Sorting out some thoughts on re-crowning a barrel.

deadshot2 · Feb 15, 2012

I have a factory rifle that shoots really nice but just can't get the last measure of accuracy out of it. On close inspection it has what is best described as a "Mass Produced Factory Crown Job" on the barrel. Someone gave it a quick swipe with the lathe bit, a bit of a counter-sink chamfer, and put it on the action. That's the only part of the rifle that was done cheaply. It's easy to tell that it's time to be re-crowned as even the "soot marks" on the muzzle are uneven.

I don't plan on pulling the barrel off and re-crowning it in a lathe but am going to pick up a 79 degree reamer with pilots and do the job by hand.

Question is, since the muzzle measures just over .800, and the max reamer dia is .750 can I continue the crown deeper and leave a protective rim around it similar to the military crown on the M-24 of should I just keep the outer edge flush with the rest of the muzzle?

What about "breaking" the edge of the crown where it joins the bore by lapping or should I just leave it as sharp as possible. The reamer I intend to use has many cutter faces and should be not only chatter free (when turned by hand) but also leave a knife edge at the bore. If the edge is clear of burrs and doesn't catch on a patch or q-tip is anything more really required. Opinions seem to vary so I'm looking for some here.

Lastly, has anyone else done this and kept a hand reamer for touching up the muzzle crown before a match?

eganx · Feb 15, 2012

So, this reamer you speak of.........will this be chucked in a drill? I find it hard to believe it would be chatter free if being done by hand. When cutting metal, you want your fixtures to be as solid as possible, with no deflection, and that goes for your chuck, quill, tool post etc(read as hand drill with reamer). Any ability to move can and will create vibration, which is the cause of chatter. Once you have chatter marks cut into your material they can be difficult to get out. You have to play with feeds and speeds to get a different frequency of vibration to cut out the original chatter.

If I were you.....and I were set of the DIY crown job, I would play around with the reamer to get a feel of its cutting action before I touched the barrel with it.

Redcap · Feb 15, 2012

You are doing it wrong.

deadshot2 · Feb 16, 2012

eganx said:
So, this reamer you speak of.........will this be chucked in a drill? I find it hard to believe it would be chatter free if being done by hand.

The reamer I intend on using is not like the PTG reamer with only a few "flutes" but has far more cutting surfaces maybe a dozen as I look at an image of it. It's more like a file than a cutting "bit".

It's a piloted reamer that's designed to be used either in a drill or by hand.
Over the last 35 years I've cut more than my share of metal chatter free.

Redcap- So did the guy in the factory and he had a "Million Dollar Shop" to do it in.

My question wasn't so much on "How", it was on whether to break the sharp edge at the bore and whether or not it should be recessed.

oregonty · Feb 16, 2012

FYI....I would break the sharp edge. I have done this (by hand) on several re-crowns with good success before I had a lathe.

motoman98 · Feb 16, 2012

I was reading on crowns by Mike Bellm. I'm pretty sure he leaves them sharp.

Redcap · Feb 16, 2012

deadshot2 said:
The reamer I intend on using is not like the PTG reamer with only a few "flutes" but has far more cutting surfaces maybe a dozen as I look at an image of it. It's more like a file than a cutting "bit".

It's a piloted reamer that's designed to be used either in a drill or by hand.
Over the last 35 years I've cut more than my share of metal chatter free.

Redcap- So did the guy in the factory and he had a "Million Dollar Shop" to do it in.

My question wasn't so much on "How", it was on whether to break the sharp edge at the bore and whether or not it should be recessed.

Ah, I understand then! Carry on. Personally, I'd leave the edge sharp.

deadshot2 · Feb 16, 2012

motoman98 said:
I was reading on crowns by Mike Bellm. I'm pretty sure he leaves them sharp.

Redcap said:
Ah, I understand then! Carry on. Personally, I'd leave the edge sharp.

