Chamber dimension, freebore -> 300PRC / Hornady ATip 250

[georgelza]

H hi all

Wonder if those that have had custom rifles build, 300PRC thats shooting the Hornady ATip what custom measurements did you go for (like Freebore), that works well with the 250gr ATips.

G

 

[high right]

Got my own Reamer from JGS. AW2 with freebore shortened. 060

 

[Emerson0311]

If I was going custom I would go 300 Norma. My 300 PRC is not quite enough to launch 245-250gr as fast as I want.

 

[georgelza]

explain aw2?

I would love to know what OAL (as that speaks to how far the 250 is seated into the case) everyone is running and freebore (resulting in boltface to rifling) space.
headspace i'd say as min as needed to get the case into the chamber.
anyone that might be willing to share a drawings would be appreciated.
G

 

[Jscb1b]

AW2: Alex Wheeler #2. SAAMI specs of the chamber size are too tight. You get "clickers" after sizing your brass. The AW2 reamer is .002 larger at the .200 line.

 

[georgelza]

hmmm, ok, but would we not rather want a tight fit... that implies less expansion during firing, aka more stable, less stress on brass.

Whats the OAL that everything is seating their 250gr ATips into brass.

Of course understanding in front of this OAL is the jump of .060

Now being very far away... how do I get the measurements of AW #2.

G

 

[secondofangle2]

If you are not constrained by magazine length, you generally want the junction of the boattail and the bearing surface to be seated to the depth of the neck, shoulder junction. That way, the projectile is fully supported in the neck, but not seated any deeper than that and unnecessarily taking up case volume.

If you want to make sure that it will chamber at whatever length that measurement comes out to be, you have to send it to a reamer maker and have a custom reamer made with whatever free bore you want on top of that length, or you have your gunsmith extend the free bore after chambering it with a standard reamer.

 

[Jscb1b]

hmmm, ok, but would we not rather want a tight fit... that implies less expansion during firing, aka more stable, less stress on brass.

My understanding is with a SAMMI chamber, there is not enough room for the brass to expand then spring back. Then there are sizing dies that don't size the brass small enough. Google Alex Wheeler. He has really good videos on his web site.

 

[Jscb1b]

And in my experience, there is not hard bolt lift like over pressure. At the top of the bolt lift your bolt handle hits the primary extraction. The click happens when the case pops loose and the handle hits the receiver.