.300 wby load development

[WestMOhunter]

Starting with an old factory Rem 721 H&H 26” barrel that was rechambered 40 yrs ago to .300 Wby. Surprisingly high velocities (3300) with first time load development (4831sc/175 Barnes LRX) has made me cautious. Hornady manual shows 82.3 max. Barnes says 83.0 is max. In either case a 24” barrel is supposed to get you 3050-3100 at max load. I’m seeing 3250 - 3300 with 82.0 grains and 26”. Primers and brass show zero signs of pressure and 0.75” at 100. I consider myself fairly experienced, but 150-200 faster with just 2” more barrel makes me wonder what’s going on. Thoughts?

Thanks.

 

[49ereric]

Those old Remington 721-722 barrels are great.

 

[intheup]

What bullets have you tried? My 300 wby mag built on a 721 action seems to be picky with bullet type.

 

[WestMOhunter]

It shoots most everything pretty well. Remington CL, Weatherby with partitions, Barnes LRX. It just shoots well. 1960s factory barrel.

 

[jimh406]

There is a reason why some magnums have 26 inch barrels. More time to burn gives more speed in the slower burning powders. I think 150-200 makes sense for a hot 300 WBY round.

I get similar speeds out of my Winchester 70 chambered in 300 WBY at 3240 with a 24 inch barrel. My brother worked up the load after trying a few different powders. He found more speed but still solid accuracy with IMR 7828 with the Federal Magnum primer which he feels is important.

Less than 1 MOA with me shooting. Frankly, I don't measure groups very closely. Obviously, each gun is different, so as alway slowly work up the load if you try this one.

Brass-Hornady
Primer-Federal 215M
Powder-IMR 7828
Grains-83.5
Bullet-Nosler Partition 180
OAL-3.52