Old powder, low velocity

I need to preface this post with the fact that I'm far from a beginner to old or surplus powder. I've used lots of old powder, and I've seen powder go bad. I also know that there are some on here who are far more knowledgeable that myself about such matters.

Powder being a bit harder to find nowadays, it seems wise to pick it up when one can. I recently acquired an older 5lb tin of SR4756. It's mostly full, missing about a half pound. It looks and smells fine. Under magnification, I can't see any sign of deterioration or anything mixed in.

I've never used 4756 before, but see that it's a tad slower than Unique, so I decided to work up a load for .45 acp. I normally use 6.0 grains of Unique with a 230gr powder coated bullets, resulting in about 850fps.

I worked up to 7.0 grains of 4756, with the highest velocity being 800fps. Same gun, same day, same chronograph that clocked the Unique loads. They shot and functioned fine, just lower than expected velocity.

Any thoughts or comments from any gunpowder experts?

If the powder has drawn a little moisture (hygroscopic), it will weigh heavier for the amount of energy it contains. That could be what you are seeing here.

well, my load for a 225gr boolit shows 7.5g 4756 =950 fps sounds pretty close.. little bit heavier boolit, a 1/2g less powder looks like close to correct fps.. i just have no data for 230g handy

7.3gr=905 fps of unique according to the book with 225g boolit..

i found it.. but its jacketed data... 7gr on a 230g bullet should be 867fps..
data from the Hogdon 2015 manual

Could be the unique is on the more energetic end of lot to lot variation while the SR4756 is on the lower end of it's acceptable lot to lot variation.

i just finished off my last 5 pound tin can of sr4756 this week. this can is from the mid 80's. yes old powder can lose some with age. i have notice it with this can. i shake my powder before i use it to mix it. don't know if it helps or not. could be many different reasons why you are seeing a difference.

Thanks, all good suggestions. Now that I think about it, I did adjust my GI Ball equivalent load last year when I opened a new jug of Unique. I had been using a vintage jug that was probably 30 or 40 years old. With the new jug, I decreased the charge several tenths for the same velocity.

I'm not too concerned about velocity. 800 fps is good enough for my purposes. I've just been wondering about pressure. 7.0 grains with a 230gr cast bullet is on the very upper end of the scale, according to all my books. If the burn rate is a little slower, or the powder has lost a little something over the years, or whatever else, I wonder about the correlation between velocity and pressure. In other words, would it be risky to up the charge a little to see how velocity responds. I'm not inclined to because there's really no reason to, but I am curious.

Velocity doesn't necessarily increase as pressure does. It's possible your pressure might rise into the high +p levels but you not have a corresponding gain in velocity or increase in felt recoil or change in ejection.

Also possible another half grain would be safe and you'd get the velocity you want. That one is more likely in my opinion and is the way I'd go if it were my gun and hand.

In propellant profiles, one article on the powder says it has a wide discrepency between lot to lot variation. I can take a picture of the article and email or message it to you if you're interested. Or I can copy it and print it out and snail mail it to you.

well, 800 does seems a bit low.. perhaps another step on the ladder is called for... 1/10th at a time and check for pressure signs.. my hogdon manual showed 7.5 is the top end.

Also, I took all my 4756 powder out of tins years ago and put them in tall plastic Alliant containers... perhaps condensation is an issue in there? just a thought.

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Originally Posted by Bazoo

Velocity doesn't necessarily increase as pressure does. It's possible your pressure might rise into the high +p levels but you not have a corresponding gain in velocity or increase in felt recoil or change in ejection.

Also possible another half grain would be safe and you'd get the velocity you want. That one is more likely in my opinion and is the way I'd go if it were my gun and hand.

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Thank you; I was thinking along the exact same lines. I'm not terribly worried about velocity, but do get concerned when something like this doesn't behave as expected. I might do a little more load work-up, out of curiosity.

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In propellant profiles, one article on the powder says it has a wide discrepency between lot to lot variation. I can take a picture of the article and email or message it to you if you're interested. Or I can copy it and print it out and snail mail it to you.

