reloading software question

[mseric]

 Cartridge          : 6.5 mm Grendel
Bullet             : .264, 107, Sierra HPBT MatchK 1715
Cartridge O.A.L. L6: 2.260 inch or 57.40 mm
Barrel Length      : 24.0 inch or 609.6 mm
Powder             : Hodgdon H335

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   76    23.12   2248    1201   28599   5044     92.1    1.495
-18.0   78    23.70   2301    1258   30488   5190     93.2    1.455
-16.0   80    24.28   2354    1317   32503   5330     94.2    1.416
-14.0   82    24.85   2407    1376   34659   5465     95.1    1.379
-12.0   84    25.43   2460    1437   36961   5593     95.9    1.342
-10.0   86    26.01   2512    1500   39424   5714     96.7    1.305
-08.0   88    26.59   2565    1563   42062   5828     97.4    1.268
-06.0   90    27.17   2617    1627   44887   5934     98.0    1.233  ! Near Maximum !
-04.0   92    27.74   2669    1693   47917   6032     98.5    1.199  ! Near Maximum !
-02.0   94    28.32   2721    1759   51170   6121     99.0    1.166  ! Near Maximum !
+00.0   96    28.90   2773    1826   54665   6201     99.3    1.134  !DANGEROUS LOAD-DO NOT USE!
+02.0   98    29.48   2824    1895   58404   6271     99.6    1.104  !DANGEROUS LOAD-DO NOT USE!
+04.0   99    30.06   2875    1964   62405   6332     99.8    1.074  !DANGEROUS LOAD-DO NOT USE!
+06.0  101    30.63   2926    2034   66708   6382    100.0    1.046  !DANGEROUS LOAD-DO NOT USE!
+08.0  103    31.21   2976    2104   71342   6421    100.0    1.018  !DANGEROUS LOAD-DO NOT USE!
+10.0  105    31.79   3026    2176   76343   6454    100.0    0.992  !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     96    28.90   2883    1974   65618   5961    100.0    1.059  !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba     96    28.90   2616    1626   44388   6151     94.7    1.234  ! Near Maximum !

[mseric]

Cool ain't it?

[LRRPF52]

That's an interesting mix with the 107 SMK and Vihtavuori N135, one of the faster rifle powders. A lot of the AA load data has info on N140 and the lighter bullets. It's too fast for heavier bullets for sure, especially the 123 Scenar, 120 SMK's, etc.

With the slower-burning powders and extended pressure curve burn parameters, I'm finding that with a gas gun, you need to be careful with how close that pressure curve's downward segment is to the gas port, as you will get violent cycling characteristics. This is at least what I suspect happens, and could feel the difference with significantly-compressed loads of H4831 in my .260 Rem AR10 pushing 139 Scenars. The point is that gas gun reloaders have a whole separate burn rate and pressure curve issue to deal with that bolt guns will never notice.

The military cartridges developed for the AR and other gas guns went through a lot of test & evaluation to optimize powder, bullet, and gas system length parameters for the specific platform they were dealing with, and military M16's/M4's run extremely well as a result, with very high pressure loads that produce fast velocities with 55gr and 62gr projectiles.

[LRRPF52]

Does QL account for barrel length and gas system length? Recall how Bwaites had a great load for his 19.5" Grendel, and then was bulging case bases in his 28" Grendel, which has waaay more dwell time...

[mseric]

Yes, but I'm not sure how to do that yet. There is a guy over at "The Firing Line" UncleNick that speaks of QL, dwell time, etc. quite often. You could swing on over there and find out a hell of a lot more about QL that I can tell you.

Barrel Time 10% Pmax to muzzle.
Tac 29.5gr 1.134ms
135 27.3gr 1.124ms
140 28.6gr 1.184ms
540 30.0gr 1.156ms
BL-C2 32gr 1.092ms
335 28.9gr 1.134ms

[JASmith]

Does QL account for barrel length and gas system length? Recall how Bwaites had a great load for his 19.5" Grendel, and then was bulging case bases in his 28" Grendel, which has waaay more dwell time...

QL can give you the amount of time the bullet spends in the barrel as well as peak pressures at specified locations in the barrel. I don't immediately recall if you can get a pressure-time history at a specified location in the barrel.

You can, however, get an idea of how long the driving pressure will be applied by subtracting the bullet toa at the gas port from the time of bullet exit.

QL shows how the peak pressure at the gas port will change with powder selection. The differences can be dramatic.