Have you slugged the barrel?
From the Lyman 44th Edition (1967) which also has load data
Jacketed bullets for this cartridge are available in .320" diameter (Rem.) and .321" diameter (Hornady). As we have encountered barrels as small as .319", we suggest that you slug your barrel before reloading (see "Accuracy with Cast Bullets" in reference section). For tight barrels, the smaller Remington bullet is recommended.
New brass cases which exceed the maximum case length listed may be encountered. We suggest that you check your case length before reloading and trim your case if necessary.
