Crowning a muzzle with Lee case trimmer

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Crowning a muzzle with Lee case trimmer

Post by Zeliard »

Original authors in bold.


Yesterday, curious how level a crown was on a sporter 1903A03 30 cal barrel that had been shortened, I decided to insert a lee case trimmer into the muzzle with a 7X57 mauser guage lenght spindle on it. I intended to give it a few light twists to check how level the crown was by examining the scratches the case trimmer would make. Of course the 7mm mauser spindle was loose in the bore, so I decided to try aluminum cut from side of a beer can as a shim to take up the slack in the bore. I cut the beer can aluminum so that I could wrap it the lenght of the 7mm spindle so that none of it would ride on the rifleing of the bore. After inserting the aluminum shim in the bore, I lightly greased the trimmer spindle and inserted it in the muzzle. It was a decent fit with very little wobble, so I made a few light twists with the case trimmer to check for high/low spots on the muzzle. Much to my surprise, the Lee case trimmer cut the metal of the barrel fairly easily. I checked the muzzle and decided to keep rotating the Lee case trimmer by hand. After about 10 minutes of rotating the case trimmer, I had put what seems to be a perfectly flat recessed surface on the end of the muzzle. I then took out my drill, put a 5/16" carriage bolt in it coated with fine valve grinding compound on its head, and worked the bore muzzle for about a minute.

Today, I tried this same technique on a sporter 7mm 93 mauser barrel. I used a case guage for 6.5 Swede on the Lee Trimmer. Again I cut another piece of aluminum from a beer can and wrapped it around the spindle to shape it. Now I could insert the aluminum shim in the bore and then insert the lightly greased case trimmer with the 6.5 Swede guage into it. It was not as tight a fit as with the 30 cal bore I had done yesterday, but acceptable to me. Like yesterday, I simply began twisting the Lee case trimmer, occassionally reapplying a light coat of grease to the muzzle area being cut and on the guage spindle. Again, when satisfied with depth of cut into the muzzle, I removed the aluminum shim from the bore, grabbed my drill with the carriage bolt and honed the muzzle of the bore till I was satisfied.

Here are a few pics of what I did.





Guys in our chat room and others wanted a range report on my muzzle crown job done with the Lee case trimmer. The rifle I shot today was the sporter 1903A03 Remington that I had cut the barrel on just behind the slot for the front sight. Don't worry, bubba had already done enough to the rifle to keep me from restoring the rifle. I just finished what he had begun by removing the cut military stock and putting it in a Boyd clearance ($20) sporter stock made for Howa 1500/Weatherby Vanguard rifles. I then dealt with the rough turned exterior of the military barrel and cold blued it with Brownell's Oxpho blue.

I had taken the rifle to the range a couple of times before using the Lee case trimmer on the muzzle. I was unhappy with how the rifle shot at 100 yards, shot groups were at least 3 inches at best. I worked on the bedding of the action a little and discovered my barrel was not free floating. So, I worked on the barrel channel in the stock and corrected it. I then used the Lee case trimmer on the muzzle. Also, I bore sighted the scope again.

Here are a picture of the rifle and the target I shot at today. The distance was 100 yards shooting from a bench. There was a gusty wind blowing 10 mph plus from left to right across the range. I shot factory Federal premium 150 grain ammo. Except for my first two shots, all were in the bullseye after I adjusted the crosshair on the scope.




Several years ago I did the same thing for a couple of 8x57 sporters. The .30 cal pilot is a near perfect fit for the 8mm bore. I burnished it with a brass case to help keep it from scratching the lands. In addition to the aluminum can shim, you can check a well-stocked harware store for thin-walled brass tubing. These are usually in displays around the hobby section. You could take the pilots with you and try for fit. Then you could spin the tubing in a drill and sand down to the right diameter.


I had read this when you first posted it. At the time I didn't have anything that needed re-crowning, but recently I acquired a Mosin 9130 that had the muzzle hogged out from years of cleaning using the original cleaning rod from the muzzle end. I first used a big countersink and put a 45 degree taper crown on it. Then, I remembered your post and since I had a couple of Lee case trimmers in my stock of stuff I decided I couldn't "bubba" it too bad by trying your idea and I could always re-crown it in the normal manner if it didn't work.

I found a .223 pilot rod with a broken tip. Of course, it was too small for the .312 bore of the Mosin, but while looking for something to shim it with, I came across some of that hard nylon tubing that is used to connect water filters to refrigerator ice makers. It was pretty loose in the bore by itself, but the inside diameter was a bit small for the .223 pilot, so I force fit a piece. The .223 pilot expanded the tubing enough where it was a nice fit in the bore so I pushed it up near the cutter and added another piece to the bottom end of the rod (see pix). This made it nice and stable, having 2 point support.

I then chucked the trimmer in my 1/2" battery drill and slowly proceeded to cut a "target crown" into the old 91/30. Wonder of wonders, it works as advertised! Kudos to you for posting this wonderful idea. The outside diameter of the cutter was sufficiently smaller the and OD of the barrel that it did a decent recess, leaving sufficient material around it for protection.

