How to Measure Seating Depth

[papajoe222]

Just curious as to how you get there. Is there only one formula? The reason I ask is that the way I've been doing it, I come up with a depth of .425in. seating 168gr Hornady Match BTHP which is almost 1/3 of the bullets length. That just seems a bit deep compared to others that were closer to the bullet's diameter.
My system is: Bullet length + Case length - OAL = Seating depth (1.220+2.005) - 2.800 = .425

 

[BigBoreBubba]

What were the bullet weights of the other bullets you were shooting? Nothing sounds too out of whack to me so far. Some bullets will have to seat deeper based on length due to weight and design.

 

[KYregular]

I always use to ogive measurement for my base measurement for rifle bullets. COAL can vary due to even the slightest meplat deformation, especially with bullets like a Nosler Partition. Just keep the COAL short enough to feed your magazine.

 

[joneb]

It would depend on the cartridge.
If I were to assume that you are loading for .308 Win. then 2.8" sounds about right.

 

[edwardware]

You might occasionally observe how many calibers of neck interaction you're seating to, but it rarely matters so closely as that. If you find yourself with insufficient bullet/neck interaction such that the cartridges are fragile, seat deeper or find a longer bullet.

 

[lordpaxman]

Your formula is correct, at least that’s how I do it. Just keep in mind measuring to the tip of the bullet can get iffy depending on how consistent that is between bullets. You’ll have to get those Al tipped bullets! Good luck.

 

[GeoDudeFlorida]

Just curious as to how you get there. Is there only one formula? The reason I ask is that the way I've been doing it, I come up with a depth of .425in. seating 168gr Hornady Match BTHP which is almost 1/3 of the bullets length. That just seems a bit deep compared to others that were closer to the bullet's diameter.
My system is: Bullet length + Case length - OAL = Seating depth (1.220+2.005) - 2.800 = .425

Here's how Berger Bullets explains it: COAL and CBTO Part 1 and COAL and CBTO Part 2. It's actually a lot simpler mechanically and you really only need to go through the measurements once per bullet lot #. For handguns, I go through this only once per bullet profile IF it isn't already documented by the manufacturer.

 

[berettaprofessor]

Uhm…why do I need to know seating depth? Isn’t OAL or ogive length consistent enough?

 

[nettlle]

Set the bullet long. Color the bullet with a Sharpie or black barker. Chamber until resistance is felt. Keep seating the bullet deeper until the markings on the bullet are barely marked by the rifling. Then seat .015" deeper. For rifle.

For automatic pistol if it won't feed the feeding dictates the COAL.

 

[Hondo 60]

Seating depth is part of the data.
The OAL is specified.

If the bullet has a cannelure, that's where I seat it.

Please stay safe & be VERY careful.

 

[nettlle]

I agree with playing it safe. If your particular gun has a much shorter chamber than the ammo/reloader component manufacturer recommends when it blows up you can say you used the recommended data.

CZ pistols have short chambers. COAL for rifles, with risk free data, will have a bullet jump to the lands so long that it will destroy the accuracy of the reloads.

Reloading is not plug and play.

 

[sugarmaker]

It matters if it’s for a single gun or multiple guns. For a single gun something like a stony point:Hornady setup can be used to dial things in very closely for precision load development. For multiple guns or more of a field load the manufacturer OAL is a good place to start.

 

[papajoe222]

OAL, or seating to the cannelure is fine for hunting, or plinking fodder, but I'm looking to duplicate pressures and velocities that result it the most accurate and consistent downrange results I can. Seating depth is one variable, although it may only offer minimal improvement, used to achieve that end result.

 

[sugarmaker]

For that I suggest the Hornady oal gauge and comparator. You can skip the gage and use a normal case with a tight slip fit on the bullet, but I find the gage setup with a threaded case is more consistent. I make my own cases for each gun using the die setup for that gun. Getting neck tension just right can be a little tricky and threading the case needs a funky tap thread pitch. You can also just buy the cases. The ides is to find the lands with your bullet, measure the length with the ogive inserts that clamp to dial calipers, then adjust your OAL relative to the lands. You may find it necessary to single load rounds as the OAL can exceed magazine length. Also some cartridges (375hh for example) designed to accept long blunt billets may have some lighter bullets out of the case before reaching the lands. There are lots of methods and opinions for the ideal seating depth and the process of locating it, lots of opportunity for experimentation.