I worked up a good load for my Ruger 300 WM using Remington brass. This load is 60.5 gr of IMR4064, Rem 9 1/2M primers and Nosler Accubond 180 bullets. It shot consistantly 1" or less 5 shot groups.
I recently bought a bag of Winchester brass and loaded up the same thing and was getting much larger groups - some up to 3"+.
I am going to shoot some more this week with the R-P brass and see it gets back to where it was.

I never change any component without reducing the charge and working the load up again.Different cases have different volumes and a load that was developed in one batch of cases,may not even be safe when loaded in another batch of cases.

Bronko, I totally agree with Stubblejumper on this, and is especially true on book maximum loads.

Just out of curiosity,why are you not using a little slower powder such as R-22, IMR-4350 or IMR-4831 instead of 4064?With those you are going to get a little more velocity.

You have just changed the pressure of the load. So of course its going to change accuracy. But usually winchester and remington are comparable. Its when you got high dollar thick brass like norma or even soft federal where it usually makes a big change and usually a shoot up in velocity. I know for my STW for instance, I have the same load for winchester brass as I do for the remington, and both shoots the exact same velocity range and grouping.

So yea, you got a strange issue.

I haven't found that to be the case with the cartridges that I have loaded with both cases.With the 7mmremmag,30-06,300winmag and 338winmag,the winchester cases have slightly more volume and produce less velocity than remington cases using the same load.I have only used remington cases with the 7mmstw.And I too question the use of 4064 in the 300winmag.It certainly is not one of the better choices if you want to see the true potential of this cartridge.

I shoot Remington and hornady brass. They both group identical and have the same speed, as per the chrony.(7mm rem mag) I have heard this before about win brass. weird stuff. but true!

i've loaded the .300 Win Mag for 40 years. Presently i load for my Ruger M77 anda Mathieuwith a28" barrel.IMR 4350 or IMR 4831 are much better powders forthe .300 Win. Mag.


"I haven't found that to be the case with the cartridges that I have loaded with both cases.With the 7mmremmag,30-06,300winmag and 338winmag,the winchester cases have slightly more volume and produce less velocity than remington cases using the same load."

Ditto for me. i often weigh and segregate my.308 and .30-06 cases.In .30-06, Winchester casesare alwayslighter than Remington by about ten grains. i alwaysuse Winchester cases for my accuracy loads.One of my .30-06 rifles likesa Winchester case and primer, ahuge quantity of IMR 3031 anda Sierra 150 grain BTSP bullet.Have put together some very accurate loads by weighing and detailing my cases.

When you change a component of a load, you stand a large chance of changing it's performance. Case capacities are a large part of this. I always move down in powder charge and work back up again if I wish to make a change, even with bullets of the same weight, but of different styles and/or manufacture. If you disregard this procedure and are working near, at, or over recommended max loads, you could be inviting serious trouble. Be safe.

I know that with the 45-70 the Winchester brass holds more black powder than any other case I have used so I think Stubble is right on the winchester holding more powder thus a little less pressure.

I've used IMR4831 and IMR4350 in the 300 for years with good results but I tried the IMR4064 and got much better accuracy with less recoil. But this is a mute point now as this rifle is sitting on the used gun rack at my local gun shop. Among other rifle chamberings, I have a .30-06 and a 325 WSM so I didn't need the 300 anymore. If any of you want these 50 cases of W-W once fired brass, send me a pm and I'll send them to you for $5 plus actual shipping.