Correct seating depth for New Case vs. x1 Fired?

[Marksman_92]

Greetings,

So I have just started loading and I will be using my federal gold medal match 308 x1 fired. The brass I have on hand has been fired from my current rebarreled 308 and from the factory remington barrel that was originally on the gun. I didnt segregate the brass after firing and now I have approx 1000 cases half from the original chamber and half from the new chamber. Given this I am going to be full length sizing the brass on the first go around until they all have been fired in the new chamber then I will bump back .002.

My question is about seating depth. I have a Hornady seating depth gauge to determine max seating length however I wont be using a once fired modified case from my rifle and will rely on the hornady modified case then measure the difference in headspace from my case to get the measurement.

I will be using Varget and 175 SMK for my loads. So say I full length size my brass and I seat the bullet to 2.800 for my first load development. Now that I have once fired brass and I will not be setting the shoulder back as far as the first size since I will only bump them back .002. Do I seat my bullet to 2.800 again? Or do I need to adjust my seating depth since my brass is now larger since it is sized for my chamber.

To simplify, how do I ensure my bullet is the same distance from my lands from the full length sized case I will be using on the first test fire to the shoulder bumped case I will be using on the second firing?

 

[spife7980]

The distance from the bolt face to the barrel leade (back of the case up to where the bullet touches the barrel) is the same regardless of where the case shoulders are.
That is dictated by the steel in the action and barrel which is steady, it’s the ammo inside that you change if you want to.

 

[charnicus]

The distance from the bolt face to the barrel leade (back of the case up to where the bullet touches the barrel) is the same regardless of where the case shoulders are.

This

 

[straightshooter1]

Greetings,

So I have just started loading and I will be using my federal gold medal match 308 x1 fired. The brass I have on hand has been fired from my current rebarreled 308 and from the factory remington barrel that was originally on the gun. I didnt segregate the brass after firing and now I have approx 1000 cases half from the original chamber and half from the new chamber. Given this I am going to be full length sizing the brass on the first go around until they all have been fired in the new chamber then I will bump back .002.

My question is about seating depth. I have a Hornady seating depth gauge to determine max seating length however I wont be using a once fired modified case from my rifle and will rely on the hornady modified case then measure the difference in headspace from my case to get the measurement.

I will be using Varget and 175 SMK for my loads. So say I full length size my brass and I seat the bullet to 2.800 for my first load development. Now that I have once fired brass and I will not be setting the shoulder back as far as the first size since I will only bump them back .002. Do I seat my bullet to 2.800 again? Or do I need to adjust my seating depth since my brass is now larger since it is sized for my chamber.

To simplify, how do I ensure my bullet is the same distance from my lands from the full length sized case I will be using on the first test fire to the shoulder bumped case I will be using on the second firing?

I hope I'm understand your question correctly . . .

If you're just bumping the shoulder (along with just neck sizing) or FL sizing, the shoulder should be in the same place if you're adjusted your dies properly. In any case, the shoulder position isn't going to determine you're distance from the lands. So, if you're going to seat your bullets COAL to the SAAMI spec of 2.800, whatever seating depth you measured with your Hornady gauge doesn't really matter nor does it matter if you're using FL sized cases, nor does it matter if you're using only neck sized cases as the seating depth is the same for either when you're COAL is the same.

 

[Marksman_92]

I guess I am curious why people use a modified case with the hornady coal tool vs using the hornady modified case? Modified case meaning they fireform a case in their rifle and then drill and tap the primer pocket to use the hornady tool.

 

[charnicus]

I guess I am curious why people use a modified case with the hornady coal tool vs using the hornady modified case? Modified case meaning they fireform a case in their rifle and then drill and tap the primer pocket to use the hornady tool.

Maybe to make the tool more accurate? This I believe to be the best way. (Link below.)



I never could get very consistent readings with the Hornady tool. Tried the above method once and threw it away.

 

[Marksman_92]

Found the answer to my own question. You can watch the whole video but the specific issue im talking about it addressed at 17:00 in the video.

 

[spife7980]

My question is about seating depth. I have a Hornady seating depth gauge to determine max seating length however I wont be using a once fired modified case from my rifle and will rely on the hornady modified case then measure the difference in headspace from my case to get the measurement.

You said as much right here.

It’s only a difference in the distance from the lands measurement due to your modified case which does not accommodate the space between the bolt face and the modified case. The actual place you seat the bullet relative to the actual rifles chamber, not your modified case, remains the same.

 

[Marksman_92]

You said as much right here.

It’s only a difference in the distance from the lands measurement due to your modified case which does not accommodate the space between the bolt face and the modified case. The actual place you seat the bullet relative to the actual rifles chamber, not your modified case, remains the same.

So say I measure my CBTO overall length in my rifle and I use the hornady case and I get 2.560 (arbitrary number) then I measure the headspace on the hornady case and my FL sized case. Hornady case is: 2.230 and fl size case is 2.228. I then would subtract.002 ( difference from hornady case to FL size case)from my measurement and then subtract the distance I want to be from my land (.020) and that gives me my measurement.

Likewise I then fire that brass and it grows .008 and I bump it’s back .002. It is now .006 longer now so I add that distance to my CBTO measurement for the next seating depth. Bc the case body is now longer.

 

[Hudsflywater]

So all of this is totally confusing to me too!! I have done it both ways (in the videos). I liked the first way, it seamed to make more since, your measuring lands touching with the back of the bolt face. but he is using a single feed action with no ejector. Its a pain in the arse to remove the ejectors every time you want to check bullet seat depth to lands, and eventually you end up bending one of the roll pins and then your stuck!

The second video he is measuring from the distance from the shoulder to the lands, but it still doesn't make since why change cases if your measuring from the shoulder? it wouldn't matter how much you "bumped" the shoulder, its the point where the case makes contact with the shoulder to the lands, and has no real reference to the back of the bolt face right??

I think I'm just going to give up and use the Hornady modified case, its a reference number and what it .002 or .004 difference really going to make??

 

[918v]

I use a slit case to find the lands. But with the components you’re using I would just start at 2.800” and tune from there. I would also sort the brass. You only have two kinds in there, so they will be readily identifiable and sortable using your dial caliper.