Bullet Seating Depth ?

[Hemingway]

I've just started getting into reloading. I've been studying hard for the past couple of months and watching videos. Some procedures seem to really be detailed and accurate and talked about a lot. Others get relatively little mention. One of those is the bullet depth when seating a new one. Where some measurements are very specific, more often than not I read stuff like, "don't seat it too deep, but seat it deep enough that it will cycle".

So, how do I ensure that I'm putting the bullets in the casings properly?

I'll be using 117 gr Hornady BTSP (#2552) for a 25-06. They have that groove around the bullet--should that fit just below the top of the case? Do I just put the calipers on the overall length after I'm done?

What do you rolling experts say?

Thank you very much.

 

[jblomenberg16]

Seating depth is typically controlled more by the Overall Length after seating. So, for the load you are looking at (specifically the bullet) you will want to control the OAL according to the load data. On magazine fed guns this is often the longest cartridge that will fit in the mag and sill function.

 

[Aszerigan]

Any manual or reloading data guide that states: "don't seat it too deep, but seat it deep enough that it will cycle"... close it up, and drop it directly in the trash.

The OAL is the overall length of the cartridge from the tip of the bullet to the base of the brass casing. This is measured using a set of calipers. A good set of calipers is the second most important tool in your reloading room. (A good powder scale - not measure, not auto disk, not scoops.... a SCALE is the most important.)

The OAL is changed by seating the bullet deeper or more shallow in the casing. This is changed by either adjusting your die higher or lower in the press, or by adjusting the bullet seating plug on the die. Since bullets of the same weight and caliber should have very similar overall dimensions, seating to a proper overall length should be fairly consistent across bullets of the same weight. Technically what this is doing is 1) allowing the cartridge to feed reliably out of the magazine and into the chamber, and 2) guaranteeing the volume inside the case is consistent from round to round.

The internal volume of the case is very, very important. This is what dictates the powder's compression burn rate. Too much space, and the powder will take longer to burn and the pressure curve pushing the bullets will be decreased in speed. Too little space - also known as 'deep seating' - can cause the powder to burn faster, increasing the pressure spike significantly, and result in a damaged or destroyed firearm, hand, eyes, person, etc.

That 'groove' in the bullet is called a cannelure. It serves three purposes. First, It's a visual sighting device for adjusting the seating depth of the bullet when rough setting your dies. Although it's not always accurate so an OAL measurement is still required. Second, that cannelure imprints the jacket into the swaged core and keeps the jacket from splitting off during firing or impact. This helps hunting bullets with weight retention upon expansion. And third, it allows the brass a place to grip the bullet in the event a roll crimp is needed.

One final note - a 117gn bullet is one of the heaviest bullets that a 25-06 will throw. Why are you going so heavy? Lighter bullets equal higher velocities and flatter shooting rounds.

 

[Hemingway]

I've got good calipers. According to Hornady, they recommend right at the maximum OAL.

But there's really no way to measure this initially other than just seating a bullet and then putting the calipers on the whole thing? If it's too deep, I adjust the die and do it again? Eventually it hits right on the number and I keep it set there?

Bottom line, it's a trial and error procedure?

 

[Yeah]

Vary seating depth according to what your rifle likes, though it is few that don't work best with the bullet seated so the lands print squares on the bullet.

With 117 Hornady's you should make that and still fit into the magazine of everything, unless you happen to have a Sako.

 

[Aszerigan]

Yes, it is a trial and error process. Get yourself an inertia puller because sometimes you'll seat them too deep. If this happens, don't shoot them 'trial and error.'

 

[Hemingway]

Vary seating depth according to what your rifle likes, though it is few that don't work best with the bullet seated so the lands print squares on the bullet.

With 117 Hornady's you should make that and still fit into the magazine of everything, unless you happen to have a Sako.

It's for my Dad's old 700 with beautiful wood

Yes, it is a trial and error process. Get yourself an inertia puller because sometimes you'll seat them too deep. If this happens, don't shoot them 'trial and error.'

Thank you. Much of my studying has consisted of reading your posts--I've learned a tremendous amount from them.

 

[Yeah]

700 long action mags will get you to the lands with a 117 Hornady in 25-06. Just find them, and load to them.

 

[U.S. Patriot]

If you have some factory ammo check the OAL as a refrence. I did so, then set my OAl shorter than factory ammo, but still within safe limits. Load a bullet into an empty case (no powder or primer) then check to make sure it seats in the chamber properly. Once you find the proper seating depth you should be good to go.

 

[Aszerigan]

If you have some factory ammo check the OAL as a refrence. I did so, then set my OAl shorter than factory ammo, but still within safe limits. Load a bullet into an empty case (no powder or primer) then check to make sure it seats in the chamber properly. Once you find the proper seating depth you should be good to go.

Patriot is correct, as long as you're using the same weight bullets and type as well - spitzer vs spitzer, fmj vs fmj and you're not loading near max charges. By shorter, I'm sure he means <0.005".

 

[Eric86]

When seating bullets to find the length you want its always best to start long and work deeper. Its easy to shorten a bullet than it is to lengthen. That is why I keep a dummy round (no powder or primer) set at exactly the length I want.

I first back out the knob on the top of my die to where it will basically not seat a bullet at all. I then place the dummy round in the shell holder and then pull the lever, pushing the dummy all the way up into my die. I then screw in my dies knob until it stops.

Next I load 1 up and measure, this should always make it a little long and you can make slight adjustments till you get it perfect.

When I think I have it where I want it I still measure the next two or so to verify I have it correct and then every 15 or so after.

 

[U.S. Patriot]

Patriot is correct, as long as you're using the same weight bullets and type as well - spitzer vs spitzer, fmj vs fmj and you're not loading near max charges. By shorter, I'm sure he means <0.005".

Acording to Hodgdons reloading data, my C.O.L. is .020"-.030" longer than what they recommend. That's also charging .1 grains under what they recommend for max charge.