The 135 grain +P is the short barrel load.
I am looking at a 50 round box right now; Speer Gold Dot 38 Special +P 135 GR. GDHP Product code 53921
The 20 round box carries product 23921
If you contact Speer they will confirm it is the same load, only the package is different.
http://le.atk.com/general/speerprodu...ortbarrel.aspx
They don't say Short barrel on the box but it is the same load. The 50 round boxes are mostly geared to Law Enforcement sales.