30-378 Wea -Substitute 180 gr Scirroco for 180 gr Interbond

[Jimbeaux82]

While I know the standard answer to any change of components is "Start low and work up", I have a maximum pressure load for a 30-378 Wea that I worked up using Retumbo and 180 gr Hornady Interbond bullets. I would like to keep the same load with a substitution of 180 gr Scirroco in place of the Interbond. Since both are similar profile (possibly some difference in bearing surface), similar construction (bonded) , has anyone done this and do you forsee any problems?

Another question - does anyone have a Swift reloading manual and what charge does it list as maximum for 30-378 with 180 gr Scirroco and Retumbo?

QL request?

 

[JD338]

Jim,

I would drop a few grains just to be safe. You can always load up one proof shell at each charge weight and work up to your normal load, saving both time and precious components.

JD338

 

[DrMike]

Though I've loaded for several 30-378s, I've not worked with the particular cartridge/bullet combination. My experience with the Scirocco would lead me to be somewhat cautious in that the bearing surface on the Scirocco is likely longer which introduces a significant difference. The Swift Manual does not list Retumbo as a powder; it lists H1000 (107 grains maximum) and H4831 (101 grains maximum).

Cartridge          : .30-378 Weath. Mag.
Bullet             : .308, 180, Swift Scirocco
Useable Case Capaci: 120.273 grain H2O = 7.809 cm³
Cartridge O.A.L. L6: 3.655 inch = 92.84 mm
Barrel Length      : 24.0 inch = 609.6 mm
Powder             : Hodgdon Retumbo

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   79    88.00   2576    2653   31710  13989     96.7    1.630
-18.0   81    90.20   2643    2793   33933  14377     97.8    1.591
-16.0   83    92.40   2710    2936   36318  14727     98.6    1.552
-14.0   85    94.60   2777    3082   38878  15038     99.3    1.515
-12.0   87    96.80   2843    3231   41626  15305     99.7    1.469
-10.0   89    99.00   2909    3382   44579  15527    100.0    1.422
-08.0   91   101.20   2974    3535   47753  15704    100.0    1.376
-06.0   93   103.40   3038    3689   51168  15870    100.0    1.333
-04.0   95   105.60   3101    3844   54818  16031    100.0    1.291  ! Near Maximum !
-02.0   97   107.80   3164    4000   58694  16188    100.0    1.250  ! Near Maximum !
+00.0   99   110.00   3225    4158   62829  16341    100.0    1.212  ! Near Maximum !
+02.0  101   112.20   3287    4318   67244  16489    100.0    1.174  !DANGEROUS LOAD-DO NOT USE!
+04.0  103   114.40   3347    4478   71960  16632    100.0    1.139  !DANGEROUS LOAD-DO NOT USE!
+06.0  105   116.60   3408    4641   77002  16769    100.0    1.104  !DANGEROUS LOAD-DO NOT USE!
+08.0  107   118.80   3467    4806   82397  16902    100.0    1.071  !DANGEROUS LOAD-DO NOT USE!
+10.0  109   121.00   3527    4972   88175  17029    100.0    1.039  !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     99   110.00   3352    4490   76778  15832    100.0    1.112  !DANGEROUS LOAD-DO NOT USE!
Data for burning rate decreased by 10% relative to nominal value:
-Ba     99   110.00   3032    3675   49339  16968     99.5    1.345

 

[FOTIS]

Remember Q/L is NOT setup to take freebore into consideration.

 

[Jimbeaux82]

Remember Q/L is NOT setup to take freebore into consideration

So that means with a Weatherby Factory chamber I should have a little less pressure than QL Indicates?

 

[FOTIS]

or same pressure and about 200 fps more----pending on rifle

 

[Jimbeaux82]

That is basically what I am seeing. Hodgdon's manual shows 113.0 gr Retumbo as maximum charge with a 180 gr Speer BTSP, listed at 3350 fps. Before I began loading, I disassembled a Superior Ammo 30-378 load with a 180 gr Scirroco and it contained 116.0 grs of ball powder, and chrono'd 3425 fps. So I worked up a load using 180 gr Interbonds using 112.0 gr Retumbo and it clocked 3475 psi. Using this load, I got loose primers after 3 loads.

So my current plan is to drop 2 grains down to 110.0 gr Retumbo and substitute a 180 gr Scirroco. Should put me pretty close to 3400 fps, where I want to be.

Any other advice?

Thanks

Jimbeaux

 

[SJB358]

My experience with the Scirocco is it is a stickier bullet than others, even is shaped similarly. Great bullet, but working up a little lower wouldn't hurt anything either.

 

[gr8hntr]

106.5 gn of retumbo in my weatherby mark v 30-378 with 180 nosler BT gives me a stiff bolt