Interesting IMR Powder Read

[mmcnx2]

I've been reloading with IMR 4756 for years and am a constant reader of reloading data as it comes out.

I have the IMR guide from 2006 and it gave a particular load with a min of Y gr and max of X gr. The span from high to low was 1.2 gr.

So I'm looking at another load on the IMR online site and as I'm looking at the numbers I noticed they have dropped the Y number by .2 gr and the X by .4 gr., for the same bullet, primer and casing. This is a 45ACP load. Cross reference to other manuals shows the old numbers seem to be more represented.

I'd guess they wouldn't have reformulated the powder(which would be a very strange thing to do and not annnounce it).

I'm overly interested becuase I was loading at .2 under X for 5 years and now it apprears I'm over loaded by .2

The loaded chrono'ed right were the old numbers said it should be, with less than 50 fps variance out of 3 different guns. The loads show no signs of pressure, primers look great and casings are clean and no cracks.

Any thoughts?

[Rip Van Winkle]

Powder burn rates vary from lot to lot which is why you should always use current reloading data. It's also a good idea to keep track of the lot numbers of the powder your using. I notice Hodgdon also cut down their Max load of Universal Clays so my "powder puff" target load is now over max. Good thing I still have a good supply of my old lot.

If your load ins't showing signs of overpressure, I would guess your load is fine. But remember to proceed with caution, it's your face, hands and pistol at risk.

[mmcnx2]

I agree with the lot varition, the bad news is they don't provide the load data by lot number so it always leaves you wondering. I was also under the impression that part of the lot control process was to insure reasonable consistancy in the burn rates. This is about a 5% change which seems ilke a lot of variance.

[Seismic Sam]

Okay - a couple of clarifications - the powder you buy in 1 - 8 pound containers does NOT, repeat NOT have any noticable variations. The whole point of cannister grade powder is to blend it very carefully like Scotch, so it's exactly the same every time. If that couldn't be done, then the whole handloading industry would have never come into being. Now, there are BULK powders out there which DO vary from lot to lot, and these are generally sold to ammunition manufacturers in whole lot quantities, which can be multiple tons in size, and the ammo manufacturer then works out their loads with a pressure gun and a chrono, aand then runs out that lot of powder making ammo in large lots. Some factory ammo (like hunting ammo) is loaded to give the same ballistics every time, and some personal defense ammo (Like CorBon) is loaded to a constant pressure to give you a near max load according to SAAMI limits every time.

Now, over a period of years or decades, powders can evolve, and this can be because new cartridges come along, or manufacturers go from a 1:12 twist to a 1:7 twist with .223's, or because that year there was a 30% spike in lazy n00bs who didn't RTFM and injured themselves, and the corporate lawyers FORCED them to lower the max loads. And no, I am not joking about this, because we had to deal with this in the medical device industry, and if there was an increase in patient injuries we HAD to do a risk review and alter the product or instructions for use to get the injury rate back to its historical levels. If you collect reloading manuals and compare them for some hot calibers like 10mm, it's not hard to tell which manuals are "lawyered up" and also by how much.

So I'm not surprised that a 6 year old manual has different data than today, because the handloading industry has grown enormously over the last 30 years, and 30 years ago you could go for years at a time without a new cartridge being introduced. Today you can call up Bell, and if you have the money you can have damn near anything made up, be it good (like the 204 Ruger) of bad (Like the 50 Beowulf) and put it out there on the market.

And this is also showing up in manual updating, and Hornady has set some sort of record going from the 7th Edition up to the 9th edition, and a lot of that has to do with the fact that they have helped develop some interesting new cartridges in partnership with gun companies, and so they have to publish the data for these new offspring of theirs. I think it took Hornady close to a decade to go from the 2nd Edition to the 3rd Edition.

