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.223 Ackley Improved Wildcat Forum:
http://www.hotboards.com/plus/plus.mirage?who=223ackleyimproved
I think that you can only check pressure in a very limited way. For one type of brass, with one type of primer, with a single type of bullet, in one firearm, you can relate muzzle velocity to pressure. Otherwise, I think you can't.
Your basic assumption is a dangerous one that can get you in trouble.
That said, the guys I read say that as you bump a charge up, 2-3 grains at a time up to and beyond published max loads, you will see velocity rise. This normally will be an even curve, such that each added grain of powder will produce a specific, predictable increase in fps. At some point, however, that velocity curve will flatten. When it does, you're at max pressure, whether the brass is showing signs of it or not.
After that flattening in the curve, sometimes there will even be some velocity loss before the pressure spikes wildly. The writers warn that as you approach this flat spot in velocity, as little as 1-2 grains can push you into the spike, although sometimes it could take as much as another 3-5 grains.
I hope that makes sense. As you see, this is indeed a method by which a chronograph can help you determine max safe pressure in a load by virtue of tracking velocity. I've read nothing that indicates whether this method is safer/better with slow powders vs. fast, but I wouldn't be surprised if that's the case. Just watch yourself if you dabble in this, and try to research the literature as much as possible.
The primary author I'm quoting on this is Glen Zediker, who has a new book out called Handloading for Competition. It's a honey of a book. I believe Rick Jameson (Shooting Times) has described this method as well.
If you have access to The Varmint Hunter magazine from several years back you will find an excellent article written by Dr. Ken Howell about calculating breech pressure from chronograph data. The article is titled "How to Chronograph Chamber Pressure" and was published in Issue #23, July 1997, Page 70 -77. Howell reduced the Powley method to a series of calculation steps using several inputs from your load and dimensions from your gun along with chronographed velocity. If you should opt to use this technique, be carefiul as there is a typographical error in one of the steps which will throw the calculated pressure off a bit. If you are not able to locate a copy of the issue of the magazine, you may be able to get this back issue from the editors by writing to them at Box 759, 436 S. Pierre St., Pierre, SD 57501, or call (605)224-6665
Don Shearer
There IS a correlation between pressure and velocity for a given powder/bullet. There is NOT a correlation between velocity and pressure across powders/bullets.
BL C2 will produce a higher velocity at lower pressure that will H-335 with lighter bullets. With heavier bullets, H-335 begins to produce higher velocities at lower pressures than BL C2. Nonetheless, as velocities increas on BOTH powders, pressures increas. At some point, increase in charge weight yeilds diminishing returns in velocity increases. That's the "flattened curve" and where the pressure begins to get dangerous.
I can plot a velocity curve and watch were the velocity begins to flatten as the charge weight is increased. That makes perfect sense.
Oehler makes a strain gauge as part of the Model 43 set up. But it requires gluing a sensor to the bbl. and that mars the finish. Also, hard to glue to a revolver cylinder.
Finally . . . "published data." Well, if you can find "published data" for .223 Ackley Improved, I'd love to see it. Saeed has a bit of data in here, but it's pretty limited. I found some reprinted data from Varmint Hunter, also limited.
I'm inclined to work up loads at 0.5 gr intervals insofar as the max load is about 0.28 gr -- a 20% jump in the load weight (circa five grains) is about where most of the "published data" on this load begins to top out with pressure signs.
This is helpful. But let's keep discussion open.
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.223 Ackley Improved Wildcat Forum:
http://www.hotboards.com/plus/plus.mirage?who=223ackleyimproved
[This message has been edited by Genghis (edited 04-17-2002).]
Sorry I left the h out of your name in the above post. Also in my haste to post the reply above I failed to add that Don Miller also published an excellent article in the same magaziine - The Varmint Hunter - about calculation of breech pressure. Miller's article is titled " Simple Formulas for Powley's Method of Pressure Estimation Using a Chronograph". It was published in Issue #31, July 1999, pages 113 to 124. This method represents setting Homer Powley's nomogram pressure method to a series of formulas which makes it much easier to use. It too uses dimensional inputs from the gun and chronograph data to calculate pressures. Use of Miller's method does require a calculator that has a y-to-the-x (power) function. His mehtod is somewhat more advanced than Powley's original work because Miller has derived several formula inputs that Powley originally gave as estimated constants. One drawback to both Howell's and Miller's methods is that they apply just to the IMR powders.
Good shooting,
Don Shearer
In my '06, RL22 produces very nearly the fastest 180 grain elk load I've tried, and the pressure is well below that of many other powders with similar MV's. An equal MV using 2015 would put you into serious excess pressure.
There was a very interesting post a few weeks ago, showing that, all other things equal, some primers produce much lower peak pressures than others, but with no penalty in MV.