Would someone using quickload please crunch the numbers on my pet 7.62x39 hunting load?

7.62x39

125grn Nosler ballistic tip

28.0g AA1680

R-P case, Win small rifle primer

c.o.l 2.310

I use pointblank already, and while it works great for external ballistics it doesn't help at all with internal ballistics.

Perhaps I should have been more clear in my OP I'm looking for pressure calculations.

whoops - my bad - just trying to help.....

To get accurate calculations from QuickLOAD you need to provide more information. The main thing that determines pressure is the volume of the case when it is expanded into your particular chamber. This is one of the principle reasons guns are individuals when it comes to loads and load performance. For QuickLOAD, fireformed case volume is the closest thing to use. It is expressed in the form of case water capacity in grains. To get this number, you take a fired, but not deprimed case, and weight it. You then fill it with water to the brim, but with no meniscus, either positive or negative; just flat level with the case mouth. Weigh it again and subtract the empty case weight from the filled case weight to get case water capacity. There must be no extra drops or wetting on the outside of the case. A standard drop (0.05 ml) weighs about 0.7 grains.

To make that capacity valid, we also need the actual case length.

Optionally, but tending to improve the resultant pressure calculation accuracy even more, is to provide your bore dimensions. This will be the diameter in the groves as taken from a pure lead slug (cast bullet alloys are too springy to give accurate slugging results; they read too big), the diameter of across the lands, and, finally, the width of the lands and the number of them in your barrel. These should be measured with a outside thimble micrometer with 10 thousandths vernier scale, and not a caliper. These can be had for as little as $15 from suppliers of Chinese tools if you are on a budget.

Finally, you need to measure your actual barrel length by the BATFE method. To do this, check that your gun is empty, close the bolt and set a cleaning rod down into it until it rests against the breechface. At the edge of the muzzle where the rifling ends (in other words, don't include the crown) mark the cleaning rod with a pencil. Pull it out and measure from the end of the rod to the pencil mark. That is the barrel length QuickLOAD needs for muzzle velocity determination.

Nick

OK I here's the missing information

avg case capacity is 33.6 grs of water

case length is 1.529

the bore measures .3105 and .300 respectively

and the barrel length is 22.5"

And: how many lands and grooves? And how wide is each land or each groove (either one, just tell me which it is)? The purpose of that last measurement is to determine what percentage of the bore is land. More land, more rifling engraving pressure. If you slugged the bore, just take the inside measuring jaws of a caliper and measure the width of an egraved spot on the bullet at the bottom. I can use that as a cord and derive the portion that is circumference.

And the bullet! You listed the 125 grain Nosler, but that bullet is .308. Your bore is clearly intended for the .310" and .311" bullets. Nosler makes a 130 grain in that latter diameter. Hornady makes 123 grain bullets in the former size. You will be able to shoot the undersize bullet, but will need to watch out for excess copper fouling.

5 grooves @ appx .085

If the information you gave me, especially the seating depth and the water capacity of fired but not resized cases, then this is a potentially dangerous load, well above industry standard safe maximum.

Calculation:

28 grains AA1680 with 15 grain Nosler BT in your chamber base on fired but not resized brass volume.

Chamber Peak Pressure, 63,896 PSI by CIP Piezo method (12,408 above listed maximum).
MV: 2,642 fps.
ME 1937 ft-lbs.
Muzzle pressure 4464 PSI.
97.96% of powder burned in bore.
BE (ballistic efficiency) 36.0%.
BT (barrel time) is 1.009 ms.

NOTE: Many guns show no pressure signs until they are already 10,000 PSI over the recommended maximum, so I would not be surprised if you saw none. Proof load pressure is probably about 70,000 PSI for this gun, so you are getting close to it. Many guns will withstand overloads, but bear in mind they are fatiguing the gun metal and eroding the throat of your chamber at an accelerated rate. In other words, you will gradually see maximum pressure tolerance decline over time with a steady diet of hot loads like this. Not a recommended practice.

really! that's interesting the MV given by quickload is over 130 fps faster that what this loading actually achieves

Interesting. Question, why is this load (28.0gr. AA1680 with a 125gr .311 bullet),or something very similar it would seem, then listed in the Speer manual?

Or is this an example of how a small change in primer or case etc. can have wildly different results?

quote:

Or is this an example of how a small change in primer or case etc. can have wildly different results?

That could very well be the case as my load came from the speer manual. But I would imagine that shooting .002" worth of undersized on bullet would result in some pressure reduction.

Then there's my using the much milder SR primers versus the LR primers most commonly encountered with 7.62x39

I wonder what pressure the exact same variables yield when you substitute the Ballistic tip for a 123grn .310 Hornady V-max

I have run into one instance (BL-C2) where there is a big discrepancy in the current powder characteristics and those in the QuickLOAD database. The QuickLOAD database produced results that matched the old Lyman loading manual data, but was way different from current Hodgdon and Hornady data. I'm talking 30.5 grains producing 37,300 CUP verses 36.0 grains producing only 34,700 CUP, both with 170 grain flat point, flat base bullets. The Lyman manual was #46, which is a little long in the tooth now. The QuickLOAD predictions agreed pretty well with it, though.

A second thing to keep in mind is that QuickLOAD is not going to allow for metal stretching. As you get up near a maximum load, your chamber and bolt lugs start to stretch and flex, and the usual symptom is you increase your powder charge but don't see an increase in velocity. At that point, QuickLOAD would still be giving you an increase in velocity.

Another thing I've seen is poor chronometer accuracy. One day my dad and I were testing moderate .308 target loads in one of his rifles. My Oehler 35P showed about 2500 fps, a reasonable expectation, with good agreement by itse middle check screen. Dad's chrony read 2700 fps. I don't have to tell you which one I believed.

