borbal

In what way is GRT good? Easy to use....? Accurate....? Lots of variables you can play with....? Good support...?

This looks like a very competent internal/external ballistics package which does very much the same as QuickLOAD but at a third the price. It comes on a disc - like QuickLOAD - and also seems to be a Windoze only program. And they do ship to Europe. Anybody...?

You could give my own humble effort a try... http://www.geoffrey-kolbe.com/trajectory.htm

Sorry for the late reply, just saw your message You don't give a barrel length, but let us assume it is 23 inches, which is the barrel length in the online Vihtavuori reloading charts for the 243 Win cartridge. There we see that with 46 grains of N165 behind a 95 grain Berger "Classic Hunter", the muzzle velocity is 2918 ft/sec. The P-Max simulator predicts 2952 ft/sec, which is pretty fair agreement. P-Max predicts a pressure of 3350 bar, which is a very reasonable pressure... and the muzzle energy is 1839 ft-lbs, which is comfortably higher than your 1700 ft-lbs requirement. You say you are "concerned about the pressure readings"..... Is that the signs of pressure in your rifle or the pressures that P-Max predicts? Geoffrey Kolbe

Yup..... as soon as I can get some data on the powder. Vihtavuori are more forthcoming than most powder companies in that data on their powders is published on various pages around the place. But I have sent them a number of emails recently asking for more detailed information and they have not even bothered to reply. There are a few data on N555 they have published, like the energy and loading density, but I really need the kernel dimensions and the vivacity data as well. If you see any data on N555, give me a shout.

It might be worth investigating the throat of your chamber with a bore scope. I have seen "carbon rings" build up which are very difficult to remove and add quite a bit to he shot start pressure.You might think you clean your gun real good, but....

All's well that ends well...

Length of your barrel...? The Viht data was with a 620mm (25 inch) barrel.

The Vihtavuori manual does not give data for the Vmax, but it does for the 60 grain SP by Hornady. The COAL was 57.0mm which gives a calculated usable case capacity of 27.5 grains of H2O. The maximum load in the manual was 23.1 grains of N130, which should leave the case about 96% full (with the bullet seated). The quoted MV was 3173 ft/sec. P-max predicts 3197 ft/sec. with a warm peak pressure of 62717 psi. 23.9 grains of N130 gives a loading density of 99%, so a full case, and an MV of 3305 ft/sec., but the P-Max pressure is now distinctly "red" at 70776 psi. It looks like P-Max agrees that reducing your load or increasing your case capacity would be a good move....

Are you using different cases as well? Sounds like you are pretty much filling the case and a slightly heavier case would make a lot of difference in peak pressure.

I have been scratching my head about this for some while, but I think I have found the answer. It is of note that as the loading density (ratio) approaches 100% (full case) the P-Max pressures climb higher and faster than the corresponding QL pressures. But I also noticed that the muzzle pressures are lower in P-Max than in QL. So, what does that indicate? It indicates that P-Max is treating the powder as more 'digressive' that QL. What does that mean? When the powder is ignited in the case, there is not much volume as the bullet has not started moving up the barrel yet. So, you do not want the powder to burn too fast or the pressures could become catastrophic. However, once the bullet has moved off down the barrel and the volume has increased and is increasing quickly, then you want the powder to burn faster to keep pushing the bullet up the barrel. So, you ideally want powders to start burning slow and then get faster (generating gas more quickly) as the bullet accelerates up the barrel and the volume is increasing quickly. This is called a 'progressive' powder where gas generation gets 'progressively' faster. Powders that have seven or even nine perforations (holes through the length of the cylindrical kernel) are common in large calibre cannons and such powders are progressive. As the powder burns from the outside and from the inside of all the perforations, the area of the kernel increases and so the gas production increases as they burn. Ball powders are 'digressive', because the area of the ball kernel decreases as it burns. But ball powders are usually coated with deterrents on the outside so that ball powders can be made to act like neutral or even progressive powders as they burn. Cylindrical powders with one perforation (most rifle powders) and flake powders are usually classed as 'neutral' powders. As they burn, the area remains constant and the gas production stays roughly constant as the powder burns. But this is actually only an approximation which is only true for cylinders of infinite length and flakes of infinite width and length. However, this is an approximation used in many powder burning models for simplicity - including, I suspect, QuickLOAD. In actual fact, the kernels in most rifle powders are only slightly longer than they are wide, and so they are not 'neutral'. These powders also burn from the ends of the cylinder and this cannot be neglected in 'short' cylinder kernels like in rifle powders. These powders are actually somewhat 'digressive', and that is how they are treated in P-max. The result is that in QL, where cylinder kernels with one perforation are assumed to be 'neutral', the peak pressures will be lower because the powder is not assumed to burn from the ends and so gas is not generated as quickly as the kernel starts burning. However, muzzle pressures will be higher because the burning area of the powder kernel stays bigger for longer - because the kernel is assumed not to be burning at the ends. I have run P-Max with the burning of the kernel ends turned off, and the results then start to look more like QL results, with lower maximum pressures, higher muzzle pressures and the powder being 'all burnt' sooner. Anyway, I leave you to decide which model treats the powder burning more correctly... Geoffrey Kolbe

Well, that is gratifying - thanks very much for that Interesting that a load which had previously shown up as "green" (under 51,450 psi) is now "orange" at 61k psi. What load was that...? Thanks again for your comments Geoffrey

The P-Max simulator needs the case length so it knows the actual distance the bullet will travel. The muzzle velocity is actually a function of the actual distance the bullet travels, not the 'barrel length' per se. Comparing one simulator against another does not get us very far. Comparing P-Max against actual results is much more interesting. Having said that, I note that the P-Max Mv is only 53 ft/sec. different that the QL result. Given that they are two completely different models and that gun-to-gun differences with the same load can easily be 100 ft/sec., I would call that a reasonable agreement. (Better than 2%) As for pressures, I do not know the details of the QL model that Hartmut Broemel used. I think he got it from a book on ballistics put out by Rheinmetall in the 1970s, but that is in German so I cannot understand the model described in detail. The RS Chemie-Swiss reloading data does give pressures with its loads and generally the P-Max pressures would seem lower than they measure, but that is a very loose correlation of P-max pressures with quoted pressures and I suspect comparing the QL predicted pressures would be frustrating as well. P-Max pressures do seem very sensitive to loads approaching 100% loading density in a way that QL is not. For safety reasons, I would be more troubled if it was the other way around. I have played around with Vihtavuouri powders for target rifle loads like yours and it would seem that N150 would be a better powder....? I know a number of shooters who use N150. Thanks for your comments Geoffrey

P-Max Internal Ballistics simulator is now back on line. The simulator has been improved slightly and as a result, all Vihtavuori and Chemi-Swiss powders have been re-calibrated. I look forward to hearing how it works for you now http://www.bbt.scot/ballistics/pressure.htm Thanks Geoffrey