Trapdoor chamber cast

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Glenn R. Latham posted this 5 days ago

I finally got around to doing a Cerrosafe chamber cast on my M1888 Trapdoor Springfield.  Not having a proper v-anvil micrometer to check the 3-groove slug I though I would measure the diameter of the throat where the rifling grooves "petered out."  HA!  There ain't no throat.  The rifling grooves run right into the angle at the end of the chamber, the grooves farther back than the lands of course.

I tried two methods of measuring the groove diameter.  I wrapped a piece of .0085" thick target paper around the slug and measured (at the corners of the lands so there would be little or no deflection) and got .479".  Subtracting 2x .0085" I come up with .462".  Checking across the corners of the naked lands I also got .462".

The chamber diameter at the case mouth was .482".  My Winchester brass is .010" thick.  Adding it all up a .462" bullet will just fit. 

Now I just need a .462" bullet....

And no I 'm not going to turn case necks.  I can't see the sights well enough to justify that.

Glenn

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Bud Hyett posted this 5 days ago

Wolfe's book on reloading the .45-70 for Trapdoors in writing the book measured several bores which were .460+. The shooters at Windhill also measured Trapdoor bores again with bores running up to .463. Wolfe thought these were deliberately oversize to lessen the effect of powder fouling.

My present Trapdoor has a bore running .460 with a smooth bore. I load a soft bullet of 30:1 Pb/Sn alloy, very soft. The bullet is the SAECO 1881 500 grain round-nose dropping from the mold at .459 from two two-cavity molds. Powder charge is 68.5 grains Swiss 1 1/2 compressed with two wads, .030 and .060.

According to Wolfe, the soft bullet will swell up to fit the bore upon the ignition of powder. I've not measured bullets after firing, but have dug them up and see the marks of the lands fully engraved on the bullets. 

This load is also what I shoot in my Sharps. The Sharps has a .458 bore. It does not have the flatter trajectory of the SAECO 540 grain semi-pointed bullet, but I score better at 600 yards with this load.

The 540 grain semi-pointed shoots as well on paper at 100 yards. I sometimes think I know more then I understand about the black powder loading for the .45-70. 

Four decades ago, I was given several .45-70 405 and 500 grain Lyman molds that came in gray boxes. These were measuring the bullets fresh out of the molds, they were .462 and 463. These did not shoot at all in my Marlin 1895 .45-70. When I complained, one Windhill shooter offered to buy these molds to be able to shoot smokeless in his Trapdoors, he got a good deal. 

This decades ago era of grey box Lyman molds were known for oversized bodies and undersized noses. In contrast, the RCBS molds 45-405-FN and 45-500-FN dropped at .459 and shot well with Reloder #7. I cast and shot the RCBS bullets. They were sized in .459 die to only add lube. This alloy was 94/4/2 Pb/Sb/Sn.

Perhaps you can find one of this earlier era gray box Lyman molds. 

Farm boy from Illinois, living in the magical Pacific Northwest

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RicinYakima posted this 5 days ago

When I was shooting Military Big Bore, that was the same dimensions I needed; a .462" bullet. So I bought a Lee 405 HB mould and cast the bullets out of linotype that came out .462" and 385 grains. Run through a 462" sizer and lubed with Grey #24. WW LR primers in WW brass with 24 grains of A2400. Seated the bullet with the first drive band in the case and no crimp. Set a 5-shot aggregate national record in 2010 (2.381 MOA) that held up for about 6 years with that load. FWIW

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Glenn R. Latham posted this 5 days ago

Bud, thanks for the info.  So far I have just shot black in this rifle with the Lee 3R bullet.  I sized it to .459" per the Wolf book but don't think I will do that anymore, although it shot well.  It's so dry around here I wipe between shots when shooting straight black.  Duplex loads show promise of holding accuracy without wiping.

Glenn

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Glenn R. Latham posted this 5 days ago

I have that mold, Ric, I may have to do some testing like that for smokeless loads.  Black seems to shoot fine with slightly undersize bullets.  I made a taller front sight so I can shoot it "on" at 100 now.

Glenn

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RicinYakima posted this 5 days ago

That seems to be the thing with black power. The pressure rise is so fast that with a soft alloy it will bump up to fill the throat. I'm just too lazy to clean that much black powder reside! From my work with trapdoor's the sight radius is so long that unless you are really close to either 1873 or 1882 loads, you have to work on the front sight to get it zeroed. Once there though, the scale on the old buckhorn sight is very accurate for yardage. 

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Glenn R. Latham posted this 4 days ago

Ric, my rifle has the Buffington sight.  With my new taller front sight, setting the lower aperture at 200 will zero it at 100.  Haven't tried farther away yet.  This was with the Lee 3R bullet doing 1175 fps.  Hope to try it at 1000 yards or more at the Whittington Center in June.  My club here has a 1000 yard high power range but I don't know what the HP shooters with their 6.5 Whatevers would think of that glorious cloud of smoke...

Glenn

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foesgth posted this 4 days ago

Ric, my rifle has the Buffington sight.  With my new taller front sight, setting the lower aperture at 200 will zero it at 100.  Haven't tried farther away yet.  This was with the Lee 3R bullet doing 1175 fps.  Hope to try it at 1000 yards or more at the Whittington Center in June.  My club here has a 1000 yard high power range but I don't know what the HP shooters with their 6.5 Whatevers would think of that glorious cloud of smoke...

Glenn

Glenn,

First the 6.5 boys will give you some strange looks for the smoke cloud.  But, when they hear that 500+ grain bullet hit the berm they will all wonder over.  Load up a few extras because you are going to make some new friends.  

Second, how much taller did you make your new front sight?  I am going to leave my rifle as is, but, I would like to get my carbine to shoot at 100 yards.

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Glenn R. Latham posted this 4 days ago

I was afraid someone was going to ask "how much."  I made it at work in my spare time and my notes are there.  Measuring on the rifle it looks like it is .127" taller than the factory sight, or about .775" above the center of the bore.

Glenn

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foesgth posted this 2 days ago

Thanks Glenn,

Normally I would just start testing as you did.  However, in today's world I am worried about running out of Black Powder.  The shop where I used to buy shut down and with Goex going under I may need to shift to substitutes.  You giving me a starting point will save a little precious black! 

Strange times we live in...

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Glenn R. Latham posted this 2 days ago

Foesgth, I used the sight correction formula:

 

amount of error times sight radius  divided by  distance to target  equals amount of correction

Glenn

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