SR 4756 Workup with Hornady 180gr HAP

[RDub01]

Hello
Per request I did a work up with 180gr Jacketed bullets and SR 4756.

As is sometimes the case, there is quite a disparity with load data with this powder.  Sierra says 7.4 is max, Lee 2nd and IMR say 7.6, an old Speer manual says 7.7grs and then there is Hornady saying 8.8grs.

In testing some .40 S&W 180gr loads, I found SR4756 following Silhouette and BE-86 very closely, so I wondered if this would be the case in the 10mm. The latest data indicates that these two max out around 8.5grs. with 180gr bullets.

I loaded five rounds of 7.6, 7.9, 8.2, 8.5, and 8.8 grs., using a Hornady 180gr HAP bullet, Winchester LP primers and new Starline brass.
Targets at 25 yards. Velocity data taken with an Oehler model 33 chronograph.  Sky screens centered 10' from muzzle.

Here is a target, some data and a graph showing how SR 4756 did against other powders in its class.  All the other data was taken with the same gun.







This is a little strange.. I would have expected more case expansion and a little more velocity.  Maybe this powder requires more barrel length.  One thing I have taken note of over the years when working with this powder.  It has a tendency to be very temperature sensitive.  In hot weather SR 4756 really spikes pressure and velocity really increases.  In very cold weather however, SR 4756 just quits performing.  This experience was derived with wheel guns. I don't have enough data to say how this powder does in autoloaders. But in any case, I would take this with a grain of salt and be careful with it. 

I wouldn't say SR 4756 is a must have powder for 10mm, but if you have some around this might come in handy.

[The_Shadow]

Very cool data on this one RDub!  If I recall SR powders are single base as compared to others that are double base.  That could explain some of the stability / temperature variations.

People were pushing this SR 4756 powder fairly hard in the revolvers in the day...Glad to see your numbers for the 10mm especially at the upper end.  Thanks for your workup and data...

[RJM52]

4756 "was" one of my favorite powders when I was shooting IPSC and also as a commercial loader making high performance rounds. Never found that it was temperature sensitive at all.

And I say "was" because I only have a pound or so left and it has been discontinued...

Bob