Got back into reloading recently after a 40 year hiatus, mostly just blasting ammo for my AR, but am now looking into doing some more precision loading for a new Savage 12 FV .223 I have coming. The contradiction I'm running into is pressure vs. bullet seating depth. On the one hand, some say pressure goes down when seated shorter, others say just the opposite, up to the point of the bullet being jammed into the lands. The latter makes more sense to me, assuming all else being equal, since more capacity should mean lower pressure. Or am I out to lunch (again!)? TIA.

Dave

What your are getting into is freebore. Weatherby uses freebore to get speed without increasing pressure. Rifles seem to be more accurate by decreasing freebore with out touching the lands. Work up slowly to max and keep the right length. Most of the time coal is based on the magazine length (unless you are single loading you want them to fit) and pressure is set at that length.

Whoever told you that pressure goes down as the bullet is seated deeper is not correct and who knows what other nonsense he is spouting.
Forget book OAL suggestions; they are, as indicated, based on magazine length, but also, that bullet makers position of the crimping cannelure. Work up your loads based on how they fit into the throat, and magazine of course, with regard to accuracy.. And realize that if you do seat them deeper, then pressure goes up. which is why you don't start with the max load in the book.

When I start loading for a rifle I measure 2 things right off the bat.
1. Overall length that will reliably operate through the magazine.
2. Overall length to the lands with the bullet I intend to use.

Both of these are helpful if not necessary.
One thing I've noticed while playing with seating depth is the longer the overall length the more velocity I've been getting albeit the increases are very slight.
I usually start at the recommended overall length and increase the length from there incrementally (.010") until I find the "sweet spot" making sure I don't touch the lands (you will get a sudden pressure spike at that point and have the potential for problems like flat or pierced primers or worse). I explore until I'm limited by either number 1 or 2 above or found the accuracy. Once I've foundan accurate load I continue to tune it in smaller increments of seating depth.
This is a simplified rundown of my methods, others do it different.

That's exactly the way I do it too. And I use a lot of long actions even for shorter cartridges, which is why I ignore mag box lengths.
But for off the rack rifles, it is usually the mag box that is the limiting factor. Throats are rarely shorter than the box will allow.

quote:

Originally posted by Daved20319:
The latter makes more sense to me, assuming all else being equal, since more capacity should mean lower pressure.

This has been my experience. With all else equal, a longer round will have less pressure until you get to the lands--then it goes back up.

For AR blasting ammo the magazine length is probably what determines your cartridge length (most types of bullets will be well short of the lands to fit the mag). With a single shot bolt action, then you can experiment with whatever length to find good accuracy. Good luck and welcome back to reloading!

Don't know about your new rifle but there's a big difference between the throats of bolt actions and AR's. For instance my one bolt action Remington .223 rifle for a hornady 55 fmj to touch the lands in it the overall length is 2.246" while you can't seat long enough to touch the lands in an AR. Two different AR's to touch the lands it would be 2.370" to 2.390". Don't think you'd be able to see the difference in pressure with your cases or primers unless you do jam the bullet into the lands. I've seen no pressure signs difference in seating ten thousands to 50 thousandths off the lands.

Below Erik Cortina of "Team Lapua USA tells you how to make accurate loads and he starts .020 off the lands. After he finds the most promising load he then experiments from Jam - 0.005" all the way out to Jam - .040" in .003" increments to "tune" the load.

Long range load development at 100 yards.
http://forum.accurateshooter.c...t-100-yards.3814361/

Bottom line, the COL in the reloading manuals is a safe point to start with the bullets used. And I would trust the manuals before Internet "myths" posted in forums. Now ask yourself who has the pressure testing equipment to backup their testing.

NOTE, the throat in my Savage .223 bolt action with a 1in9 twist is longer than the throats in my two AR15 rifles.

Look at the freebore lengths and diameters below.

I do as Snellstrom, ie., first consider box mag allowable length. With most factory bbls - and especially the WBY rounds - there's no sense measuring to lands unless you intend to single load. You can still play with length working down incrementally from max allowable by the mag box.

Add a 3rd consideration: sufficient neck purchase. I will sometimes seat to less than one caliber, but not much less. Neck purchase gets a bit more complicated with long BTs in combination with secant ogive.