Setting seating die for BTO.

[ArtBanks]

In the process of changing bullets for one of my precision rifles. Savage Model 12 FVSS in .223. I am working at setting the seating die to provide a finished cartridge that will allow the ogive on the Berger 55 gn fb target bullet to just kiss the lands. Painstaking measuring and setting up can help produce the best results.

Step 1. Determine the exact BTO, Base to Ogive, for the particular rifle using a Hornady OAL guage and they exact type bullet that is being used. I like the curved gauge so it can be used on both semi auto and bolt rifles. Lock the length of the moveable bullet when it is touching the lands. Remove tool and bullet.

Step 2. Measure the BTO of the cartridge while still in the gauge.

Step 3. Measure the cartridge separately from the gauge and determine the exact BTO needed for this rifle.

Step 4. Set up micrometer seating die to measurements acquired previously. Usually takes a few tries to get it correct, by trial and error method.

Step 5. Load away and enjoy your time knowing you have done your best.

Whatta Hobby!

 

[STG_58_guy]

I have the CBTO gage and have tested where the lands are in all of my Savages. But the cartridge locates on the shoulder, not the base. I suppose if you only knock the shoulder back a thou and always use fire formed brass, CBTO will put you on the lands. CBTO is way more consistent than COAL, that's for sure.

 

[ArtBanks]

I have the CBTO gage and have tested where the lands are in all of my Savages. But the cartridge locates on the shoulder, not the base. I suppose if you only knock the shoulder back a thou and always use fire formed brass, CBTO will put you on the lands. CBTO is way more consistent than COAL, that's for sure.

Now, there is a very good topic of discussion Sir. I think you will find that the cartridge headspace is exactly that and provides a space or set back from shoulder to chamber shoulder and does not actually locate from or by the shoulder at all. The measurement from the base to the lands should be a consistent and much more accurate. We are in agreement that the OAL is not particularly accurate and only gives a basic minimum safe length for a particular combination.

 

[ammolab]

Almost as good and without tools. Easiest with boat tail bullets but can work with flat base.

Get a fired case that chambers in your rifle and is a slip fit on the bullet you are using. Run a ring of GEL super glue around the inside of your case. Now with the rifle muzzle down, drop your bullet into the chamber point first. Insert the case carefully into the chamber over the bullet and seat it gently with your finge.. Close the bolt and store the rifle muzzle down for a few hours. When you eject the round you will have a “dummy“ round that shows you how long that bullet is seated to “kiss the lands”. Adjust your die as desired.

I do this with all my milsurps but honestly I must default to “magazine length“ in many loads.

 

[STG_58_guy]

Now, there is a very good topic of discussion Sir. I think you will find that the cartridge headspace is exactly that and provides a space or set back from shoulder to chamber shoulder and does not actually locate from or by the shoulder at all. The measurement from the base to the lands should be a consistent and much more accurate. We are in agreement that the OAL is not particularly accurate and only gives a basic minimum safe length for a particular combination.

I certainly agree with your description for a factory round. But these fire formed lovelies we're talking about, is that still true?

I do believe the chamber is designed to leave a little clearance between the bolt face and shoulder. I suppose in your set up, the bolt face pushes the base forward until either the shoulder contacts or the ogive touches the lands. Do you think it's the latter the way you're setting up your loads?

Do you think you could close the bolt on a well made round where the shoulder bottoms out and the bolt face pushes the base forward another 1000th of an inch? But since the shoulder stopped forward movement, that additional thousandth didn't get your ogive any closer to the lands. I don't know. I bet you could get at least 5/10,000 of "crush" on a 7.62 x 51 after the shoulder bottomed out. Could you get 2/1000? I'm starting to think the bolt would get hard to close on 2/1000.

I've seen video of bolts rotating closed under the force of gravity. Mine never do that.

 

[ArtBanks]

I am full length sizing my brass which is setting the shoulders back a couple thousandths and rely on the BTO to contact the lands. Just my way of achieving the results I am looking for. I keep thousands of prepped case at the ready and seat for each rifle separately. Should have made that clearer. Gave up the fire forming and neck sizing only for bench rest decades ago. Just loading for too many different rifles and as throats differ, dimensions change.