Did you ever find any differnet loads for your 6.5x300WBY?? Im thinking Retumbo should do the trick.. Im just not sure where to begin lol.. Im thinking about 80grains of retumbo should be a starting point... Let me know if ya tried anything else..


Brock

Hey Bandit . . . man, I sure am sorry to have just now seen this post!

If you haven't yet answered your question . . .yes, I have tried Retumbo.

Using new Norma .300 Wby brass necked & turned, Federal 215M primers and Lapua 139 Scenars.

I went to the Sierra manual and found all of the cartridges that used both Retumbo and H-870; 7mmWby, 7mmSTW, .300Wby & .30-378. I logged the charge weights and bullets weights in columns and did the math with the mid-to-heavy weight bullets in each cartridge.

Turns out that the closest matches in bullet to powder weight ratio and in the heavy bullet ranges all came to Retumbo being about 90-92% of the H-870 listed charge weight.

Since I'm using 83.0 grains of H-870, this multiplied by the factor of .90 comes to 74.7, I called that "Max" and loaded 1/2 grain increments down from that point to 72.0, which I used as a start load.

Honestly, I was more concerned for detonation, than for linear pressures, and felt like I was jumping into the abyss when I pulled the trigger on the first load. They shot fine.

I shot 72, 72.5, 73, 73.5, 74 & 74.5 grains of Retumbo and got mild primer extrusion at 73.5, slightly more extrusion at 74.0, and at 74.5, I got barely discernable ejector marks where brass was beginning to flow. Yup, 74.0 is gonna be "max", dang close to the expected 74.5.

My three-shot, 100 yard group with 73.5 was .200", at 74.0 it was .330 (one went horizontal) and at 74.5, it was almost an inch and plenty round - dunno why.

I was VERY pleased to note that powder fouling is reduced somewhat, and the case necks were not smoked (as is normal for H-870). Even the starting loads were "crisp" and expanded the case neck well.

I'm going to load a few more test loads at 73.5 and play with them a little - wish I had a chronograph . . . as well as that whole thing went, my velocity is probably down about 2,200 fps. . .

Finally shot the 73.5 grains of Retumbo with the 139 Scenars: 3,184 fps average for 5 shots - my suspicions confirmed - velocity too low to be useful. Extreme spread was ugly.

I was getting 3,400 fps with 83.0 H-870 when the barrel was 30".

So, between losing 3" of barrel to the setback, rechambering and recrown and going to a faster powder, I lost 200 fps.

Since Retumbo is obviously too fast for the 139's in this cartridge, I tried a few with the 123 Scenars:

73.5 ~ 3,250
74.0 ~ 3,275
74.5 ~ 3,325

No pressure signs . . . looks like I should be able to get the 123's to speed, but must have a slower powder for the 139's.

Since the 139's seem too heavy to use with Retumbo, I went to the 123 grain Scenars with the Retumbo/Fed215M's and shot three of each over the chronograph:

74.5 ~ 3351 avg / 31 ES
75.0 ~ 3375 avg / 75 ES
75.5 ~ 3390 avg / 29 ES
76.0 ~ 3434 avg / 52 ES
76.5 ~ 3466 avg / 42 ES

I didn't shoot these for groups, only shot through the screens - no sense in wasting time shooting more groups with sub-vel loads. . . .
No pressure indications in my rifle with these loads. Velocities approaching usable ranges, but the extreme spreads remain very large.

At 3,466 fps and a 100 yard zero, I'd only need 18.35 MOA to get back on at 1,000 yards, and it looks like I should be able to get faster yet.

The 123 Scenar has a relatively good BC, but energy is down and wind is up, compared to the 139 at 'potential' velocities. IMHO, this caliber is better with heavier bullets anyway, but before abandoning this powder in this cartridge, I'm planning to do a quick try with non-magnum primers. Starting at 76.0 and hoping to reduce the ES numbers and/or see how far velocity will go.