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jhm
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40-70 SS chamber
Mar 5th, 2026 at 5:41pm
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Can you use a 405 win. reamer to short chamber a 40-70 straight chamber then cut the rim recess? There isn't a lot of difference in the chamber length of the 405 and the 40-70. Worried the neck area might be too tight.



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ssdave
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Re: 40-70 SS chamber
Reply #1 - Mar 5th, 2026 at 6:38pm
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I'll send you my reamers again if you want to chamber one.  Would be easier and more accurate dimensionally than using a 405 reamer.  But, the 405 is fairly close.
  
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marlinguy
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Re: 40-70 SS chamber
Reply #2 - Mar 5th, 2026 at 8:14pm
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If you measure a .405 case about .10" above the rim on the base diameter you'll notice how much smaller your chamber will be. I think you'll discover your chamber will be too tight for the brass to fit.
  
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jhm
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Re: 40-70 SS chamber
Reply #3 - Mar 5th, 2026 at 9:53pm
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That is what I was afraid of. I called Shiloh and ask Lucinda (she actually answered the phone) but she couldn't tell me the difference between a Shiloh chamber and a "standard" one. Said she would ask Kirk and he would call me  but I guess he forgot. Thanks Mr Sam. I haven't got that far yet but I will be in touch later. Thanks guys for the help.


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Old-Win
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Re: 40-70 SS chamber
Reply #4 - Mar 5th, 2026 at 10:45pm
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No, the .405 Winchester is based on a larger bore/groove diameter than the 40-70 Sharps Straight.  .411 - .412 groove instead of .408 - .409. You may then have a sloppy chamber.  What are the bore and groove diameter of your barrel? Ideally you want your chamber to have .004" of relief on the bullet just inside the mouth of the chamber. What is the thickness of your brass at the mouth of the cartridge?
« Last Edit: Mar 6th, 2026 at 1:28am by Old-Win »  
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Deadeye Bly
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Re: 40-70 SS chamber
Reply #5 - Mar 8th, 2026 at 9:48am
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Most original 40/70 SS were for .403" diameter paper patch bullets and chambered accordingly. The chambers are too tight for our modern version with .408" diameter lubed bullets. The 405 used .412 diameter bullets and the chambers may be too big for .408 bullets. At one time Pacific Tool, PTG made a reamer specifically to use 405 brass in a 40/70 SS chambering. I'm sure Shiloh uses a reamer to allow the use of .408" diameter bullets because I have a Shiloh in 40/70 and I shoot .408" bullets in it.
  
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marlinguy
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Re: 40-70 SS chamber
Reply #6 - Mar 8th, 2026 at 11:02am
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My Hepburn in .40-70SS has a .410" groove diameter barrel, so at least Remington used a larger groove.
The Ballard .40-63/70 chambers are identical to .40-70SS and I use .40-70SS dies to reload them. I have six or seven Ballards in this chambering and they all have .410"-.411" groove diameters.
  
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