Uh-oh! 20 Practical in AR format, what Neck Bushing do You use?

[L.Sherm]

As you can see hogs with zero freebore is 1.795 your print says 1.80 with .020

 

[L.Sherm]

Anyway you look at in i will bet your into the lands alot.

 

[L.Sherm]

Easy to test seat a bullet at 1.75 and chamber it in the rifle and see what happens on a dummy round

 

[jelenko]

Easy to test seat a bullet at 1.75 and chamber it in the rifle and see what happens on a dummy round

Exactly.
When you do, ease the bolt carrier forward - letting it engage the lands. Once you start pushing on the bolt/bolt carrier, it'll get tight into the lands.

 

[TheCZKid]

Okay, I made up a dummy case, with enough neck tension to make the bullet very tight but still slide if it had pressure on it, and yet wouldn't move once the bullet was pushed in. I'm glad you guys suggested that...

 

[jepp2]

So, I was curious if you guys who use AR's use the 225 bushing?

Back to your original question on sizing die neck diameter. It all depends on:

- do you anneal and how long (how many firings) since you last annealed? And the amount of work you put into reducing and expanding the size of the neck can dictate the frequency you need to anneal.
- and in followup to the 1'st question, what did you use for your brass to form the 20 Practical brass? If it was fired brass (and it almost certainly was) then it already had at least 1 firing after annealing. You added a lot of work hardening when you sized the neck down to 20 Practical.
- the neck thickness of the brass you are using. LC tends to be on the thin side, Lapua is the thickest.
- how much neck tension you want to use

The bushing diameter you need to use depends on the neck diameter of the brass you are using and the work hardening of the brass.

I have 3 20 Practical die sets. I don't like using bushings and the runout they induce. But the most recent of those 3 die sets was from Whidden. When I ordered them, I told them I wanted a 0.224" neck + zero, take the tolerance on the - side. It came to me exactly 0.224" (Good Job John!). I use that die exclusively for my LC brass since I found the other 2 die sets didn't give me quite enough neck tension on the LC brass. I anneal every 3 firings.

 

[dellet]

You can pull the upper and bolt carrier , seat a bullet long, and push it into the chamber with your finger. Then gradually seat it deeper until no longer sticks in the lands. When it drops out under its own weight you’re there.

It the Hornady case is not sized the same as what you are shooting, it will give a false reading. Remember that with the comparator tool you are really checking shoulder datum to lands, not headspace. You’re looking for when the shoulder starts touching the chamber instead of the bullet in the lands. If headspace changes, base to shoulder, seated depth or jump will also change, but base to ogive measurement will remain constant.

You might also want to check base to to shoulder datum after chambering. make sure chambering the round with basically with a hammer, is not setting the shoulder back and driving the bullet into the lands.

One last thing to consider is that a compressed load puts pressure behind the bullet, so with the inertia of chambering, a compressed load is more likely to have the bullet move forward, than a dummy round.