OK. Did some more checking. I don't think the QuickLOAD powder database is wrong here. The Accurate site puts the maximum safe load at just 25.5 grains. No accounting for Speer, I guess, except to say their older manuals had a reputation for very hot loads. Some of the loads in their current manuals may be carry-overs?

Second, QuickLOAD normally uses very conservative case capacity defaults, but for the 7.62x39, the default (35.5 grains H2O capacity) is actually a larger volume than your R-P cases have. So, I think your cases are exceptionally tight. I have seen that in military brass in other chamberings before, but not in commercial. R-P usually is smaller than Winchester, though.

If I run Accurate's posted maximum with QuickLOAD's default case capacity and your bore area and the same Nosler bullet, I get a very close match to their data.

                 Accurate      QuickLOAD
 
peak pressure  48,500 C.U.P    47,991 PSI
20" MV          2,368 fps       2,382 fps

So, my conclusion is that the QuickLOAD prediction is good and that this is about the capacity of the R-P cases. The velocity difference is likely due to your gun starting to stretch, which enlarges the chamber capacity, reducing both pressure and velocity some. Not something you really want to be doing if you can avoid it.

QuickLOAD says your smaller capacity cases will be at about dead maximum pressure with 24.8 grains of 1680. I think I would back off to at least that number. Chris Long's optimum barrel time criteria says there should be an accuracy sweet spot between 24.1 and 24.2 grains of 1680 in that 33.6 grain H20 capacity case. That is where I would be conducting experiments.

OK. I found one part of the problem. My fault. Sorry.

Because QuickLOAD normally expects to see bullets no more than 1.6 thousandths over or under bore size, when I was tweaking the barrel for actual area, unnoticed by me, the fact the program did not find the bullet within its normal limits caused me to go back and forth with it a bit. In the process I failed to notice this had reset the cartridge OAL to its default 2.19" length. Went back today and recalculated. It's not a big difference, but some.

Also, note that I habitually refer to SAMMI limits, but should have said these are figured against the CIP pressure maximum of 3550 bar, or 51488 lb/in². The SAMMI maximum is lower, at 45,000 lb/in². The SAMMI and CIP Piezo transducer designs produce somewhat different results, but not that much, as far as I've noticed. Mostly it is just a disagreement between these two organizations about where the safe limits lie for this round.

 Charge      Peak       Difference      MV       ME      %burned   %BE    Barrel
   in      Pressure      from CIP       in       in      in tube          Time in    Comments
 grains    in lb/in²   max in lb/in²   ft/s     ft-lbs                       ms

 28.00       63,142       11,654       2,637    1,930     97.87    35.9    1.012   Existing Load
 26.33       51,476          -12       2,491    1,722     95.98    34.0    1.098   CIP Maximum load to nearest 0.01 grain
 25.35       45,745       -5,743       2,405    1,605     94.61    33.0    1.152   OBT load from Chris Long's theory

Substituting the 0.310" 123 grain Hornady V-max:

 28.00       49,600        -1,888      2,545    1,769     96.53    32.9    1.093   Existing Load
 28.34       51,478           -10      2,573    1,808     96.91    33.2    1.076   CIP Maximum load to nearest 0.01 grain
 26.85       43,767        -7,721      2,450    1,639     95.10    31.8    1.152   OBT load from Chris Long's theory

The diffeence in pressure may be because most 7.62x39 rifles are semi-auto's some of them not the strongest actions in the world. My CZ 527 is a bit stronger than a SKS. I was looking for a 50K psi load that would get a 123gr bullet close to 2500. This load seems to do that without any visable high pressure indication in my rifle.
123gr. Hornady
WW cases
Fed 210 primers
28.0gr AA1680
COL 2.175

It could well be. I'll bet dollars to donuts that if you measure the water capacity of your fired, but not yet resized cases, the way I described to Krochus, you'll get a bigger volume in your Winchester brass than he did in his R-P cases. If you look at the last loads I listed for him, even his case capacity stays in the range of pressure you want when you go to the 123. It is shorter and leaves more powder room.

quote:

If I run Accurate's posted maximum with QuickLOAD's default case capacity and your bore area and the same Nosler bullet, I get a very close match to their data.



Accurate QuickLOAD

peak pressure 48,500 C.U.P 47,991 PSI
20" MV 2,368 fps 2,382 fps

Correct me if I am wrong or missed something, but 48,500 C.U.P. and 47,991 PSI are really not a close match. The 48,500 C.U.P. would be much higher pressure than 47,991 PSI, yes, no??

Steve4102,

No. Not necessarily so. Indeed, more likely the other way around. You will notice that SAMMI .45-70 spec calls for 28,000 CUP and 28,000 PSI. Both instruments got the same number for that cartridge and pressure level. There is a tendency for CUP to be higher below 28,000 and for PSI to be higher above 28,000, but even for the highest pressure cartridges the difference seldom exceeds 15%, give or take. For a good article on the relationship, look at the second article down on the list here:

http://www.shootingsoftware.com/tech.htm

The author of the article above does derive a linear least square fit relationship between the two systems, with an R test result of 0.927 (1.000 would be a perfect fit) but it has a lot of scatter and the zeros don't coincide. I reordered his same data and got a power fit that results in a slightly higher R=0.936, and has coinciding zeros. That formula is: .02324×CUP^3.6076=PSI. It says 48,500 CUP=55,259 PSI. However, the scatter is so great in the data that is could actually be anywhere between equal to one another and about 58,000. A chart of the error of the best fit conversion from published SAMMI CUP to PSI and published SAMMI PSI numbers is below.