Actually your right where you should be velocity wise with those 180gr xtp"s.
A link to the lyman 48th reloading manual (free download), on page #352 lyman has load data for the 44mag/ww231 using a 4" barrel.
http://marvinstuart.com/firearm/Man...ding Handbook - 48th Edition - 2002 - ocr.pdf
The 44cal's (44mag/44spl) are fantastic cartridges. Unfortunately they are also the most misunderstood/mis-used cartridges for the last 40+ years. Dirty harry and full house loads are the modern 44mag. The 44spl has been tossed to the wayside since the 60's.
The 44spl/mag has always been known for their accuracy. What most shooters don't realize is just how easy to control the lighter 44mag loads are. What light loads like your 5.5gr/ww231/240gr bullet bring to the table is a target load that can be shot 1 handed (nra style bullseye) that has a power factor in the +/- 190 range.
Duster340 is a member on this website that had a nice collection of 44cal wc molds. Perhaps you could do a search and see if he listed any good/bad loads/testing. I've owned a lot of 44cal wc molds over the years, this is the last batch I owned.
Of those wc's/hbwc's pictured above, I sold 3 of them off and still own the 200gr and 220gr molds. The 200gr wc pictured above is a type III wc that was cast from an old cramer nose pour mold. The 220gr cast wc is actually a 220gr hbwc.
6.0gr to 6.5gr of clays and any 180gr to 250gr cast bullet in 44mag cases produce extremely accurate loads. That 200gr nose pour wc (perfect bullet bases every cast bullet) is a type III style wc that has a tapered nose that excellent for bullet/forcing cone alignment. 25yd 6-shot test group
Low pressure loads and cast bullets in the 44mag (16,000psi or less):
Typically you want to look for bullets that are made with low bhn alloys. You also want small bottom drive bands/bullet bases and square lube grooved bullets if you can find them. The short bullet base/bottom drive band will collapse/seal faster than it's larger counterpart increasing velocity. Same with a soft alloy VS hard alloy along with a square lube groove will collapse at less pressure than a rounded lube groove.
Both these bullets are cast with 8/9bhn alloy and then pc'd. The red bullet is a 245gr Keith style swc hp. The green bullet is the cramer 200gr wc.
I used those 2 bullets to do a little testing with a 2 1/2" bbl'd charter arms bulldog/44spl. I used 8.0gr of power pistol with both bullets which is a standard pressure 15,000psi load. I wanted to see if these loads would hit to the poa @ 25ft using a 6-oclock hold on the small white inner circle of the target.
While 5 shots aren't definitive by any means, that target pictured above was very telling.
Both bullets used the same load. The swc is heavier and seats deeper in the case (less case volume ='s more pressure). Yet the 200gr wc had a higher velocity. This is because of the smaller bottom drive band/bullet base being more efficient sealing faster/better so less gas/pressure escaped with the short start pressure of the load.
The other thing that target told me it was defiantly time to get rid of the wood grips. The heavier longer bodied bullet had more twist/grabbed the rifling better. My grip/hands aren't what they used to be and the revolver was twisting in my hand (low right group).
Anyway something to think about. Low pressure loads ='s small bases with lube grooves that collapse easily and soft alloys.
