by Hoot » Thu Jan 24, 2019 6:05 pm
Using QuickLoad, I modeled a 1.71" case with an estimated fired case capacity of 35gr H2O. Pushing a 140gr Barnes XPB ahead of 26gr H110 at 2.20 COL, it yielded a predicted MV of 2377fps from a 20" barrel. All my AR's have a minimum barrel length of 20", so I used that. Obviously, shorter barrels = lower speeds. This caliber model has not been justified against actual field results. In practice (see sig), it could prefer a different powder and/or produce different speeds. I used a max chamber pressure of 44962 psi, per the CIP spec for a 357 Maximum. In this model, the 26gr H110 represents a charge of 95% capacity and burns at 97.8% by the time the bullet exits a 20" barrel. That burn rate is in the vicinity if ideal for a straight wall case from my experience. All else being equal, the same charge of Lil Gun burns all the powder in a 16" barrel for the same resultant velocity but at a chamber pressure that's slightly higher than the H110.
All these variables serve to demonstrate that we just don't know until some field reports start coming in.
Hoot
In Theory, there is no difference between theory and practice. In Practice, there is.