Help with Bullseye Load

[Brian Pfleuger]

Originally Posted by Jim Watson

Quickload is a computer program. $150 from Neco.
http://www.neconos.com/category/Software-2

I do not recall seeing a report on how closely its predictions match up with shooting in real guns. Of course the only thing you can really measure at the consumer level is velocity and hope the pressure is ok.

QuickLoad's accuracy ranges from "Dead Nutz" to "So-So". Usually, once the parameters are changed to match the exact firearm and shooting conditions, it is very close.

It predicts my 7mm-08 to within an average of 1.9fps over a wide range of loads with H380 and Hornady 139gr SPs, my 357sig to 2fps using several loads of Power Pistol and 2 different bullets and my 204Ruger is off by 1fps of the average velocity... true velocity if 4030fps average while QuickLoad predicts 4031. On the 204, that's an accuracy of 99.975%

There are a number of parameters that need to be tweaked. Case capacity, true bullet length and weight, powder temperature, sometimes the powder burn rates and a mysterious thing called "weighting factor".
I have found that once I get the concrete items set correctly, like bullet weight. case capacity and OAL then all I need do is tweak the "weighting factor" very slightly to get an exact match.

[Unclenick]

In addition to the tweaking, it needs to be kept in mind the model was developed for bottleneck rifle cases. It is less precise with straight was pistol cases, but as Peetzakilla says, tweaking can often fix that.

A chronograph will tend to confirm velocities. This is complicated by not knowing how much post-muzzle acceleration of the bullet by muzzle blast occurs? The program seems to default to matching readings taken at 15 feet, though that means it over estimates velocities reached in the barrel by a bit.

In addition to a chronograph, the RSI Pressure Trace seems to validate QuickLOAD as well as to pressure and barrel time. That's a second cross check available to consumers.


Arizona98tj.

The thing observed by Feamster, IIRC, is that the quantity of IMR 4064 needed to reach 2200 and 2300 fps in his M1A firing a 168 grain SMK was lower than for IMR 4895. That would mean it is faster if the energy content of the two powders were the same (they aren't, quite). It has to be pointed out, those are low pressure loads for the .308, and therefore lower than either powder is usually operating at. At 2400 fps the two powders needed the same charge weight. At pressures producing higher velocities than that, the 4064 needed more charge weight, indicating it was now the slower of the two.

Both powders have excellent accuracy reputations, but some guns prefer one over the other, likely due to their different burn curves producing different barrel times at most velocities. You need to match a barrel time to a vibration sweet spot for best accuracy. The 4064 in that example needed bigger charge increases to achieve the velocity increases. This means decreasing efficiency, but it also means less charge weight sensitivity and probably less temperature sensitivity, therefore. You can see how those would be advantageous.

I suspect a factor in Feamster's results is that 4064 is bulkier and uses up more space than 4895. You can't fit as much into a case (another reason for needing both available to choose from, depending on the chambering) and that the apparent difference in burn rate was actually a difference in ease of ignition with the primer used, and may have had nothing to do with how the powder burn rate would have compared at those same pressures in a caloric bomb? It might be that switching to a magnum primer would have reversed the results? You'd have to try it to see?

The grains of those two powders are not the same size, and I don't know how the perforation pattern or the deterrent coatings compare? My old (1995) Vihtavuori Oy manual has some nice illustrations of the effect of grain geometry on burning curves.