Powder densities

[shootinmiles]

I have a question about what the optimal density is inside of a case. I have found two conflicting answers on different sites.

One site said that a compressed load was more accurate since the powder will alway be the same wether you're shooting straight up or straight down. It said to find a powder that will fill the case completely.

The other site said,'Load density is the determining factor in selecting powder for a particular rifle cartridge with 86% density just about ideal in most cases...1. You should never exceed 95% load density.
a. Primers need room to flame through the powder charge which gives uniform velocity and pressure.
b. Cases that are full or compressed charges of powder will accelerate barrel wear in the rifle barrels throat area.'

Is the info from the second site true? If it is then why would hodgdon post information for loads of 95% much less a compressed load?

Thanks for all of your help

 

[GermanS1]

Miles, in over 100 years of smokless powder reloading for accuracy, the effort of most careful reloaders has been to minimize air space in the cartridge case. This has proven itself over time to yield the best accuracy. However, and this is the big however, you can't always get there and if you don't, that's OK, you're likely to be able to get pretty close and have perfectly good accuracy.

How full the case is depends on how closely you can match a given powder's burn rate and density to the requirements of the cartridge/bullet combination you've selected. Let me give you a couple of examples.

1. .30-06, Lake City brass, PMC primer, 190 Sierra moly, 53.5 gr. H4350. There's a great shooting load for me in modern bolt action rifles. It doesn't fill the case, in fact, I can hear the powder shake a bit. But, that's the pressure limit of this cartridge/powder/bullet combination - I actually test pressures. This load generates 58,000 psi and 2800 fps in my rifle.

2. .30-06, Lake City brass, PMC primer, 190 Sierra moly, 58.0 gr. H4831sc. This load fills the case, and there is even some compression of the powder. It generates 54,000 psi and 2720 fps. It also is not as accurate as the 4350 load.

Those examples are provided to show that while case filling is a good objective, it isn't the only factor. A good match of the bullet, powder, case and primer is even more important. In the example, H4831sc is simply not the correct burn rate for the bullet/cartridge combination, the burn rate is too slow to generate the desired pressure/velocity before you simply run out of room for more powder.

A general note on compressed charges - I prefer to avoid them because heavy compression can ruin the bullet and the seating die and can lead to the bullet actually being pushed up in the neck over time. If I have a load that will require a slight bit of compression but is otherwise acceptable, I will usually vibrate the charged cases to settle the powder deeper and eliminate the compression. I do this by placing a second loading block face down over the chagred cases and pressing this 'sandwich' against a vibratory tumbler for about 30 seconds. It works wonders.

Selecting a powder that can come close to filling the case,with a bullet seated) and provide the desired velocity at safe pressures is a good start on the search for accuracy but 'a full case' isn't the goal - accuracy is and you may find it somewhere short of full or even slightly compressed, there is a useful range from 'near full' to 'full'. Closer to full is usually more accurate than further from full, but that assumes correct burn rate for the combination and, of course, that all other reloading practices are up to the task.

 

[shootinmiles]

Thanks for the clarification about accuracy. That makes perfect sense to me.

My next question is does a compressed load cause more barrel wear than a non-compressed load? I had some Varget left over from reloading a 22-250. I used it in my 204 and had great results. After reading that a compressed load was bad for the barrel I stopped the Varget. I am also worried about my 300rum, I run a compressed load with Barnes' TTSX and Retumbo.

Should I have anything to worry about?

 

[spclark]

'Should I have anything to worry about?'

In a practical sense, I'd venture to say no.

Generally speaking, the more powder you burn with each cartridge's firing, the greater the relative barrel wear from the resulting hot gasses. Compressed loads maximize the powder charge for a given cartridge, so using them is going to put more burning powder into your barrel than if you back off on the charge weight.

Over the life of most barrels, I doubt you could actually measure the difference in wear or number of rounds fired. 22-250 is notoriously bad anyway for barrel longevity; 204 ought to be far better but your experience will be welcome as they're a lot newer.

If your goal is accuracy first & not just to burn powder, you should be able to get more for less.,Compressed loads aren't often the most accurate; we already touched on that in German's post.) That alone'll boost your barrel's useful lifetime, but by how much is hard to quantify.

 

[chambered221]

The term “load density” and the load density percentages that are listed in some re-loading manuals are often misunderstood.

Load density is actually a dimensionless ratio between the charge weight and the water weight that fill the available space to the bullet base.
It has no barring whatsoever if the space is full or only half full.
This is were its confusing, a re-loader will see a load density listed at say 95% and think he’s almost filling the case when in fact the case may only be about ¾ full of powder.

So as you see technically both sites are correct because it is entirely possible to have a load density of less than 100% but the case is full of powder.

 

[shootinmiles]

Thanks for the info