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I just worked up a really great load in my Colt 6940 using 24.5 gr of W748 and Sierra 69hpbt mk bullets and was wondering how sierra 77 gr or Horn 75 hps would do with the same powder before I buy a load of it. Does anyone have any experience with the w748 powder and these heavier bullets or are there better choices. Im trying to standardize my components as much as possible. thanks
If you know how to read this graph, you'll have a reasonable estimate of how 748 does with the 69 and 77 MatchKings. Consider both "maximum" and drop back 5-10% to start.
https://www.milsurps.com/images/impo...QL223mks-1.gif
This model of the 69-gr. MK load agrees closely with Hodgdon's published data for 748. I see no data for the 77 with 748 on their website. Their data for the fairly similar H335 shows a 5.8% charge reduction when going from the 69 to the 77 (but they seat the 69's a bit deeper at 2.235"). Pressures in graph are estimates of piezo measurements, not CUP as found on Hodgdon data for 748 and H335.
If your Colt is An AR type rifle 77 and 75 grain bullets usually require a 1/7 or1/8 twist to stabalize them but not always a 1/9 will work for the 75 in some cases. The shootersI know use Reloader 15 or Varget powder for there 223 service rifle ammo and don't change . Hope this helps, and as always this is just my opinion.