Home Forums Reloading Big Game Rifles 300 Weatherby and Norma MRP Question

I was wondering if anybody out there is reloading the 300 Weatherby with the current MRP powder. I recieved a couple of new cans recently and am a bit hesitant to use the older data. I have a early Mk 5 Japanese production rifle and am using once fired Weatherby brass, Fed 215 primers and Nosler 165's and 180's and am looking for the safe and sane loads.
Any help is greatly appreciated. Thanks

MRP/R-22 is the chiz in the Roy....throws 168TTSX to 3325fps and sub MOA in my Vanguard.

Make sure these cases will work in your gun. Weatherby cartridges have much higher pressure than standard rifles, I had tried using once fired cases from a different rifle and even with full length re-sizing, wasn't able to chamber the rounds...

yep rl22 is the way to go 150gr barnes 3550fps works great

Thanks Shrapnel, I've encountered that also.
It seems fairly difficult to find any current data using MRP powder for the 300 Roy, though that is what it was loaded with years ago. I have data that was published in the Weatherby guide in the 70's but as I pointed out, I'm a little hesitant to use it since the powder mix may have changed. I suppose I could start with loads 5% below those old numbers, but I was hoping somebody might be loading it now and might share some of their information.
Thanks

Re22 is sweet in mine with 168 VLDs at a tick above 3200fps.

I can't speak for MRP, but I tried H-1000 and IMR 7828 and found the IMR 7828 to be quite accurate with good velocity. I am shooting 180 grain Nosler Ballistic Tips at just over 3200 FPS. These loads are Chronographed and not speculated.

I am also shooting a 26 inch barreled Sako Deluxe. A shorter barrel will suffer some velocity loss.

This group, although only 2 shots, is just a zero check before hunting. You can see the potential of this load and accuracy. IMR 7828 did the same in my 30-378, better accuracy than the H-1000.

What pressures do 300 Weatherby's run at?



Casey

In the older Weatherby guides I have the hottest
180gr load listed says it has a avg pressure of 57,620 psi
My Speer reloading guide #14 says the industry pressure limit
is 65,000 psi

Yes--which was kind've my point Lots of cartridges run the same max pressures as the Weatherby's. Heck, the 80 year old 270W operates at those pressures......


Casey

It's a good bet that in those old Wby. guides where they write PSI it should really be CUP. I'm at work and don't have mine in front of me, but IIRC they also cautioned against using the loads above 55,000.

If you go with Denton Bramwell's linear regression for ANSI CUP and PSI, that 57620 CUP is going to come in around 69,400 PSI. Also, 55,000 CUP is about 65,500 PSI.

I'm guessing Schrapnels experience may have been similar to mine in that the chambering issue may have been from rounds fired through a fairly generous chamber in a particular rifle and the subsequent full length resizing didn't bump the shoulder back far enough for it to chamber on the belt with just enough room for the shoulder to expand. I've owned a few 300 Roy's and saved the brass from all of them and and ran into this same problem where after full length resizing I couldn't get the brass to chamber easily in one particular rifle.

Great point Mathman!!!
The front page in the Weatherby guige reloading I have does say exactly what you
you pointed out and also goes on to say that "loads over 55,000psi should not be used and are shown for reference only"

Like shrapnel, 7828 was THE powder in my .300 Wby Sako with 180 gr. bullets:

7828 is a great powder for the 300. I've been using Rl-22 or MRP (same thing) for years out of both my 300s. 180gr TSX and 81gr gets me right at 3240 or so and sub MOA. jorge

Thanks for the tips and thoughts fellas, Its great to get such a diverse set of thoughts and suggestions. I ended up receiving a few cans of the current MRP for free from my Dad who at 70+ years of age is still shooting his Mk 5 .300 Roy but doesn't handload. He purchased several pounds of it for $15 a can recently and wanted to load some up for both our rifles.
IIRC the Norma produced ammo for Weatherby that was sold here in the states was loaded with MRP for a number of years and may still be? and it produced the 1 1/2 inch or better accuracy in our rifles that Weatherby guaranteed. I have the other powders that some of you listed here. I was primarily interested to see if any of you were currently loading your 300 Roys with MRP and Nosler 165-180 Partitions and if you might have a good starting load.
I have reviewed Normas website but their load data is based around their Oryx bullet witch I am not familiar with, and I am not sure if they bump up or have the bearing length that the Partitions do, consequently
Normas starting data with the Oryx might be higher than if a Partition is used.
Also as I mentioned in my OP I was concerned that the current MRP may be a little hotter than the older MRP and the data in the older Weatherby guides would be suspect.

Thanks Again
BD1

I've used the data on the old Weatherby guides extensively and the only ones you need to be careful with are the 4831 loads as those were crafted with the old WWII stuf which was somewhat different of what we have today. The loads with MRP are still sopt on today and I've used them in my 257,7mm,300 and 340 Weatherbys. Also remember you can use RL-22 and MRP interchangeably.

This was taken from SAAMI specs. .270 Winchesters and similar cartridges of that era were less than 55,000 PSI and more likely 52,000 PSI

Maximum Pressure ( in PSI Unless Noted )
Recommended By SAAMI
The Sporting Arms and Ammunition Manufacturers' Institute

300 Weatherby Magnum - 65,000 PSI

Long throats in Weatherby calibers are common to accomodate the higher pressures the Weatherby cartridges generate. Seating bullets at the right depth is essential in the reloading of these same cartridges.

Despite the erroneous use of PSI in much of the literature, when 52,000 is mentioned as the limit for the 270 it's CUP. That translates to about 61,000 PSI.

I checked SAAMI and it does list the 270 at 65,000 PSI, I guess I was assuming a 30-06 case and it is rated lower, but only by 5,000 PSI, at 60,000