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I have an 1886, SR # 92,XXX in .45-70. I’ve slugged the barrel three times with Lyman #2 lead .457 bullets. The bore is bright and shinny with very clear and sharp, though typically shallow, rifling. I have mic’d the bullets 3 times and each time it indicates a bore diameter between .452 and .453!! Is that possible??
Would greatly appreciate any input…
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I’ve had several original 1886 45-70’s and slugged them. They all come in with a groove diameter around .4575 with less than half a thou plus or minus. Yours is so far out, the first thing I would check is your vernier. Don’t use the .457 cast bullets as a reference, but some jacketed bullets of known diameter. I find it very difficult to believe your groove diameter is actually that small. Of course, I am assuming that by ‘bore diameter’ you are referring to the groove diameter. If your vernier is accurate and the groove diameter is actually .4525, then sizing your cast bullets down to about .454 should give good results.
Thanks for the response. I took your suggestion and re-“slugged” the bore with a jacketed bullet measuring .543 . The resulting reading from 2 dial calipers and 1 Starret micrometer was .450 for the imprinted rifle lands and .4525 on the imprinted groove. I checked these me3asurement several times with the same (curious) result.
Guess my question is, have you ever heard of a Win. 1886, .45-70 being that far off the normal .457 ?
I didn’t mean to slug your bore with a jacketed bullet; I meant to use the JSP bullet as something with a known diameter, to measure to see if your callipers were off. You must have got some exercise pounding that jacketed bullet through!!
Sorry for the confusion. Anyway, with so many measurement devices, it sounds like your bore is what the devices say.
I just checked an old drawing for the 45-70 specs. It states:
Groove Diameter: .456 – .458
Bore (land) Diameter: .450 – .452
Your bore diameter of .4525 is just a tad above spec but your groove diameter of .450 is way below spec. I’ve never heard of such a tight groove diameter for a 45-70 or 45-90 (or 45-60). I’ve measured, or seen the results for more than half a dozen 45-70’s and they were all around .4575 plus or minus a half thou. I wonder if yours was rifled with a worn broach, but surely they wouldn’t use a broach so badly out of spec. That raises the question of whether the barrel is an original Winchester barrel? Maybe a sharp photograph of the barrel address and caliber stamp would help ascertain its originality.
Regardless, looks like you got a nice tight bore. No problem at all …. just size to one thou over groove diameter and you’ll be in business. Some fellows like 2 thou over groove diameter (.454 – .455). The advantage of this is that if you have an original 1st Gen Colt SAA, you can use the same sized bullets in both.
P.S. I and I’m sure others here would sure be curious to see a nice sharp photo of the barrel address and the caliber stamp.
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