Work has introduced me to using AI and I often use to check my work and also to revise emails to make then sound more professional and organized. I encourage people to play with and see if it is of use.
Some of you have read the thread about resizing RMC hulls. I took "resizing RMC brass shotgun hulls" and dumped into Microsoft Copilot and here is the answer:
Resizing RMC all‑brass shotgun hulls is a very different process from resizing modern plastic hulls, and it catches a lot of people off‑guard. These hulls are essentially turned brass cases, closer to rifle brass than to traditional drawn‑brass shotshells like old Winchester or current Magtech.
Here’s the full, practical rundown so you know exactly what works—and what doesn’t.
🧭 First: What RMC hulls actually are
RMC (Rocky Mountain Cartridge) hulls are:
Machined from solid bar stock, not drawn
Thicker and stronger than Magtech or old balloon‑head brass
Sized to match chamber dimensions, not SAAMI brass dimensions
Designed to be fire‑formed to your gun, then loaded with minimal resizing
This last point is the key: RMC hulls are not meant to be fully resized every cycle.
🔧 Do you need to resize them?
Usually no—or only minimally.
RMC’s own guidance has always been:
Fire‑form the hull in your shotgun
After that, only resize the mouth if necessary
Do not attempt to full‑length resize unless absolutely required
Why?
Because the hull walls are thick, and full‑length resizing requires enormous force. Standard shotshell dies simply cannot do it.
🛠 If you do need to resize, here are the working methods
1. RMC’s proprietary resizing die (best option)
RMC used to sell a dedicated resizing die that:
Works in a standard reloading press
Resizes only the upper portion of the hull
Is designed specifically for their brass dimensions
If you have one, use it. If not, they are hard to find but occasionally appear on forums or auction sites.
2. A custom full‑length resizing die (rare, expensive)
A few machinists have made:
Full‑length resizing dies
Push‑through dies
Hydraulic dies
These work, but:
They require a heavy press (Rock Chucker or larger)
They require case lube
They are slow and labor‑intensive
Most shooters never bother.
3. Partial resizing using a steel sizing ring
Some people use:
A steel ring sized to the chamber
A press or arbor press to push the hull through
This only works if the hull expanded slightly. If it expanded a lot, you’ll never get it through without damaging it.
4. Annealing the mouth only
If the mouth is slightly out‑of‑round:
Light annealing
Then use a tapered mandrel or expander plug
This is the most common “resizing” done on RMC hulls.
❌ What doesn’t work
Standard shotshell resizing dies (MEC, Lee, RCBS shotshell dies)
They are made for thin drawn brass or plastic bases. RMC brass is far too thick.
Magtech brass dies
Magtech brass is balloon‑head and much thinner. Completely different dimensions.
Hammer‑type Lee Loader tools
You will damage the hull.
📏 Why resizing is rarely needed
RMC hulls:
Don’t expand much
Are extremely strong
Are designed to be used in one specific gun
If you keep them dedicated to that gun, you may never need to resize them at all.
If you switch guns, you might need to resize—but often the new chamber is close enough that they still fit.
🧩 The practical advice most experienced loaders follow
Fire‑form once
Load and shoot
Only fix the mouth
Avoid full‑length resizing unless absolutely necessary
Most people who try full‑length resizing eventually stop doing it because it’s too much work for too little benefit.
