bullet seating depth

[shredder4286]

ok, newb here. just wondering what some of you experienced gentlemen have to say about this. When you're reloading a cartridge that you've never loaded before, and you're experimenting with bullet seating depth to find that sweet spot for the freebore, do you generally start with the deepest seating depth, and then work your way up until you find the right spot? obviously, your reload manual gives you a maximum C.O.L. not to exceed, so you should know when too far is too far. thanks in advance gents

 

[Nnobby45]

Start with the bullet barely touching the lands and work backwards so pressure will decrease with each step (even if only slightly) as you seat deeper.

If you have too much freebore, then you won't be able to seat touching or even close to the lands and still have enough seating depth to hold the bullet securely.

A typical .30 caliber likes the bullet about .020 to .030 from the lands.
Typical doesn't mean always.

Before you start looing for the sweet spot, start with bullets known for accuracy. I'd suggest the Nosler BT for working up loads to get a feel for your rifle's potential. Then, of course, try the other bullets you wish to use.

Some bullets seated out too far may not fit the magazine.

If the bullet is close to the lands, and you have enough seating depth, and the ammo fits the magazine, then don't worry about max. lengths listed in the manual.

 

[ryalred]

Well, I do it just the opposite. I start with the recommended COL for the bullet and powder being used and then move closer to the lands, but I'm not sure which is supposed to be the best way.

 

[Nnobby45]

Well, I do it just the opposite. I start with the recommended COL for the bullet and powder being used and then move closer to the lands, but I'm not sure which is supposed to be the best way.

The recommended COL isn't designed to turn your rifle into a tack driver. To get the best accuracy possible, you need to get the bullet near or just barely touching, the lands.

If you start with the COL at it's longest and pressure is safe, then seating the bullet progressively deeper during testing reduces pressure. That's why some of the more experienced hand loaders use that practice. If your load is well below max to start with, it doesn't matter where you start, since pressure won't be an issue.

Since accuracy is often best touching the lands--and I mean just touching, not jammed in there--that's a good place to start.

For good quality hunting loads, just make sure the bullet is seated deep enough to secure it and that it fits the mag. Tack driving accuracy is less important than properly functioning ammo for hunting. I don't recommend touching the lands for big game loads where risking a stuck bullet in the lands is unacceptable.

 

[steve4102]

your reload manual gives you a maximum C.O.L. not to exceed,

Not necessarily, some manuals call their listed OAL the Minimum OAL, some call it Max and some don't even list an OAL. What does it all mean, it means that the OAL listed in your manuals has little if anything to do with your rifle. There are three basic rules for seating depth, 1, the round fits into the mag, 2, the bullet is seated deep enough so as not to get jammed into the lands (unless intentional) and 3 at least one diameter of bullet is seated into the case.

 

[PA-Joe]

That is the purpose of using an ogive gauge! You start by getting the max length for the specific ogive of your bullet. Then back off from there. Assuming you are not using max loads.

 

[snuffy]

WARNING!

This is completely untrue! The deeper the bullet is seated the HIGHER the pressure will be. As the size of the combustion chamber created by powder space gets smaller the pressure goes higher.

If you start with the COL at it's longest and pressure is safe, then seating the bullet progressively deeper during testing reduces pressure. That's why some of the more experienced hand loaders use that practice. If your load is well below max to start with, it doesn't matter where you start, since pressure won't be an issue.

Seating the bullet out farther drops pressure because the powder has more space in which to burn. There's a limit though, because if the bullet is jammed into the rifling, it can't move. THEN the pressure spikes to a value higher than it would be if the bullet could move freely,=freebore.

Once the pressure has built enough to move a bullet jammed into the rifling, the pressure will drop to a safe level. It depends a lot on bullet construction. Heavy, stoutly constructed bullets will resist engraving causing high pressure if jammed into the rifling,(read solid copper barnes and others).

 

[Brian Pfleuger]

This is completely untrue! The deeper the bullet is seated the HIGHER the pressure will be. As the size of the combustion chamber created by powder space gets smaller the pressure goes higher.

Actually, neither statement is true or false without specific information.

If you start with the bullet touching the lands and leave everything else the same but shorten COAL slightly, then pressure will often decrease because the bullet gets a "running start" and engraves easier into the rifling.

However, as the length is shortened further, the situation described by you does begin to take effect.... less burning room means higher pressure.

However again, as the length is shortened further, pressure will sometimes begin to decrease again because the escaping gases are able to move around the bullet before it engages the rifling and "plugs the hole".

One of the many reasons why we should avoid speaking "short hand" in regards to reloading. While we may know what variables are assumed, someone else may not and could do something very dangerous because they are not following our assumptions.

 

[Sensai]

Ya nailed it again, Pizza Man!
This is one of those instances where a little knowledge could be a dangerous thing. The practice of starting with the "Starting" load and working up is a good one. When I'm working with a new bullet, I normally make a dummy load with the bullet seated as far out as possible (without crimping). I then chamber that dummy round and carefully extract it. The resulting cartridge overall length (COL) is my absolute maximum for that bullet. I normally load for .010" less than that, if that length functions in my gun. As a general rule, the closer the bullet is seated to the lands the better the accuracy; but I have seen exceptions to that rule.

 

[snuffy]

However again, as the length is shortened further, pressure will sometimes begin to decrease again because the escaping gases are able to move around the bullet before it engages the rifling and "plugs the hole".

