I have a newish BCM that has just started denting brass and I don’t know what is causing the denting. I’m too computer illiterate to post an mage, so I’ll try a word picture: The dent is a small(1/8 inch) triangle shape, with the base of the triangle right where the brass begins to angle in to form the shoulder. The base is almost exactly 1/8 inch long. The side extend down (towards the primer end) for about 1/8 inch, so you have roughly an upside down equilateral triangle.
On another case, the base of the triangle is about an 1/8 inch below the beginning of the shoulder and the triangle extends downward more, so it is not an equilateral triangle.
These are reloads that I’ve shot out of another AR with no dinged brass. I’ve shot a few rounds of this same load of this gun before and I don’t recall seeing these marks before. The gun runs fine; no jams.
I’m not particularly worried, but I’m hoping y’all can educate me on this curiosity.
Likely the brass hitting your shell deflector. If it really bugs you stick a piece of velcro tape over it (the deflector) to cushion the impact and move on.
I think you are 100% correct. I’m still a bit puzzled why only two rounds out of that batch were dinged at that location and those two rounds were the last two round fired. But, I’m not going to loose any sleep over it. Thanks.
Most likely shell deflector, Velcro tape should be a standard for shell deflectors, but I find it mostly dents necks. You didn’t supply a picture but one thing I have seen is the media in imperial dry neck lube gets stuck in the case lube along the shoulder when you dip the neck and when run through a sizing die it dents the shoulder. A kernel of powder will do the same thing.
