Expanding Mandrels
Perfect neck tension and a precisely rounded case neck are the basis for exceptional reloading precision. Expanding mandrels are specialized tools that ensure that the neck of your brass becomes perfectly round, regardless of the shell's previous history. At Hop.nl, we offer carefully selected expanding mandrels from leading brands such as L.E. Wilson and K&M Precision, designed specifically for reloaders who strive for optimal neck tension and therefore superior accuracy in their ammunition.
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What an expanding mandrel does
After sizing, your case neck is not always perfectly round. Especially after full length sizing. The neck can be slightly oval, and that ovality causes uneven tension around your projectile. At short range you might not notice. At 600 metres and beyond you will. An expanding mandrel pushes the neck open from the inside to an exact diameter, making it perfectly round again. At the same time, the size of your mandrel determines exactly how much neck tension you end up with after seating your projectile.
Why neck tension matters
Too tight and your pressure build up becomes unpredictable. Too loose and your projectile does not stay put, which creates risks during handling and loading. The sweet spot is somewhere in between, and it differs for every combination of brass, projectile and calibre. By trying mandrels in different sizes you can find out what works best for your specific setup. A difference in neck tension of a few thousandths of an inch can show up in your ES and SD.
K&M Precision mandrels
K&M Precision has been making tools for serious reloaders for years. Their mandrel system consists of a mandrel holder that fits in your press, with interchangeable mandrels. The bullet tension mandrels are for setting your neck tension, and the neck turning mandrels provide support during neck turning. Everything fits the same holder.
L.E. Wilson mandrels
L.E. Wilson offers their mandrels as a complete system including holder, or as a standalone mandrel if you already have a holder. Wilson mandrels are available in 0.001 inch increments, so you can dial in very precisely.
Sinclair die bodies and mandrels
From Sinclair we stock the Gen II Expander Die Body in stainless steel, compatible with calibres from .17 to .338. Combined with their TiN coated mandrels you get a system that runs smoothly and lasts a long time. The titanium nitride coating reduces friction, so the mandrel glides through the neck more easily and you are less likely to pull the neck.
How to use a mandrel
Lightly lubricate your mandrel with a thin layer of Imperial Die Wax or another case lube. Place the mandrel in the holder, mount it in your press and pull the case over it. The mandrel pushes the neck open to its own diameter. After that you size the neck to your desired dimension with your sizing die, or you leave it as is if the mandrel gives you the exact size you want.
The order you follow depends on your method. Some reloaders size first and expand after. Others expand as the last step. Experiment to see what produces the best results for your brass and calibre.
Not sure which size you need?
The right mandrel size depends on your bore diameter, your projectile diameter and how much neck tension you want. Sounds complicated, but it comes down to a few thousandths difference. Get in touch with your calibre and projectile details and we will help you pick the right size.