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Note (link) how they got into an argument about pressures, etc, with the fellow from Alaska talking about breech-bolt thrust from straighter sided cases being less than more tapered cases, along with the 'proof' of Ackley's testing. Anyone who's read those books, knows he knew what he was talking about, in those tests he peformed.

The opinion armed fellows used the highly tapered 9mm case as an example of severe back thrust in a virtually straight case. Unfortunately, their opinions are greatly flawed. First of all, it's a very short case and even though it has only .005" taper per side it only has .5" of case wall contact with the chamber. That sounds like an almost straight case. Not so. Multiply that taper by 5.166, which is the difference in length of bearing surface, and we find the rate of taper of the 9mm would be .0258 per side, 51.6 thousandths total which is more than double what the .405's taper is and even .0088" more per side than the sloping sided Krag case. That makes the Krag case look straight. No wonder the blow-back aciton works so well with the 9mm case. Only .5" bearing and far from a straight sided case as well. Thus it has very little purchase on the chamber walls. Thus it is a poor example of anything other than a "spray and pray" pistol round.

Now, getting back to the situation at hand, the funny thing is the Krag has virtually the same rim diameter as the .405Winchester,thus if developing the same pressure, would have the same breech thrust, if of the same taper - but they aren't. Case diameters are slightly different, but not very much - .003" total. That isn't enoug to make one iota of difference. Now, another aspect in favor of the .405 in this situation, is it also is almost 1/2" longer adn indeed, has 1/2'longer bearing surface on the chamber. Since the .405 has less taper as well, it developes less breech thrust than the more tapered case, if both are fired in dry chambers. Oil the chamber and the breech thrust increases - as in not wiping all sizing lube from the case. Most actions don't care with normal under 60,00psi rounds, but I'd made sure I cleaned all ctgs. for the weaker actions.
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Those who undestand this sort of thing, know this as fact. Those who use their opinions as fact, will dispute this- it's a free world. Some people seem to think that the straight tapered case has more bolt thrust than one with a neck - again, their opinion is flawed - it doesn't happen that way. The sloping neck of the Krag round does not help the round 'stick' in the chamber under maximum pressure due to it's more radical taper.

The fellows on the link forum spoke of chamber pressure differences - all their own speculations - no facts were given. Here are the facts.

Taper
.30/40 taper - .017" per side, .034" total.
.405 taper---- .012" per side, .024" total ie; winner

Pressure ratings
.30/40 Krag - 47,000psi CIP
.405 Win - 36,000PSI CIP and 44,000PSI SAAMI - ie: winner

Now, would someone with actual facts instead of merley their, in all likelyhood, honest opinion, please tell me why this conversion is unsafe when made with a modern 4140 or 4150 rifle barrel from a reputable company, like Pac-Nor, Shilen, Badger, Kreiger, Hart or McGowen. Sorry about the multitude of good barrels I omitted.

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Daryl

"a gun without hammers is like a Spaniel without ears" King George V

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