300 Remington ultra mag reloading book difference?

In Nosler reloading manual 6 in states that the max load for retumbo in a 300 rum is 99 grains for a 180 grain AccuBond, with 97 being the most accurate. In the latest version online from their website, it lists 95 grains as being max for 180 grain accubonds, with 93 grains being the most accurate? I have not tried 93 which think it would be an anemic load for the 300 rum as I have been shooting 97 grains for years with sub moa results. So what is the professional opinion here? I am interested in the correction? or revision, if anyone knows what changed?

Jon

fwood":1vcd6oxb said:

In Nosler reloading manual 6 in states that the max load for retumbo in a 300 rum is 99 grains for a 180 grain AccuBond, with 97 being the most accurate. In the latest version online from their website, it lists 95 grains as being max for 180 grain accubonds, with 93 grains being the most accurate? I have not tried 93 which think it would be an anemic load for the 300 rum as I have been shooting 97 grains for years with sub moa results. So what is the professional opinion here? I am interested in the correction? or revision, if anyone knows what changed?

Jon

Click to expand...

More lawyers involved with the book. Modern reality is litigation is expensive and the attempt to avoid it is necessary. I had a look at some old books from the 70’s and they were pretty stout loads, way above max data now.

I found similar thing in Lyman #46 vs Lyman #49. in #46 For 300 WBY 180 grn IMR4350 had a MAX of 79 grn which was the most accurate for my old Weatherby. In #49 MAX for IMR4350 and 180 grn bullet is 73 grn. Lyman claimed the powder changed. IMR said IMR4350 Has NOT changed, how ever I should follow current recommendations.
I think if you look, you will find many similar situations

I suspect that the reason for the difference has to do with lot-to-lot variation and inherent differences in the firing systems employed when testing.

Mike that may be but, 4 grains seems to be a large amount. The difference between 3/4 moa and 2 moa in real terms of shooting. I checked other loads with retumbo and nothing changed. It would reason that it would change for all if your hypothesis were true. it may just be a error earlier or now.

Your observation should definitely give one pause. I agree that it is somewhat worrisome when you see such differences in published data that has been pressure tested. However, the case takes a large charge, and large charges are different animals sometimes. It is a 4% differential in charge weight, which isn't all that great. The pressure differential is observed as ~2000 psi/grain, which isn't all that great when everything is considered. Velocities at this upper level varies only ~30 fps/grain. This is with the current date generated by QL. I've discarded my old load data, so I'm unable to verify the matter by appeal to what would have previously been listed. I have witnessed similar disparities in some powders that could readily be accounted for by lot-to-lot variation.

What is apparent is that the habit of verifying what is published rests upon the hand loader. We are responsible for safety by applying all the old standards we learned years ago that lead us to review the various criteria for excessive pressure. I don't like to shoot without a chronograph or a doppler radar to verify velocities. And I do review all my cases and such mundane matters such as bolt lift, sound, etc. I've been surprised on more than a few occasions by disparities between published data (sometimes data that was relatively recent) and propellants.

It is definitely a reminder to start low and work up carefully. It should give anyone pause that thinks they can simply pick a charge and shoot it without observing reasonable rules of safety. Fascinating post. I haven't loaded for the 300 RUM in several years. If I was doing so, I'd definitely need to give this a more careful review.

Here is my email exchange with Hogdon back in 2017. First my question, then their reply

I have been using IMR and HODGDON powders for over 30 years. Lyman 46th edition For Weatherby 300 WBY Magnum, 180 grain jacketed bullet, it list for IMR 4350 71-79 grains of powder with Federal 215 primer. Lyman 49 edition for the same load it lists IMR 4350 68.5 -73 grains. Has the IMR 4350 changed since 1982? Thank you
Regards,

Response

No, the formula for the IMR 4350 has not changed since it was first brought in the early 1950’s. Data does change as the ability to more accurately measure the pressure goes up and brass and especially primers and bullets have changed a great deal. As a rule, primers are much hotter than they used to be and they contribute much more energy to the load now. Brass is different in capacity from brand to brand and bullets are generally longer in bearing surface as well as being of a harder gilding metal. All of these things drive pressure up meaning the data has to be reduced to keep the pressures from being excessively high

Like Dr. Mike says, start low and work up for safety. That advice always works!!!

I have been busy for a while, but thanks for all the input. The load was worked up with 97g of retumbo yielding nearly 3370fps and 1/2 moa out of a custom Montana gun. The elk never knew the data was from an old manual.

fwood":21bpdmdr said:

I have been busy for a while, but thanks for all the input. The load was worked up with 97g of retumbo yielding nearly 3370fps and 1/2 moa out of a custom Montana gun. The elk never knew the data was from an old manual.

Click to expand...

Lots of suds right there!

DrMike":2bjswxj3 said:

I suspect that the reason for the difference has to do with lot-to-lot variation and inherent differences in the firing systems employed when testing.

Click to expand...

I’d vote the same way. I let the chrono and gun tell me where to be. Too many differences in the things used to develop data. 3350’ish for a 180 in a 300 RUM and 3100-3200 for a 200.

Take a look at barrel lengths as well. A lot of data is using a 24” barrel.