Punching Holes Gently

I loaded up some soft shooting 40S&W ammo to take to Winchester last Thursday. In the past, I have loaded a lot of 165 gr RNFP rounds and got very comfortable with them. 4.5 gr of TiteGroup send those at about 960 fps (per chrono stage at a major match) for power factor of 158. That round worked really well. Hotter than necessary, perhaps, but as I say, I had gotten pretty comfortable with them. I never did chrono the 155 gr RNFP with the same charge, but those are probably a little faster, still in the 160 or so range in power factor.

I decided that since I espouse custom ammunition as one of the two main reasons to handload (economy being the other) that I could probably do better.

The rule of thumb is that, for a given power factor, heavier bullets at lower velocities will recoil with less energy. The math works because power factor is a simple momentum calculation of mass time velocity whereas energy involves the square of the velocity. So, the next heavier common 10mm bullet is 180 gr. To make minimum power factor of 125, the 180 gr needs only run at a pretty pokey 695 fps, as opposed to 758 fps for a 165 gr bullet. I consulted various load data sources and found a few loads with fast powders that showed 180 gr bullets at 750-ish fps and I decided to try 4.4 grains of Power Pistol. The slightly longer 180 gr bullet was seated a little bit deeper in the case, but as the profile/ogive is the same as the 165 gr, I used the same OAL of 1.125" and all rounds gauged properly in my EGW case gauge.

There is, however, a caveat.

Using the math referred to above, my 165 gr bullets at 962 fps works out to 339 foot-pounds of muzzle energy and by inescapable physical law, 339 foot-pounds of recoil, though a goodly portion of that is used to operate the pistol. My 180 gr bullets at an estimated 750 fps works out to 225 foot-pounds, 34% less energy. That, it turns out, is enough reduction to make the pistol cycle less reliably.

The round was an absolute joy to shoot. Reacquiring the front sight was fast. Power Pistol is a bit flashy and boomy (and I have in fact some pretty smokin' hot, bright and loud loads using Power Pistol) but in this charge, it was a nice report and very light recoil. It won't be confused with a 22, but very gentle. On the other hand, I had several jams that centered around incomplete extraction and ejection. I was initially disappointed, fearing I had a dimensional issue, but as I paid closer attention to the jams and noticed that it was empty brass gumming up the works, I realized that my pistol just has too much recoil spring for these far-lighter-than-factory loads.

This is a Glock 20 with a Lone Wolf 40S&W conversion barrel but the stock recoil spring designed for 10mm Auto. It kind of surprised me to learn that the stock recoil spring for the Glock 20 is the same 17 pound rating as the stock spring on almost all other models. Then I realized that what is different for the Glock 20 (and 21) is the larger, heavier slide. The combination of the heavier slide and the 17 pound spring is what helps the pistol cope with the 575 to 800 foot pounds of recoil energy of full power 10mm ammo. Compared to that, its no surprise that my 225 foot pounds, a paltry 60% less energy, might have trouble operating the pistol reliably.

I ordered a 13 pound spring on Friday. Tracking said it woudl be here by Friday, but it arrived today! Bonus!