 Western would be considered overbore? My .257 Wby shoots a 120 gr bullet 3300 fps using 68 grs of reloader 25, Federal 215 primers. 3 shots and you cant touch the barrel. I have a barrel cooler and if I'm serious about groups I'll cool the barrel to ambient temperature for each shot. Best bring along a couple of good cigars to help pass the time...

 

[Phil Rizzo]

Anything with awesome performance is "overbore".

Or 100% normal to Me.

 

[Calvin45]

I answered what was the worst for me, but if we are all adding other rounds that are also overbore, I will add a few.
25-06, 25-300WSM, 6.5-300WSM, 257 Weatherby & 270 Weatherby. I don't feel the 300 & 340 Weatherby are truly overbore, but my 300RUM probably is…
I am also a believer in Expansion Ratio and shoulder angles making huge differences to outcomes on cartridge design.

Cheers.

I might be out to lunch but I am convinced that the dual radius weatherby shoulder in conjunction with the freebore actually smooths things out…I couldn't believe how tight the es and sd numbers could be in my .257 wby, by all accounts it should be finicky and picky and a pain in the butt but she just shoots! The overbore cartridge I plan to build around in the year or three ahead is a .25-300 weatherby. I chose that over the STW and RUM cases for this reason, I'm also convinced a curvier "edgeless" shoulder ought to mitigate the powder bridging problems endemic to big cases with small exit holes.

 

[MagnumManiac]

I feel the same, long sloping shoulders should be avoided, the radius shoulder does lend itself to prolonging throats, but many coindexters attribute the neck length to this. I disagree…

Cheers.

 

[MagnumManiac]

I wonder if 6.5 PRC or 6.8 Western would be considered overbore? My .257 Wby shoots a 120 gr bullet 3300 fps using 68 grs of reloader 25, Federal 215 primers. 3 shots and you cant touch the barrel. I have a barrel cooler and if I'm serious about groups I'll cool the barrel to ambient temperature for each shot. Best bring along a couple of good cigars to help pass the time...

I had factory loads from Weatherby in 257, 270 & 340 shoot way faster than the box said on numerous occasions. 257 100g TTSX was doing 3600+fps, 270 130g was doing 3500+fps and 340 225g was doing 3200+fps. I cannot come close to those numbers handloading…

Cheers.

 

[Phil Rizzo]

MM, seems like a .257/100ttsx would be doable.
Try r25?

 

[LBEdgin]

In order the 7mnm rum, 300 rum & 257 Wby. The 7 rum was tough on the barrel for sure, as was the 300 rum but not as much, but it had to be the most accurate over bore I have ever sat behind. As for the 257 Wby yes over bore but fun to hunt with and a small bit of long range fun. Dropping just 25" at 500yds is a lot of fun.

 

[cape cove]

If I'm shooting a factory rifle aka weatherby in 30-378 with 26" tube vs custom rifle I'll shoot whatever it comes with till it's gone for rebarreling. Then it's gonna be longer 28" minimum if not 30"

Yes I agree. When my 26" Mark V 30/378 barrel gives up the ghost I will go with at least a 28" or maybe a 30" with no brake. You just don't get the true potential of these big cases with 26" barrels. JMO

 

[freefloater59]

Just now getting into this thread.... my most over-bore was a 22 Cheetah Mk II, built on a Browning B78 w/26" bbl. My 264 Win Mag is next in line.

 

[MagnumManiac]

Just now getting into this thread.... my most over-bore was a 22 Cheetah Mk II, built on a Browning B78 w/26" bbl. My 264 Win Mag is next in line.

I have a custom chambered long throat 264WM with 29.5" 8" twist barrel, I don't see any overbore issues with it at all. It will accept really slow powders and still perform with increasing velocities.
The .220" long throat makes all the difference.

Cheers.

 

[HRM Johnny]

The expansion velocity is a good bit faster than that, I know the .22-284 has exceeded 5000, and the 300 win mag with those accelerator type sabots has exceeded 5200 with 22 cal sabots bullets.
The 30-378 was originally meant to test shrapnel armor and used a weird 30 grain (I think) tin/aluminum type alloy at 6000+ feet per second.

I honestly think with the super overbore cartridges you just need to accept ridiculously looooong barrels to realize the increases possible.

For what it's worth, I've exceeded 4000 fps in my .300 win with 120 Barnes tac tx and in my .257 weatherby with 75 grain hammers.

How long is ridiculously long in your opinion? I have long thought that the over bore cartridges required longer barrels to reach their full potential. I suspect that a large maybe excessive muzzle blast indicates that the barrel is too short. I have no facts/data to back this up. For example, with 257 Weatherby, what would you consider an ideal length to maximize potential (mv) if there is no concern regarding the rifle being cumbersome due to length?

You state that you have exceeded 4000 fps with a 75 grain hammer bullet in your 257 Weatherby. How long is the barrel that you used to accomplish this?

Thanks,
Johnny

 

[Calvin45]

How long is ridiculously long in your opinion? I have long thought that the over bore cartridges required longer barrels to reach their full potential. I suspect that a large maybe excessive muzzle blast indicates that the barrel is too short. I have no facts/data to back this up. For example, with 257 Weatherby, what would you consider an ideal length to maximize potential (mv) if there is no concern regarding the rifle being cumbersome due to length?

You state that you have exceeded 4000 fps with a 75 grain hammer bullet in your 257 Weatherby. How long is the barrel that you used to accomplish this?

Thanks,
Johnny

Funny you should mention that….its a stumpy 24 inch vanguard!

 

[Calvin45]

Funny you should mention that….its a stumpy 24 inch vanguard!

I wish it had a longer barrel, just think of the speed!

 

[HRM Johnny]

any feeling regarding what length would be ideal?