Handloads for 1911 vs M&P 45
I have an unusual issue that, frankly, has me a bit stumped.
A while back, I purchased an RIA 1911 - amazingly my first 1911 after many years of owning firearms. After some initial finicky behavior due to an overly tight extractor, it has behaved very well. I have developed about 8 different loads for this 1911. All are based on either FMJ or plated rounds, and all but one of them is based on Round Nose bullets -- simple, basic ammo. Nothing fancy.
** All of them fire and cycle flawlessly in my 1911 **
Recently, I purchased an M&P45 (full size) with a round count of ~ 800. Great condition - very clean, etc. I took it to the range for the first time yesterday to see how it performed. Some factory ammo, as well as a sampling of my handloads went with me.
Factory ammo (Aguila) chambered, cycled, and shot perfectly from the M&P. Some of my handloads did not. All failures of my handloads had the exact same problem: failure to feed. This included my 1911 "go to" round (230 FMJ RN/5.2 Win231). This was VERY surprising to me. I would expect the M&P to be forgiving and the 1911 to be picky, yet ammo that works flawlessly time after time in my 1911 won't feed in the M&P. I have no idea how some of the recipes shoot from the M&P as I was never able to get a single round to chamber! The range was busy, so I didn't have a lot of time to mess with it, or even take pictures, but after I got home I noted the following:
* The Aguila ammo has a longer OAL (1.262) than any of my handloads (1.240).
* Some of my handloads with shorter OAL (185 grain HB-RN) worked, however.
* The Aguila ammo is undersized slightly. Case diameter at the mouth is 0.466. My handloads are all set to 0.469
* The Aguila ammo *and* ALL the handloads pass the "plunk test" using the barrel as a headspace gauge. They are all headspacing on the case mouth. I had cleaned the barrel prior to running this test.
* My dummy rounds (no powder/primer) that I make when developing a new recipe all fed properly -- even when I was intentionally guiding the slide. This was tested after I disassembled and cleaned the firearm.
* Comparing bullet and shoulder profiles to the Aguila ammo revealed significant overlap, although different OALs, of course. Nothing stood out as an abnormally unusual slope, angle, or profile.
* Two of the recipes were post-sized with the Lee FCD and they happened to work. This may be simple coincidence, as I stupidly forgot to mark whether the other handloads had been post-sized or not. (I'm not trying or wanting to make another darn FCD thread -- I'm merely adding this as a note)
* One batch of reloads was working and shooting exceptionally well. Halfway through the box, they flat-out refused to feed. I don't change process or specs halfway through a run, so this one really boggled me...
* Factory ammo worked every time.
I'm at a bit of a loss and could use some advice/opinion -- especially from fellow M&P owners that also handload. I have a couple of theories, but I'd like to hear other thoughts before I share them.