Ever see a crown/counter bore like this?

[Tired Retired]

Just got an IBM delivered today from CMP. Nothing special, just a run of the mill racker. Anyway, while I was cleaning her up, I found the most crooked rifling-line I have ever seen. I assume that someone tried to counter-bore it or that it was done when it was re-crowned.

Has anyone ever seen a crown this messed up before?


I am thinking about keeping it just for the novelty of it. It gauges at a 1.5, and it appears to to be straight enough to be safe. Anyone want to guess as to how accurate it is going to be?

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[chainsaw]

I'm gonna say it will be accurate,that crown shouldn't decrease accuracy.

[jimb16]

Typical IBM.....not counterbored. That is just the way they were made.

[Tired Retired]

Jim, My pictures don't show the issue as clearly as you can see it in person and my description is lacking....

I am not talking about the flat crown of the barrel. I am talking about the way the rifling ends. If you look closely at the pics, you will see that on one side of the the barrel, the rifling comes right up to the end of where the crown starts (its the 1 oclock to 3 oclock position). On the opposite side of the barrel, the rifling is cut down and starts about .07 inches below where the flat crown starts ( about the 7 oclock postion). This leaves the rifling lopsided as it ends in the barrel.

I admit that this is my first IBM, but in all my years of dealing with weapons in the military, I never saw rifling that ended in a barrel at different points of the barrel. IBM got away with this with the inspectors?

[Tired Retired]

This highlights what I am seeing a little bit better....

[imarangemaster]

I had an 1873 Winchester made in 1881 that had a muzzle like that. It shot 44-40s as well as the new replica 1873s. Try it and see what accuracy you get. Aesthetics aside, it is the accuracy that counts.

[JBS]

That is called a "lapped" muzzle. It is normally not that deep. It is normally found on high grade barrel work. Accuracy is increased because the termination of the lands is made concentric by this process. Many firearms can be enhanced by the process. It is done with a brass ball and lapping compound. The cheep way with lesser results is done with a cutter.

[Tired Retired]

Thanks guys, I will shoot it and check the accuracy the first chance I get (probably next week). I honestly have never seen anything done like that to a barrel - I learned something today! Maybe this rough "just-a-racker" is more of a diamond than I realize...

[Patrick Chadwick]

I know nothing about the 30M1, but have had a bit of experience with freshening up milsurp muzzles. So, on the basis of not having a reputation to lose, here goes my 2 cents worth of prediction.

1. EITHER the end of the bore is not square to the bore axis OR the crown cutter/lap was not aligned with the bore OR a bit of both.

2. As the bullet exits the bore, gas will blow past, starting where the gap opens first. If the end of the bore was square, but the crowning was at an angle to the bore axis, then the gas blow-by will be where the cut is deepest.

3. The gas blow-by will therefore tend to push the bullet away from the larger gap, i.e. skew it towards the region where there is more metal left.

4. I therefore predict that the shots will be off-line, in the direction where the cut is shallowest.

5) Alternatively, if the cutter was truly on axis, but the end of the barrel is not square, the shots will be off-line in the direction where the barrel is longer, i.e. the cut is deeper.

b) If both effects are present, then they might just cancel out, but only for a specific load and bullet. Murphy's Law doesn't usually work like that!

Summary: anyone recrowning a barrel should first check that the end of the muzzle is square to the axis. This should be corrected, if necessary, before applying the cutter or lap exactly along the bore axis.

In other words: the muzzle looks Bubba'ed and should be corrected.

Nevertheless, it would be interesting to try shooting the rifle first, to see if my prediction is correct!

Patrick

[browningautorifle]

Just shoot it and see.