May 24, 2006, 12:33 PM | #1 |
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Heat sensitive H4895?
Ok, so I've worked up an ultra accurate load for my savage 10fp using 25.5g of H4895 under a 68gr match hpbt with a cci small rifle primer, winchester case. I worked these up when it was cooler and had no pressure signs. Now that the weather is getting hot here in S. GA (last weekend was 95 degrees) I'm getting blown primers. No other signs of pressure just a firing pin sized hole in the primer. How heat sensitive is H4895? I'm going to back off just a bit to see if I can still get the accuracy without the primer problems. What do you guys think?
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May 24, 2006, 02:54 PM | #2 |
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The modern "Extreme" line of Hodgdon powders are less sensitive than others I have used. I don't have much experience with H4895 but I have loaded a fair amount of Varget and IMR4064. I found 4064 to be more heat sensitive than Varget but neither were as heat sensitive as AA2520.
If your load is at the edge of maximum pressure then even mild heat sensitivity could push your loads over the edge. You didn't say which cartridge but I am going to assume .223 Remington which puts your load about half a grain over the max listed in Hodgdon #27. |
May 24, 2006, 04:14 PM | #3 |
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Caution!
Edit: Lengthy diatribe about .308 low pressure loads removed for irrelevance.
Nick
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May 24, 2006, 06:01 PM | #4 |
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Uh, Nick, I think he's shooting a .223.
Something about "a 68gr match hpbt with a cci small rifle primer" But he should have said so. In 1964 Hodgdon said of 4895 (then army surplus made by DuPont) "Reduced loads, as little as 3/5 of maximum, still give target accuracy." |
May 24, 2006, 06:31 PM | #5 |
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Jim,
Well, look at that: I wrote a solution in search of a problem. I looked at "68" and read "168". That coupled with my 10FP being in .308 and . . . I think that's the sound of gas escaping my brain. I always forget that Hornady makes their match bullet in 68 grains instead of the more usual 69 grains. Well, this is a horse of a different color. In the Winchester case this .223 load this is about 104% full and thus is highly compressed. It will run about 2500 PSI over SAMMI max, according to QuickLOAD, so the temperature change can indeed spell trouble. The Hodgdon Extreme powders are not totally immune to temperature change and are not as good as some of the Vihtavuori powder, if I recall correctly? The details are in this Denton Bramwell article. Thanks for catching my blunder. And yes, 3/5 (60%) is still what they stick to, even in the Extreme series variant of 4895. At least, that is what their tech said today. Nothing about accuracy; just that it is a minimum. Nick
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May 24, 2006, 09:50 PM | #6 |
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Thanks guys. Sorry I didn't make myself clear that I was shooting a .223.
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May 25, 2006, 09:57 AM | #7 |
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Is H4895 one of the "extreme" powders? I know it's been around for a while and I would expect to see a fair increase in pressure with temperature. Not as bad as ball powder, but certainly some. Varget is very good in this respect.
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May 25, 2006, 11:34 AM | #8 |
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Yes, H prefix stick powders are now all in the "Extreme" series, I believe. Made in Australia employing proprietary methods of that reduce temperature sensitivity over their IMR equivalents - at least, that's the claim. Check out the Bramwell article I linked to above.
Nick
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May 26, 2006, 09:08 PM | #9 |
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H4895 is temperature sensitive, in my experience. I noticed major accuracy changes in my batch, tossing 77 and 80gr .223s through my AR-15. On a cool day, it would hammer. Warm up and I noticed a drop off in X-count.
It is not nearly as tempermental as say, Winchester 748 ball powder, but it is less stable than Varget, IMO. I've left Varget in a car trunk for 8 hours before shooting it in the evening (accidently, I assure you) and noticed no difference in on target performance at practice. X-count was right where it normally is.
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May 26, 2006, 09:15 PM | #10 |
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If your loads are riding the safety "edge" I sure wouldn't count on Hogdons claim of not being effected by heat. If you are getting pressure signs, what does that tell you?
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