Larry, First, unless you can call my attention to any contrary publication on the M1A that is cited as a standard reference work by the experts at the M14 forum, you and I must agree that the Author is an expert on the RIFLE. With full an open respect to your cast bullet expertise, I see nothing in your writings referencing Port Pressure, the crux of my concerns.
Let us get to the core issue and my priorities I attach to any load from my 50 + years of handloading experience;
1. SAFETY, Shooter and Rifle
2. Accuracy
3. Ease of duplicating
With my criteria established, here are the author's AFETY concerns:
"Powder and Port Pressure
Yet another safety issue: which propellant to use. (Yes, there is a time when everyone gets to just go shoot their rifle, coming soon.)
For the M14 to function as a self loader, gases from firing are bled into the gas
cylinder from a port hole in the barrel; these gases are fed through a corresponding hole in the piston, which has a forward facing (into the cylinder) hollow end. When sufficient pressure has accumulated inside the cylinder, the piston moves rearward, the gas port inlet hole misaligns with that in the barrel and shuts off the flow, and the action stroke commences. The piston butts up against the operating rod at rest (before firing) so that when the piston moves to the rear it moves the op rod back, which, being connected to the bolt, opens the bolt and cycles the action. Legions of linkage.
Design specs call for the vicinity of 12,000 psi port pressure. The level of pressure that exists when the majority of gas reaches the barrel port is port pressure. Staying within this figure is easy provided we know propellant burning rate rankings. Port pressure is not the same as chamber pressure, nor are there direct corollaries: low chamber pressures do not necessarily mean low port pressures, and vice versa. Slow burning powders, which generally test to lower chamber pressures in .308 W., escalate port pressures to well above the limit for the M14. This has to do with the volume inside the barrel, which is increasing in front of the case as the bullet travels outward, and the amount of gas pressure behind the bullet during this journey, which can be greater with a “late blooming” powder. When port pressure exceeds specs, “blooms” at the port, the piston moves at excessive speed, which also moves back the op rod and bolt too quickly and forcibly. The gun gets battered or broken and the cases take that much more abuse due to faster unlocking of the bolt. I don’t know what port pressures are with all available gun powders, but that doesn’t matter as long as I know this: the burning rate that defines the upper limit is IMR® 4064. Use nothing slower. Ever.
This is not to say it’s necessary to use a “fast”powder. Then the same standards apply here as for most everything else. Fast powders (like H322) can overblow chamber pressures before producing adequate velocity, or port pressure, in a .308 W. case. However, anyone who sneezes dust might remember that one of the all-time greats in this use is IMR® 3031 at 39.5 grains (this was original in the original black and white boxed Federal® Match that shot so well). The time-proven performer in this rifle is one of the “4895s.” There are at least three and all are suitable, even though they’re not precisely the same. The 4895s are excellent, flexible performers: there’s a wide range of charge volumes that still produces top accuracy — just tune the speed. This, by the way, may be the only easy part of handloading for an M14: finding “the load” is not difficult. That’s been done."
Satisfy the port pressure concerns with listed loads and we are in sync.
Cordially,
overbore