MINIMUM seating depth

[SKULLANDCROSSBONES65]

G'day. Is there a minimum seating depth for any given projectile ? I think that I read somewhere that the seating depth should = projectile diameter. I understand that it is also important to seat the projectile close to the Lands.

[mrawesome22]

As long as the bullet is held in place, your good to go.

[Art Eatman]

Most reloading data includes the overall length (OAL) for cartridges. Often, it has to do with the magazine length.

If you seat a bullet too far out, it can be embarrassing if you then open the bolt to remove an unfired cartridge and the bullet doesn't come out with the case--and you have a bunch of powder loose in the receiver.

[butta9999]

Skulls, bullet seating can play a big part in accuracy. Generally with varmint rifles its best to keep close to the lands maybe 2 thou off. in saying that my .222 shoots better with bullets 15 thou off lands. With lighter bullets and quick burning powder it does pay to be close or even touch the lands if you can. If your touching the lands you want to make sure you have good measuring equipment, because pressures can spike if your off.

With the larger calibers, example my .300win mag i have to go by my mag length first. No matter what bullet i choose i have to use my mag length as my guide. In saying this there are large calibers which have long throats, eg Mausers.

With heavier bullets and slower buring powder it pays to have the bullet off the lands. If the heavier bullet is kissing the lands or only a couple of thou off then pressures will spike.

This is because pressure builds slower and the bullet needs room to move. Therefore a little free travel to the lands is necessary in a hunting rifle.

Benchrest shooters can have the bullet well in to the lands but this is with the most perfect equipment, and to insure the bullet enters the barrel on perfect allignment.

Look at the Weatherby rifles they are free bore, where the bullet makes a huge jump to engrave the rifling and they shoot great. The 6.5x55 swede is on the opposite end of the scale with a long throat, it shots great.

Remember every bullet has a different ogive so ever bullet has to be re set. I mean brands of bullets not in the same batch.

There are plenty of methods of how to achieve correct overall length for your rifle. And as Art said you dont want it out oo far so that the bullet gets stuck in your rifling and when you eject you end up with a heap of powder in your action.

Im sure fellow members will share with you on how to seat your bullet to your desired length.

I hope this helps you with your reloading journey

[mkg]

S&C, Most knowledgable handloaders that I have talked to consider one bullet diameter inside the neck to be minimum seating depth.
However , as has been said, the chamber of your rifle and magazine length will have an effect as far as how the round physically "FITS" in your rifle. There is another issue though, it's called runout . Runout has to do with how the bullet aligns with the case . If you could draw and imaginary line down the center of the case it should also be down the center of the bullet when seated. Any variation of the bullet from center is called runout and will effect the accuracy and the way the round chambers. Extreme runout for instance could put the bullet in contact with the rifleing of the barrel on one side and off considerably on the other .
Runout target should be in the (.00X) single digit thousandths . Several companies make runout gauges.
As far as measuring the OAL of a given cartridge . It's not really an accurate way to do business if you will. Every bullet has a different shape and the manufactures have come up with a way to describe them . The MEPLAT ( or pointed tip of the bullet ) the OGIVE ( the part of the bullet that first reaches the caliber diameter ).
The OAL measurment is from the meplat to the base of the case . This is miss leading because the meplat is usually made of a soft material lead or poly tips that can deform easily. The OAL really tells you nothing except that it will or won't fit in your magaizne

The OGIVE to the rifleing or lands and grooves is the critical measurement . Hornaday makes a tool called a bullet comparator to measure the cartridge lenght, OGIVE to the base of the case. This tool is basically like having a piece of you barrel attached to one side of your caliper you set the loaded cartridge's bullet into this "barrel " and measure the distance to the base. That is how you should determine/describe the seating depth.

I hope this helps,

Mike

[Bullet94]

I tend to believe what William C. Davis, Jr. says here –

“It is obviously possible also to increase the free run simply by seating the bullet more deeply in the case. That has two effects on chamber pressure, which are in opposite directions. The increased free run tends to decrease pressure, but the decrease in powder space increases the loading density, which tends to increase pressure. Which effect will predominate depends on the characteristics of the particular load and gun. In most full-charge loads, it is found that the pressure decreases at first as the bullet is seated farther away from the lands, but beyond some particular seating depth, the pressure begins to rise again as the powder space is further reduced. In revolvers, the free run through the cylinder is always relatively great, and increased seating depth always increases the chamber pressures.”

[T. O'Heir]

"...Often, it has to do with the magazine length..." SAAMI standard chamber dimensions. Mind you, if a loaded cartridge doesn't fit in any kind of mag....