I got a super deal on factory Winchester 300 gn FMC 375 H&H ammo from Cheaper than Dirt of all places??? $29.97 per box. There was one review stating the cases and tips were corroded. I bought 3 boxes hoping to salvage 40 good cases. Two boxes were one lot and were perfect; the one box was a different lot and had a few corroded rounds in it with one being pretty bad.

I am wanting to pull the 300 gn FMC and replace with either Hornady 300 gn DGX round nose or 300 gn Nosler Partitions. What does anyone think? Do I need to work up loads or just use as is with new tips?

I'd use Hornady or Nosler data from the books or websites.

Put a strong magnet to the bullets you have to see if they have steel in the jackets. They might actually be steel jacket (copper clad) bullets from Hornady. If they are you might want to use them as solids as-is.

I've dumped the powder from ten cases of milsurp .308 and weighed them and then divided by ten and recorded the weight. Then pulled milsurp bullets from 280 of them and installed the same weight bullet from Swift (Scirocco II) using the same powder and weight.
(Well the bullets I pulled were 147 grain and I installed 150 grains) The ammo was all from the same lot however. I got away with it!

There is a small chance the powder used in your winchester ammo is not the same powder in each box....unlikely, yes, but possible. You could pull the bullet and seat a new bullet without removing the powder and likely be just fine.

I'd sure like to resize the case after pulling the bullet to re-establish a proper seating tension.

Here's another thing.....the 300 grain .375 H&H is rarely used on a cheap hunt.....and the price of a pound of new powder just might be a good investment.

Yes, you'll probably be just fine substituting bullets but are you sure you want to?

I am thinking of leaving one box intact as it is good ammunition. Although I don't need a 375 H&H to hunt bear in PA, I am in the process of building one up (had 4 in my life that I should have kept, all pre 64 M70's) and may as well use it. We must use expanding ammo in PA.

I don't have an RCBS #4 shell holder to pull a bullet; the powder may end up being 760 or some other uniform powder, but it may be some blend. If it is a blend, I am not comfortable mixing it all up and working up a load and hoping that the blend stays balanced. I would just dump it before doing that.

I tested the tips and they are magnetic. This is older Winchester, Red-Orange-White box. The older books list Win velocity @ 2550 for 300 gn FMC or Silvertips. I am sure the Hornady roundnose DGX would be a safe substitute. Also wouldn't my new crimp handle the neck tension part? I use to always use IMR 4064 in my 300 gn 375 loads with some guns getting 2600 fps and some getting 2660.

Well I dug up a shell holder and pulled the bullets from the corroded box of ammo. The powder is a fairly fine extruded powder, finer than IMR 4064 and the charges averaged to 66.5 gns. I will work up the loads with new projectiles and see how the powder works. If unsat, I have a few pounds of both IMR 4064 and IMR 4350. I ought to be able to get something cooking with that. Now if I only had some Fed 215 primers!