My 38 super... I noticed something interesting

[c1skout]

I was going over my load notes last night to be sure I wasn't trying a combo that I had tried before, and I noticed that with the Lee .358 125rfn bullet in my super the accuracy always started to get worse at slightly more that 1100fps. I only size to .357 for this gun but have tried this bullet cast from range scrap, wheelweights, and a 50/50 mix of those 2, both water dropped and air-cooled, and using either "simple lube" or LLA. I've also used HP38, Accurate#7, and Bullseye powder. In each case when the speed gets nearer to 1200fps than 1100, the groups start to open up. I haven't had any problems with leading if I keep it under 1400fps. My best shooting load so far is with the HP38 at 1145fps, 12 shots at 25yds into 3.13", best 3 shots were .998".

I haven't tested any other gun/bullet combo's so extensively, so I was wondering if this was normally the case... does each bullet/barrel pair have a speed where they are happiest?

It can be a pain sometimes to take the time to keep good load notes, but without them I'd never see a pattern like this.

[Harry O]

I don't have any direct experience with the .38 Super. I do use .38 Super brass in my 9mm Largo's, though. To answer your general questions:
1) Yes, each bullet/barrel pair does have a speed where they are the happiest. Above that, accuracy goes to hell quickly. I think it is because the strength of the bullet against the sides of the rifling is not enough and it fails. Below that, accuracy gets a little worse the lower you go. I think it is because the bullet does not obturate enough.
2) Like you, I have found out that when working up a load, the accuracy goes bad BEFORE the leading occurs. That is a warning sign that the bullet has failed before you have to start cleaning out leading. If you keep a close eye on group size, you can save yourself a lot of work.
3) I have never had a bullet that reduces the group size again once it starts enlarging. Sometimes it is hard to tell for sure where that point is, when you get a really great single group, but if you shoot enough groups, the great group will average out. As you say, keeping good notes is important. I find that when working up a load, the groups will usually get slowly smaller until they start opening up, usually very quickly. Once they start opening up, they don't close back down at higher loads. When you are sure it has opened up, dismantle the rest of the (stiffer) loads rather than shoot them.

[c1skout]

Thanks for confirming my thoughts. I figured I wasn't the only one to notice this.
I've been working up my loads in sets of 12, usually only 2 or 3 different ones at a time, and I only have an impact-style puller so I just shoot off the loads that don't work as well anyways..... I can always use more trigger practice!

Have you noticed the same thing with jacketed rifle loads (your point #3)? I don't load nearly as much rifle as pistol but was just curious what you've found.

[Harry O]

It does happen somewhat, but there is much less of this stuff going on with jacketed bullets.

With my higher pressure rifle rounds (30-06. .280 Rem, etc), the best group size is sometimes slightly less than the highest pressure loads. Even then, the group size does not increase as dramatically when I go over that point like it does with lead. Higher pressures just get slowly bigger. I have wondered if going to a heavier jacket (or a totally brass) bullet would cure that. I don't know since I have never tested that.

I do not see that stuff with lower pressure rifle loads (30-40 Krag, 30-30, etc) or with any of my handgun loads. With them, the groups slowly get smaller up to the maximum pressure.