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Yes, that sounds interesting. I'll PM you with my email.

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well, 800 does seems a bit low.. perhaps another step on the ladder is called for... 1/10th at a time and check for pressure signs.. my hogdon manual showed 7.5 is the top end.

Also, I took all my 4756 powder out of tins years ago and put them in tall plastic Alliant containers... perhaps condensation is an issue in there? just a thought.

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I saw that. The Lyman 49th edition also lists 7.5gr as the max with 4756 and the 452374. I use both the 452374 and the Lee 452-230-TC. With Unique, the both seem to behave the same with the same charge. I'll cautiously work up the charge to 7.5, just to see what happens.

I don't know the history of this powder; it was from an estate. The tins look fine though, not even the slightest hint of any rust, and it smells just like it should.

I have one of the old 8 lb metal powder cans of IMR 4350. All I ever used it for was 30-06 loads. Can is early 90's and has about a pound left. Used the same load plus or minus 1 grain. 54.5,55.5 grs behind either a SMK 168 grain match bullet or 165 grain Nosler Ballistic tip. I'm getting a hair over 2800fps with match accuracy. I've always wondered how they manage to get max book loads of IMR 4350 into an '06 case as mine are slightly compressed. Using a CCI 250 mag primer. That load has been used in 5 pre '64 M70's and a Sako 75 Hunter all in 30-06. Powder has always been stored in a cool dry place and for the last 25 years full air conditioned home. Frank

5% +/- in burn rate is common between lots. Older powders loose weight as it outgasses, overtime.

I find new lots of same powder are most always heavier when compared, weight checked by volume.

Data for 230 gr SR-4756 From 4.8 grains to 8.0 grains. 45 acp.

Coated bullets may produce less friction/pressure. This may produce less velocity?

Interestingly enough, a couple years ago I fired a few rounds of 100 year old WWI vintage .45 ammo. It shot just fine, and the couple rounds that I fired across the chronograph clocked right at 800 FPS.

Last summer I bought a box full of old powder from an estate sale. In the box were 4 metal cans of 2400, all sealed and 3 cardboard cans of 2400, also sealed.

I opened one of the metal cans and tested it in my 357 mag rifle loads. My usual load of 12.5 gr of new 2400 gives me 1500 fps in my Marlin. The same charge with the old metal can gave me 1400 fps. The powder looks good and smells good. So I bumped the load up to 13 gr and got to where I wanted to be. The powder from the cardboard can matched the new stuff with no adjustment.

When I go through this metal can and open another sealed metal can I will start all over.

For the little I paid for them the extra effort is insignificant.


Steve in N CA

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Originally Posted by Bazoo

Could be the unique is on the more energetic end of lot to lot variation while the SR4756 is on the lower end of it's acceptable lot to lot variation.

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Now there is a ballistic reality that few "web experts" recognise. It's not uncommon for reloaders to suggest powder makers have "changed their formulas" over time but haven't told us; that would be legal foolishness and they are not foolish people. What ever changes they may make, if a powder carries the same label it meets the performance levels as the others.

Powders are organic chemistry, their lot composition does vary a bit. But, each powder has a narrow burn rate that must be met for it to be sold to the public but different lots of the "same" powder simply cannot be exactly the same. That's part of why every loading manual tells us that we cannot safely mix powder lots without testing.

Printed powder burn rates are misleading because they are not static; they change under pressure. Hot loads simply don't burn at the same rate as moderate loads of the same powder.

For those two reasons, many powders can and do overlap somewhat with others.

I want to sincerely thank everyone who has contributed to this thread. You all are great, and make this forum an excellent resource. There hasn't been any "you'll shoot your eye out" type replies that are common in so many places. Every single reply here has been well-reasoned and informative. Thank you!

I moved about a year ago just got things back to semi normal and back into reloading
When I took the cover off my Dillion I forgot to take the powder out of the hopper and the lid had come off
The powder smelt off like ammonia naturally I dumped it and cleaned it all up.
I do have some old tin imr 4198 I still use and give the same poi I haven’t cronied them


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