pitted bore wrote:brewdos wrote: . . . How can I calculate kinetic energy and chamber pressure? . . .
brewdos-
Kinetic energy is found with this calculation, where weight is bullet weight in grains, and velocity is feet per second: Energy = weight * velocity * velocity / 450450
If you are obtaining 2600 fps with a 200-grain bullet, your muzzle energy is about 3001 foot-pounds.
There is no reliable way to estimate chamber pressure except the use of apparatus designed and set up to measure pressure. I'd guess it's somewhere between 30,000 and 70,000 psi, but that isn't very helpful <grin>.
--Bob
This is absolutely true, but we can get "Fairly" good indications by how flat the primers are. Or, do you see ejector and/or extractor marks on the face of the rim, not the grove, but the face. This is a big one as bolt thrust is coming up. If marks are seen in the rim groove (better known as the extractor groove), this is a good indication that the bolt is opening to soon, usually from too much port pressure, caused from to slow of a powder or too much powder. There are other causers that the bolt is opening to soon, but all of them are trying to rip the rim off, because the case is still sealed in the chamber. The effect is that the bolt is opening before the case releases from the chamber, putting stresses on the rim or ripping the rim off. Assuming that you like the given load, but are ripping the rims off and otherwise the pressures are very manageable and acceptable, then a longer gas tube/block system is in order, this to change the timing.
I use all of these methods, and the big one for me is case head expansion. Normal High is 1.5 thou or .0015" from the resized case to the fired case. I will use up to 3.0 thou, but case life starts to become an issue and the pressures are assuredly more than most consider safe.
Bottom line is, all these methods are good indicators, but fall far short of the best knowledge from actual pressure equipment, which I have but my Range Lab is not quite done, so sometime about June, I'll start to have pressure data for you all. In the meantime consider these methods, but as Bob has so succinctly put it, they are not "Reliable"!!
Hoot,
To speed up your milk jug production, I use an outfit that processes the milk and fills the jugs. You've got to have one within 50 miles of you and when bought in twenty-five jug bags, they usually cost me about 10 cents apiece.
Some thoughts about milk jugs for all other interested parties: They make great comparators. That is to say, when using a know bullet/Cartridge, one can compare your loading to the known. Let's use the example of a 45-70 factory loading for our thesis here. They advertise them at about 1880fps with a 300 grain bullet. Even though they are loaded for the Old Trap-Doors (which is to say they are tame compared to what can be done in a bolt gun), none would argue that they will not easily kill anything in North America, indeed, the 45-70 and other cartridges, took out millions of tons of Buffalo during the Great Buffalo Culling Exercise (fuel for thought here, using Modern Genealogy/Forensics Technologies, we now have a "THE" Smoking-Gun, it was "NOT" the Market Hunters that took out the Buff, but it “WAS” a simple Brain Worm, much like the brain worm that wiped out the elk in Michigan, years ago, though they are making a comeback now). Is the Factory Loaded 45-70 capable of easily killing all African Plains Game? Yes, hands down!
So here is a good comparison. But we need to compare Apples to Apples, or realize that the 1880fps speeds were done in 24” barrels. What would be the speed of that bullet in a 20” or 16” barrel? Well, unless you have a 45-70 you want to hack up, better use a rule of thumb, that will kinda-sorta work (I know Doc, just trying to keep it real, as they say). Try 25fps/inch of barrel. Or if you take off 4 inches for a 20” barrel comparison, you end up at 1780fps adjusted. Now we’ve only to shoot a lined up set of milk jugs, with the 300gr 45-70 at speeds of 1780fps. Get that speed anyway you want, either load them down to 1780fps or shoot them at a range that will yield you 1780fps. Counting the penetrated jugs will give you a sort of rum-line as to Relative-Penetration of the 45-70 at the muzzle (History already tells us what they’ll do at 100-300yds), to a drawn down 300gr .458 bullet to .452”.
We’ll get two things from this comparison; one is a confirmation that we are not destroying the jackets, which exact penetration comparisons of .458 - .452 are equal now and we’ll also have data that tells us a Relative Comparison to any other .452 bullet we might want to use (Yes, I know Doc, but this is field expedient stuff that works and works well, and on the cheap, wouldn’t you say?).
As you fire and record more and more bullets, you’ll get a relative picture of what you can expect in the field. For instance, a 300 magnum, using say a 165gr bullet, makes a Super Great Deer Killer, and how many jugs does it penetrate? Even if your chosen 452b bullet does as many jugs as the 300 mag does, and expands and looks much like the 300m after expansion, you’ll still out kill it by virtue of the bullet diameter advantages, but you’ll end up knowing how well your .452 bullet is doing, by the fact it opened up nicely and penetrated the similar depth of the 165, at 300 mag speeds. Get it? Now try it against a 338 win-mag or a 375H&H, I think you’ll be pleasantly surprised, as many of our bullets outperform and out kill the 338 and the 375. I see typically 7 jugs with some of our bullets, but only say about 5 with the 338/375, depending on load/bullet chosen. You won’t go through one, if you use a hollow point 185/230gr on a 450b, but the 45acp will do about two jugs, sometimes into a third, with the same bullet. This is because our bullet just explodes on contact, into thousands of pieces.
Now, let’s make a milk jug Jig. You’ll need three 2x6’s say 8 to 10 feet long. Lay one done flat, with the turned up others, Screw attach them (use screws, because there is so much lateral pressure, nails won’t hold them) to the sides of the flat one, making a sort of “U” shaped trough. You’ve made a jig that perfectly supports the milk jugs, with 4” supporting sides. Make sure the jugs are touching each other well, to keep things samey-samey and go for it.
For you guys that are somewhat more precise, here’s the source for Ballistic Gelatin that is affordable and used by the Myth Busters.. http://www.gelita.com/ 25 Lbs for $234.50 bucks less shipping.
I like milk jugs and their relative comparisons, allot less bother, there are plenty of examples of good "Knowns" and besides I’m only really interested in Terminal Results.
..t