A bit of polishing with the Dremel and some Brownell's "Oxpho Blue" and it looks almost like a professional crown job. It will be after Thanksgiving before I can get to the range to see how she shoots but I don't see how it could have hurt anything compared to what it did before.


This is one of the most helpful stickies i've read. Just seconds after reading it, I ran outside, got my cutter and went to work on the crown of my 71/84 mauser. It had a nice ding in the crown, which I think is why it was shooting to the right too much. In 10 minutes I had a brand new crown, and I only had to cut down about the thickness of a penny.

I used a .30 cal mandrel on the cutter head. Which as you may guess is way to small for a .446 bored rifle. I used duct tape carefully wrapped around the mandrel to get it a snug fit in the bore. If you wrap it correctly, it will not unwrap as you turn the cutter head.

Excellent sticky, saved me a $75 trip to the gunsmith! =D> =D> =D>

Just an FYI, I did do this to my 71/84 which had a purdy ding in the crown. It caused the rifle to shoot WAY off center, and grouped horribly.

I got to test it out recently after doing the crown job, and this is how it shoots now, WITH a fouled barrel using dirty old blackpowder.

Image Missing

It even put 2 shots into the same hole. :D


I know this thread is a little on the old side, but I'm a new lurker and member, so :roll: :idea: . If you were to take an aluminum arrow shaft and use it for a guide bushing, you could get down to .001 play using the lee case trimmer. Which in a 4 inch length virtually eliminate all wobble. The arrow shafts come in different diameters and wall thicknesses and could be split length wise to custom the guide bushing, (possibly to put one inside an other). The sticky sounds like a good idea, especially on a milsurp or any other rifle barrel that has a bad crown when they're only in the $100 - $250 category with a wore throat, pitted bore, dark bore, bad headspace, etc. and you might be hundred miles from the nearest GS.


I will say the Lee Case trimmer had no trouble cutting the chrome-lined barrel of my .308 Saiga. It took a few minutes to get it cut. Because of the weird taper right at the end of the barrel, it left a knife-like edge around the outside. It took a bit longer to file it flat, but the cutter worked like a charm.

The chrome lining did chew up the brass screw head I was using to debur the crown. I used a spherical, mounted stone point to break the edge and then used the brass screw and grinding compound to polish the chamfer.


Been awhile since I made the original post bout using a Lee Case trimmer to crown a barrel. Hope its been useful and worked for anyone who tried my technique.

Few days ago, I again tried my hand at dealing with a heavy barrel on my Marlin XS 308 Varmit rifle that I'd shortened from 26" to 24" and recrowned with the Lee case trimmer. Why did I shorten the barrel? Well, the rifling near the muzzle had a problem. Guess the button cutting the rifling had chattered or something. You'd think someone had run a screw or tap down the muzzle due to the copper fouling running across the lands and not along it. This particular Marlin X rifle had come out of the Mayfield Ky Marlin plant not that long after it began production. I''d had a gunsmith borescope the barrel and he confirmed what I thought I could see just looking down the bore. Gunsmith recommended shortening the barrel to get rid of the bad rifling. I'd used a hacksaw to cut the barrel and as typical of me with a hacksaw, not the most even/smooth cut was done. Since the case trimmer has a diameter of about 1/2", I had a 1/4" ring around the crown that needed additional work. Spent a lot of time with a file, honing stone and etc., working on the ring around the crown. Barrel has a slight taper, so difficult for me to check just how level the ring was to the crown I'd cut. Needed a way to be pretty sure it was level.

Happen to have a flat washer on my workbench near my case trimmer.....Hmmmmmmmm, I wonder if I could put the spindle of the case trimmer thru a flat washer, coat one side of the washer with valve grinding compound and use it to work the ring around the crown. Found the appropriate sized flat washer, slipped it over the shimmed up spindle, applied a little fine valve grinding compound and inserted the spindle in the bore and began hand turning it. Providing I did not apply too much pressure, the cutting edges of the case trimmer held the flat washer allowing it to turn. Took awhile, but got to a point that I'd corrected my previous file and honing work on the 1/4" ring, leaving what I believe is a flat muzzle.

Next day I was at range with the rifle and showed the muzzle work on the ring to a couple of other gents at the range I know. They chuckled when I explained what I'd used, but both agreed it looked good to them. I only had some experimental 308 reloads with me that I'd never tried before, so only fired around 5 rounds downrange. So, can't write of any outstanding results for accuracy improvement and etc. Just know I feel better about the end of the barrel.


Well, its been quite awhile since my last post about using a flat washer with valve grinding compound with a lee case trimmer to level a muzzle.

Since then, I've taken the Marlin X heavy barrel .308 to range many a time. The flat washer trick did work well for me to level the muzzle ridge around the crown cut with the lee case trimmer. Its one of my more accurate rifles.
Proud alumni of Transylvanian Polygnostic University. "Know enough to be afraid."

"Vertroue in God en die Mauser".-Faith in God and the Mauser.

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