I want to apologize in advance, I know this topic has been brought up before. I've combed through the first 100 pages on this reloading board and the single shot rifle board. When I use the search I'm not getting results, my fault I'm sure. 
I have an original 32/40 with a six o'clock extractor and a lugged hammer. The bore slugs at .320 and I can get .321 on 1 part of the slug. The barrel and serial numbers match. I started by casting bullets with a Jerry Barnett 198 grain breach seat mould, the only mould I have since my other one is out on loan. Some with pure lead, some with 1/20 alloy which was in one of my lead pots. They both taper from .3145-.320. Both were loaded with 38 grains 2f Triple 7 and 2f swiss with a meat tray wad. I loaded these as fixed ammo so most of the bullet was out of the case but being a single shot OAL is obviously not an issue. An older gentleman at my club gave me hell for using that much triple 7 since he said it's hotter than black. My chrono says differently. 1/20 alloy with T7 is 1359 fps average of 6 shots. Swiss with  1/20 is 1382 average for 5 shots. Pure lead T7 is 1345 average for 5 shots. Swiss 2f 1371 average for 5 shots. I've since ordered a double cavity mould from Accurate with a 125 grain and 165 grain cavities. sorry for the long question but I figured I should give as much info prior to asking if I'm pushing this beautiful old rifle too hard? The rifle is in amazing shape with a 99% bore and still locks up tight. I have no plans to shoot smokeless in it at this time. Thanks in advance for all your replies and again I apologize for the repeated topic. I also don't plan to shoot the rifle very much as far pounding away on a firing line 100 shot match but I do like figuring them out.

This one you will get a lot of 2nd hand info on. My personal feeling is that smokeless powder loads are what tainted the M44's reputation. There are sure a lot of loose ones around. 
  My personal first hand experience is this; About 30 years ago I was shooting schuetzen matches where it was cast bullet, black powder only loads. I built an offhand rifle out of a M44 that was originally a 25/20SS which did not have a lugged hammer. I put a Douglas 1-18 .375 barrel on it. I shot it with Cartridge Goex and the old Lyman 250 gr. bullet. I set up the breech block pretty snug to the barrel and the new lever so it barely went over center. I shot that rifle 1000's of rounds and when I eventually tore it down and put it back together with the original parts it had not loosened any discernible amount. 
  I think if you have a tight gun, original loads aren't likely to cause trouble. by original loads, I mean;
1. Original weight bullets
2. Not harder than 25/1 alloy
3. Not over groove diameter
4. No duplexing with smokess
5. Original twist
6. Use Fg or FFg blackpowder
A lot of "modern" black powder culture breaks from these concepts and are likely to raise pressures.

Welcome to the forum

I don't think there is always a good correlation between pressure and velocity.  Look at Trail Boss for example.  Much more pressure than most powders for a given velocity.

Everything I've heard about 777 says it's higher pressure than real black powder.

I don't know anything about the safety margins in those actions, but if it's tight I'd shoot Fg in it and keep an eye on it.  You aren't going to find lighter loads than Fg.   

Chris.

Some things to check out: 

How much clearance is there between the hammer lug and the breechblock with the action closed?  Has to be some, but not much.  Maybe .002".   

How much clearance is there between the rear of the breechblock and the curved shoulders in the frame with the action closed?  Best is zero, but rarely achieved. I use thin cellophane for feelers.  It's a fussy job to get them to stay in place, but keep at it.  If it'll trap .0015' it's good.  

Is the breechblock clamped against the barrel face with the action closed?  The lever should "snap" closed as the linkage goes over-center.

Is there any detectable play in the link pins?  Should be under .001", but if the lever still snaps closed it can be more.

Phil

I just wrote this rough draft for Tom Rowe's upcoming book:

"Limitations were encountered".  The geometry of the swinging-block action transmits a load onto the toggle link almost equal to the direct breech thrust.  To add to that, the internal parts, especially the link, were just case-hardened mild steel, not heat treated high carbon as they should have been.** Stevens was always building to enable a low price.   The lugged hammer was a work-around, taking most of the stress off the link.

The receiver itself isn't fragile.  I once fired a double charge of AA#9 in a .25-20 I'd just rebuilt.  Pressure later estimated at over 80,000 psi, and  the breech thrust at something over 5000 lbf.  What happened?  Nothing. I didn't even realize it had happened until I opened the action and the primer fell out. 

But that was a singular event.  What DOES happen with constant repetition, even with reasonable loads, is that the holes in the link get worn and battered oval, loosening up the headspace. While the Schuetzen men must have fired an awful lot of .32-40 black-powder rounds through their high grade lugged-hammer actions, the assembly of those premium rifles would necessarily have required careful and costly hand fitting to handle 1500 lbf. breech thrust. By 1900 the new smokeless hunting loads were generating more than double that.  So Stevens correctly judged that, to provide a reasonable service life, the low-cost 44 action would be restricted to cartridges generating much less breech thrust. The rimfire cartridges that were the bulk of 44 production after 1903 produce less than 600 lbf. thrust, and give no trouble.  Even the popular .25-20 generates only about 850 lbf. The 44 remained an excellent rifle for small game and .22 rimfire competition right up to the end.   

Well, yes....I've seen a few pages of his working draft.  As always some stunning photography of some stunning rifles.

That's decent for what is probably a much-used gun.  I'd leave it alone.  For the rimfires and the .25-20 SS the gun would be perfectly fine.  Only for a .32-40 or .32 Ideal would I want the shoulders in actual contact, and then only if I were rebuilding it.

Maybe also for a gun being converted to .22 Magnum or .17 WSM.