Wadcutter brass can be distinguished from regular brass by the double crimp, as seen in the nitro-express photo, on the right.
Wadcutter brass has a longer straight untapered inner case wall than the standard case. This allows the deep seated wadcutter bullet to not hit the thicker wall of the case toward the case head. This can cause the loaded case to bulge and the bullet to be damaged. This also gives an even case tension on the entire length of the bullets.
Don't use wadcutter brass for higher pressure loads.
Did a quick check comparing the 38 Spcl wadcutter double cannelure brass walls to a 38 Spcl (+P)'s brass walls:
Using a .350" plug gage (the biggest that would pass by the inside ridges caused by the double cannelures), it would extend ~.725" into the wadcutter double cannelure case but only ~.460" into the (+P) case, a difference of ~.260".
That shows that the wadcutter has straighter walls & the (+P)'s thicker more tapered lower walls.
The wadcutter's walls only start getting thick just below it's lower cannelure while the (+P)'s starts getting thicker higher, where the upper cannelure would be on it, if it had one.
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