Importance of expander die for cast bullets?

First topic message reminder :

How important is getting a Lyman Type M or one of PhotoEscape's HTC expander dies when loading cast 45 SWCs? I've been using the standard Dillon powder die, but for whatever reason I'm REALLY struggling to get anything that will group decently; 3" at 25 yards (and up) is the norm.  I'm using 160 - 200 grain SWC from different manufacturers (Brazos, Summers, etc.) and W231, Red Dot, and Bullseye loads over a range of powder charges and am getting really frustrated.  I'm assuming it's not a gun problem as it's pretty much the same using either of 2 Tanfoglios or a Pardini. It's either me or some fundamental loading problem.  (Don't even get me started on the tribulations of trying to load decent cast 9mm).

Could it be something as simple as a slightly deformed bullet base from seating? I've pulled a few bullets after seating and crimping and swaging doesn't seem to be a significant problem.  When I rest the bullet on the case mouth it's sometimes slightly askew, but they appear to seat straight.  I seat and crimp in separate steps.

DA/SA wrote:What have you been shooting in these pistols prior to this, and how did it group at 25 yards?

Prior to this I just used centerfire for plinking - bowling pin shoots and steel plates at 15-25 yards.  That's my excuse for saying I just used cheap Aguila 230 gr and various brands of inexpensive remanufactured 230gr FMJ.  It groups about the same as what I'm loading with the 160 - 200 gr SWC.  I thought <5" at 25 yards was normal for inexpensive remanufactured ammo.

I loaded and then pulled a 185 uncoated (bevel base) SWC. Although the bullet didn't measure out as swaged (well, maybe a little; .452 going in, .451 to .4515 coming out) there was some deformation at the skirt where it was pushed into the brass.  It amazes me that that would be enough to make a difference.  I figure guys have been loading and shooting high master scores using basic expanders for years.

Once I started reloading rifle I thought "I should reload pistol, too, and try a 2700 match".  For pistol I shot/shoot air pistol, free pistol, and the local indoor 50' .22 league.  With those I have no problems getting good groups offhand, let alone off a bench, so I don't think it's my shooting that's the problem.

You said one of your pistols is a Pardini, I don't have one, but others on this board shoot them.  Based on what I have seen from other posts, with Zero 185 JHP bullets, it should group one ragged hole at 25 yards.

50 years ago my coach and mentor said crimp until you can't push the bullet down with your thumb

Old School