Fixing to take a nap, but in catching-up noticed a thing on Twitter about the bore centerline of what appears to be a Russian 30mm barrel. A few things (from memory).
Almost all mass produced barrels have centerline drift, the smaller the caliber the more the drift. Even hand produced match barrels are rarely perfect. On a finished barrel, that has been OD cut on centering tools, the muzzle end will look fine, however, if you cut the barrel off, that is when you will find the drift – and this barrel has obviously been cut off.
Almost all long medium caliber barrels start developing drift after about 30 inches from the breech. this is from traditional barrel drilling techniques. Per a typical US 20mm barrel, you might find one with a max of 0.5mm drift, but you can also find plenty with up to 4.5mm drift. This is from vertical measurements, thus excluding gravity droop.
This does have some effect on repeatable accuracy, especially through cold/heat cycles. Also, changing barrels means a change in dead center. On non-compensated guns, if this anomaly is known, and the barrels can be sighted and indexed indexed, it is less of a problem. larger barrels such as the Abrams main gun, runout is almost always less than 1.5mm over their entire length, plus, they are sight compensated.
So, in my view, what is being seen on the 30mm Russian gun is actually pretty normal, and for its intended use, is not really that much of an issue.
Don’t quote me, but I think the acceptance criteria for the Abrams 120mm is gun is 2.0mm over the entire barrel length, and 0.5mm over any 600mm length. This does not include barrel droop from gravity. This is very difficult to maintain over a smaller barrel like a 20mm or 30mm.
The 4.5mm drift is the max off-center from two different directions. So, total non-concentric drift from a true chamber centerline. In practice, it does not seem to have a large impact on accuracy, as long as the chamber is concentric, and the throat is parallel to the barrel bore.
Hmm thanks, wasn’t aware this much drift was acceptable.
I don’t know the acceptance criteria on the US 20mm barrel, but Aberdeen pulled a bunch out of stock and found these kind of numbers. It is a mass production thing, and I assume the Russians suffer with maybe even more. I have seen a lot of barrels cut-off from troop and civilian rifles, and seen obvious drift. Any barrel over about 31 inches length in medium to small calibers is subject to drift without expensive manufacturing techniques.
Also, you can’t measure from barrel OD, since that may or may not be true.
It seems to be common knowledge that the Russians and Yooks are both going to run-up again barrel replacement issues. On the big guns that have barrel liners, if the throat gets too worn, the projectile starts going into the barrel cocked, and can start loosening the liner. If it peels enough back, the next round might jam it into the barrel, and there goes your barrel, in a very spectacular fashion.
You have to punch a pig through the barrel pretty often when they get worn to check it is clear.
Pretty quiet here right now. They have been making small probes north and south, but nothing serious. I can hear stuff in the distance right now.
A few years ago there was a military sci-fi short story contest. I had a germ of an idea but I never wrote it out. The story was about an ordinary guy who could message a front line soldier in a future conflict and search the Internet for information the soldier needed. I was looking for plausibility. It seemed plausible but I could not make it really exciting.
It literally just occurred to me I have been doing exactly that since March.
Lol! I get more in-country and regional info from you than I do battalion.
I didn’t want to bring it up, since I was unclear how to tell it. One of the South Africans left a few days ago. We had become pretty good friends. He is young, not a lot of experience. He came to me and —— and just said he had had enough.
He said he could not get rid of the smell of death on him, and was not sure he ever could. His eyes, staring at me, reminded me of an old dog I had who was dying, and he kept his eyes on me, asking if there was something I could do. There was nothing.
After he walked away, I could see that —— was close to having a human reaction. But, he couldn’t go there. He stood up, said, “Never discuss your casualties,” then stomped away. I couldn’t get that old dog out of my head.
Later
Ukraine Volunteer Transcripts 