Chainsaw Repair

Run whatever gauge that matches the bar you end up with.  Easiest/cheapest large frame Mac bars to find are 16-24" hardnoses.  They're usually either .058G or .063G.  If the bar's .058G you might as well run 3/8" pitch chain, as that'll be cheaper and easier to get than .404-.063G.  Get the bar first.....

These saws use their own bar mount.  I don't have the Oregon, Windsor, Sandvik, GB, etc bar mount codes for the large frame Macs, as folks with old bar catalogs seem to guard that info like it's their bank account # and pin #.  Not sure why...

In any case, there were two bar mount patterns used by McCulloch on the large frame saws (and a couple variations within those two).  They all have 3/8" slots, as these saws have 3/8" studs.  The differences are in the tail profiles and details of the oiler holes/slots. 

As long as you use the corresponding bar plates (early or late style) you can use all the variants on almost any large frame Mac saw.  There is a detail regarding the tensioner setup on very early saws (your 1-40 may fit into this category) that does limit your options somewhat.  Still, finding a 16-20" bar that will work with that saw is easy (I have a few and would probably part with one).  You'll probably want to put a 20-24" bar on that 250 as well.  I may have one of those for you too.  Can't remember what's left in the stack.  Done a lot of horsetrading over the last year....

I did a long winded 2-part writeup (with pics) on the large frame Mac bars in the McCulloch thread on AS.  Will have to dig that up and post it here.  That may take a while to find....