300 RUM, 240 SMK, US869 Initial Results

[Jon A]

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I might have to try a little of that stuff w/the 240s. Your getting 150 fps more than I am w/Retumbo.

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Yeah, and your barrel is longer! I think you'll be able to find a nice accurate load in the 3050-3100 range pretty easily. That's a huge jump from your current load. It'll be like a completely different rifle--I'll bet it takes care of the 1500-1600 yd problem for you.
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Heard any timeframe on Richard's heavier .308 bullets?

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I haven't heard from him lately. I was hoping to have some by now but I'll just have to make due with the 240's until I do.

 

[Jon A]

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I haven't heard from him lately. I was hoping to have some by now but I'll just have to make due with the 240's until I do.

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Scratch that. The jackets exist! It won't be long now!

 

[ol mike]

Hey Jon -why did you bed the barrel channel?
It looks great ,this is a real good post -thanks Mike

 

[Jon A]

It helps add a little stiffness to the forend of the stock. When using a sporter/hunting sized stock with a bipod, all the stiffness you can get in the forend helps. Beyond that, it sort of "finishes" the bedding job and looks nice. /ubbthreads/images/graemlins/wink.gif You don't need to do the inletting quite as perfectly to end up with the barrel channel perfectly matching the contour of the barrel with exactly as much freefloat as you want for its entire length.

Not really a big deal, but I thought it was sort of a "nice touch" to finish off the job.

 

[Jon A]

Some more data. While it wasn't my intention to conduct a scientific test of temp stability (or I obviously would have kept everything the same), I did want to double check the 103 grain load in warm weather (it was about 20 degrees warmer this time than last time I chronoed them) but I also changed the seating depth by .020". So the difference could have come from either one or a combination of both. Anyway, here are the final results:

I ran six rounds over the chronograph at 103 grains. Average was 3031, which is a bit hot. Those that were at or under that average probably wouldn't be a problem. It's those that are over that are. A couple were over 3050 which is obviously too hot. But here's the worst part--in both three shot groups, two landed in under 1/4 MOA. But in each case, the round that chronographed the highest was a flier about 1 MOA from the first two--which is what one would expect when the pressure gets that high.

Since I'll stick to this seating depth and most of my shooting this summer will be at 85+ degrees, I'm going to knock that load down two full grains, to 101. That should put me in the 2970-2980 range (at 80 degrees at least) and give me a nice healthy margin for hot days.

Keep in mind, I never expected this powder to be 100% temp insensitive (I still can't say with any certainty that it's not), just better than H870 and WC872 (which isn't too difficult). But I think using some common sense as the summer heats up is probably a good call until proven otherwise.

Also keep in mind H50BMG would have been popping primers at those velocities...and Retumbo likely would have been blowing cases. And neither of those is 100% temp insensitive either. So, I still feel US 869 is working perfectly for this application. Nothing else comes close.

 

[Boss Hoss]

Glad to see some 240 gr 869 loads!!! I got the reamer a couple of weeks ago and will use your loads to start with on my 300 RUM ack imp when Speedy gets it finished! /ubbthreads/images/graemlins/grin.gif

 

[Fiftydriver]

Jon A,

Your results are echoing what I am seeing with US869 in my testing so far. I would say much better stability then WC872 but still need to be cautions with wide temp changes.

If you load to max and the temp increases +20 degrees you will see pressure issues but as you say, no powder is totally stable over all temp ranges. Just another reason not to load to red line!!

Good report!!

Kirby Allen(50)

 

[Jon A]

Yeah, I figure dropping only one grain would be plenty safe for any weather I want to shoot in...but I'll give up 30 fps or so to keep away from those fliers.