What size expander should I make..

[Bill in Ky]

I am new to casting and to this site. I have gained a lot of information in the week I have been coming here.
The bore on my XDs 45 is .450 I have been advised to size my boolits to .452. I am a home machinist/gunsmith and I am planning on making my own expander die.
My question to those of you in the know is... If you were sizing your boolits to .452 what size would you want your expander to be? I have a 3 die RCBS dies and the expander in it measures .450, that got me to thinking that it would size my boolit down. Would an expander of .4515 be better, or would it not hold the boolit securely?
As I have said, I'm new, haven't loaded a round yet, so if you have any information, please let me know...
Thanks in advance !!
d:^)

[Doc Highwall]

Do you mean groove size? The groove size is larger then the bore size. In a typical 30 caliber rifle barrel the groove is .308" and the bore is .300 for a .008" divided by 2 equals .004" high lands.

I make my expander dies .001" to .002" smaller then the bullet size that I am shooting. In my 308 Winchester I am shooting bullets that are .310" to .311" and I am using a .309" expander.

[wv109323]

Usually it takes .001 or .002 interference to have enough neck tension to hold the bullet during firing and feeding.My experience says .450 or .451. though you not not want bullet distortsion during seating.

[Mk42gunner]

You need neck tension to hold the boolit firmly to prevent the boolit telescoping into the case and raising pressures drastically while feeding in semi-auto pistol, especially since most of them are only taper crimped these days.

I would size at the recommended .452" and use the .450" expander that you already have. If it works, you are good to go. If not, then you can experiment.

I can only think of a very few (like maybe three) .45 ACP's that needed a smaller cast boolit than .452".

Robert

[Bill in Ky]

Yes Doc, I am talking about the groove diameter being .450.

I am also casting 9mm's and I don't have a gun yet... When I get one and slug the barrel should I size my boolits .002 over the groove diameter??
Thanks for all the information!!