|Originally Posted By Keith_J:
Originally Posted By ggibbs:
As a cast bullet lover, I'd like to hear details about your loads. I don't worry about the gas tube stopping or any other such nonsense, but I'm afraid that in order to build enough pressure/velocity to cycle the action, barrel leading would be inevitable.
Port pressure to cycle is 12,000 PSI. With a gas check, this is an easily tolerated pressure with hard bullets. Figure on a compressive yield strength of 16,000 PSI which means peak pressure with gas check in the 30,000 PSI range. With bare based bullets, peak pressure must be kept under the compressive yield point, otherwise the lead tends to obturate into the bore, increasing the contact pressure on the bore. Couple this obturation force with velocity and you get leading.
This phenomena was discovered by Richard Lee and it was floating around in my head for a while before I realized how simple it is. For the longest time, reloaders had been experimenting with light charges of very fast powder and often, getting leading even at low velocity.
The new thought is not matching bullet alloy hardness to velocity but rather hardness must be matched by peak pressure. Or, in other words, use slower powder. For .223 Remington, a good choice would be IMR 3031. To assure function, slower powder in the 4064 range may allow for higher charges which will make port pressure.
Interesting stuff. I may try some as I have a few .224" RCBS bullets.
Regarding the "new thought", it's really not new at all. Veral Smith of Lead Bullet Technology wrote a book (JACKETED PERFORMANCE WITH CAST BULLETS
) years ago, I think back in the 90's, where he describes in detail how to calculate the necessary bullet hardness with regards to chamber pressure so that a bullet will obturate fully and properly. I have the book somewhere and it's an "must read" for any bullet caster. Mr. Smith also makes moulds that are extremely well designed and of very, very high quality.
Thanks for the responce.