Because the CMMG 9mm carbine mimic the .223 version almost completely, the shooter loses very little when switch to the pistol caliber over rifle for training scenarios. Comparing apple to apples, 9mm FMJ ammo costs about half that of .223 FMJ ammo. Twice as much trigger time, for half the cost, is a pretty good exchange in my book.
As a bonus for the readers, I took the controlled expansion ammunition from both calibers and tested them against barrier material backed up by ballistic test medium. Up first would be an interior wall façade. This barrier was built using two layers of half-inch sheet rock and a single layer of quarter-inch plywood. This would represent a standard interior wall construction, minus 2x4 studs. An additional portion of the “wall” would include two 2x4 boards combined with the original sheet rock and plywood construction.
Capturing the fired bullets would be accomplished through the construction of a bullet trap of sorts. This contraption was more of a rectangular trough made of wood with an open top. Into the bullet box I place thick squares of waxy ballistic media. This set up actually worked out better than I anticipated and will be repeated in future tests.
Loading all the guns, ammo, and target material up in the truck we drove to the range on a very pleasant afternoon. First up would be the 9mm carbine. Placing the wall board material in front of the bullet trap I took aim. From a distance of seven yards I fired a single round of the Winchester ammunition. The bullet passed completely through and entered the waxy media.
Step two was to fire the .223 cartridge from Hornady. Same scenario, shot through the wall board into the wax media at seven yards. On the outside of the wall board was an unimpressive .22 caliber hole. However, on the other side the results were a bit more spectacular. The projectile did its job very well and expanded violently. A hole nearly three inches across and as deep was left in the wax media.
Next on the agenda was to fire both carbines into the 2x4 and wall board material. This would represent nearly six inches of common building material found inside normal interior walls. Both the 9mm and .223 Remington rounds passed completely through.
Taking a moment to closely examine the bullet box, I pried apart the layers of wax media and found that the .223 TAP round had penetrated just shy of 8 inches. At that depth I discovered several bullet fragments. The projectile had come apart completely.
Moving on we found that the 9mm projectile had traveled a full 15 inches into the wax media after passing through the wall façade. It had not deformed and looked almost good enough to be reloaded. So much for the .223 will over-penetrate theory.