Data for .270 with Nosler 130 gr BT and IMR powders

[SL1]

I am playing with powder parameters in QuickLOAD, trying to guestimate the pressure that I am actually getting with MY can of IMR-4831 and Nosler's 130 grain Ballistic Tip bullets in MY .270 Winchester. My gun is giving me more velocity than either QuickLOAD or my old Nosler manual says it should. But, my Nosler manual is so l old that it has Solid Base bullets instead of Ballistic Tips.

So, would somebody with a recent Nosler manual please post the data in it for IMR-4831 and IMR-4350 for the 130 grain Ballistic Tip bullets? My old manual listed 3 charge weights and velocities for each powder, so if the new manuals does that also, I would like to have all 3 data points. My old manual did not list pressures, but I would especially like those too, if the new manual has them. Finally, I would like to know barrel length for those velocities, the make of brass, and the cartridge COL if the new manual has that information (mine only has barrel length).

SL1

[Unclenick]

I've run into the over-performance velocity thing before with compressed loads. Are your's compressed?

[SL1]

The load eventually becomes compressed a little as it is increaed to max, but starts significantly below compressed. The "over-performance" occurs at all charges, and is 50 fps compared to the manual over the whole range and increases from 25 fps to 80 fps compared to QuickLOAD.

I can match the velocities with a variety of different manipulations of the QuickLOAD powder characteristics. But, without pressure data, I can't do what the manual suggests to match BOTH velocity and pressure. SO, I can get various pressure estimates with various parameter selections that match the velocities.

That is why I am requesting data that I hope will also have pressures with the velocities. (Also, it would help to start with data for the SAME bullet that I am using.) I am trying to get some idea of what QuickLOAD can and can't do with respect to predicting pressure.

SL1

[GeauxTide]

In my 6.5-06, I get better performance with 129gr Horn under H4831.

[Unclenick]

50 fps that's constant isn't bad. It's within powder lot variance. I would do two things. First, maximize your settings. This means:

• Get the water weight capacity of your fireformed case correct. I have an Excel file you can download from my file repository that compensates for water expansion with temperature. http://drop.io/unclenick.
  
• Slug your bore and get the cross-sectional area of your bore entered in the program correctly. That can change results 10 fps or so. Click the icon with calipers over a cartridge case, and the upper button in that flyout window will let you set that up.
  
• Make sure you're using the same primer the original data used. It should be as mild as possible to match QL. I saw an article by Charles Petty one time in which he got a .223 load of 24 grains RL10X to increase bullet velocity from 3150 to 3300 fps just going from Federal 205's to Remington's 7 1/2 primer. The latter is magnum, of course, while the former is not, but the example gives you some sense of the range of influence involved.

Second, put the chronograph out at twenty-five or thirty yards or so. Here's the dirty little secret. Most guns are not as tight as the pressure test barrels used to fire a good many test loads, so they achieve lower pressure and velocity at the muzzle. The spoiler is muzzle blast acceleration. I first read of it being quantified by Harold Vaughn in his book, Rifle Accuracy Facts. He was using a magnetometer to measure bullet spin to detect core stripping from excessive rotational acceleration and noticed the rate of rotation was too slow for for the measured velocity near the muzzle. From the two measurements he calculated his rifle bullet was gaining about 84 fps after leaving the muzzle. I have subsequently seen a Doppler radar trace of a .40 S&W round showing it gaining about 35 fps after muzzle exit. The two instances were 2.7% and 2.9% greater than actual velocity at the moment the base was even with the muzzle, respectively. I don't have enough data to say how typical they are, but I've been estimating 2.8% until I could find out more.

My point is, for the bullet to fall back to what QuickLOAD predicts, you'll need to get the chronograph out there a distance. The Army's insistence on using 78 feet years after they've had instruments that could do it at any distance they preferred, that old standard starts to seem sensible. You could calculate a 3% velocity loss for your bullet with tables, but bullets don't get their full BC until the coning and nutation motions in the tip plus any wobble from the base have time to settle, so I like to try at 10 yards and again at 30 with a test load to see how fast the bullet is actually losing velocity before I declare exactly where to put the machine for most of the work. 40 yards with a high BC bullet has been about as far as I've had to go.

