An issue we hear...
I purchased a new Tromix case gauge to double check my ammo before using it in my new rifle. I notice some of it is hanging up and the projectile appears to be marked up in front of the case mouth. I’ve cleaned the case gauge with a 20 gauge brass bore brush and contact cleaner (brake cleaner) but the rounds are still hanging up. Is this ammunition out of spec?
This issue you are experiencing is due to a reamer change at Tromix in late summer and early fall of 2016. This new reamer was incorrect and not to the specs requested by Tromix. The chamber on the new barrels and case gauges has a tighter throat which pinches into rounds with a square “OG”. The issue is that the projectile is bumping the rifling throat entrance. If you have a rifle made by CMMG, SBR, Rock River, Wilson Combat, Radical or any other manufacturer your head space will have a longer throat which will accept this round with no issues. Tromix is aware of this issue and soon as it was discovered they started working to correct the problem. In the event you have a Tromix rifle or case gauge purchased in the late summer to early fall of 2016, and are having spacing issues, they will happy to inspect the barrel or gauge and re-ream the chamber to correct this tightness if this is the problem. This only affected a handful of rifles and case gauges. We highly recommend Tromix rifles and they are one of the premier .458 SOCOM rifle builders.
As I side note, this typically only affects the Plated Round Shoulder Rounds made to a length of 2.00 OAL or greater and or other square OG rounds typically seen in subsonic applications.