Impact of changing bullet seat depth?

[matto]

Let's say you have a pistol that will run just about any length round you feed it, which my Beretta LTT 92 seems to do.

This means that for a given bullet and desired muzzle velocity, I can vary the seat depth to whatever I want and still achieve the that velocity as long as I adapt the powder volume appropriately.

In this scenario, what information do I use to select the bullet seat depth? Why would I pick one seat depth (and corresponding OAL) over another?

Here are my thoughts / questions / what I've read so far. I'd love to hear the experts confirm or deny these claims!

• Larger powder measurements should have less variance (as a %) from the powder drop, resulting in more consistent velocities
• Larger internal volume will reduce pressure, putting less wear on the gun (not sure this matters if you're loading minor power factor)
• Smaller internal volume increases pressure which helps burn cleaner if you're running really light loads
• I read that loading short and getting near peak pressure (but with the same velocity) makes the gun feel softer shooting. Is this true or urban legend?
• I suppose at some point you need enough seat depth just to hold the bullet properly. But I'm thinking if you're within any reasonable range this is a non factor?

Am I missing anything? And does any of the above really make a significant difference? Or is it the case that if your gun can run any length, just pick something in the middle and never think about it again?

[BN]

Or is it the case that if your gun can run any length, just pick something in the middle and never think about it again?

I'd just load to the length the manuals say and don't worry.

[matto]

I'd just load to the length the manuals say and don't worry.

"the manuals"? Each one has different data points with different lengths.

[JAD]

"the manuals"? Each one has different data points with different lengths.

Where possible go by loads for the very specific profile you’re running. Pick one manual and develop your load at the length specified in that manual.

For this reason I always preferred bullet maker’s manuals.

[willie]

You can assume that up to a point there is a positive correlation between pressure and velocity and in this instance the relationship is cause and effect. But first consider that powder burning rates vary from fast to slow. When we discuss pressure and velocity relationships, we are more likely to make valid generalizations when discussing loads using the same powder. If not the same powder, we ought to stay within powder burning rate groups like fast, medium, and slow burning rates. This statement applies to both handgun and rifle cartridges.

Soft shooting loads are soft because of lower recoil. The burned portion including gases of fired cartridges is called ejecta. This has mass which for our purpose can be considered weight. Heavy charges of slow burning powder have more ejecta than lighter charges of fast burning powder. If the round with the fast burning powder has the same velocity as the other one, then the former will be softer shooting because recoil will be less. Why? The ejecta is less in amount.

My advice is to select a load from a manual and follow recommendations. OAL can be varied to improve functioning. The other points may be overthinking the issue.

[JohnO]

Am I missing anything?

Bullet profile and when OAL causes to bullet to contact the rifling.

[Wise_A]

Presuming you're legitimately not getting rifling contact, my next step would be to forget about the gun I'm loading for and find a length that works with my shortest-chambered gun, even if I was overwhelmingly loading for one. I'm guessing you're really just loading for this one gun, however, so I would suggest removing the recoil spring from the Beretta and hand-cycling some different lengths to figure out which length feeds the smoothest. Aside from just feeling nice, it'll give you more leeway when it comes to a dirty gun, retarded slide operation, and out-of-spec ammunition.

Soft shooting loads are soft because of lower recoil. The burned portion including gases of fired cartridges is called ejecta. This has mass which for our purpose can be considered weight. Heavy charges of slow burning powder have more ejecta than lighter charges of fast burning powder. If the round with the fast burning powder has the same velocity as the other one, then the former will be softer shooting because recoil will be less. Why? The ejecta is less in amount.

While both really aren't relevant to seating depth, and admitting that lighter/faster tends to result in lower felt recoil for most people, some folks prefer powders towards the medium end of a given cartridge/bullet combination's spectrum, on the theory that the slower-burning powder spreads the recoil out better. I would also add that I think it's hugely unscientific and really, there's probably not a ton of difference between the two. I know some people contend that the ejecta and gas expulsion actually has an effect disproportionate to its share of the "projected mass" on account of that stuff moving much faster than the bullet, but there's a reason lots of pin shooters and silhouette guys go with heavy-for-caliber bullets.

[matto]

Bullet profile and when OAL causes to bullet to contact the rifling.

I don't think I'm missing either of those things actually.

I'm assuming the bullet is not contacting the rifling. I'm only considering varying OAL within that range.

And the bullet profile is irrelevant in this case because I'm not changing bullets. I'm asking how to come up with a recipe for a given bullet.

[matto]

Presuming you're legitimately not getting rifling contact, my next step would be to forget about the gun I'm loading for and find a length that works with my shortest-chambered gun, even if I was overwhelmingly loading for one. I'm guessing you're really just loading for this one gun, however, so I would suggest removing the recoil spring from the Beretta and hand-cycling some different lengths to figure out which length feeds the smoothest. Aside from just feeling nice, it'll give you more leeway when it comes to a dirty gun, retarded slide operation, and out-of-spec ammunition.

Thanks, that makes a lot of sense.

[matto]

Where possible go by loads for the very specific profile you’re running. Pick one manual and develop your load at the length specified in that manual.

For this reason I always preferred bullet maker’s manuals.

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?