In another thread it was suggested to use both full length bushing dies, and a mandrel. Can someone explain the reason for needing both? I haven't been able to fully wrap my mind around the idea of needing a mandrel because I thought the reason for using a bushing die was to get exact neck tension.
top of page
bottom of page
I believe Sinclair does have one. But they do bot have to match. It’s ok if you use a bushing to go mildly past it. .001 smaller than a mandrel is certainly mild, and won’t work the brass that much. The brass will spring back some, as well. So if you use a mandrel .001” smaller than bullet diameter, it’ll end up around .0015-.002 depending if it’s annealed brass or not.
So I'll use 6.5mm as an example here... I see that the Sinclair expander mandrel for 6.5mm is .263 (which would make -.001 neck tension). Do they make one that is .262 instead? If I get a bushing size to get -.002 neck tension, wouldn't I want a mandrel size to match?
Unless it’s a custom non bushing die, a traditional non bushing die will size the neck down smaller than necessary. A bushing die allows you to size the neck down just enough for gripping the bullet for your desired neck tension. Usually the bushing will be about .002-.003” neck tension. You will still want to run a mandrel to make sure the inside diameter is perfectly concentric, since that will be the part in direct contact with the bullet. The mandrel will usually be .001-.002” under bullet diameter to set final neck tension. The less you work the brass, will typically yield longer brass life, which is an added plus. A standard non bushing die coupled with the typical elliptical expander in the sizing die stretches and works the brass way more than necessary making it more brittle and less consistent bullet release. Hope this helps. Tried to just hit the main points 👍