So, going faster than the manual loads is simply within the realm of possible error, especially if the manual didn't use a test barrel. Getting a match to QuickLOAD at close range is common, but is because the real gun actually has a slower muzzle velocity than the ideal gun represented by QuickLOAD gets. If you've got the rare gun with chamber and bore dimensions that let the cartridge shoot up to its potential, then you need an actual match to adjust the pressure, and that's going to mean putting the chronograph further from the muzzle than you expected to.

If you can borrow a Pressure Trace and are willing to drop $25 to put a strain gauge on your barrel, then go for it. That will be the final word on pressure determination anyway.

Spouse is calling so I don't have time to edit. Please excuse any typos. Later.

Nick

[wncchester]

"My gun is giving me more velocity than either QuickLOAD or my old Nosler manual says it should."

Be greatful! It's uncommon but it happens. Far more are slower or MUCH slower tban manuals project.

[SL1]

Unclenick,

First, the "50 fps" more velocity from my gun was comparing my 22" barrel to the 26" barrel "Custom Mauser" in the "Nosler Manual Number Two." If I try to take into account the barrel-length difference by using QuickLOAD (which also doesn't match my gun's velocities) then I would need to add about 130 fps for my top load, so my gun seems to be getting something like 180 fps more than "expected" from the manual.

The manual used Norma cases, I used Federal. The manual used Remington 9½ primers, I used Winchester WLRs (which might be a lot of the difference). The manual data was shot at 68° F and my data was shot at 75°F. The Mauser has 1-in-10" twist; I think I remember mine has 1-in-9½" twist. My fired case capacity averages 70.0 grains of water. I don't know what the "Custom Mauser" has in the way of chamber dimensions, throat length or bore cross-section, so making these corrections is not possible. The case volume would need to be 76.2 grains in QuickLOAD to completely compensate for the difference in muzzle velocity for the 4" difference in barrel-length alone, so I don't think that is likely to be the whole story.

With respect to being "happy" about the difference, I am happy with this particular load. I load to around 3,000 fps, so I am not at the top of the range in the manual, and the load shoots a little less than MOA, so I am "happy" enough with the accuracy.

In another thread on this forum ( http://www.thefiringline.com/forums/...d.php?t=370767 ) "Major Dave" was asking questions about what to do when your gun is not matching the velocities in the manual, and I had spent some time thinking about it and trying to post some guidance for him. His situation was that he was getting less velocity than expected with one powder and bullet and more than expected with another powder and bullet, both with same weight bullets in the same rifle. He wanted to know if he could use the second powder with the first bullet and just keep adding powder until he achieved the velocity in the first situation.

"Major Dave" seems to have lost interest in that discussion, so I am not getting any more information from him to try to fine-tune my thinking. So, I turned to some similar old data that I had to see if I could learn some more about QuickLOAD and internal ballistics.

So, it is not my load that I am "unhappy" with, and I am not "unhappy" with QuickLOAD. It is just that I think I can improve my understanding of these things with some more work. And, it would help to have the data I asked for to achieve that.

SO, does anybody have the data I asked for in the original post?

And, any ideas on how best to adjust QuickLOAD powder parameters to match a series of velocity measurements so as to best estimate the pressures (which I don't have) would also be welcomed. The manual suggests matching a series of velocity + pressure measurements TOGETHER by varying the burning rate factor and the specific heats ratio, but NOT the heat of explosion. That seems wierd to me, in my current state of advanced education in gas dynamics but lack of formal education in internal ballistics. My training says that the specific heats ratio of a mixture of gases is a physical function that is controlled by the specific heats ratios of those gases and their fractional contribution to the gas mixture. So, I don't understand how the specific heats ratio would change from one lot of nitrocellulous to another without changing the amount of nitrating, which I would expect to also change the heat of explosion. On the other hand, I can fully understand that the QuickLOAD model results can be changed by tweaking parameters, even if those tweaks don't match physical reality. So, I am wondering what tweaks are "best" for inferring pressure from velocity when there are no pressure measurements and the velocity needs tweaking to match measurements.

