Overbore debate

[Hengehold]

The daily bulletin recently posted an overbore index guide. I found it interesting that the 6xc and the 300 WSM had a very similar overbore rating. The 6XC barrel is typically good for at least 2000rds. Will a 300 WSM typically have a similar barrel life?

Thanks,

-Trevor

 

[scope eye]

2000 rounds not even close, with the 300 WSM having more than twice the case capacity, and running at a higher pressure it's round count is greatly diminished. 1000 rounds would be a more realistic count, inevitably someone will chime in that there uncle has a 300 WSM with 3872 rounds and is still going strong. I still stand by my convictions.

Dean

 

[jghoghunter]

My heavy bench gun in 300wsm quite shooting 1.5" groups at 500 yds at 1400 rnds.

 

[Milo 2.0]

What is the formula for determining overbore ratio? I multiplied, divided, etc... and it's over my pay grade.

 

[Tommie]

Honestly the "overbore" discussion is old, tired and pointless. Ask a shooter to define the term and you'll hear something about an inefficient barrel-burning cartridge.

If the 264 Win Mag is overbore, is the 26 Nosler double overbore?

This is how I see it: If a cartridge has a powder capacity so large that it cannot produce higher velocities than a smaller-cased cartridge, then and only then is it overbore. In other words, the powder capacity is OVER the BORE capacity. Other than that scenario it's just an debate of relative efficiency.

 

[dkhunt14]

My heavy WSM broke Records in 1000 yard BR with 1400 rounds down the barrel. Other things also determine how many rounds. Rate of fire is the biggest hurt on a barrel. In BR, after sighters, we dump 10 records down a barrel in a short time. That is hard on barrels. Length of neck and shoulder angle is another thing that can chew up a barrel. Look at a 243 verses 6MM REM. Type of powder used also. Size of bore also determines barrel wear. Look at a 264 WIN MAG verses a 7 MAG. Matt

 

[ShootDots]

My heavy WSM broke Records in 1000 yard BR with 1400 rounds down the barrel. Other things also determine how many rounds. Rate of fire is the biggest hurt on a barrel. In BR, after sighters, we dump 10 records down a barrel in a short time. That is hard on barrels. Length of neck and shoulder angle is another thing that can chew up a barrel. Look at a 243 verses 6MM REM. Type of powder used also. Size of bore also determines barrel wear. Look at a 264 WIN MAG verses a 7 MAG. Matt

I believe what Matt is saying here (and he is correct) is that the expansion ratio of a cartridge, along with the amount of powder being burned, has A LOT to do with the concept of "overbore". Take a 6mm Rem, which if used in competition, will burn a barrel up pretty quick. However, take the EXACT SAME CARTRIDGE and neck it down to .22 and you will FRY a barrel in no time at all in competition. The difference being the "expansion ratio" of one to the other. Take a .458 Win Mag, which is the parent case of BOTH the 7mm Rem Mag and the .264 Win Mag. It is doubtful you could burn the barrel out on a 458 Win, however, neck it down to either of those, and barrel life diminishes quickly! The difference is "expansion ratio" of the cases. Couple all of that under rapid, L-O-N-G strings of fire in competition, and you can see how the MORE the overbore, the less the barrel life. HOWEVER, without some form of "overbore" we would still all be shooting cartridges such as the .45 / 70 and the like! So, HOO-RAH for "overbore"!!

 

[JRS]

The chart can't possibly be accurate. My 257 Weatherby isn't overbore. How can any cartridge (257 Weatherby, 264 Wn Mag, etc) based on the 72MM H&H Belted Magnum case be overbore