M1 Dilemma

[Sur5er]

Got a curious situation developing in reloading for my rebarreled .308 M1. I'm using 147gr FMJBT bullets that were resized from .311 to .308. They are 7.62X54 Russian military pulldown and the bullets are copper washed steel jacketed. In developing a load for my M1, I got up to 45gr of WC846T (the original US GI weight is 46gr of WC846T) in my 308 bolt action Remington. No signs of pressure, velocity in the 2550-2650 range and some pretty decent accuracy so I tried four in the M1. The case heads had expanded .002"-.003", primers were cratered but not flattened (they looked like a low pressure load that pushes the primer back) and the action failed to cycle twice in 4 rounds. I believe a lot of my problem is due to the increased amount of bearing surface that the resized bullets have on the rifling. The USGI 147gr bullet has roughly .25" of the bullet in contact with the barrel while the resized bullets are about 1/4" longer and have over twice that amount contacting the barrel. More surface equals more friction, more pressure (at least initially), lower velocity (POI was 3" lower than Ball ammo) and then lower operating pressure at the gas port.

I'll post some pics of the two different bullets and hopefully by then someone will have illuminated this old grunt.

Thanks,

[versifier]

Welcome to Gunloads.

Yes, I think you have hit the nail on the head. The longer bearing surface has increased the bullet's friction coefficient and raised pressures to an unacceptable level. If you continue to shoot them out of your M1 you risk at the very least damaging the op rod. It is never a good idea to resize jacketed bullets. Even if they are consistently sized after coming out of the die, the jackets often separate and their performance can be erratic. While a decent bolt action might be able to handle loads hot enough to crater the primers (though it is NEVER a good idea), such loads far exceed the envelope of acceptable pressure/function in a semi auto. Your case head measurements confirm it. Garand's designs and their descendants are especially vulnerable to damage from loads that are too hot. The lower POI is indicative of a hotter and faster load as the muzzle has not risen to the same point when the bullet exits the barrel. The cycling failures are due to the over expanded case heads increasing the difficulty of extraction (in a bolt action the same problem would result in a bolt handle that was difficult to lift). Bolt actions can almost always handle much hotter loads than other actions before they start to show signs of high pressures.

[Sur5er]

Thanks for the welcome and the info. I've been hanging over in the cast and surplus powder sections for a couple of years and up until recently really didn't know that this side of the board existed. I appreciate your input and concur. The last thing I want to do is screw up the op rod on this piece. Since the M118 Match bullet is longer and weighs 173gr, perhaps I can use a slower powder for these bullets. I have 2,000 of them and it would really tick me off if I was restricted to the bolt action. BTW, they were commercially resized and I have had no problems with either my 308 or 300 Win Mag bolt actions in the accuracy or pressure areas. The GI ball ammo I used as a control was actually 75fps faster out of my bolt gun than the reloads, that's why I figured that I had a velocity drop.
The WC846T lot I have is 4 or 5 places faster compared to BL(C)2 on the burn charts.

Again, thanks for the input.

Dick

[Sur5er]

Here's a pic of the two bullets. As you can see, they are different lengths.

Dick

[Sur5er]

Dropped the powder weight to 42gr and while it won't lock the bolt to the rear everytime, it does strip a new round from the clip. Primers are still a little flatter than I'd like, case heads are at spec so as near as I can figure the pressure must drop very quickly after ignition and be below optimum at the gas port.

I also loaded up some rounds with 42.2 of IMR4064 and even this load shows some slight pressure indications on the primers. This load won't lock the bolt back either evertime, but does load a new round. Case heads are at resized demensions so I know the load won't hurt the Op Rod. Both the loads hold 2" groups at 100yds from the bench.

Ball ammo feeds and cycles flawlessly, no signs of pressure and has a POI 1" higher at 100yds.