I am pretty new to the casting for handgun scene. Have used cast successfully in several rifles. I recently acquired a M&P 2.0 chambered in 10mm. I cast some bullets from the Lee 175 TC mold, and powder coated them with Smokes clear. Sized to .4015. Loaded some up with Unique and was getting around 1100 fps which is great for simple practice. The problem I am having is they will not all chamber correctly. When the slide comes forward , there is a slight overhang in the back indicating the slide is not fully forward. Sometimes I can just push it forward, sometimes I need to pull back and release the slide. Yes, all these passes the test where I dropped them into the barrel, they all seemed to drop in just fine. For comparison the factory ammo I shot functioned perfectly.
So I dod a bit of comparison between my loads and factory, and found 2 main differences. First, when measuring the case right behind the bullet, my hand loads measure .422, factory is .419. I tried getting mine down further, but I am already applying a pretty good crimp. Crimp is being applied with the Hornady taper crimp a separate step from bullet seating.
The 2nd main difference I can tell is factory ammo has a COAL of 1.250. Originally mine were 1.260, loaded a few more at 1.255. I had fewer failures with the 1.255 than the 1.26. I am a bit hesitant to go all the way to 1.25 because according to manuals, that can drastically increase pressures.
The other thing that I thought may be causing this is I was not trimming my cases. I measured some, and they were all within.008 of each other. The brass came from a friend of mine, he picked it up at a range for me. Headstamp is mixed.
So with what I described, where should I start? I should also note that my powder coating process adds about .0025-.003 thickness. Is there a chance the nose of the bullet is too large?
I am tempted to increase seating depth to 1.250, back off a bit on the powder charge, and see what happens.
As an aside, the primers are a bit proud of the base of the brass, so measuring the COAL can be a bit challenging.