9mm bullet weight for USPSA

[elpac3]

I just spent two hours at the range last night (Friday) with multiple boxes of 40c ammo, different manufactures, different bullet weights.
All of the 165 gr 40c hit low. Depending on manufacturer, two to three inches low.
At 25'+ the 180 gr hit on line or slightly high (same sight picture)
I was at the range killing time and ammo waiting for my gunsmith to finish the new FO front sights and Apex upgrades to my M&P9.
I've had issues with the 40c before being low and left and my LGS GS knew about the issues so we talked about ammo difference. He stated 40c does not like 165 gr and shoots better at 180 and 200. He said 165 shoots low. Looking at the stack of calibration targets he agreed, shoot 180 gr and we need to push the rear sights right, their off.
Moral of story (do not know why) heavier grain bullets have a higher POI
Now for the physics class for those than can explain ???

Slower bullets are in the barrel for a longer time and hit higher due to recoil raiding the barrel before the bullet exits

 

[fredj338]

Slower bullets are in the barrel for a longer time and hit higher due to recoil raiding the barrel before the bullet exits

Again, bbl time is not the issue, it is recoil. A 200gr 45 vs a 300gr 45, both going 800fps. The 300gr will always shoot higher, identical bbl time.

 

[WR Moore]

About steel target knockdown. If you're talking Pepper Poppers, they're supposed to be calibrated so that a 115 gr. 9mm from a 3 1/2" barrel will take them down. If you're talking plates, doesn't make any difference.

About the 47% using heavy bullets. Don't know where the stat comes from but if some well known hot gun uses any product, many will do so in slavish imitation.

Ah Fred, unless the 200 gr and 300 gr bullets are moving at the same muzzle velocity, the barrel time will not be the same. Faster/lighter pistol bullets will impact lower on the target because they leave the barrel before it raises to the same point as where a slower, heavier bullet does. Recoil does enter into it, but because the handgun is rotating around the grip.

 

[S&WIowegan]

The 47% using 147gr bullets comes from the survey USPSA does at the Nationals, presumably the production match. The next most popular weight is 124-5gr so clearly some people like to have a snappier feel and slide action. I like 147s loaded fairly light at 130 power factor. However I have discovered that my M&P CORE doesn't reliably feed 147s from S&W mags. The same bullets do feed with non-factory mags.

 

[DIYguy]

I've loaded up a bunch of 147gr FP rounds and was using them for the tail end of the indoor Winter matches just fine. Like the feel.
Ran my first Spring match last Thursday after couple months off and had three stove pipe on three out of four stages. One was stove pipe and jam, had to drop mag, clear and replace and unfortunately it was on the classifier.
One of the senior RO's came up and said he was watching my gun and ejection and my casings were dribbling out of my gun, ejection maybe two feet or so. That weekend I went back to the club with the Chrono and checked readings.
I was running 4.4 gr of Power Pistol and loaded and tested a bunch in February when it was a balmy 38 degrees. I was getting readings at 917 to 921 ft and average PF around 138. Last week end they tested at 910 ft and PF around 134. I was expecting my readings to be higher at 81 degrees ambient that the ones at 38 degrees.
???

 

[S&WIowegan]

Welcome to the puzzling world of chronography. There are so many variables at work in what we do that your slight difference in velocity is meaningless. It looks like a big deal when you calculate PF but it is not. You need to tailor the load to get the gun performance you need, i.e. strong slide action and ejection. I suggest Power Pistol is a bit slow for your purpose, try TiteGroup, 231 or Bullseye.

The more you experiment, the more you learn.