So, again, DATA PLEASE, and ideas, too.

SL1

[Unclenick]

SL1,

I don't have the Nosler manual, but I can refer you to Chris Long's paper on tweaking performance matches in QuickLOAD. Burn rate gets adjusted first because lot variance in deterrent penetration of the grain surface changes that, even if the nitrocellulose is the all the same hexanitrate form. In the double-base powders the nitroglycerin percentage might not match perfectly from one lot to the next either, so the energy densities could be off, but I don't believe that part of the process is as hard to control as the deterrent coating penetration.

If you run a magnum pistol load with QuickLOAD's H110, then sub in its 296 model, even though H110 and 296 are the same exact St. Marks-made powder, you get about 10% difference in pressure. That's just lot variance from samples taken at different times. So, having a different powder lot could certainly do it, as could the primers, cases, and other factors you mentioned.

If someone has the Nosler manual and can give you its numbers, I believe their data includes the % case fill? Ask to get that, too, so you can do apples to apples.

[SL1]

Nick,

Thanks for the link to Chris's paper.

I have been looking at the differences in the powder factors for several of the powders that are supposed to be identical, including H-110 and WW-296, plus some of the ADI-Hodgdon pairs. I notice that there are differences in ALL of the parameters, not just Ba, and Cp/Cv. I also noticed that some of the IMR powders have big changes between "steps" in that brand's burning rates that tend to be off-setting, like a big change in burning-rate factor offset by a big change in progressivity. Other powder brands seem to have a little more orderly march of the burning-rate factor as you step through their powders in the order that they typically appear on buring rate charts.

I have also noticed that, to match some velocity measurements, I can need to change the burning rate of some powders by more than it takes to get several steps away on the powders of that manufacturer's powder on the burn-rate charts, (although it has never been more than 10% of Ba). SO, I am thinking that I need to consider changing things besides Ba. And, I have a tendency to NOT want to change the things that I can actually measure, such as case capacity and bullet weight (which I DO measure). It seems that there are many more than one way to achieve a match to any particular velocity and charge weight pair. But, they can give substantially different pressures, and I don't know which pressure is most realistic.

I am thinking that if I have a series of charge weight and velocity measurements, then I might find that there are not so many ways to change powder parameters in order to match the whole series. IF so, then I might be be able to get a better idea of what combination of parameters is the most realistic, and that MIGHT give me a more realistic estimate of pressures for that series of charge weights. But, all of that is speculation. And, I need some series of pressure measurements along with the corresponding charge weights and velocities to test that theory once I find a (or more than one) way to match the velocities and charge weights, only.

Steve

[Unclenick]

Gotcha. Through email communication with Hartmut over the years, I gather he does some of the testing but that he has built relationships with some of the powder companies so that he can get them to give him their target characteristics. Hodgdon once told me it costs them $50K to have a lab do the full set of characteristic evaluations, so they don't. I'm sure they leave all that up to the manufacturers they buy from. I know the manufacturers blend canister grade powders with portions of faster and slower lots to achieve an average burning rate number. I don't know if they also do some shooting tests in a pressure test barrel at the same time to ensure some of the same load recipes are still valid? I know I would.

I was in Gander Mountain poking around yesterday and decided I ought to own a current Nosler manual, so I picked one up. It is the #6 manual. It lumps all their 130 grain bullets together.

It specifies a Winchester case, Federal 210 primer, and that they used a 24" Shilen barrel with 10" twist. The receiver and COL are not specified, so I assume the latter, at least, is the 3.340" maximum.

Their IMR4350 loads are:

51 grains 2828 fps., 84%
53 grains 2953 fps., 87%
55 grains 3078 fps., 90%

They have no IMR4831 data. Only H4831, for which they claimed the lightest load was their most accurate load among all those tested.

For H4831:

55 grains 2909 fps, 89%
57 grains 2997 fps, 92%
59 grains 3124 fps, 95%

[SL1]

I guess Nosler still doesn't publish pressures for their loads. That would have helped.

SL1