"Theoretically empirical" load data

[spitballer]

I consider published load data "theoretically empirical". That is, in theory the data has been obtained by active tests, and not simply cooked up in a computer.

When I tried dialing in IMR 4198 powder with 55 grain bullets, I kept in mind that published load data suggested a velocity of 3122 FPS with a max charge of 20.4 grains. I was somewhat startled, then, to find that even after fifty rounds, my max velocity was only 3094 FPS.

Not having access to pressure measuring equipment, I make use of my chrony to help dial in my loads. It would seem to me that in this case, I could afford to go just a bit higher, especially when the faster shots seem to be squeezing into a small hole up toward the top of the target, rather than scattering down lower. I think a slightly higher charge will do it. therefore I have loaded 25 20.5's and 25 25.55's for the next shoot.

I am conscious of pressure, but I'm generally conservative when I load and the only time I really got nervous was when I got a batch of cases with oversized flash holes (Federals?) that were difficult to extract. My bolt gun is pretty beefy and the weak link is always the case and cartridge.

Is it safe to say that published load data is empirical, even when careful experiments dispute that data? Yes, I think so. Slight differences in powder from batch to batch is probably likely.

Is it considered a safe practice to aim for published velocity figures when adjusting a load? Any thoughts on this? Thanks in advance...

 

[LivewireBlanco]

Woah! Max load is 20.4 and you loaded some up with 25.5?!?!??

I would NOT go that much over max. That little velocity below published figures isn't that concerning. Was the test barrel length longer than your barrel? Could it be that you have a slower barrel than the test gun? What was the temperature on the day the test gun was fired? These are questions that may account for the difference in velocity. Going 5 grains over max charge is downright scary!

 

[RPRNY]

I do hope that 25.5 grss IMR4198 is a typo and you meant 21.5grs.

Your surprise at a 28 fps gap between published data and your Chrony...surprises me.

The 3122 fps provided by Hodgdon (if indeed that is the source) is not theoretically empirical. Indeed, they provide the full parameters under which the results were achieved: primers used, exact bullet make, and barrel length as well as temp. Not perhaps altitude, humidity, solar flare activity, or the price of tea in China on the test date however.

That you were only 28 fps off the published results is itself remarkable only for the close proximity to the published rate that you were able to register.

You should view load data provided by Powder Manufacturers as "Actually Empirical", if perhaps more conservative than you might be inclined. You should view load data published by sources other than the manufacturer of the powder in question as Secondary or Supporting material. Many times, that data is simply published data by the powder manufacturer, reprinted. In the case of Hornady, for example, it is somebody's Actually Empirical Data massaged by a committee of hand-wringing old women and their litigaphobic lawyers...

 

[koz4guns]

Umm, What caliber? What bullet? What primer? and what gun?

Koz

 

[Sam1911]

Is it considered a safe practice to aim for published velocity figures when adjusting a load?

Not necessarily. Published velocity figures are not what matter to your gun. The pressure in your gun is what matters to your gun. The velocity you get is the velocity you get -- whatever that is. There's no great reason to push for the last 50 fps when you're already at the book maximum load.

Accuracy is the only real goal that matters, and if your accuracy is improving as you move up in charge weight, great, keep going ... until you get to book maximum. That's plenty and enough. Many reloaders have pushed beyond the published maximum until they saw "pressure signs." (Flattened primers, tough extraction, etc.) But now we know that's a pretty BAD "measure" of pressure and by the time you see those signs you're very likely far beyond safe pressures.

I'm sure the 25.55 gr. must be a typo (please, in heaven's name say it's a typo) as I can't believe you could jam 5 more grains in the case. But even if you're only ONE grain heavier than the book maximum, that's a pretty significant amount with VERY unpredictable results. If you get good accuracy, so be it. But what real powder testers have found is that over-pressure charges don't make a nice smooth, predictable increase in pressure, but start to have very disproportionate effects.

As PRNY said, if you're only 30 fps off the published velocity? Well that's GREAT! That's what your rifle does with that bullet and powder. That's perfectly respectable and common. If it shoots accurately right at the max charge, call it a day -- you've found your load. If it isn't accurate enough for you, start over with another bullet and/or other powder. Don't keep stuffing powder in because you think you've got to hit the published speed.

That published velocity is just about the LEAST important number in the load book.

 

[Andrew Leigh]

I consider published load data "theoretically empirical". That is, in theory the data has been obtained by active tests, and not simply cooked up in a computer.

There are some rather accurate computer models that will predict pressure and velocities based on actual results. I offered you help but have yet to hear from you?

When I tried dialing in IMR 4198 powder with 55 grain bullets, I kept in mind that published load data suggested a velocity of 3122 FPS with a max charge of 20.4 grains. I was somewhat startled, then, to find that even after fifty rounds, my max velocity was only 3094 FPS.

Published loads are with a specific set of components and chamber. Your chamber could be cut slightly larger, your brass could have slightly more internal volume, your jump could be different, your barrel could be shorter, different primers, crimp or no crimp, there are many factors that could lead to that drop in velocity. Give us more data and perhaps we could help.

Not having access to pressure measuring equipment, I make use of my chrony to help dial in my loads. It would seem to me that in this case, I could afford to go just a bit higher, especially when the faster shots seem to be squeezing into a small hole up toward the top of the target, rather than scattering down lower. I think a slightly higher charge will do it. therefore I have loaded 25 20.5's and 25 25.55's for the next shoot.

You may well have found an accuracy node above the acceptable pressure limit. Simulating your load in QuickLOAD at 20.4gr, using the SAAMI spec case capacity, a 2.260" COL and a 24" barrel QL presents a speed of 3 092fps to give a barrel time of 1.044ms. Now for a 24" barrel the accuracy nodes closest on the faster side is 1.022ms which explains why chasing the velocity more the groups tighten up. To meet Accuracy node 3 of 1.022ms would require a charge of 20.8gr. to give a speed of 3 139fps. You mentioned a load of 25.5gr will give a pressure of 90 863psi and a velocity of 3 500fps.

I am conscious of pressure, but I'm generally conservative when I load and the only time I really got nervous was when I got a batch of cases with oversized flash holes (Federals?) that were difficult to extract. My bolt gun is pretty beefy and the weak link is always the case and cartridge.

With all due respect you appear to be neither conscious of pressure nor conservative in your loads. Oversize flash holes do not create pressure, you overloaded. You are ignoring sound advice that could get your hurt. We are not trying to pee on your battery but to offer some real help. I iterate, send me a PM and we can tell you exactly where you should be.

Is it considered a safe practice to aim for published velocity figures when adjusting a load? Any thoughts on this? Thanks in advance...

Yes and no, as explained you have different components to those used to develop the load and therefore variations should be considered. If you aim for published velocity figures then too must you keep to the published COL etc.

 

[dragon813gt]

I'm not sure I should even mention Quick Load to the OP. Going that far over published max is a recipe for disaster. Quick Load is scary accurate with it's predictions of both pressure and velocity. But you have to take the time to enter all of the info. Because like any computer program, garbage in means garbage out.

 

[Walkalong]

Here at THR we do not look lightly on suggesting that the load data in the books is just a guide and that you can go higher to try to match the velocity given. You cannot know what pressures you have. Some powders can reach X velocity safely, while others cannot. They use pressure equipment, while we are just guessing.

As Sam posted, the velocity listed is not particularly important. I touched on the reason above.

If you want to follow unsafe reloading practices I cannot tell you not to, but we will not continue to suggest such here at THR.