I have been fooling around with this internal ballistic program lately but can't say I have formed much of an opinion yet. It seems to be as much in the ballpark as other published data, but sometimes it tneds to be quite a bit off from the velocity standpoint.

One of the nice aspects of the program is helping one pick powders that provide the ratio of good velocity and low pressure. But, given some anomalies in velocity (what it says I should get vs. my 35p) I am concerned if these anomalies extend equally to pressure.

Steve

i had someone on here run a load through the program. 300 RUM 150 sierra gameking 96.5 gr. rl 22 fed 210 gm primers. he said it would give roughly 3515 fps at 62,000 psi. i was getting signs at 98 gr. but not at 96.5 so i figured the pressure was about right. had a chance to chrony the load the other day. 9 shots avg 3611,but no pressure signs.3 3 shot groups avg right at .525.i would say its about like anything else ,use your head.

I use QuickLoad a lot. It is a tool just like any other. It has limitations. It is good for choosing the powder, just as you say, and has more than paid for itself doing just that.

It does not do a good job with straight-wall cases, or cases with minimal shoulders.

It does not directly model the different primers - you have to modify the start pressure to compensate.

Since the velocity is the integral of the pressure, and since the powder type sets the shape of the curve, IMHO once you adjust the starting pressure and/or case volume so the results match the measured velocity, then you have a very close model of the actual pressures involved.

I have never yet found a case where the QL results were dangerous. On the bottleneck cases it is usually within 2% on velocity, which I consider very close, indeed. You see that much variation rifle-to-rifle.

I wish H. Broemel would find a better way to model the straight wall cases. That's really my only gripe.

Don

I don't have nearly as much experience with it as Don does, but so far, I'm impressed. I was working up a load with the 160 grain Hornady in my Swede, and after altering QL's defaults for case capacity and bullet length to match my samples, QL's prediction was less than 10 fps off the actual muzzle velocity.

Once I've chronographed a load, I'm never quite sure which QuickLoad parameters to "tweak" -- weighing factor, start pressure, case capacity, mean burning rate, etc. What I have found, however, is that when the prediction is relatively close to the actual velocity, it doesn't make much difference which one you change; for similar powder charges, the results of changing any one of these parameters are all within one or two percent.

As Don said, QL isn't at its best with the straight-walled cases -- I have a tough time modelling my .45-70's or my .458. I'm also a little leary of its predictions for "extreme" combinations. By that I mean things like really overbore cases, bullets that are very light/heavy for caliber, etc. I did some modelling for my brother's .22-6mm Improved, and depending on which parameters I tweaked to match his velocities, predicted pressures ran from the mid 50k range to 65k+. I had similar results trying to model 35 grain bullets in a .223.

Cannon,

As the cases get bigger I tend to lower the start pressure a little, as the primer has a bigger volume to drive.

On the straightwall cases I lower the start pressure, then just bump up the volume to get a match in velocity.

I have found that for 223, 243, 308 and cases with similar good bottlenecks that variations are usaully small - and if the variation is big on those cases, only then do I change the powder rates.

Sometimes even the good powder companies put out a fast or slow batch.

Don

Don/Cannon,

Thanks for the comments. Now I realize just how little I know about this program. I want to make sure I understand you correctly.

You are saying that you put together a load with using the program, test it, and then adjust the program (via case capacity) until the load ready the same velocity as tested.

Is this correct?

Cannon, a comment you made confuses me.

"...weighing factor, start pressure, case capacity, mean burning rate, etc."

I understand tweaking case capacity, but not sure I understand the rest of the comment.

Thanks,
Steve

holz,

With most loads on most cartridge cases with reasonably effective bottlenecks (22-250. 30-06, 308, 300 winmag, 338 WinMag etc.) simply using measured case capacity and COL puts the model right on the money, and you measure at the range what you predict with QL.

But suppose you have a .458 Lott (straight-wall case) you've never shot and you use QuickLoad to choose RL-15 as the powder for a 500 gr. Hornady. Desiring 55,000 PSI as a safe working pressure, you find you need 79 grains according to QL, yielding 2220 fps.

You go out and shoot a progression starting at 72 grains, and find that at 79 grains you have no pressure signs at all, and you are only getting 2060 fps. You now need to figure out how to make the model match your results. Knowing that you have new, soft cases you figure the start pressure might be low due to low bullet retention, so you re-model with 1600 PSI start pressure. That still predicts 2200 fps. Now you go read the fine print in the readme file, and find that on straightwall cases the author recommends adding 10% to the case capacity to get more accurate predictions.

So you go back to the model, and you find that you actually have to go up from 110 to 127 grains in case capacity, even with the low start pressure, to get a predicted 2060 fps.

Then you model a load for 55000 PSI with the new "tweaked" values and you predict that you need 91 grains to get 55000 PSI, and that now yields 2339 fps.

Not being crazy you load up a sequence from 81 to 93 grains in two grain steps, and go try it out. Now you find that 91 grains gets you 2300 and 93 grains gets you 2345 fps. You tweak the model again, and you find that the effective volume at this load is 131.5 grains of water!

The utility of the model is that now you know what the effective volume is for that primer and powders of that burn rate, so you don't take two trips to the range to find the working max pressure even if you change powders and bullets within practical ranges. Note that you can often find some printed data on powders similar to the one you are using, and you can use that to get started tweaking the model.

I suspect that on these straightwall cases the primer pops the bullet (and a lot of the powder)out of the case into the long throat. The "case volume" just changed before the model really gets started.

This points out the strength of the bottleneck case design. The working pressure becomes only weakly affected by bullet retention forces and long throats, so the results are more dependable in the model and in reality. That's why all the benchrest cases are short fat powder kegs. The shoulder keeps the powder in the case until pressure builds up pretty high.

Note that if the bullet sticks hard in the case, or someone puts the load in a short-throated rifle, the case colume goes back to 110 grains and the pressure peaks at 90,000 PSI. You just set back the lugs on an expensive rifle!

Something very similar to the above sequence (except the horror story at the end) happened the first time I tried modelling a Lott. (Right, Paul?) The numbers are somewhat made up, but it was a similar progression.

There is a "subset demo model" of QuickLoad somewhere on NECO . It takes a while to download, but you can see all the screens and model one or two cartridges

HTH,
Don

Don,

Once again I thank you for your detailed comments. Very helpful.

Steve

Steve,

The weighing factor is an estimate of the
percent of unburned powder charge that starts moving down the barrel before it ignites. I think QL suggests .33 for really overbore cases, .5 for average bottle-necked cases and .75 for straight-walled cases, but sometimes the default values in the database don't match their suggestions. If you use the utility for finding case volume given outside dimensions and case weight, QL will suggest a weighing factor for that specific case. Generally, I only change this when dealing with cartridges with a minimal shoulder, or something like my brother's .22-6mm Improved which has very little body taper and a very sharp shoulder.

I was working from memory when I typed "mean buring rate," and made a mistake. What I should have typed was "Ratio of Specific Heats". As Don mentioned, when dealing with straight-walled cases, the documentation suggests increasing the case capacity incrementally until the predictions match your results. In the same section of the book, it suggests an alternate approach -- decrease the ratio of specific heats (in the Charge window) in increments of .01.

Cannon,

I thought H. Broemel said to do that only if you knew what you were doing.

I figured that left me out!

Don