Home Forums Hunting & Shooting Handguns Mackay’s 170gr 40S&W +P and the old M&P

Mackay’s +P 40 load is the real deal.
I plan on running this and other heavy loads in my M&P 40 on a regular basis. This is a police trade in and most likely is ready for a recoil spring replacement. For those with a lot more experience with M&P’s what would you recommend for a spring for it?

I have no experience with .40s. That said up front, my own general rule with 1911s is, factory spec +2lbs, is what I generally do with those pistols, when using stout loads. If you can ascertain what Smith uses in their M&P .40s (example 16lb., then I'd use 18lb springs.)

Mackay knows his ammo better than I know .40s, so I'll defer to his expertise, but that's not a bad general rule.

According to the link they ship with 18 but recommend 22.

https://gallowayprecision.com/assembled-guide-rod-for-m-and-p-full-size-pistols

I use 20's in my Glock 40 that ships with 18.

I would recommend, and personally use a 20# Wolff spring in my own.

The ammo was designed to function with a stock weight spring that is fresh. However to reduce frame to slide battery, as well as to shoot faster controlled pairs and recover from recoil quicker, I found the 20# spring to work great. You can go heavier, but I found the 20# Wolff spring worked with all types of ammo from some old cheap FMJ I had on the shelf, to the high performance 170s.

And you may be surprised at how much more accurate this load is compared to regular .40 ammo. This is very much a tack driving load.

As far as accuracy, once I figured out POI was 14” low at 25 yards, I was able to hold at a point high enough that the rounds landed on paper.
Pics would help, but I’m not taking the time right now, so till then I’m going to say accuracy is stellar. 15 shot groups typically were 2-1/2 to 3-1/2” @ 25 yards. That’s with forearms rested on bean bags. Extraordinarily good for my rusty handgun shooting skills. I can’t see well enough to do any better with iron sights. This needs an optics cut on the slide for an RMR or Holosun.
It will be interesting to see how this turns out once the Timney Competition trigger kit and a dot optic are installed.

I shoot NATO ammo through my 9x19 pistol with standard factory spring. I would order recoil assembly from S&W. They list one for .40 S&W (green coded spring) not blue coded spring that vendors claim is for 9x19, .357 Sig,....

Keep at it. It is hard with older eyes. The RDOs have made a world of difference in terms of shooting groups. I cannot even come close to shooting groups like I did in my 20s with iron sights. Those days are gone. But with the RDOs, it is amazing how well you can shoot some guns.