New 300 WinMag 215 Bergers


Well-Known Member
Feb 21, 2018
So I recently finished building my 300 WinMag. It is Defiance Action, Manners stock, 28” Proof CF 1:9 twist barrel. I set out to do a load developement with 215 Bergers and found myself confused.

Load = Hornady Brass, 215M primers, CBTO 2.95 .010 off the lands. It has custom throat.
I started with 74.5 grains and worked up. 77, 77.5, 78, 78.5 and STILL NO real pressure signs. Maybe a “hint” of flattened primers. Velocities increased as one would expect in a ladder test until...

77.5gr 2980fps ES=8 SD=3
78gr 2966fps ES=36 SD=21
78.5gr 3022fps ES=33 SD=17

It was weird to see velocity DECREASE. My question is...Is my high accuracy node gonna be around 77.5gr or do I keep going up looking for signs (ejector marks/heavy bolt lift)?

I know Broz has a handle on 215 Bergers and 300 WinMag but anyone with insight is appreciated. Also I know Hornady brass is no desired but I have over 300 rounds of once fired from previous build I am full length sizing. Thanks
What does your brass weigh?

I found that the first firing in my 300 win with new brass didn’t shot pressure signs until very high but subsequent firings pressures out lower. I’m at 78 in Nosler brass in a 28 inch 9 twist for 2975 FPS. Seated to 2.965 bto my brass weighs around 217 grains
If no pressure signs, I’d try going up. Just keep that 77.5 gr load in mind.

Volume check that Hornady brass. You may be surprised.

Probably wouldn’t have much problem with that brass at 77.5. All bets are off if you find something higher.

Good luck with your new build and your load development!!
I doubt you will get much higher than that. Remember that the case will grow around .022 first firing. You go try and shoot a hot load on virgin brass with fired and you’ll see some pressure signs. 77.5 sounds right. I would get some more fired brass and then do it all over again.
Sounds like your close to max to me as well. I stopped at 79 gr H1000. Gets me right at 3000 fps out of a 26” Brux.
Rhovee, OP stated they are once fired brass, although not in this rifle. The large part of case growing is over.

OP is running a 28" barrel. I would think his max will be about 40-60 fps faster than most are thinking with a 26" barrel. Could be at 79, that's why I suggested he continued his search for pressure.

Either way, decision is on him.
I think that 77.5 is telling you something. I would work around that to start. Every barrel is different I've seen 26" shoot as fast as 28 so dont let that get you side tracked chasing that last few feet of FPS
Thanks for some good stuff here. And thanks wildcat for pointing out that it is once fired already. Our hunting seasons other than duck and goose are all but over here in Kansas, so I have some time. I think I am going to search on this high end. Maybe load 78.3, 78.6, 78.9, 79.2 and see if I see any signs. Like I mentioned earlier I am also .010 to the lands. If I find the top around 78.5-79 I can come back down .3-.5gr and come off the lands some more and lower pressures. I have noticed most guys with 215 hybrids are having good luck at .030-.040 jump.
Based on your data I would test for accuracy and do some seating depth testing at 77.5 +- .2 grains. As stated earlier in the thread sometimes once fired brass will show pressure sooner. I would not waste my time chasing it in new brass.
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I have to agree with DUSTY that with that ES and SD, and if accurate, I'd run with that for awhile. Sounds like it's a fresh barrel too so if it's not broken in yet I'd run that load for a couple of hundred rounds and then experiment with loads again.
Agree with others. run the 77.5 load. How many rounds did you fire to determine the ES and SD velocity data? It is possible that the random distribution of velocities would give you a lower AVG velocity if you only fired 3-5 rounds to come up with your data. If you fired 20 rounds to get the velocity data, then it is possible that you mixed up the charge weights.
I guess I’m one of the only hold outs for saving the 77.5 load and taking a look up higher.

It isn’t like it’s gonna cost you a bunch of brass, barrel wear or time.
If you don’t find anything you like up there, you know where your low node is, go shoot it.

If you’re like me, it’ll just bug you that it might be there, and you don’t know because you haven’t looked.

Accurate guns are interesting. Fast accurate guns are more interesting.

You mentioned Broz in your original post, I think he shoots his high node somewhere around about 3030 FPS.

I’m not telling you all this to get you to do it. You either will or you won’t it is and always will be your choice.

Whatever you decide, be sensible and safe first and foremost.
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