25 WSSM load dev question

[NapalmCheese]

I know a couple of people in here load for WSSMs, maybe not the 25 specifically, but WSSM nonetheless.

I was doing a work up yesterday on a 22 inch pencil barrel factory model 70 and had some questions. Are bolt lift, sooty case necks, and velocity going to be the only pressure signs I see?

• 120 Speer Hot Cor (flat base spitter soft point)
• Fed 210 primer
• Twice fired Winchester Nickel plated brass
• Win 760 powder
• 43-45 grains in half grain increments

I limited it to 3 rounds for each step and took my time shooting, but didn't let the barrel go completely cold between groups. I'm shooting over a Chrony and it was variously overcast, so take that for what it's worth (I.e. not the best chronograph out there). Also I put these together back when I only had a terrible digital scale, so I'm sure charge weights aren't exactly the same in any group.

Avg velocities were:

1. 43.5 - 2863
2. 44.0 - 2982
3. 44.5 - 2942
4. 45.0 - 3005

When I started with a cold bore at 43.5 I noticed the bolt lift was somewhat heavy, I honestly don't remember if it's like that with factory ammo or not. What I do know is that the factory Winchester 120 grain load has an average velocity of 2817 FPS from this rifle (with and advertised velocity of 2990, from a 24 inch barrel I'd guess).

I was getting plenty of soot back over the shoulder until 44.5 grains. At that point it was just sooting up the case neck as I've seen from factory ammo. Bolt lift stayed consistent from the 43.5 charge to the 45.0 charge. Primers are flat, but that's typical for factory ammo too. The brass doesn't show any other signs of over pressure from what I can tell. I don't have a mic to measure caseheads, but if I use my calipers both once fired factory rounds and my reloads measure .5530; without a mic however I don't think that's a meaningful measurement.

I've seen velocities dip as charge increases, I've always taken that to mean I'm at the practical limit for powder efficiency and pressure. Or maybe it's my chrono that sucks.

[ar15barrels]

24" is the SAAMi standard velocity test length for 25wssm.
If you don't trust your chronograph, borrow a couple more and stack them in front of each other so you get 2-3 sets of velocities.
If two are matching or very close assuming the loss over a few feet, then the outlier is the one not to trust.

Cartridge          : .25 WSSM
Bullet             : .257, 120, Speer SP 1411
Useable Case Capaci: 47.742 grain H2O = 3.100 cm³
Cartridge O.A.L. L6: 2.250 inch = 57.15 mm
Barrel Length      : 22.0 inch = 558.8 mm
Powder             : Winchester 760

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.568% 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

-05.7   89    41.50   2776    2053   49669  10989     97.1    1.207
-05.1   90    41.75   2792    2077   50578  11049     97.3    1.197
-04.5   90    42.00   2809    2102   51504  11109     97.4    1.187
-04.0   91    42.25   2825    2127   52446  11167     97.6    1.177
-03.4   91    42.50   2842    2152   53406  11224     97.8    1.168
-02.8   92    42.75   2858    2177   54384  11279     98.0    1.158  ! Near Maximum !
-02.3   92    43.00   2875    2202   55380  11334     98.2    1.148  ! Near Maximum !
-01.7   93    43.25   2891    2227   56394  11386     98.3    1.139  ! Near Maximum !
-01.1   93    43.50   2908    2253   57427  11438     98.5    1.129  ! Near Maximum !
-00.6   94    43.75   2924    2278   58479  11488     98.6    1.120  ! Near Maximum !
+00.0   95    44.00   2940    2304   59551  11537     98.8    1.111  ! Near Maximum !
+00.6   95    44.25   2957    2329   60643  11584     98.9    1.102  ! Near Maximum !
+01.1   96    44.50   2973    2355   61756  11630     99.0    1.093  ! Near Maximum !
+01.7   96    44.75   2989    2381   62889  11674     99.1    1.084  ! Near Maximum !
+02.3   97    45.00   3006    2407   64044  11717     99.2    1.075  !DANGEROUS LOAD-DO NOT USE!
+02.8   97    45.25   3022    2433   65221  11758     99.3    1.066  !DANGEROUS LOAD-DO NOT USE!

Results caused by ± 3% powder lot-to-lot burning rate variation using nominal charge
Data for burning rate increased by 3% relative to nominal value:
+Ba     95    44.00   2985    2374   63023  11495     99.5    1.084  ! Near Maximum !
Data for burning rate decreased by 3% relative to nominal value:
-Ba     95    44.00   2891    2228   56111  11522     97.6    1.140  ! Near Maximum !

[NapalmCheese]

I'm an idiot, the Model 70 is cock on open, I wasn't experiencing sticky bolt lift; I was just cocking the gun... I've been shooting my AR so much lately I forgot that was a thing, d'oh.

Thanks for the quick load info.

That being said the the 45 grain load was the best shooter of the bunch, 44 had the best STDEV but a crap group and I was still getting soot all the way back over the shoulder. I don't mind working at max charges but would just as soon not if I don't have too. Though I know the WSSMs need to be near max to work well, and I know quickload isn't definitive but it's a good approximation (lot to lot variance, chamber variance, etc.) of course it seems pretty spot on with the data I collected yesterday. I had these loaded out long, so some seating depth work is in order I think.

It would be nice to have an inexpensive and non intrusive method for accurately measuring chamber pressure. You'd think with technological advances we'd have a big cheap ADC and a strain gauge set up readily available for reloaders. I thought I saw one somewhere, but then again internal ballistics happens fast and fast accurate measurements are rarely cheap.

Thanks!