When does velocity not equate to pressure?

[bowji john]

I noted that your case capacity was a bit low - yours is set at 60 when mine is set at 74.5 H2O

I shall recheck that with this latest fire formed case

Rechecked - 75 grains H2)

 

[zambezi]

75 grains H2)

GRT still thinks that even your Nosler partition load is hot.

Have I input all known parameters correctly? A 2mm reduction in case length tames the curve, for example.

By way of cross-check: what MV do you get from your Nosler partitions? Around 2500fps or lower? Does your chrono agree with the QL predicted MV for that load?

It could well be that GRT is not sufficiently groomed to make accurate 9.3x62+RL17 predictions yet.

 

[bowji john]

This seems to accord with mine

I have a 23 inch barrel so my predicted MV is a little less than what yours shows

The big difference is the warning - QL doesn't think that the pressure at 4200 is excessive

I have not measured MV for the nosler partitions as I did a ladder test with them seeking a sweet spot - I think I'll go back to them and remeasure

It could be that I've been playing with fire all along ......

 

[hw101]

Assuming you use a similar weight nosler partition, by my reckoning for that single shot you have 'apparently' about doubled your muzzle energy for less powder charge.
Surely a chronograph error?

 

[zambezi]

QL doesn't think that the pressure at 4200 is excessive

The C.I.P spec sets pmax at 3900 bar:

https://bobp.cip-bobp.org/uploads/tdcc/tab-i/tabical-en-page69.pdf

 

[Laurie]

Check the sensitivity setting on the chronograph (with the Bayo plugged in). From the V3 manual:

2. If you are getting strange readings, it could be that device is too sensitive and you are picking up random “noise”. In rare cases when the sensitivity is too high, on very large muzzle blast weapons this may cause erroneous readings. The bayo must be plugged in to set the sensitivity as the device can set the input stages properly. The three following sensitivity presets cover most situations: Normal: This corresponds to level 2 out of the 11 levels. This is the correct sensitivity level for most centerfire rifle ammunition, assuming the bayo spacing is correct. Works well on: -Copper-jacketed lead bullets moving over 1000 fps -Solid copper bullets moving over 1000 fps -Steel-core -Steel shot

 

[Muir]

Interesting topic.
In general, velocity has nothing to do with pressure. They are not linked hand in hand. "X" amount of pressure in a given cartridge doesn't not equal a set velocity. Many of Lyman's 308 180 grain cast bullet loads utilizing shotgun powders delivered 1700-1800 fps with 45K PSI pressures, when H4895 gave 2400 fps at 35K PSI. ~Muir

(Which is why I stopped loading cast bullets to a velocity limit, and began loading to a pressure limit.)

 

[scrumbag]

I would shoot the load again and see if Chrono said same thing.

 

[Selous]

I just plugged the numbers into Quickload by way of a comparison. It looks like 62g is predicted to be at the limit of pressure. Velocity in the region of 2500fps which seems to agree well with the GRT




Cartridge : 9.3 x 62
Bullet : .365 / 9.3mm (.365 / 9.28), 286gr VRG-1, Peregrine
Useable Case Capaci: 59.889 grain H2O = 3.889 cm³
Cartridge O.A.L. L6: 3.290 inch = 83.57 mm
Barrel Length : 23.6 inch = 600.0 mm
Powder : Alliant Reloder-17 *T

Predicted data by increasing and decreasing the given charge,
incremented in steps of 2.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step Fill. Charge Vel. Energy Pmax Pmuz Prop.Burnt B_Time
% % Grains fps ft.lbs psi psi % ms

-20.0 86 49.60 1973 2473 27145 6424 91.6 1.700
-18.0 88 50.84 2028 2612 29182 6633 93.0 1.643
-16.0 90 52.08 2083 2755 31375 6829 94.3 1.588
-14.0 92 53.32 2138 2902 33736 7013 95.5 1.535
-12.0 94 54.56 2192 3052 36281 7183 96.5 1.484
-10.0 96 55.80 2247 3206 39024 7338 97.4 1.435
-08.0 98 57.04 2301 3363 41991 7478 98.2 1.389
-06.0 101 58.28 2355 3522 45199 7600 98.8 1.343
-04.0 103 59.52 2409 3685 48673 7705 99.3 1.300 ! Near Maximum !
-02.0 105 60.76 2462 3851 52444 7792 99.7 1.259 ! Near Maximum !
+00.0 107 62.00 2516 4019 56544 7859 99.9 1.219 !DANGEROUS LOAD-DO NOT USE!
+02.0 109 63.24 2568 4189 61009 7907 100.0 1.180 !DANGEROUS LOAD-DO NOT USE!
+04.0 111 64.48 2621 4361 65883 7940 100.0 1.143 !DANGEROUS LOAD-DO NOT USE!
+06.0 113 65.72 2673 4536 71215 7970 100.0 1.108 !DANGEROUS LOAD-DO NOT USE!
+08.0 116 66.96 2724 4713 77065 7996 100.0 1.073 !DANGEROUS LOAD-DO NOT USE!
+10.0 118 68.20 2776 4892 83503 8018 100.0 1.040 !DANGEROUS LOAD-DO NOT USE!

Results caused by ± 10% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 10% relative to nominal value:
+Ba 107 62.00 2627 4383 69301 7440 100.0 1.127 !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba 107 62.00 2346 3496 45455 7915 95.4 1.343

 

[bowji john]

Yup - that is what mine showed

Of course I wasn’t using 62 gn

It was a 58 gn load

 

[Selous]

Yup - that is what mine showed

Of course I wasn’t using 62 gn

It was a 58 gn load

Sorry...my bad

 

[bowji john]

Sorry...my bad

62 would have been “interesting” though

 

[zambezi]

Is the H2O volume correct?

 

[bowji john]

Is the H2O volume correct?



View attachment 233148

View attachment 233146

I think so

That is ''useable capacity'' after the bullet is seated

 

[Eddie P]

RL17 has odd internal ballistics due to the flame retarder. It is designed to flatten the pressure curve.



























































My understanding is that QL strghles

 

[Neddle]

I noted that your case capacity was a bit low - yours is set at 60 when mine is set at 74.5 H2O

I shall recheck that with this latest fire formed case

Rechecked - 75 grains H2)

All irrelevant if the correct oal is not used, substitution of bullets even if the same weight screws the whole calculation up as the bullet length is different, equates to different seating depths, so different pressures