Blaine
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<br>I picked a poor example with the 257. According to an arcticle recently, the writers formula for overbore has the 257 at or close to the top, for being overbore.
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<br>Something like the 7mag compared to the 7X61 S&H would be a better choice. The shoulder lines of the 7 Rem mag would indicate it was harder on barrels than the Sharpe and Harte. After comparing these two rounds, it occured to me there could be another reason besides the turbulence point, for the faster throat errosion, on some cartridges. Everyone is theororizing on what takes place in the throat causing premature wear, so I'll throw my version in and see what you think.
<br>No doubt higher pressures create more heat, and when the throat material is hot, it is much easier for the unburned powder to have a sandblasting effect on the rifling.
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<br>In the 7 Rem mag, because of it's funnel shape, it has powder unignited following the bullet down the bore. The powder directly behind the bullet, with it's deterrant coating, is hard and abrasive. If this coating hasn't already burnt off, as it passes the throat, it wears progressively more with each shot. Now every barrel experiences wear, but the Sharpe and Harte cartridge, with is sharper shoulder, has the ability to form a bridge so to speak. This allows the powder to have a more complete ignition, inside the case. If the hard retardant coating has burnt off the powder granules, before the unburnt powder follows the bullet down the bore, it would be less abrasive to the barrel material. Make any sense????
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<br>I'd proof read what I just wrote, but I ran out of smokes an hour ago. I'm tooo dizzy to read it , and don't feel like typing this again so ...........bye
