Reducing loads on the 9mm

[HighValleyRanch]

Just experimenting today with soft loads for my 9mm's.

Started with 3.5 hp38 and 115 Berrys plated, and had to hand cycle.
Then with 3.9 hp38 it was very soft and cycling reliable in both my Glock 19 and Shield 1.0 40 with 40 to 9 conversion barrel and the original 40 spring.

But only have a limited amount of 115 grain, and found I had a ton of 124 grain plated RN flat base.

So loaded the 124 grain with 4.0 hp38 and it seemed a little snappier, but reliable.

So the question is, when loading a heavier bullet, the bullet takes more case space and is heavier to move, so I imagine there is a pressure increase with the same amount of powder, right? So can I decrease the powder amount so that given a heavier bullet and less case space, the pressure would stay the same as the 115 grain?
In other words, pressure wise, would 124 grain with 3.7 hp38 be similar pressure to 115 grain bullet and 3.9 gr. HP38?

Any problem on downloading until the pistol does not cycle properly to find the minimum load? This is just for paper and practice.

[Shotgun Slim]

Every time I try a new bullet or powder I always load down to failure so that I will know where that is. I test the light loads with my weak hand so that I know it will be reliable in the strong hand and in colder weather. I can't answer your question about pressures honestly because I don't have pressure test equipment and conjecture and assumptions don't do a serious handloader much good. Take your 124s and the HP38 and start on the low end of the Hodgdon data and stairstep down to failure. That way safe pressure is not an issue. Something else to try in the 9mm is the heavier 147 gr bullets. They can be very nice and soft on the bottom end. Understand that some powders don't like the lack of heat and pressure and become erratic on the low end. I won't give you my preferences here. You'll be better off figuring your own. Some people on this forum find it ridiculous to load anything but firewall stuff,but I find many uses for powderpuff ammo,including providing a pleasant experince for beginners with centerfire pistols.Trying different recipes is half the fun so have at it and post your experience for us please.

[Marco Califo]

I do not like the idea of knowingly loading semi-auto ammo that will not cycle a typical pistol in that cartridge.
I know that every loaded round in my ammo boxes will function almost any pistol reliably. I have never considered 9mm to need loading down. I think it is an excellent cartridge, particularly in small pistols.

[jetinteriorguy]

If you’re after a softer shooting/softer recoil load try Clays. My go to load is 3.2gr with either Copper coated or Hitec coated 124 gr bullets. They shoot notably softer and cycle reliably in my wide variety of 9mm pistols. For whatever reason the recoil impulse is more of a push and less snappy than other loads I’ve tried.

[Jim Watson]

You are at or below "starting load" level, at 88% of maximum powder charge, 82% of maximum pressure in Hodgdon data, but no reason not to come down a little more as long as your gun functions.

I have some underloads for my Glock 43 in GSSF Pocket and IDPA BUG. They will not function other guns so they are labeled and kept separate. The gun gets factory hollow points on the mean streets.

[Unclenick]

The standard rule of thumb is to take 10% off a maximum load of a canister grade powder to establish a starting load. Western powder used to recommend that for rifle loads, but 15% off maximum for handgun cartridges. They didn't say, but I suspect the reason for this is that the auto pistol rounds often have very short powder spaces with the result a little seating depth change, whether by adjustment or a change to a longer bullet make that seats deeper, can affect the pressure significantly more than it does in a rifle case, with its much bigger powder space.

Bullet design can have a lot of effect on pressure. Allan Jones found up to thirty percent pressure difference could be had from the same bullet weight by changing designs. This included copper solids and the like, but the point is that you don't want to stray too far from the design the load manual used.

That said, if we pretend all else is equal, going to a heavier bullet does increase pressure for a couple of reasons. First, the greater mass's inertia makes it harder to accelerate, so it starts out more gradually, giving the powder time to make more gas before as much expansion has occurred, and therefore that greater gas quantity is more tightly confined,raising pressure. Second, a heavier bullet of the same design is longer, so it seats deeper into the case for a given COL, reducing the volume the powder starts burning in.

How much pressure will rise depends on more factors than just bullet weight. You will need to look at that and at the change in water capacity under the bullet. The easiest thing to do is to us QuickLOAD or Gordon's Reloading Tool to model your load. It won't match pressure perfectly, but the percent change in pressure due to the change in bullet mass and seating depth will likely match your percent change pretty well. That is, if the software raises pressure X percent in the program, it will raise it about that percent in the cartridge.
Same for the percent change in powder charge.

[HighValleyRanch]

So here's the results.
115 grain Berrry's RN flat base at 3.5 grains of HP38 would not even cycle the slides on the Shield or Glock 19. It took about 4.1 grains to become reliable. Very soft.

When I went to the 124 g. Berrys RN flat base, I got down to 3.4 grains with occasional failure to feed. It looked like the slide was not going all the way back, so a round would jam in feeding.

When I got to 3.7 grains of HP38 with the slightly heavier 124 g. bullet, then the load became reliable in the Shield.

So 3.7 grains with 115 g. 9mm didn't work, but 3.7 grains of HP38 with 124 g. 9mm Berrys did work. So my concoction is that the heavier bullet caused enough more pressure with the same amount of powder to cycle the slide.

[Unclenick]

Sounds like you have a handle on it. When I was active in bull's-eye target shooting, with the m.1911 I found I could change to a lighter recoil spring for lighter loads, but recoil for a load that functioned would get sharper if the spring was too light. I finally figured out that for each recoil spring weight, there was a narrow sweet spot load range that functioned every round without quite getting the slide fully back that last millimeter or two, so the slide was being stopped purely by spring compression and not by the slide banging into the frame. That collision was the source of the sharp feeling, and without it, recoil was soft and spongy every time. You may well be experiencing the same lack of solid slide/frame impact thing with the soft recoil.

[HighValleyRanch]

I think that you are exactly right, about that sweet spot without the slide slamming back, yet enough momentum to cycle properly.
So I test this same load in my Glock 19 and 34 and this load would not push the slide back enough to cycle at all. Mostly failure to feed and a couple of stovepipes. Then tested it again in the Shield and it worked perfectly.

So the slide on the Shield has less mass, but amazing that it still has the .40/9 original spring in it.