LEE 90309 9MM .356 mold

[knifeman85]

I have been searching the stickies for info on bullet molds. This is the mold I have..Its 124 gr round nose with single lube groove.The question is this.. its been suggested I need to slug my barrel and determine what dia cast bullets to shoot...356,.357 etc.DO I really need to do this since the original factory ammo is .356? and DID I buy the wrong mold? The stickies suggest this I understand...but my factory projectiles are .356 I am reloading now.

[JonB_in_Glencoe]

There is two choices here.
Slug your bore to know what size your boolits should be,
OR
Just go with .356 and if you get Lead fouling, then increase the boolit size by .001 and see how that goes.
Good Luck.

[tazman]

You get by with .356 in factory because they are loaded with jacketed. Cast needs to be a bit larger to make sure the bore seals.
The boolit you get from your mold usually drops a bit larger than the stated dimension so you can resize to what your pistol needs.
The mold you purchase should work fine.
Slug your bore, it will save you a world of headaches. Go with a boolit diameter 1 or 2 thousandths larger than your groove diameter. This will provide a good boolit fit and reduce or stop leading all together.
My barrel slugged at .3553. I size to .357 for my 9mm using the same type mold you have. I get excellent feeding and accuracy in my pt92.
The mold drops at .358 for me and can be used in 38/357 if I wish.

[tazman]

You will want to read this link. It cover the issues you are asking about and may well be the best article I have ever seen for starting to load cast for the 9mm.
http://castboolits.gunloads.com/showthread.php?121607-Setting-up-for-boolits-in-a-new-9mm

[oso]

Have you actually measured original factory ammo? How many brands at which bullet weights were actually (as opposed to nominally) .356" diameter?
You do not need to slug your barrel unless you want to actually know something as opposed to believing whatever.
By the way, not all Lee 90309 356-125-2R molds cast exactly the same boolit. Don't worry, if you did buy the wrong mold I'd be happy to have another one of those!