doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com MACNAUGHTON Double Rifle - Unknown Caliber

Hello All,

Thanks for your reply.

Now that I've determined that its a 577-500 No.2 chambering, all the back and forth banter about measuring the bores isn't necessary.

I'd really like to know the answer to the question: "... What is the meaning of the "stars" stamped on the breech end of the barrels over the chambers?..."

They are located almost exactly at the center of each chamber. They appear to have been stamped "after" the last refinishing / re-blackening based on the raised edges.

Hello,

As the picture showed in my 5th post, I made a chamber cast which extends into the rifling. These barrels have 7-groove Henry-Style rifling which makes measuring across the lands difficult. Nearest can I measure is 0.506" - 0.507" groove dia.

Today I lathe turned a ball gauge to measure the bore diameter. It measured exactly 0.490" in both barrels. This would explain why the barrel flats are marked "40" and not "39". When gauging the bore a 39 gauge would not fit, but a 40 gauge would. (see chart)

Yep, as part of my "Banter" that was the figures, I posted on the bore diameter. .488" for 40 & .492" for 39. Even though you asked about the 40 mark in your original post I got the impression you didn't truly appreciate us answering that part.

The actual cartridge to use could of course only be determined by the chamber cast so was not of any use to try & answer that part without dimensions from the cast.

Hello 2-piper,

Thanks for your reply.

Don't get me wrong, I appreciate your input. But I'm not sure if all the side-tracked back-and-forth debate between forum members on how to measure the bores, and how the gauges worked, and how to use them, really had anything to do with my post. I'm not a machinist and didn't have any of those gauges or access to them.

I simply turned a ball, kept decreasing its size and testing it in the barrels, until I felt a "slip-fit" into the bores - and then I measured it with a micrometer - hence the 0.490" measurement.

.
anyway -
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Here's the results of today's shooting.

Although I never did precisely measure the chamber cast, I got some "new" 577-500 No.2 cases which seemed to match the chamber cast. I inserted the new brass in the chambers, and they easily fit - even when loaded. I loaded 3 different bullets, an fired them. (see below) After firing, I tried slippng some of the .511 dia bullets back into the fired brass, and it was a very close "slide-fit" - perfect!

I'll test some more loads with slightly more powder to increase velocity. Pressures with all 3 loads were light with easy extraction with the fingers.

I hate paper patching so I use that method only as a last resort. Based on my results below, I don't think I'll need to go there.

The gas-checked bullets were both .511" dia and the Woodleigh SP bullets were .510" dia. This rifle really likes the Woodleigh bullets. I think all went well.

Stix,what's the foam?

Hello justin,

Thanks for the reply.

Its 1/2" dia "backing rod" cut to length. You can buy it at the local hardware store. Its available in 1/4", 3/8", 1/2", 5.8", 3/4", and 1" dia x 25 foot length. Or, you can find it on amazon in 100 foot lengths. That's where I buy it.

Thanks

You are welcome.

I'm still trying to discover the meaning of the "stars"stamped on the barrels.