Bullet Seating Depth

[Coot]

I'm a little puzzled by information I've read regarding seating depth.

Sierra Bullets Tech Newletter Volume 9, No. 3 states:
"It is highly recommended that a bullet be seated so that it has at least one bullet diameter amount of the bearing surface in contact with the neck of the cartridge case. This helps to provide uniform tension as well as to hold the bullet concentric with the case and will help accuracy considerably"

Nosler Reloading Guide #Four, page 35 says: "Set your seating die to seat at a depth between .015 and .030 inches less than your rifle seating depth (this is generally where the best accuracy is found)..."

For target loads where OAL could exceed the interior length of the magazine, I have routinely seated bullets around .015 to .030 off of the rifling, and had good results. If I take Sierra's advice and seat to one bullet diameter, I'd be generally much deeper that.

What are other people's thoughts on this?

 

[mete]

For semiautomatics a firm grip on the bullet prevents bullet setback as the round chambers. Set bback can raise pressures greatly. A firm grip also insures proper combustion of the powder.People talk about length of throat vs accuracy but diameter of the throat is critical ,if it is bullet diameter even a long throat will be accurate , if it is greater than bullet diameter you'll have a problem.

 

[Poodleshooter]

I have routinely seated bullets around .015 to .030 off of the rifling, and had good results. If I take Sierra's advice and seat to one bullet diameter, I'd be generally much deeper that.

I think they're probably referring to rifle bullet diameters in the usual range of .224-.308". Sounds a little deep to me too, but if that's what they recommend.... I usually try for .010 or .015, though taking the measurement is somewhat less accurate than I would like. The really hard part is to find a rifle that hasn't had it's throat pushed way forward by lawyers.

 

[Freedom in theSkies]

I load alot of cannelured bullets for my semi-autos, so I crimp those ones on the cannelure.

For match/varmint/hunting loads, I use the Stony Point guage (As a matter of fact I had it out last night and explained it to my wife when she asked what it was. - I load these rounds .010-.020" off the lands.
For 9mm Luger, I don't seat shorter than 1.080", as pressures can rise dramatically (Speer Vol.10)



Crimp is usually about medium.

 

[Archie]

The "one-caliber" seating depth ...

is partially to insure the bullet stays put while in a magazine.
Obviously, if you're reloading for a heavy recoiling rifle, or an autoloader, or a lever gun, the bullet is going to get banged around in the process.

For single loaded ammo, like a varmint or target gun, I put that bullet out either touching or nearly touching the lands.

Note: If you seat into or touching the lands, start from the minimal loading data and develop. If you have an established load and change the bullet seating to rest on the lands, you will have unpredictable pressure surges. Probably higher. If you have any doubts, don't.

 

[KP95DAO]

And then there is how I seat my 308 loads for my Sav 10FP. Its throat has receded .2" and I have to load to 3.02" to touch the lands with my moly coated Sierra 180 Sptz GK. So I load to 3.06" and let the lands seat the bullet .04" while chambering. No big deal as they are only shot off the bench. But, those <.0625" 10 shot groups sure are nice. Oh yeah, it has had over 4500 rounds put through it.

 

[Coot]

Thanks for your replies; they really helped to clarify that issue for me. Guess I'll continue to load my target ammo close to the lands (love my Stoney Point guage) and the hunting ammo deeper.