Federal primer interchange, Gold Medal vs Standard LR?

[emcon5]

Federal Gold Medal large rifle match primers (210M) are still impossible to find, and I am almost out. Can the standard Federal Large Rifle (210) primers be substituted without having to work up new loads?

Or, does anyone know of a vendor with Fed 210M in stock?

Thanks,

[Unclenick]

You should do fine.

Any time I change primer lot numbers, even if it's the same primer number, I knock the load down 5% and make one round of each 1% increment and shoot them up in steps to verify no pressure signs show. I only expect to see anything close to 5% worth of charge difference switching between some standard and some magnum primers (205 to Rem 7½, for example, has done that for me in .223), but it's a good safety habit and only costs 5 rounds. Usually the new primers are within 1% of velocity if the same lot of powder is in use, but safety first.

Once you get within 2% of original velocity, provided you are not running a compressed load, then figure the percent change in velocity will more or less track the change in powder charge. You'd think the velocity would only change as the square root of powder charge because you are adding a certain percent energy and energy is proportional to the square of velocity. However, as you add powder the pressure also goes up (disproportionately to the charge), increasing the efficiency with which energy is converted from the chemical potential energy stored in the powder to bullet muzzle energy. So, you now get a little more bullet energy out of all the powder than you were getting from it before. The net result is velocity and powder charge change percentages come close to tracking over a range. It's not uncommon.

Do keep in mind peak pressure is going up anywhere from about the square of the charge increase percentage to more than the cube of it, depending on the powder and the bullet weight (lighter makes the pressure change more rapid). If you figure just to get even more velocity, you pay a rapid penalty in increased peak pressure because the higher pressure from more powder burning at once causes the whole case full to burn up more rapidly and earlier in bullet travel.

[emcon5]

Thanks for the reply. My loads are not anywhere close to maximum.

I contacted Federal, this is what they said:

The GM primers have tighter specs. But both primers have the exact same components and result in the same output and can be substituted without changing the load recipe.

Thanks,

Federal Ammunition

[Unclenick]

Yep. I still do the 5% thing when I know the lot numbers are different, but usually end up right back where I started. Safety first.

BTW, if you've read through Dan Newberry's site, you can also run a round robin with the new primer, to verify an accuracy load. Charles Petty had an article in 2006 on the .223 and changed primers, including 205 and 205M. I've forgotten the exact results, but do recall the 205's ran the powder charge a little slower. Both were at the low pressure end of the range of primers he ran.