.300 Win. Mag, Loads 210gr,SMK


Well-Known Member
Jun 17, 2009
Hello all, I recently put together a custom .300 win mag and am planning on shooting the 210 Grain Sierra MK bullets out of it and was wondering if any one had any pet loads with this cartridge/bullet combo. Thank ya much.
76.3 gr H-1000 with a Fed 215M will shoot those bullets and Berger 210's very well in my 300 win. I neck size with a Lee collet die and seat with a Redding comp seater. I bump the shoulder back with a Redding body die when I need to. I use R-P brass for paper and RWS for hunting. I anneal every 5-6 loadings. Good Luck

Pray tell just what kind of "custom" did you "put together"???

Will your barrel twist rate handle the 210gr bullets? Probably but if you have an 11 or 12 twist rate it may not do so well.
Was your barrel throated long enough to handle that particular bullet? Most .300win mags, unless your gunsmith knew in advance, are throated for 180 or 200gr bullets. Do you know how long the ogive measures on that matchking bullet?

"Putting together" a rifle out of some generic parts, or stuff your gunsmith gave you a "good deal" on; and then expecting it to handle a specific and specialized longrange load is only rarely going to work out.

Most guys who "put together" a custom know the reamer specs, twist rate, and know enough of their starting component interplay, or have seen that Sierra's accuracy loads are often right-on.

Wish you the best of luck.

The rifle has a 28" 1-10" twist Hart Barrel with a chamber tha has been reamed for 200-220 grain bullets. chambering has already been discussed with my gunsmith.
Always helps to know the details. Likely you mean barrel is throated for the longer bullets or was a custom reamer prepared for this special barrel?

I would consult the Sierra Manual as a starting guideline. Their "accuracy load" is often a benchmark to be heeded. Unless you have in-depth information describing the rifle of anyone supplying you with "load data" or "pet loads" it is likely to disappoint. If you start off with data from your bulletmaker, especially old-reliable Sierra, you are that much closer to the goal you seek.

Good Luck!
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