In my reading there seems to be two schools of thought. There are those that use a lap, brass acorn nut, or oval headed screw, with some lapping compound and lap the edge until the edge is broken about .010"-0.20". Then there are those that leave it sharp, just check for any burrs by running a patch through, or q-tip, to see if anything snags threads. I get the feeling that those that "lap" are just doing it as a quick finish rather than some micro-hand detail with a small (very small) stone to remove only the burrs that snag.

In reviewing the "science" I would certainly think that the sharp edge would release gases the most even. Just needs to be protected but then again, isn't that what muzzle protectors are for???

deadshot2 · Feb 28, 2012

Update:

Well, I finally received my Brownell's 11 degree Muzzle "Reamer" and attacked the mess that was the factory crown on my 5R Milspec. Using the brass pilot, I greased it up with some nice thick slide grease to keep the chips out of the bore. A little cutting fluid on the flutes and away I went. Working slowly, keeping balanced pressure on the handle, side to side, and doing all possible to avoid chatter marks I cut my way through the rough terrain the factory machinist left.

The area immediately adjacent to the bore was actually dish shaped. Instead of being straight, as expected, it had a pronounced radius that showed up as the first cuts were made. About half way from bore to edge, there was a dome shaped area. It looked like the machine operator, rather than cutting the crown by setting the cross feed at the correct angle and cutting across the face, he left it set for 90 degrees and just worked carriage and tool head handles together until he had what looked like a "taper". It also looked like he finished the crown with a reamer more suitable for opening up the end of a pipe after being threaded than for "lapping" a rifle crown.

OK, now for the results. The crown is now cut on the barrel, the edges were left sharp as a razor with no lapping and the results at the range were fantastic.

Groups at 300 yards are now averaging .3 MOA. Since I left the finish as shiny as possible. so smooth I now see only "light lines" radiating from the bore, I now can see the carbon marks on the crown. Rather than the previous flares off to one side with irregular shadows at the end of the 5 rifling lands, there are now 5 evenly pronounced shadows with carbon "flares" that look like they were evenly applied by an artist.

Now all I need to do is keep my brushes from chewing up the edges. Of course I have the reamer handy to touch things up if necessary.

Sure did make a difference.

Velzey · Feb 28, 2012

After I do a crown I use a piece of the maroon scotch brite pad, put the muzzle down on it and rotate..You can also put the the pad in the palm of your hand, and rotate back and fourth. Get rid of that sharp edge! It will hurt you, or someone else.
I learned the hard way.

Or maybe get a muzzle cap for it...

deadshot2 · Feb 29, 2012

Velzey said:
After I do a crown I use a piece of the maroon scotch brite pad, put the muzzle down on it and rotate..You can also put the the pad in the palm of your hand, and rotate back and fourth. Get rid of that sharp edge! It will hurt you, or someone else.
I learned the hard way.

Or maybe get a muzzle cap for it...

I made a muzzle cap out of the cover for the tube the reamer was shipped in. Slips over the end of the barrel just great. The other piece I leave over the reamer itself, secured with a rubber band.

I kind of like the "shine" of the crown face.

HollisOR · Feb 29, 2012

Brownell's crown tool for the win. Crown is probably the biggest factor for accuracy out side of trigger jerk.

deadshot2 · Feb 29, 2012

HollisOR said:
Brownell's crown tool for the win. Crown is probably the biggest factor for accuracy out side of trigger jerk.

Was that "trigger jerk", "THE trigger jerk", or "the jerk pulling the trigger"

???

deadshot2 · Mar 8, 2012

OK, here are the Before and After photos:

Before

After

Easy to do with the Brownell's "Reamer". All I need to do now is radius off the edge of the barrel but that little "rim" really isn't doing anything so maybe I'll just leave it.

Results were very noticable even at 100 yards.

Looking forward to 300 yard performance but need a day with less than 25mph gusting wind like last Monday.