August 7, 2011, 11:52 AM | #26 |
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Reloading manuals give charges in grains because the powders we use are blended so that from lot to lot, X grains of lot X gives the same pressure curve as X grains of lot Y.
This is not true for the volume of powder. Powder volume is not controlled from lot to lot. I have one cuckoo bud who load his surplus IMR 4895 to the same volume as commercial. He gets away with it because through happenstance, the lots are close enough in density for the volume not to matter. Bud's who are long range F class champs, they weigh their charges. I have been told everything makes a difference at 1000 yards. Like bullet lots, primer lots, etc. I am a rotten 1000 yard shooter, but at 600 yards I weigh my charges because they are maximum charges, and everything makes a difference with a max charge. Out to 300 yards I shoot HM scores sitting and prone RF with thrown charges. Have shot some darn good HM scores at 600 yards with thrown charges, but that is only when I have run out of my weighed match ammunition.
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August 7, 2011, 12:23 PM | #27 | |
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August 7, 2011, 12:43 PM | #28 | |
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Cooler air = more O2 in the same volume = more effective combustion of fuel = more energy released = more efficient engine = more power from the same amount of fuel. The same principle is applied to alcohol and acetone injection systems. They aren't there to be 'extra' fuel. They're used to cool the air charge, due to their high volatility (relative to H2O).
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August 7, 2011, 03:18 PM | #29 |
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Energy content per unit powder weight is probably the most consistent part of the loading equation. The recipes for powder are the same, even from one lot to the next of bulk powders, and that determines energy content. However, as was mentioned earlier, that's not the only factor. Burn rate, which affects how that energy is delivered, is important, too. It changes with pressure and temperature and lot numbers for the powder. The result is a change in Ballistic Efficiency (BE), which is the percent of the energy content in the powder that is converted to kinetic energy in the bullet. For medium power rifles numbers around 30% are common, but it changes with charge weight (better when peak pressure is higher) so that's why it can also change with burn rate.
Hodgdon says they blend to keep burn rate in a standard test the same ±3% for their stick rifle powders. I have seen up to 10% difference in a Winchester Ball powder (296/H110) but don't know if that's changed with Hodgdon's having taken over their distribution. The best advice I have is to keep aside a few rounds from your last lot of powder, then use your chronograph to adjust your new powder lot's load by velocity. If it's the same powder number, that should be safe (if it's not the same powder, it isn't safe). Be sure to fire both test sets on the same day and under the same conditions, or you may not have a true match. It's not good enough just to keep old velocity data records. The other thing worth doing is to try to find loads with as little sensitivity to the environment as possible. Dan Newberry's site describes a systematic method of finding loads that have minimum charge sensitivity, and that's one way to help overcome the lot differences.
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August 7, 2011, 03:39 PM | #30 |
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I guess I'm missing the whole point of this debate. I'm more interested in consistency from cartridge to cartridge within the same lot. I don't think the variation from day to day would make a difference I would notice, I just want safe, consistent loads. I would never start throwing powder in a batch of ammo based on what the powder measure was throwing last time I used it. I hope OP understands the concept now, at the moment I'm not so sure I do.
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August 8, 2011, 07:21 AM | #31 |
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one measure, same powder, same setting, 16 years
I have one measure that holds W231 for my 45 load. I haven't adjusted it since I set it up in 1995.
It still throws the same volume of W231. Weight can vary a wee bit. Volume doesn't. My powders don't swell or shrink. Similar measures, but not quite as long, hold AA9 and Power Pistol and WAP and Universal; I gotta lotta measures still.
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August 8, 2011, 01:40 PM | #32 |
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I kinda think we are all just showing off now....
Energy per gram is different for single, double, or triple base powders. My favorite rifle powder, IMR 4064, which I use to reload everything from 223 to 9.3x62, is a "single base extruded powder" Extruded means "stick" and is during the manufacturing process pushed through a form (like making pasta) to achieve that stick shape. To control burn rate things like graphite or inorganic salts are often be added to the surface of the stick. Ball powders are formed by precipitating nitrocellulose from the solution, hence the uneven sizes of ball powder noted. It would be simple enough to shake powder through various screens to uniform the powder, but it really isn't necessary for what most customers need ball powders to do. Cordite, once used by the British for the 303 Enfield, is very long threads of nitrocellulose. One can find almost the complete history of firearms propellants in the Enfield line of rifles. Flake powders are simply nitrocellulose that has been dried on a sheet then cut into flakes. Single base means just nitrocellulose. Double base means nitrocellulose and nitroglycerin or nitroguanidine Triple base means nitrocellulose, nitroglycerin and nitroguanidine. So between three different powders you can have three different energy per gram values, and based on the shape of the powder and any coatings, three vastly different burn rates. Ackley experimented quite a bit on how the geometry of powder settling caused performance differences. But when it is all said and done, weigh your charges, because while you can control the burn rate a bit by making sure your powder is settled, you can't change the laws of physics that say the amount of solid mass will equal the amount of gaseous mass. As far as humidity content, it does not have the same affect on accuracy as a single tenth of a grain difference in powder charge. Jimro
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August 11, 2011, 02:39 PM | #33 | |
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Remember, this is all premised on using a powder that responds to packing in a fairly orderly fashion. Some do and some don't, at least not in some case shapes with some bullet weights. I think this has a lot to do with why some powders become favorite target accuracy powders in some cartridges, while others do not, even if they have essentially the same burn rate. The ignition characteristics don't always play nicely.
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