IMR 4955 - odd burn rate

[big5ifty]

I been using IMR 4955 for a while now. I keep buying it because even though it's discontinued, Dave Sheer still has stock, the price is at R700, and I figured out how to use it in the calibers I shoot.

I have found that the burn rate is higher than what the manufacturer says it should be, by such a high margin that it may in some cases be unsafe to use the IMR load data.

The indicated equivalency to H4831 is very wrong.

I find that the burn rate is higher than N204, where Hodgdon says it's below N560.

[oafpatroll]

I'm amazed that such an established manufacturer from the most litigious country on the planet would get something that wrong.

[big5ifty]

Something wasn't lekker there, they even discontinued that product line.

I understand that powder burn rates are relative for a particular case capacity, usually .308 size.

I also know that the burn rate can change with the volume of powder.

But this 4955 was not kosher to start - even in my .243 it burns more like a slightly slower Varget.

[Treeman]

Remember that one batch of S365 ?
Does this container have a burn rate on it or a deviance indication?

[Tripodmvr]

I did a QL calc for a 243 with a 87gr Vmax. Propellant was IMR4451. I had to reduce the burn rate from .575 down to .528 to get the numbers to agree. Rather significant change - possible long freebore?

[big5ifty]

Remember that one batch of S365 ?
Does this container have a burn rate on it or a deviance indication?

I think this is just a case of mis-labelled product. The discrepency is very consistent over all the years the powder was produced.

I've read on a few forums people trying the powder using the provided equivalency, and blowing primers on the start load, in various calibers.

[Againstthegrains]

I found the opposite with IMR4350. It needed a grain more to get the predicted velocity on QL.

I do believe that the story that imported powders are 100% consistent between batches was hyped up and sold to us by importers (who had never used the stuff before) when there was no Somchem to go around.

[oafpatroll]

100% consistency isn't a story I'd buy readily about any propellant.

[Treeman]

100% consistency isn't a story I'd buy readily about any propellant.

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I think much larger batches lead to greater consistency. Making a 100 bottles 10 times to a consistency is far harder than making 1000 bottles that are all the same one time.

[oafpatroll]

100% consistency isn't a story I'd buy readily about any propellant.

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I think much larger batches lead to greater consistency. Making a 100 bottles 10 times to a consistency is far harder than making 1000 bottles that are all the same one time.

If a propellant manufacturer failed to achieve consistency tin to tin from the same batch I wouldn't think they were worthy of having a license to produce the stuff. Perfect consistency (i.e. 0% deviation) across batches however sounds like a theoretical possibility rather than a realistic target unless the budget to achieve that was vast.     

[janfred]

Wow.

I found the opposite with IMR4350. It needed a grain more to get the predicted velocity on QL.

I do believe that the story that imported powders are 100% consistent between batches was hyped up and sold to us by importers (who had never used the stuff before) when there was no Somchem to go around.

No. Blame the shooters that demanded foreign powder. They got all hyped up about forum posts where American reloaders talk about how consistent powders X is and how they haven't changed their load in decades and still shoots "1/2 MOA all day long" "when they do their part". Further reading would have shown that said marksman doesn't even have a chrony, but people lose their critical thinking skills on the internet.

I remember those threads where people swore high and low that it makes more economic sense to buy powder at 3 times the Somchem price because "you only have to do load development once". Having been forced to use Varget and N140 I can say that they must have been smoking something. And by above posts seems like other expensive powders suffer the same problems.

[big5ifty]

I do believe that the story that imported powders are 100% consistent between batches was hyped up and sold to us by importers (who had never used the stuff before) when there was no Somchem to go around.

The obviously sensible thing to avoid is a manufacturer that repeatedly blows up their own factory.

There is no such thing as 100% consistency across batches by any manufacturer, as stated by @oafpatroll.

However, you can be certain that your regular load is not suddenly going to bind the bolt in the next batch number.

Or that the powder in the tin is not incorrectly labelled.

I won't use Somchem powder even if you give it to me for free, except as plant fertilizer.

[big5ifty]

I remember those threads where people swore high and low that it makes more economic sense to buy powder at 3 times the Somchem price because "you only have to do load development once". Having been forced to use Varget and N140 I can say that they must have been smoking something. And by above posts seems like other expensive powders suffer the same problems.

If you found that you needed to redo load development with Varget and N140, it would have been worth knowing the batch numbers.

I'd be interested to know what you observed, or what was the measured criteria in your case that made you decide it was due to powder inconsistency.

I've used multiple tins of Vihtavuori and IMR in three target rifles, and I've not yet had to backtrack to find out why the load changed. I stopped recording batch numbers years ago, so I don't have record of if the batch numbers have changed across the tins.

[oafpatroll]

I came to rifle reloading relatively recently so have never used somchem powder for that application as it its availability was already iffy. My main rifle powders have been IMR 4350 and 4198 and they have given me consistency across 15+ bottles of each such that velocity differences with the same loads have fallen with shot to shot variation.

I have used somchem powder in pistols and shotguns for > 25 years of which 10 or so was as an enthusiastic amateur competitor who trained a great deal and sometimes shot 500 handgun rounds a week. Been through countless tins of MS, MP and more recently 121 without any issues of any sort. The stuff may not be the gold standard but it's also not kryptonite across the board.     

[Tripodmvr]

I found the opposite with IMR4350. It needed a grain more to get the predicted velocity on QL.

From 243 upwards a normal load is 40gr or more. One grain then relates to a 2,5% decrease in volatility, which is way below the 10% norm that is normally mentioned. A QL prediction is just that, although I find that the foreign propellants give fairly accurate predictions if you give measured data for your firearm.