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Joined: Aug 2017
Posts: 1
New Member
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OP
New Member
Joined: Aug 2017
Posts: 1 |
Hi,
This is my first post on this forum, I have 10 years reloading experience but none with subsonics. I have been playing around with quickload software to see what is possible, I have no intention to go this low with my powder charge but I am attempting to understand the principals. Once you go below a certain charge you seem to get a “Shot start pressure for this data too high” message. This is an odd message to get because maximum pressure and start pressure should drop as the charge drops (unless I am mistaken). Here is the data I am entering and the output data -
Cartridge: 308 Winchester For reference I have selected COAL 2.81” Barnes 180gr boat tail projectile
Powder Fill % Start Pressure Max chamber pressure M.V.
14gr 99.9 4351 PSI 33372 PSI 1475 fps 13gr 92.8 4351 30080 1419 12gr 85.7 4351 26922 1360 11gr 78.6 4351 23890 1299 10gr 71.4 4351 20978 1236 9gr 64.2 4351 18176 1168 8gr 57.1 4351 15469 1097 7gr 50 4351 12801 1019 6gr 42.9 Shot start pressure for this data too high, max 4075 5gr 35.7 Shot start pressure for this data too high, max 3341
This data proves that the start pressure does eventually drop slightly. However I basically don’t understand what is going on here; I don’t understand how start pressure can be constant from 14 to 7 grains then suddenly the “maximum start pressure” starts dropping, it drops to 4075 PSI, which is lower than 4351 PSI, but it is still too high all of a sudden? I thought maximum start pressure should be the same no matter how much powder is in the case?
Matt.
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Joined: Oct 2008
Posts: 1,187
Campfire Regular
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Campfire Regular
Joined: Oct 2008
Posts: 1,187 |
From how you've written your post, it's not clear to me that you understand what Shot Start Pressure is in QuickLOAD. SSP is a variable that you enter. Hartmut put suggestions in; you can see them all if you just hover your mouse pointer over the SSP window. That will cause a help box to open and you can read his suggested pressures. You will also see that he has this parameter listed as the "pressure needed to drive bullet from case and into rifling."
All you've discovered is that when you put too little powder into the case, the total pressure QL predicts it will generate may be lower than the amount of pressure needed to drive the bullet into the rifling. Or, in other words, it's telling you you're gonna stick a bullet in the barrel.
BE WARNED: QL isn't the very best at predicting pressure, particularly when you're using powder-bullet-cartridge combos outside their 'normal' usage windows. I know you said this was just for fun; I'm re-posting this as a warning to those who may have missed the concept in the first place.
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Joined: Jan 2018
Posts: 25
Campfire Greenhorn
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Campfire Greenhorn
Joined: Jan 2018
Posts: 25 |
QL is just what MZ5 said..it's a PREDICTIVE software program...that means it used data collected from MANY sources and mathematically constructed using algorithms that fit certain parameters. READ THE FINE PRINT in the introduction...it states all the "wiggle words" and warnings.
Some of the powder data is linear and some only fits a narrow range and can go from nice and safe to "dig a hole and get laid to rest" very quickly.
QL should be used WITH A CHRONO (or two as I do)...and you should set the program up with the notices that give you information every time you point to a data box because you can change pretty much ALL the various parameters...INCLUDING shot start pressure which can change depending on the bullet construction and bullet length.
It has always been my contention that QL, Powley and other "predictive software" programs should only be used by advanced reloaders that have more than a passing grasp of ballistics because ALL of them can get you into trouble, basically, very quickly if used without recourse too additional data.
This statement isn't in any way deriding or dissing anyone, I've just read way to many online questions that indicate to me the level of MISUNDERSTANDING or NON-UNDERSTANDING many reloaders have when USING these software programs.
Happy hunting.
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Joined: Sep 2015
Posts: 56
Campfire Greenhorn
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Campfire Greenhorn
Joined: Sep 2015
Posts: 56 |
From my 6 yrs experience with QL software the default predictions means little other than ballpark unless used in tandem with a chronograph. Powder burn rates vary with individual cartridges, loads and temperature making it imperative that QL powder burn rates (Ba) be adjusted to coincide with chronograph results for any particular load. From that point, using the adjusted burn rate, QL will provide very accurate predictions for that load in the same rifle at any given temperature. Often, burn rates have to be adjusted as much as 10% +/- to make a reliable prediction. Failure to adjust the burn rates accordingly can lead to some very high pressures. Been there, done that.
When applied by competent people,with the right intent, common sense goes along wayt
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