With the 45 ACP, however, if you have a chrono it's no big deal if the data in the manuals changes a bit. You can always do something about it if your chrono data changes, but the 45 ACP is a century old very low pressure cartridge whose max PSI is only 21,000, and 1911's today are better machined and built, plus have much more consistent metallurgy than back in WWII. With a max load for a357 Sig or a 338 Ultramag it IS a different story, and there you have to be fairly careful in what you're doing. Retumbo did have a recall because some of their early lots had a different density, so if you threw the same charge of 98.3 grains with a certain measure setting, the load was noticably hotter.

[mmcnx2]

Thanks Sam, figured you would pipe in. I do buy 8lb kegs and yes I chrono everything with each new keg and honestly I do it each time I change over from calibers too(what can I say I'm a little retentive). I also monitor the IMR site every few months. And until recently they have matched the 2006 paper guide I have; so after all this time I was surprised to see this change. Yes it is 45ACP which you would have to try real hard to screw up but the change had me concerned because I also use 4756 in other calibers and I have not seen the same change in that data. Which I now assume is because they reran 45ACP but not the other calibers yet or if they indend to.

Like I said when I started 'Intersting'

[Seismic Sam]

Well, I'm impressed with the care you exercise in reloading, and the thought you put into it! I would also guess that the change in 45 ACP only is related to only testing that cartridge, and Bullseye is used in so many damn loads that it would be a very costly and back breaking task to update everything. What makes the most sense to me if I were a manufacturer would be to do the ranking of testing by the numbers of rounds manufactured, which means that 45 ACP 38 Spl, 9mm, and 40 S&W would be the ones you would test first.

And as far as blending, I have no idea about powder blending, but I do know that a blended Scotch like Johnny Walker Black can have up to FIFTY different Scotches in it, and it's up to the Master Blender to make sure that the final flavor stays the same. One of the things the Master Blender has to keep track of is the avialability of all the Scotches used, and what's left out there to buy, and plan ahead of time when one of the major components runs out so you can substitute it properly. Probably a little less complex for powders, but certain bulk powder do go obsolete, so it's still an issue to have to think about.

[OldmanFCSA]

One of the things i sometimes cover in my training classes is the differences in load data between Hornady #3 and #8.
New equipment that measures directly in PSI instead of using CUP and a conversion chart, enables better data and also stays current to powders available today.

Example:
I bought 96 pounds of H5010 Virgin powder about 5 years ago.
The H5010 Virgin powder available today is 10% hotter than mine and requires different load density to achieve same pressures and accuracies.
If I were to recommend MY load to someone using newer powder, results may be BAD.

Newer manuals also take this into consideration.

Buy a current manual, RTFM, and USE IT PROPERLY.

[mmcnx2]

Buy a current manual, RTFM, and USE IT PROPERLY.

I have a number of new manuals and I've RTFM thank you very much! And they seem to post hotter loads than the IMR site for 4756. As an example IMR now shows a 7.8 grain max for this load Hornady #8 shows 9.0! Speer shows 8.4. IMR use to say 8.2 which seemed to line up with Speer but not Hornday. Now all three do use different primers, but same bullet weight and type. So when IMR dropped is load even lower than the others it rasied a concern for me.

I lean toward the more conservtive so I had been using the old IMR info and had worked the load from 7.4 to 8.2, settling on 8.0 with excellent results.

So now it is a year later and and I'm set to load my next batch and here comes IMR and drops their numbers even further. Making the span 1.2 on max load and similar on starting depending on the source of load data. Thats almost a 20% variance in the manuals. And my 8.0gr loads appear to be .6gr over max according to the new IMR, .2 over minimum according to Hornady and right in the sweet spot according to Speer and the old IMR data.

So in this case reading the manuals and using the manufacturers website published data is what has caused the question.

Trust me I'm start at the min from IMR and chrono at .2gr increments. But the data is all over the place on this particular recipe whic as I said 'Interesting'.

[OldmanFCSA]

Did you check whether different test guns or pressure barrels were used in conjunction with different primers and bullets with different bearing lengths?