Powder compressibility


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TroyB
July 15, 2013, 07:04 PM
Many published maximum loads indicate compressed charges. Does anyone know how much compression is safe? At some point there must be a risk of breaking granules and causing a sudden increase in burn rate. My specific problem concerns my version of .300 Blackout optimized for light to medium weight bullets. Case neck is .150" longer than standard to allow seating 125gr bullets to magazine length. I have not been able to find Ac 1680, and H110 starts showing pressure signs before reaching target velocity. Ac 2200 shows no sign of excessive pressure with the case filled to bullet base. At that point velocity is just reaching the lower end of the velocity range that I hope to reach.

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tightgroup tiger
July 15, 2013, 07:28 PM
At some point there must be a risk of breaking granules and causing a sudden increase in burn rate.

I've heard from some reloaders that had problem getting their shells to chamber from compressing loads so much that they bulged the case over max dia.

I also heard from some reloaders that they have compressed their loads so much that the bullet wouldn't stay seated to the OAL that they were loading for.

I don't think you'll hurt the powder from compressing it to much but you will end up with other problems as a result of it.

When you say your version of 300 blackout, what do you mean. Are you not loading it to published data?

jwrowland77
July 15, 2013, 07:30 PM
If it was me, I would probably look for a different powder to help reach my velocity goal, rather than compressing a load, IF that's a possibility.

Walkalong
July 15, 2013, 07:45 PM
At some point there must be a risk of breaking granules and causing a sudden increase in burn rate.Not going to happen. What will happen is you will get to the point where the compression will not let you seat the bullet any deeper. Seating will get very difficult.

125gr bulletsWhat velocity are you hoping to reach from what barrel length?

Can you get any Enforcer or 4100 (http://www.accuratepowder.com/wp-content/uploads/2010/09/WP_LoadSpec_7-2-13.pdf)?

TroyB
July 15, 2013, 08:29 PM
Thanks for the good info. I had Dave Manson make a special reamer with the neck lengthened by .150", no other changes. This provides up to about 10% extra case capacity, depending on seating depth. I used a retired heavy palma barrel with most of the length removed from the chamber end. I would like to try Ac1680, but have been unable to locate any. I hope to reach at least 2200fps with the 125gr. out of the 16.5" barrel. I haven't tried Enforcer or 4100, but I think they would be too fast. H110 appears to reach the high end of my comfort zone well below case capacity. I will try compressed loads of 2200 until I can find some 1680. I don't know of any other high density powders with the right burn rate.

Walkalong
July 15, 2013, 10:15 PM
I hope to reach at least 2200fps with the 125gr. out of the 16.5" barrel. I haven't tried Enforcer or 4100, but I think they would be too fast. I just got some Enforcer to try out, and my first test in a 16" barrel looks like it is going to do it just fine. With the extra room you had built in, I do not see why it would not for you.

Walkalong
July 15, 2013, 10:17 PM
Oh yea, your going to have a hard time getting enough 1680 in the case as well.

ArchAngelCD
July 16, 2013, 01:17 AM
Lil'Gun will give you more velocity than H110/W296 and at lower pressures too with a 125gr bullet.

If you want to stick with Accurate powders I have to agree with Walkalong, Enforcer and 4100 are good choice too. I would recommend AA5744 but it's a bulky powders so you probably will run out of case space before you achieve your target velocity.

Out of all of the "Magnum Class" powders I personally think Alliant's Power Pro 300-MP will probably deliver the highest velocities because it's a new powder and it seems to generate a lot of energy in the cartridges I've seen it used in. According to Alliant in the .357 Magnum the Max charge of 2400 will deliver 1265 fps from a 10" barrel and Power Pro 300-MP is reported at an amazing 1686 fps. 400 fps is A LOT more velocity especially since that's over a 30% increase. Unfortunately Alliant doesn't have any .300 AAC Blackout data on their site but I feel this powder might be just what you're looking for.

Walkalong
July 16, 2013, 07:31 AM
Too bad they don't. Hopefully they will soon, although I am not of big fan of the high energy, high nitro content, hot burning powders for general plinking where you will be shooting a lot of rounds.

2400 works great for plinking loads in .300 BLK. I am running 123/125/130 Gr bullets at around 2050 +/- FPS with it for plinking. 147s at a little under 1900 FPS using AA #9 or 2400. The 147 Gr pulled bullets, when you can find them before, are cheap and shoot pretty well. Plenty good enough to bounce cans around at 100 yards.

Hondo 60
July 16, 2013, 12:56 PM
Does anyone know how much compression is safe?

There is no "one answer" as each powder is different.
As long as you stick with published loads you'll be fine.

And by "published" I mean by bullet or powder manufacturers, not Joe's internet reloading page.

gamestalker
July 18, 2013, 05:00 AM
I've been working with compressed charges for many years. At first, I was very apprehensive about the thought that I was possibly crushing the powder up, or that the charge would be way over the top simply because I was forcing more powder into the cartridge than it was intended to contain. But the bottom line is, if you are working your charges up from a safe starting point, and your not having issues with the case bulging, or primers or bullets aren't getting pushed up, and most importantly is the published data supports a compressed charge, then there is no reason to be concerned. The powder / bullet manufactures certainly wouldn't publish compressed charges if there was a serious concern in doing so.

My experience with compressed charges has been that often my velocity and accuracy is more consistent. I've also noticed that some powders will actually produce slightly lower velocities with pressure signs following suit once I reach that compressed point. And when working with solids, such as Barns, the charge can become compressed with some powders simply because solids are longer and set deeper into the case. This can drive pressures up if your not expecting a compressed charge, but if your doing a proper load work up you'll be just fine.

GS

TroyB
August 17, 2013, 07:45 PM
Thanks to all who took the trouble to offer advice. I have settled on a load using 300mp that yields 2250 fps with the Speer 125 TNT. I went somewhat higher before I reached what I consider to be borderline pressure indications, but accuracy was not as good. Enforcer was no better than H110. I found data on 7.62x40 WT, which is very similar and less than 4% greater useable case capacity than mine. That data was very consistent with what I found with the powders I have tried. It also shows a sizable advantage for A1680, so I am still looking for that powder.

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