Couple questions regarding seating depth

[SnowDrifter]

Ok so I've been reading about reloading. Understanding things for the most part except for a few things:

Suppose a given system (bullet, powder charge, case, weapon) might allow a range of seating depths/OALs. Assuming all else is a constant, what effect does seating depth have on average pressure and muzzle velocity?

I know as the bullet is seated deeper in the case, the instantaneous pressure increases. Does this effect the final velocity in any way?

What about the changes in airspace within the cartridge with seating depths? What effect does this air have?

What risk is there when the bullet is not seated deep enough, but usable by the weapon and magazine?

[ROLEXrifleman]

Bullet seated long = extra internal volume you will have less pressure and less velocity produced because of the extra empty space when compared to to the same cartridge seated deeper in the case. At that point you will loose internal air volume and have an increase in pressure thus an increase in velocity.

the effects will differ depending on the cartridge in question and also between rifle and pistols calibers.

seat to deep and have a pressure exceeding that of the cartridge an you will have a catastrophic failure

one thing to be aware of as well is if you seat to long and are using a light load you could also get pressure spikes due to way the powder ignites. In this case to a catastrophic failure could occur

[ROLEXrifleman]

another thing with this is the burn rate of the powder you are using. Slower burning powders are more dense than faster burning powders and will not allow for excess air space in pistol rounds if the round is loaded to light or an excess of COAL is used

[SnowDrifter]

Cool thanks for the help!

one thing to be aware of as well is if you seat to long and are using a light load you could also get pressure spikes due to way the powder ignites. In this case to a catastrophic failure could occur

Could you elaborate on this? I believe you, just curious as to what goes on behind the scenes, so to speak.

[ROLEXrifleman]

It's called detonation. You can look it up by that term or also by looking up undercharged loads.

I have never experienced it but play on the edge of what causes it. It revolves more on your powder charge more than seating depth, but if you seatto far out it could theoretically cause the powder to shift to a point where it could be placed in this category.

here is my half ass drawing for you:

in pic one you can see how the powder is horizontal in the case. When the primer ignites it has more surface area to act upon and ignition could happen at all points across the surface area as opposed to pic #2 where ignition happens at the rear and the powder burns back to front consistently.

In pic one this can apparently cause havoc with pressure and depending of the burn rate of the powder cause a Kaboom. Again, it's nothing I've ever experienced and many say is impossible but something every reloader should know about.

[Broke_Audio_Addict]

And this is why I just buy it off the shelf.

Still interesting to learn though.

[n8ball2013]

You just have to pay attention it's really not that hard. Proper tools for the proper job really help