1873 Trapdoor leading issue question

[Rapidrob]

Been shooting cast for 60 years now and ran into a leading issue on my Trapdoor rifle I've not seen before.
I was shooting a RCBS 460 grain RNFB bullet lubed with Red Rooster bullet lube and bullets sized to .458. Smokeless powder load at 1,200 FPS.
The bore of this rifle is bright and shiny with no pitting or other Black Powder caused problems.
Right at the forward barrel band the barrel started to lead up. No where else in the bore. The barrel band is about 5" from the muzzle. I could feel the lead build up with the bore brush and the patches being run though the bore.
The lead was very easy to remove and there was more than I though there would be as it came out in flakes.
Any idea as to why just at the barrel band and further out to the muzzle leaving the rest of the bore lead free?
The bullet was a full speed there? Max barrel friction heat?
What say you?

[cwtebay]

I had a similar experience with a rolling block Remington in 43 Spanish. I was told that this is due to uneven barrel heating and vibration from the barrel band contact. The effect is amplified with extended shooting and is also more noticeable the farther away from the breech it is. Of course cleaning rod damage is very common, as are bulges from squib loads. Perhaps I had smoke blown up my trapdoor, but it sounds reasonable.
Mine doesn't seem to detract from accuracy using either cast or jacketed bullets.
I'm sure there will be more qualified contributors here shortly.

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[Larry Gibson]

Specifications for the M1873 "Trapdoor" call for a bore of .450 and a groove depth of .005" Of course there are + tolerances but that means basically the groove diameter is more than likely .460 to as much as a reported .466 + groove diameter. Thus, first of all, the bullet is too small.

Then given the long barrel of a trapdoor rifle the lube is probably giving out. You might try an application of a thin coat of LLA (let dry thoroughly before loading) if have any of those bullets left. If you don't cast your own and order more bullets suggest you find some at least .460 cast of soft alloy such as 20-1 and lubed with a soft lube such as SPG. That lube is soft for BP use but will do just fine in a TD with smokeless.

Suggest you read my posts in ; https://castboolits.gunloads.com/showthread.php?190999-My-Trapdoor-Loads-Technique-and-Equipment

[cwtebay]

(more qualified = Larry Gibson)

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[M-Tecs]

I've owned about a dozen originals. Other than rebarrels or replicas I've never found one under .460" with most being .461" to 463". Largest I've owned was .465"

[Rapidrob]

Thank you CWTEBAY, that makes sense.
I think I will just powder coat the bullets from now on and be done with the leading. The coating will bring the bullet up to .460 anyway.
The rifle shoots very well with .458 bullets now. See my recent post.

[gwpercle]

Thank you CWTEBAY, that makes sense.
I think I will just powder coat the bullets from now on and be done with the leading. The coating will bring the bullet up to .460 anyway.
The rifle shoots very well with .458 bullets now. See my recent post.
I was going to suggest trying another lube , like a soft Lithi-Bee or SPG , it sorta sounds like the lube was running out at that distance down the barrel ...But , powder coating should cure the problem nicely .
Gary

[Terryrm1-03]

I shoot a .463+ 450 gr with LLA.
I run them at 1100 fps.
22 caliber speed.
They are 1-2" groups at 100yds.
And can shoot all day long.
That's with my Rifle & Carbine.
Just wanted to share, hopefully will help you out.
Good luck!
I just LOVE my TD's!!

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[Rapidrob]

I cast up 100 bullets today and double powder coated them. They now read .461. I test fired one into my bullet trap from a dry bore and there was no leading as one would expect.
I'll try again this Saturday to see if the rifles shoots a little better with no leading!:bigsmyl2: