Question on Working up a Load

[spencerhut]

This is a load for my 38 Super SA MIL-SPEC.
I loaded some Speer 124g TMJ bullets in Starline Super Comp Brass with from 6.8g to 7.2g of Power Pistol in .1g increments. All had CCI #500 Small Pistol primers.
6.8g = 1242
6.9g = 1255
7.0g = 1275
7.1g = 1291
7.2g = 1290
7.2g = 1281 w/Fed 100 Sm Pis Primer

Can anyone explain the drop in velocity from 7.1g to 7.2g? Not a hot enough primer? Is this why I hear about the IPSC folks using small rifle primers? The CCI primer showed no signs of flattening out. Of course the Federals did. Any advice/wisdom would be welcome.

Spencer

 

[B36]

What powder??

 

[spencerhut]

Doh! Power Pistol.

 

[LHB1]

Spencer,
My guess would be just natural velocity variation between loaded rounds, especially since the two groups are separated by only .1 gr of powder. (Assuming your powder charge was accurate.)

Good shooting and be safe.
LB

 

[spencerhut]

I measued the charges individually with my Lyman 1200 Digital Powder Scale. Hopefully they were dead on. Does that mean you think the CCI #500 should be able to light off all 7.2g of Power Pistol in my load?

Spencer

 

[WayneConrad]

Cool data! Did you fire one shot at each powder weight, or more than one and average them?

If only one shot per weight, you might be seeing statistical variation, as mentioned. Even though you measured each charge, your scale can only measure so precisely, your bullets are only so-much the same, your neck tension only so much the same, etc.

To really tell you need more than one shot of each load. 10 would be nice. 20 would be even better, as that'd be enough to calculate a useful standard deviation.

Velocity is not linear with powder charge, either. It flattens off. Perhaps you hit that part of the curve where adding more powder gets you more pressure but not much more velocity. That plus statistical variation is one way to explain the numbers you got.

 

[LHB1]

It's been a long time since I loaded .38 size cases and used CCI primers but would think the primer should handle 7-8 gr of powder. Perhaps someone else is using that CCI primer and can answer with more certainty from their current experience. You could try some CCI #550 Mag primers and see what difference it makes in your gun/load. Good luck.

Good shooting and be safe.
LB

 

[JackOfAllTradesMasterAtNone]

I've never actually loaded for .38 super. But if I were answering the same for .38spl or .357mag or .44spl or .44mag, ... Well, I'd have copied what WayneConrad wrote.

-Steve

 

[spencerhut]

I shot (5) of each. All were loaded w/Lee dies and crimped with a Lee FCD. Loading was done on my RCBS Pro2000 in semi-progressive (skipped the powder charge step) mode. Each bullet was weighed and all were within +or- .1g of each other. All cases were brand new.
Am I to understand there is a charge level (7g-8g) at which the CCI #500 primers will no longer effectively light off the charge?

Thanks,

Spencer