Huh? WHAT! Show me a modern rifle that has enough freebore to allow a bullet to completely leave the neck of the cartridge, before engaging the rifling. Wheatherby rifles DO have a lot of freebore, but loaded with heavy for caliber bullets still have case support before engaging the bore. Besides that, the area in front of the case neck is lands diameter for any given chambering. Meaning if you're shooting a 30 cal, the freebore in front of the case neck is .308, how does gasses escape around a bullet in a smooth tube the same diameter as the bullet?

 

[Brian Pfleuger]

I normally make a dummy load with the bullet seated as far out as possible (without crimping). I then chamber that dummy round and carefully extract it.

I've tried this in 3 different guns and can't get a reliable result. I put quite a lot of effort into it too, using a Lee Collet neck die to try to get juuusst the right tension. It never gave me the same number twice. I found and easier way though.... suggested, I think by Jim243. My method is slightly modified but it goes like this. Tape a bullet to the end of a wooden dowel, push said bullet into the rifle and hold it there. Slide another wooden dowel down the barrel from the muzzle and mark the edge where it is at the muzzle. Remove the bullet and dowel from the chamber, close the action and slide the dowel in the barrel down to the breech. Mark the dowel again and you have the EXACT length of your cartridge.

This method works most reliable with a bullet comparator tool since measuring from the tip is less reliable than the ogive.




Snuffy,

My Ruger M77 MkII in 204 Ruger can not be loaded long enough with 32gr bullets to engage the rifling. There would certainly be some "blow by" at ANY length with that bullet.

However, I believe that the reason that the pressure is able to get around the bullet is because it expands the case and gets between the neck and the bullet before the bullet can engage the rifling and prevent the gas escaping. I don't believe that it leaks between the bullet and the barrel/chamber but between the bullet and the case neck.

 

[Sensai]

I don't know why you're not getting consistant results with the dummy rounds. I have not had a problem with repeatability. I do use a lot of cast bullets, however. Maybe the lead bullets have something to do with the difference. Your method with the dowels sounds like a failsafe alternative though.

 

[k4swb]

OAL Handguns

So far you guys have been talking about rifle loads. Do any of you bother to check your handgun chambers for OAL seating depth?
I have 4 totally different .45 ACP handguns (one with 2 bbls) and optimal seating depth is different in each. In order to have ammo fully function in all five barrels, I must seat to the shortest chamber and live with it. I can see a very slight difference if each barrel is fired with its own optimal OAL. On one bbl the optimal will not quite go into the mag so i have to fit that one to it's magazines.
This stuff makes shooting a lot of fun and i enjoy the tinkering aspects of the hobby about as much as the banging.

 

[Brian Pfleuger]

So far you guys have been talking about rifle loads. Do any of you bother to check your handgun chambers for OAL seating depth?

I have stuff called Cerro-safe that I use to make a casting of my handgun chambers.

No guess work. Perfect copy, easily measured. Though you do half to remember to subtract the growth factor, which is like .0025 inches after 24 hours, or something like that.

I only have two, a 7mm-08 and a 357sig, so compatibility is not much of an issue.

 

[steve4102]

WARNING!

This is completely untrue! The deeper the bullet is seated the HIGHER the pressure will be. As the size of the combustion chamber created by powder space gets smaller the pressure goes higher.

Maybe is straight walled pistol cases, but in bottle necked rifle rounds, not so much. In fact just the opposite is true.

Barnes did a study awhile back on the affects of pressure/velocity vs seating depth. What they found was that in most instances the deeper the bullet is seated the less the pressure.
Scroll down to "From the Lab", note the pressure vs OAL graph.

http://www.barnesbullets.com/resources/newsletters/september-2007-barnes-bullet-n/

Here is another graph.

 

[Nnobby45]

If you start with the bullet touching the lands and leave everything else the same but shorten COAL slightly, then pressure will often decrease because the bullet gets a "running start" and engraves easier into the rifling.

However, as the length is shortened further, the situation described by you does begin to take effect.... less burning room means higher pressure.

I agree. However, the pressure doesn't increase to a significant degree, until seating depth is enough to intrude into the case, where it can reduce it's capacity. Loads listed for long bullets, that must be seated that deep take that in to account, I believe.

It's a long way between being close to the lands and being down in the powder case. Lots of room in between to experiment with different seating depths without going deep enough to worry about it.

Additionally, the larger the case capacity, the less the effect. Only handloaders who like to be flirting with maximum pressures need worry about such things.

Always remember, however, that starting in the lands means JUST TOUCHING. A bullet jammed into the lands enough to stick the bullet may very well raise pressures significantly.

 

[Nnobby45]

Just remember that a bullet touching the lands raises pressures slightly and deeper seating will slightly lower pressures, and may continue to do so until an equilibrium is reached where there's no effect until the bullet begins to reduce case volume enough to cause pressures to rise. The more case volume to begin with, the less the pressure will rise.

We aren't talking about pistol cases with very limited capacity where increasing seating depth seriously reduces case volume and can cause pressures to rise significantly. .40 caliber may be the worst offender in that reagard.

 

[4runnerman]

Knobby45.. That statement is not true. I will attempt to find the artical and send it to you.Right off the lands is not always the most accurate round.

 

[steve4102]

Right off the lands is not always the most accurate round.

Correct, seating close to the land is not always the most accurate.. Hey 4R, if you look at my post above and go to the article by Barnes you will see that they found more than one accuracy OAL sweet spot. One up close to the lands and one wayyy far away.

 

[4runnerman]

Steve41- Im with ya on that.I have a custom 223 and 2.29 is my sweet spot ,Have tried from 2.20 to 2.39 and 2.29 was the ticket.