Impact of changing bullet seat depth?

[Wise_A]

Thanks, that makes a lot of sense.

No problem. Forgot to mention,my experience with charge volumes and their relation to accuracy is that while heavier charges tend to drop more accurately as a proportion, it's really only at impractical extremes that you can notice it. For instance, 14 grains of 2400 might only be off +/-.2-.3 grains compared to 2.8 grains of BE being +/-.1 grains. But it's less relevant to the SDs and ESs than how well the powder choice correlates to the bullet and velocity. I guess you could try variations in seating depth to improve SD/ES, but tbh, I think that it would be a fool's errand with anything but batched brass, and might not yield any usable results anyway. It might be a worthwhile avenue to explore if you ran into a situation where you were loading light and had an occasional cartridge develop a much lower velocity than the rest: something like 950, 940, 960, 820, 945, 955, 960, 940, 830, etc, and were sure your velocity readings were good. It would also be a little dependent on the cartridge--.38Spl won't care, but 9mm or .380 would be more sensitive.

[EricM]

I have yet to embark on my reloading journey, but I'm always reading and filing away little nuggets that seem useful. The following stood out to me, emphasis mine:

I'm far from a reloading expert, but I personally load for powerfactor first, then work on accuracy.

I tend to use powders that have a reputation for constancy and accuracy, such as VV N320.

For example, in 9mm, I found 3.0, 3.1, and 3.2 grains of N320 under a 145gr bayou bullet got me about 129, 133, and 136 PF.

I prefer the 133 because it gives me a good buffer for chrono variation. Then I'll load 10 rounds each at various OAL's like 1.090, 1.100, 1.110, 1.120, 1.130.

I'll take these out and shoot them off a sandbag rest or ransom rest and find the one with the smallest group size. I'll typically see a huge variation in group size caused by the OAL. I've seen as big as 4-5" groups and as small as 1.5" groups using the exact same bullet, powder, and charge but loaded to different OAL's.

[JAD]

I found that in 9mm the biggest accuracy gains came from bullet selection, followed by powder selection, followed by crimp profile, followed by realizing that loading 9 is about volume and consistency and that my precision interests were better served by rifle calibers.

[willie]

When using cast bullets in 9mm, you can avoid leading by selecting a bullet sized .357 and then using an expander that that prevents the case from sizing down the bullet when seated. NOE offers custom expanders that can be incorporated in one of the Lee dies. The Lee expander for the .38 S&W cartridge works nicely for this. I refer to the powder through the expander type. The only reason I can surmise about the large extent of oversized 9mm groove diameters is that manufacturers opt for these to reduce chamber pressure and thus force that cases exert against the slide upon firing. In today's manufacturing, companies have the ability to control groove diameter.

[Jim Watson]

Right now I'm loading for Precision Bullets. I don't know of a manual that lists these.

So while I could try to find a manual with something similar-ish, I'm also happy to experiment and see what works best for me. That's part of the fun of reloading. The question is - what should I be looking for as I make changes?

Precision has a video on OAL. I didn't sit through it so I don't know how much help it will be.
https://precisionbullets.com/2019/06...length-basics/

As said, I seat my bullets to suit the shortest throated gun in the safe; that works in the others.

Which Precision bullet are you using?
Their 9mm roundnose look a bit blunt and will usually come out shorter than factory.
Their flat points might do well at the length of a hollow point; a place to start, at least.

[ranger]

9mm OAL in my experience:
1) Is it short enough OAL to fit inside magazine of said 9mm?
2) If I take the barrel out and "plunk" drop loaded round in the chamber of said barrel, does it fit (not too long)?
3) Is it close to a generic OAL for that style bullet in a manual (example 124 FMJ, 115 FMJ, etc.)
4) Is it a CZ (CZs seem to require shorter OAL but you will find that at step 2).
5) head to the range and try it out.

Typically, if it fits in the mag it will work. I have never tried to improve accuracy of a 9mm pistol load by adjusting OAL. I do that for precision rifle.

[olstyn]

4) Is it a CZ (CZs seem to require shorter OAL but you will find that at step 2).

This is true of Walther as well, but it varies greatly with different bullet profiles.

Hornady 115 grain XTPs had to be loaded to 1.08" in my P99 and P99c, and Montana Gold 124 grain JHPs had to be loaded to 1.075". Blue Bullets 125 grain truncated cone bullets do fine for me at 1.100 - initially I was loading them to 1.110 or 1.120, I forget which, but I got a few too many rejects that way, and shortening the OAL slightly fixed the problem for me. Berry's plated round nose stuff goes out to 1.15" (and probably would work even longer than that) due to the long, shallow angle the profile uses.

Shorter total length bullets, JHPs especially, tend to reach full caliber diameter much nearer the bullet's nose, and therefore have to be seated deeper in order to avoid jamming them into the rifling. That said, the real offender for me was the "old" profile Acme 124 grain round-nose. They were super stubby and wouldn't plunk in my barrels when loaded any longer than 1.037". I sold them to a friend who had a gun that could tolerate them loaded longer and moved on with life because I didn't want to deal with loading that short. They've changed the profile since, and supposedly it's much more short/tight chamber friendly now, but I haven't had occasion to try them again, so I can't speak from experience on that. YMMV, of course.

[revchuck38]

4) Is it a CZ (CZs seem to require shorter OAL but you will find that at step 2)

This is true of Walther as well, but it varies greatly with different bullet profiles.

FWIW, if it runs in my P99Cs, it'll run in my CZ-75Bs. I determine OAL for bullets I haven't used by using a Walther barrel for the plunk test.