A couple loads for the 300 mag

[irocbarry]

LOADS EXCEED PUBLISHED MAXIMUMS, START LOW AND APPROACH WITH CAUTION

I went and shot some loads today for mine and my dads 300mags today, had some great and some interesting results.

First the great.
200gr AB, R-P brass, WLRM primer, 3.35 COL, 72gr H4831

Four shot .75" at a hundred, with a average speed of 2795fps. Was very happy it the accuracy and consistency of the load, ES was 23fps for the four shots, the best of any load I've done to date. These should wreak havoc on anything that gets in the way of them. Would like to get it closer to the lands but the 3.35" is as long as the magazine will let me go. The gun is a ~1974 Win. M70


Now for the interesting part.
In my rifle (MK77 300mag) going from 73gr of R22 up through 75gr i was getting in between 30 and 50 fps gain per half grain of powder. When the load went to 75.5gr it jumped from 3035 to 3148 average for three rounds.
This was also my most accurate load, just under an inch. Is that large of a jump in ave speed a sign I need to back off because of pressure? Everything looked fine on the brass, same as the other loadings, and bolt lift was same as normal.
Load info:
180AB, R-P brass, WLRM primer, 3.35" COL (magazine limit again) 75.5gr R22

Any input would be greatly appreciated, thanks in advance.

 

[JD338]

irocbarry

I have loaded for 3 different 300 Win Mags using 75.0 grs RL22 and 180 gr PT's with no pressure signs and sub MOA accuracy.
If you are using 200 gr bullets at that charge weight, you are running at 300 RUM levels! My guess is that you are at some very high pressusres.
Better to back off, Max listing is 72.5 grs.

JD338

 

[Guest]

That load is for a 180AB, I believe, but it still makes me nervous to see a big jump like that. That sounds like a pressure spike starting to happen. Of course, if you're anywhere that it is brutally hot, like about 2/3 of the country, you could just wait until later in the year, try it again, and see if the heat had anything to do with it. If you know someone with quickload, have them run it to see. I did a quick check through Nosler's most recent online data, and they are showing 75.5gr as a max load for the 180gr, so you aren't above published max charge, but that doesn't mean you aren't hitting a pressure spike. The data can be viewed here:

http://nosler.com/index.php?p=15&b=30cal&s=349

Now, that said, your velocity is a tad above Nosler's, so I might think about backing down maybe .25-.5gr and see if you can duplicate the accuracy without the slight pressure sign (velocity). On the other hand, you know your rifle better than any of us do, and you have to be the one shooting this, not us. As far as being 'above book max' you aren't, but I would approach this load with caution, especially in mid-July! Good luck with the season. Sounds like you have a real hammer on your hands.

 

[irocbarry]

JD338- the 200gr load was with 72 grains of 4831.

dubyam- It was around 60-65 when we were shooting yesterday, so not that much higher then it will be first couple weeks of the season next month.

I'm probably going to back off to 75gr, and work up in .2 till 75.5 to see what i get for accuracy, even the 75gr load was not bad for a hunting round ~1.5".

My gun does seem to get a bit more velocity then what is usually expected, with the chronograph 15' from the muzzle factory Win AccuBond 180gr's are going 2970, and Federal power shock 180gr's go around 3040. Both loads are listed at 2960 MV.

 

[JD338]

JD338- the 200gr load was with 72 grains of 4831.

dubyam- It was around 60-65 when we were shooting yesterday, so not that much higher then it will be first couple weeks of the season next month.

I'm probably going to back off to 75gr, and work up in .2 till 75.5 to see what i get for accuracy, even the 75gr load was not bad for a hunting round ~1.5".

My gun does seem to get a bit more velocity then what is usually expected, with the chronograph 15' from the muzzle factory Win AccuBond 180gr's are going 2970, and Federal power shock 180gr's go around 3040. Both loads are listed at 2960 MV.

irocbarry,

Thanks for the clarification, missed the load data in your first post.
Like I said, 75.0 grs RL22 with a 180 gr PT shoots well under MOA in 3 different rifles. After you settle on your charge weight, work with your COL. Sounds like you are loading to your magazine max. Try seating deeper, you may find a sweet spot and shrink your group size. Also try a different primer. I would suggest Federal GM215M.

Let us know your range results.

JD338