How much difference in burning rate between these 2 powders is there?

I know they're close in the grand scheme but I ask because I have one load for plinking with my .460 Waetherby that seems just right. 115 gr. of IMR4350 gives me 2410 fps from a 24" tube, about 150 fps slower than a factry 500 gr. solid. A safe margin, I think.

Can I use H4350 interchangeably?

They are not interchangeable. That IMR4350 charge seems to be a bit on the high side of things according to my manual. Switching to H4350 and using the same charge would not affect things since you are using a slower powder. However, I still would back off a few grains and work your way up.

Joe,
In 1989 I tested 3 shots of IMR-4350 against 3 shots of H4350 over the chronograph in a Wby Mk V Custom Deluxe with 26" barrel (length included integral Pilkington porting/muzzle brake).

115 grains of each powder. Federal 215 primer, Hornady 500 gr RNSP, Norma-made Weatherby brass, 460 Wby.

Results were nearly identical.

H4350: 2508 fps
IMR-4350: 2513 fps.

About 15 years later, I tried 88 grains of both powders and AA-4350 in the .375 Wby with 300-grain Sierra.
H4350 was about 50 fps faster than IMR-4350, and AA-4350 was about midway between the other two.

Powder lots vary through the decades, and year to year, lot to lot.

115 grains of any of the 4350 powders seems to be a universal "happy load" for 500-grain cup&core bullets in the 460 Wby.
I would consider it just as good with 450-grain monometals like the Barnes TSX.

But of course we all will tell you to start below that by about 5% and work up to maybe 5% more than that and pick the load you and your rifle are "happiest" with.

Thanks for the input, everyone. I asked this question because of powder availability. I haven't seen any IMR4350 for a while now.

That load was suggested by Seyfried as being less than a maximum load and offering plenty of power. When I chrono'd it and saw it was about 150 fps under an average factory load, I just kind of stuck with it. Neck sized cases.

Joe,
I forsook IMR for the Hodgdon Extreme line of powders, after seeing Hodgdon Extreme temperature insensitivity with with my own eyeballs.

Part of the variation in IMR-4350 versus H4350 is the great temperature sensitivity of IMR-4350 versus very low temperature sensitivity of H-4350.

This was true in the .375 Wby, over a 40-degree-F temperature range from winter to summer testing:

Hodgdon H-4350 Extreme: about 0.5 fps per degree F
IMR-4350: about 2.0 fps per degree F.
(RL-15: about 1.0 fps per degree F)

If you cannot find IMR-4350 right now, but you can get your hands on H4350, then switch over to Hodgdon Extreme H-4350 and do not look back.
I am sure Ross would approve.

I am glad I did not buy that 8-pound jug of IMR-4895, but waited for the H4895 Extreme.

Assuming "average" lots of IMR-4350 and H4350:
If weather is hot, the IMR 4350 will shoot faster and higher pressure than H4350,
and if weather is cold, the IMR-4350 will shoot slower and lower pressure than H4350 ... on average.

Great answer RIP. That pretty much boils the fat off the pig.

4-5-0,
Thanks. Chronographing a lot of .375 Wby loads outdoors
at various winter and summer temperatures allowed
me to finally render that pig.
Moral of the story: Stock up on H4350.

Great info RIP.

Thank you.

quote:

Originally posted by thecanadian:
They are not interchangeable. That IMR4350 charge seems to be a bit on the high side of things according to my manual. Switching to H4350 and using the same charge would not affect things since you are using a slower powder. However, I still would back off a few grains and work your way up.

Im just curious as to what manual you are looking at. I have here my dad's 4th edition Hornady manual he gave me after he bought the new one.
In it for the 460 Wby and IMR 4350 it starts at 104.9 grains and goes up to 123.6 grains which is a lot more than 115 grains. Have they lawyered the current manual back that much?

With my lock and load press I could not get H4350 to meter with in 5 grs. It was bridgeing bad.

The 4350s not so much but the 4831s....pretty big difference.

.

quote:

Originally posted by JTEX:
The 4350s not so much but the 4831s....pretty big difference.

.

Yup. IMR-4831 was noticeably faster than H4831 Extreme or H4831SC Extreme, especially in hot weather.