How critical is the crown?

[saands]

I know that if you want sub MOA out of a rifle, then you have to have a perfect muzzle crown, but I was wondering just how much variation an imperfectly cut muzzle crown will really cause. I'm not talking about a benchrest crown that has been buggered up by being dropped onto the cement, but an SKS that would like to be a couple of inches shorter (18" instead of 22" bbl) but still shoot in the neighborhood of 2-2.5 MOA. I have heard of people squaring the muzzle up by eye and then using a countersink to deburr the crown, but it runs counter to the "Muzzle has to be perfect" paradigm that I have. I see that Brownells has the "right" tool for the job, but the cutter, pilot, and handle will run $70 after shipping, so I was looking for a more economical (but acceptable) solution ... if such a thing exists.

Any thoughts?

Thanks,
Saands

 

[Dave P]

For a 2-2.5 MOA gun, I imagine just eyeballing it will work fine.

 

[swifter]

Get a round-head screw or bolt of appropriate size & some emery cloth, chuck the screw shaft in a drill, use the head to spin the emery cloth to make a crown. Just take it down to the rifling, use finer grits to polish. Don't leave burrs. Swab a Q-tip across to check for burrs...

Tom

 

[ThreadKiller]

I've heard that the steel ball that is inside your typical PC mouse and some valve grinding compound are the way to get a good crown on a rifle.

Never tried it myself, but it sounds reasonable enough.

Tim

 

[stans]

The ball in most pc mice is no longer steel, it is plastic or rubber.

 

[Jim K]

The critical area is not the crown, which is the raised and often rounded part. The critical area is the end of the rifling, which is what the crown protects.

If the bullet exit point is not straight, the bolt and valve grinding compound trick or ball bearing trick will NOT straighten it out, it will only smooth it down crooked. (If you used a hacksaw to cut a barrel at a 45 degree angle, how would grinding on the hole straighten it out?)

To properly cut the barrel, chamfer the bullet exit point, and keep it perfectly even, you need a lathe. Period. No ball bearings. No mouse balls. (No balls from bigger animals, either.) No round head bolts. No drill bit in an hand drill. No case trimmer or case neck reamer. Even some crowning tools used in a hand held drill can ruin the rifling.

A lathe. A good lathe. Then you can cut whatever kind of crown you want to protect that critical end of the rifling.

Jim

 

[saands]

Jim ... I was hoping that you would chime in here! I had come to the same conclusion about using a ball ... it would just smooth out whatever I screwed up with the removal tool. Can the hand tools that brownells sells be used on a bbl that is just not going to come off (like that on an old SKS)?

Thanks,
Saands

 

[Jim K]

I have never used one of those tools, and my Brownells catalog has been loaned out, so I really cannot comment. I believe they have a spud that goes down in the barrel to keep things pretty even. Hand operated, it shouldn't hurt the rifling, but as I say, I have never used one. Still, unless the original cut is even, it seems to me that there would be a lot of metal removal.

The way I used to do it in a lathe was to use a home-made crowning tool, which was just a lathe tool, but instead of having a point, it had a concave curve, sort of a shallow U. This was set up almost parallel to the barrel and then just moved in so that one end of the U was in the bore and the other end outside the barrel edge. The concave cutter cut the crown and chamferred the exit point at the same time. If the customer wanted a target crown, that was done with a regular cutting tool. (A target crown is a flat ridge of metal around the outside edge of the barrel; except for a slight chamferring of the exit point, the rest of the muzzle is perfectly flat. Some experts don't even like any chamferring and say a perfectly sharp edge is better. What the customer wants....)

Jim

 

[mark mcj]

With a SKS the best crown in the world wouldn't matter. Beside that, once you shorten the barrel you will most likely run into cycling problems.
Cut, grind, file and crown. It will be a good lesson in basic gunsmithing.

 

[Jim K]

"With a SKS the best crown in the world wouldn't matter."

If by crown you mean the end of the bore, I think you are under-rating the SKS just because they have been cheap. Most are pretty accurate. Maybe the "best crown" won't make a difference, but the worst sure will.

Jim

 

[mondocomputerman]

The ball inside the mouse is not plastic, it is a rubber sheathed metal ball. I have one in my desk taken apart at the moment.

 

[stans]

Nothing better to do than play with mouse balls?

 

[mrmeval]

Eh, mine has a little red light where they'd be. I'm thinking it's eville!

Nothing better to do than play with mouse balls?

 

[Rem700SD]

A good smith should be able to cut and crown that bbl for around $50, and do a good job.

 

[slopemeno]

Before you think the crown doesnt really matter, I used to offer that as a service on paintball guns that I built. A precise 11 degree crown made a world of difference in the accuracy of a stock barrel. I've used the brownells kit as well with decent results.

 

[jaybar]

Brownell's tooling

Have shortened and recrowned many a .22 rimfire barrel (pistol and rifle) using a hacksaw and Brownell's facing/crowning hand tools. Cut barrel to slightly longer than desired length with hacksaw eyeballing as close as possible to a 90 degree cut, use the 1", 90 degree facing cutter to square up the muzzle face to the bore, then use the 11 degree cutter and remove enough metal to recess the crown until about a 1/8" ring remains of the flat surface around the outside of the muzzle. Look goods with outstanding accuracy. You really don't need the 11 degree cut but it does recess the ends of the rifling from the muzzle face providing protection. The initial 90 degree cut would work just fine. After all benchrest shooters have their muzzles lathe cut at 90 degrees with no crown at all.
Works for me !!

 

[Standing Wolf]

To properly cut the barrel, chamfer the bullet exit point, and keep it perfectly even, you need a lathe. Period. No ball bearings. No mouse balls. (No balls from bigger animals, either.) No round head bolts. No drill bit in an hand drill. No case trimmer or case neck reamer. Even some crowning tools used in a hand held drill can ruin the rifling.

Thanks, eh? Kitchen table gunsmithing doesn't produce top quality crowns. I had to send a Python to the good folks at http://www.magnaport.com for recrowning after a local yokel did a quick and dirty job.