ONE OF THESE THINGS IS NOT LIKE THE OTHER
MIM (or even traditional casting, which I think would be quite rare for this part) isn’t a bad process by nature, but it’s really not appropriate for an application like an extractor. In use, extractor claws are constantly changing tension as they step over the rims of casings when chambering a fresh round and flinging the spent ones. Like casting, MIM parts have an ambiguous substructure. While they have less risk of porosity, this still tends to lead to a more brittle part, which is quite the opposite of the desired material property.
While this example has a mold or lot number (T11), that is not the tell-tale sign of a MIM part. Rather, there are a few small details of which to take note. In the second picture on the extractor on the right, you can see small defects that remain from the injection site. Also note the lack of tool marks in the pocket for the extractor spring. While there may be final machining or honing done to a MIM part, open details like that pocket are quite easy to work into a mold.
In this first picture, you can see another piece of evidence when comparing the MIM claw (left) to the billet claw (right). On the MIM claw, there is a stark straight line at the peak dimension. Since it isn’t an interfacing surface, the line left from the mold isn’t planed away. On the right claw, you can see a light tool mark that follows the curvature of the surface, which is much different in appearance than the mold marking.
In this second picture, you can see light tool marks in the channel of the billet claw (right) compared to the essentially featureless face on the MIM claw (left). The tool marks are much more pronounced in the picture than they appear to be in-person, but that is a typical place to find such marks by the nature of the cut.
In the last 3 pictures, you can see similar comparisons between a billet extractor (right) and cold-drawn one (left). Looking past the difference in oil coating, you can see similar tool marking in the extractor spring pocket and rim channel. These two are more difficult to distinguish, but the most important detail is the lack of mold markings as you see on the MIM extractor. By nature of their production process, both of these will last many more cycles than a MIM part, which will develop small fissures and snap much sooner, especially when using a higher-power spring like the Sprinco XP-5 found in our BCGs.
If you have a MIM extractor in your bolt, it may help you sleep better at night to order up one of the others. If it doesn’t bug you, keep ‘er movin’ I suppose!