"alinwa" Crown by SEM

H

HuskerP7M8

Member
Al,

You made mention of SEM pics of barrel crowns on anothre thread, so this is for you.
I have 7 different images of crowns by SEM. I can post or email to you.
Don't know where I got them, but here's one:

L1_CROWN11.jpg
 
I'll bet one of those is going to cost more than a borescope. Sometimes ignorance is bliss.
 
Please post the other pics if you can. They sure show some great detail. I remember seeing those last time they were posted.

Thanks
Joe Hynes
 
I second!

I dabble in photography and might take a shot at some muzzle close ups.
That photo gives a new meaning to the term precision machining.

Aloha, Les
 
Neat pictures, but some of us that are newbies could use some explanatory text to go with them.
 
Husker,

Those are some very good pictures!

- Innovative
 
Thanks for the interesting pics. Would be great to get some explanatory text.

Looking at some of the pics, would I be right in saying that they look like they were crowned from the barrel OD towards the bore.

Thanks
Ian
 
Some of the images have a scaled measurement watermarked on them and also have the magnification level too. (X230 100 um) as an example.
um is a metric measurement known as a “micrometer” and 100um = 0.00394”.
1 mm = 0.03937”

Some of the images portray very good crowns, but at high magnification….even the highest quality of metal workmanship appears like the cratered surface of the moon or family snapshots of the Grand Canyon.
 
At those magnifications I'll bet that a lot of topnotch machinists would have tears in their eyes looking at their work....
 
Well done to the picture taker.

I've spent a couple of hundred hours at the controls of an electron microscope (looking for failure causes in semiconductor junctions) so this doesn't surprise me. What is a surprise is how good some of the crowns in the pictures really are. Those are actually rather low (though appropriate to the subject matter) magnifications for an SEM, but very revealing all the same.

Fitch
 
THANK YOU Husker!!!!


Yes these are the Walley pix and great scale too..... time for me to print them off.

Maybe Greg will see these and post some commentary.

thanxagain


al
 
These pictures taken with an electron microscope had text with them originally and were showing just how bad crowns can look under this extreme power .... and how inclusions can be in the steel.

Back when Greg had posted these I sent him a sample piece of barrel stock that I had finished a flat crown using a 60 degree piloted chamfer reamer. I asked him to inspect and see how smooth the finish was in comparison to lathe cut only.

He was unable to post any more pictures at that time but I received confirmation from him that the finish the reamer left was extremely smooth and burr free.

I saved the text from back then but how it corresponds with the order of the above pictures you will have to figure out your self...

SEM barrel photos
Posted By: Greg Walley (65.24.135.221)
Date: Monday, 10 December 2001, at 12:05 a.m.
Over the past year I've had the opportunity to check a few 416 SS match barrel section samples on an electron microscope.
1st. picture: New 90º crown from unfired barrel. Barrel steel treated with 1-3 µM colloidal graphite, which are the visible black streaks in the lapping scratches. Note the small "burr" at the edge of the crown (all new cut crowns have a burr).

2nd. picture: Crown after approximately 70 rounds. Barrel patched and brushed with "Butches Bore Shine". Note the cleaning patch fiber on the edge of the sample.

3rd. picture: Crown after 660 rounds. The barrel was still shooting excellent groups at this stage, but shot better after recrowning.
Barrel brushed and patched clean every 10 to 20 rounds with "Butches Bore Shine".
"Sweets" and JB compound used periodically (usually after an aggregate) to keep copper and powder foulding in check. JB compound removed with vigorous patching and brushing with Naphtha.
Note the scratching on the end of the crown face produced from bronze-bristle brushing, yet a lack of lateral scratching on the surface of the bore . Evidently these scratches are "ironed-out" under heat and pressure. Note the small inclusion, or pit in the metal on top of the land.

4th. picture: Section from a new, unfired barrel. Note the lapping scratches running parallel with the rifling.
One of the points I wanted to make concerning this post is that the edges of the lands on the sample from the 660 round barrel are not "rounded-off" any more than the sample from the barrel shot only 70 times, without the use of abrasive cleaning agents. All of my barrels are flushed clean of solvents and abrasives (white patch test) and given a very light coat of oil before use.
 
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Why??

Why would this make a "top notch" machinist cry. Ever looked at the surface of a ball bearing magnified at 50+ x. It looks like the surface of the moon. But to the naked eye it looks dead smooth.

Different jobs call for, or require, different surface finishes. You do not spend time and resources trying tomake something "better" than the job requires, or is called for on the design print.

Many of those crowns do look terrible, but if you have a 10x loop, you can inspect any crown to the degree of correctness that it requires.

Here is a good test. Take your new crown, after 10 rounds have been fired, and run a patch through the barrel. Then, with a magnifyer, look to see if any "hair" is torn off the patch. If it is clean, your crown is ok.

........jackie
 
THE REASON THAT THESE PICTURES WERE POSTED originally was to show damage done by pulling a bronze brush back into the bore. There was no mention in Walley's descriptions of "shooting and how quickly they can wear from shooting and the particles that blow out of the muzzle".

We the unwashed SPECULATED about "shooting and particles" but Greg stated unequivocally that the damage was from brushing.

Following these postings my bro-in-law took a brass brush wet with solvent and proceeded to use it to forevermore MAR the finish on a SS barrel, proving to US at least that Mr Walley was right.

al
 
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