Just curious, thinking about a chronograph and wonder if I can use specific ballistic tables for a bullet type to find working pressure (internal) according to muzzle velocity?

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.223 Ackley Improved Wildcat Forum:
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This may be vague and it is only my opinion.
I'd say that the bullet manufacturers and powder people pretty much set their max loads in manuals about 5,000 psi below a "max" where you are going to start seeing ejector marks or tough bolt opening. NOw the problem is that some of these guys use high quality test barrels so even though they may have given us "reloaders" a cushion it doesn't mean that we can't have one of those "max" published loads BE MAX in our factory guns. Especially some of the guns out there that seem to have alot of headspace. Also, I live in Wisconsin and just cause I don't run into trouble shooting in 30-70 degree weather doesn't mean a load couldn't be a problem in Arizona in 100 degree heat!! I have a chrony and I guess what I would say is that you will see pressure at the same time you just "bump past" the velocities in the manual. BUT, what the chrono is good for is to show me some really slow loads that I might CAREFULLY start moving up towards the velocity shown in manuals. I don't know if this is making sense--but, I think it is a very valuable tool for all reloaders to use.
Also--be sure to be "crossreferencing" as many manuals as you can--you will sure see a HUGE difference in data for certain cartridges.

I've wondered about the same thing. For one thing, a chronograph is a much more precise tool than either the piezoelectric or the copper crusher method.

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.

No! No! No! Can't be done. If you have access to the A-Square Reloading Manual there is a perfect example of this. Same rifle, same brass, same bullets, same primers but different powders were used to come to similar velocities...but...depending on the powder used, the pressures varied by quite a bit AND the highest velocity DID NOT have the highest pressure.

Your basic assumption is a dangerous one that can get you in trouble.

In general, if you work up to published velocities in load books you should be near their pressures. Of course, you may require another 5 grains more to get there.
If you really want to have a better idea of what is going on, get a peak strain meter(www.fabriquescietific.com). Then you can have load, velocity, and pressure data.

Genghis, I haven't used my Chrony in a search for max safe pressure, but the reloading writers I respect the most say it can be a helpful tool. Before I explain, let me add that every one of these writers caution that a chrony WILL NOT positively warn you of peaking pressures every time, so great caution should be used.

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.

Kentucky drilled it right on the head and saved me alot of typing.
When the consistant increases in speed per grain increase- "flatten" out- your at the max load that rifle and the components can handle comfortably.

Genhis, kentucky said the same thing we were talking about in another thread and we were told there was no correlation between velocity, pressure, etc. I still stand by my statement that ammo companies load to pressure not volume.

Gengis,

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

Well . . .

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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[This message has been edited by Genghis (edited 04-17-2002).]

Genghis,

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

OOps... I stand corrected. DBill is correct. I should have included powder type in the list of things you can't casually change.

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.