10-29-2021, 02:30 AM
(This post was last modified: 10-29-2021, 02:39 AM by trianglevelvet.)
I'm guessing you're talking about small base dies.
The usual way that people make the decision on whether they're needed is by sizing some brass and seeing how it chambers.
A standard way to do this is to start with some factory ammo.
This will be sized to SAAMI specs. Fire some in your gun and collect the brass.
Use a headspace comparator to measure some of the fired brass.
Write down the measurement.
If its a bolt gun you usually want to size your brass "0.002 shorter than the fired size.
For a gas gun you'll be looking to size it "0.003-" 0.005 shorter than fired size.
Test your sized brass to see if it chambers smoothly in your gun.
Most of the time as long as you're full length sizing you won't need a small base die.
The reason small base dies were invented is because people had the idea back in yesteryear that neck sizing might be the key to accuracy.
After a few firings the body of the brass would no longer fit the chamber.
And if it was full length sized after that it would still be a tight fit since the brass was springy and work hardened and would spring back.
So small base dies were introduced to help get the brass back to a decent size.
If your chamber is made to spec and your dies are made to spec and you full length size after every firing you'll likely never need a small base die.
Now the other question:
I think you're asking if using a small base die will decrease your case capacity and increase pressure.
Yes.
How much?
No way to know without measurement of case capacity between brass sized in each die.
If you switch to using a small base die its probably good idea to test charge weights starting low and working up,.
This difference is probably very small , but if you're working near max charges it could be enough to make a real difference.
The usual way that people make the decision on whether they're needed is by sizing some brass and seeing how it chambers.
A standard way to do this is to start with some factory ammo.
This will be sized to SAAMI specs. Fire some in your gun and collect the brass.
Use a headspace comparator to measure some of the fired brass.
Write down the measurement.
If its a bolt gun you usually want to size your brass "0.002 shorter than the fired size.
For a gas gun you'll be looking to size it "0.003-" 0.005 shorter than fired size.
Test your sized brass to see if it chambers smoothly in your gun.
Most of the time as long as you're full length sizing you won't need a small base die.
The reason small base dies were invented is because people had the idea back in yesteryear that neck sizing might be the key to accuracy.
After a few firings the body of the brass would no longer fit the chamber.
And if it was full length sized after that it would still be a tight fit since the brass was springy and work hardened and would spring back.
So small base dies were introduced to help get the brass back to a decent size.
If your chamber is made to spec and your dies are made to spec and you full length size after every firing you'll likely never need a small base die.
Now the other question:
I think you're asking if using a small base die will decrease your case capacity and increase pressure.
Yes.
How much?
No way to know without measurement of case capacity between brass sized in each die.
If you switch to using a small base die its probably good idea to test charge weights starting low and working up,.
This difference is probably very small , but if you're working near max charges it could be enough to make a real difference.