I am trying to determine a better load for my m1888 trapdoor. Up until now I have been using 52gr by volume of 2f 777 with a 500gr LRN bullet SPG lube and a .030 gasket wad. I have been happy with this 1250fps load for a while in that it follows the trajectory of the military load. The issue I have always had was with accuracy. I have a great bore on the rifle but I will get 3-4moa groups. I have been loading to the SAMMI length all this time however which apparently the length for the 45-70-405. The 500gr bullet has a longer shank and I want to start loading it further out in the case but this will mean needing to use fillers and loosing velocity with the 52gr load. I was referencing the hodgedon load data and they suggest a 485gr bullet 60gr of 2f 777 and a velocity of 1161fps. I am a little hesitant to just throw 60 gr behind the 500gr bullet which in actuality casts out to a weight closer to 550gr because of my near pure lead alloy but I am wondering if starting at 55gr and working my way up 1gr at a time might not be a bad idea. I know that 777 is more energetic than holy black but up in AK I cannot get black powder and unlike pyrodex  777 gives me single digit velocity SD's like black does.

here is the load data. Its on the bottom right of the second page.

here is a diagram of the load I'm trying to replicate. I'm going to use the COL of the top one for the 45-70-500

Like I said I still want to achieve 1250 fps of velocity so the bullet will match up with the sights

Have you slugged your bore to make sure your cast bullet is 0.001" larger that the bore size?  The original bore sizes were all over the map.  I know BP will bump a soft bullet up to bore dia. but I don't know about 777.  If the bore and bullet are mismatched you may never get good accuracy.

I haven't slugged it but recovered bullets measure at .462" and I size to .458 right now it will shoot 2-3 moa at 100y. So it seems like the bullets are bumping up but I guess we will see the accuracy this weekend. I'll try to remember to take photos of the groups. I'm going to test 55gr 57.5gr and 60gr by volume. Only the 60gr load approaches the same amount of compression with the new COL as did the old 52 gr load so I'm guessing that will be the closest to the target velocity of 1150 which I confirmed in my load books. 1250 was a mis quote

I love it when I answer my own questions and the answer is one I want to hear.

So here is a group shot with my old load with the bullet loaded to SAMMI COL



Here is my group with the bullet loaded to the new COL and 55gr of 777 which is what I need to push the 500gr pill at 1150. One interesting thing I noted is that the velocity only goes up 25 fps when I added 5gr more powder. I'm glad I found my new sweet load on the first try. On other interesting thing is that since the smaller dia shank of the forward part of the bullet sits into the rifling quite a ways the breech is harder to close as the barrel fouls but I noticed no abnormal pressure indicators. I wonder if this was a common experience with soldiers when the new 500 gr load was adopted. Too bad there aren't any around to ask.

Pretty common with BP.  My .50-70 does this as well.  Do you blow tube or swap to keep the fouling soft or in check?

No but I'll have to wait until its warmer out its impossible to keep anything but your dick soft when its -10 to -20 out.

Should be able to condense lots of moisture out of your breath into the bore at -10 to -20 out.  Of course, it will be frozen 7 seconds later.

It was 20 above this past Saturday but it will be well in the negatives all this week. The smoke sure stays around a lot longer when its this cold