New vs 1X Fired Brass...POI Change?

[Ingwe]

Hello Fellas, I would just like to pick your brains here about New vs 1X Fired Brass.

As for my first question, I already know that the answer is "Shoot it and see" but until I do, can you guys tell me if POI will change when I use my 1X Fired Brass in my rifle?
I am full-length sizing my brass so I am thinking that it "shouldn't."

What are your thoughts/experiences on this?

Also, why do people seem to covet 1X fired brass from their rifles?? What is the benefit of it?

Thanks Fellas!

 

[Capt RB]

When you reload for the first time after firing in your chamber you have a match to it's dimensions. In the past I would just use a lee collet neck sizing die for my match rifles. Today I will set up my die to push the shoulder back .0015-.003. I run .0025 neck tension in just about every rifle I own except the lever guns. The advantage is your not wasting any energy pushing the case to form to seal your chamber. Done right you can get very good characteristics if you have optimized your given load to your barrel's harmonic mode. Start pushing the shoulder much more than .002 and your losing energy again which can show up in excessive deviations in velocity which will show up vertically on target at distance.

 

[Ingwe]

When you reload for the first time after firing in your chamber you have a match to it's dimensions. In the past I would just use a lee collet neck sizing die for my match rifles. Today I will set up my die to push the shoulder back .0015-.003. I run .0025 neck tension in just about every rifle I own except the lever guns. The advantage is your not wasting any energy pushing the case to form to seal your chamber. Done right you can get very good characteristics if you have optimized your given load to your barrel's harmonic mode. Start pushing the shoulder much more than .002 and your losing energy again which can show up in excessive deviations in velocity which will show up vertically on target at distance.

So what is the benefit of doing this?
That is my original question....why do you do this?

How about my POI question?

 

[FURMAN]

The answer to your question is most often but not always. New brass is often much smaller than your chamber. Some of the energy is used to expand the brass to the chamber wall. After firing and sizing the brass is closer to the chamber dimensions. To what extant has many variables including chamber design and dies. This will use less energy to expand the brass and chamber pressures will rise. You will see this, when it happens, in higher velocity and often pressure signs with the exact same powder charge. When it happens you will most likely see a poi shift and will need to back the powder charge off to get to the same velocity.

Practical application is lets say you found an accurate load with a 180 grain bullet in a 7mm Rem Mag at 2950fps with new brass. Now you have fired all your brass and you reload the same load and velocity is near 3000fps. You will need to back powder charge off to get back to the 2950fps.