I often have this problem with feigning ignorance--I'm believed.

Otto

Been a Trapdoor BP shooter 40 odd years half a dozen different full rifles, carbines and one H&R reproduction. Plinking Hunting and Match shooting even a little bit of 1000 yard competition. Almost all Black powder. Only one I never used was a copy of the Arsenal long range match rifles used in competition against Sharps Remingtons and the like.   I like them much better than the period commercial actions. Excepting the Long range guns or a few one off light sporting rifles Springfields were Military rifles not built for competition.

Due stock shape ill suited to sand bags. Sight on the barrel not close to your eye & short sight radius. Large side hammer, heavy trigger pull, variable bore sizes & "bumped up" bullets, Trapdoors are 4 moa Rifles.  Not to say a few shots may land close, 10 shot groups under 4 inches at 100 yards is normal performance.

I doubt if anybody can refine or even tell one black powder load from another way a Trapdoor handles on bags.  Use a bullet that fits the bore, lubed with good grease properly seated, consistent black powder charge with a hot primer is about all you need to do to get Arsenal quality ammunition. 

Best book on the topic is Wolfe's "Loading for the original Trapdoor". Wolfe draws heavaly on Arsenal loaded ammunition specs with modern components Government arsenals did extensive work on 45/70 performance in Springfield rifles, no one has come up with anything better

Enjoy it for what it is, a retired War Horse. Don't pay any attention to Internet group sizes.

Boats

You may want to compress the wad and powder just a tiny bit as you seat the round, maybe a 64th of an inch.

Your lube should work fine to start.

Make sure your wad matches the size of your bore.

I am not a fan of lee molds, but what really matters is this, what is the diameter of the slug's nose and the diameter on the grease grooves?  The nose should be about 2/1000 narrower than your barrel diameter, and the grease grooves about 1/1000 wider than the barrel diameter.  What sort of alloy are you casting?  Changing alloy can change the size of the round as cast, and some rifles prefer different alloys.

There are much better molds out there.  You get what you pay for.  Any mass produced molds are risky, as they can vary in diameter from one mold to the next.  Today's mold may fit your rifle, tomorrow's will not. This is probably historically accurate though - in the old days there was more variation than today.

Store bought bullets does not compare well to properly home cast rounds.

Quote:

There are several better moulds than Lee, who is the 'low price leader' for a reason. Generally, the more you pay the better you get with moulds. But, depending on what you are trying to accomplish, Lee may be fine. Lee, Lyman, RCBS, Saeco, BACo and then custom by Brooks, Hoch, Jones and others is a reasonable bottom-to-top rule-of-thumb. 

Have you slugged your barrel? If not, then your bullet could be either too large or too small. If too large, then you can often size to the correct dimension. If too small, then you are generally in need of another mould/bullet. 

If you were shooting brass for the first time, you may find that your fire-formed brass gives better results the second and subsequent times out.

Can you tell us what 'custom' means in relation to your TD? Lined or after-market barrel, etc.

What mix of lead are you casting with? As mentioned above, you may using too soft a mix and the bullet is not holding its shape.

Where do you live? You may be close to someone who would be more then happy to help get you rolling with BP. However, think you are well on your way and asking questions here is a good place for additional info. 

Generally, with a trapdoor, you will get a bit better accuracy with a 400 grain slug, as that was how the trapdoor was first set up.  Most modern repo's have a tighter twist for the longer slugs we prefer today.

And another.  Not really satisfied with the metal finish.

Damn, Otto, I like those!  They're very close to what I intend to do with the old trapdoor in my safe.  Where did you get those steel pistol grips, or are those part of the trigger guard?