Crowning barrels

[Styrak]

I was just wondering, does anyone know the proper process or who I could take my inner barrel to, to get it properly crowned? I've already cut it.

[dpvu]

That cone-like bit on a dremel tool apparently does the trick.

[Styrak]

Originally Posted by dpvu

That cone-like bit on a dremel tool apparently does the trick.

Tried that, seems kinda rough though and I'm not sure if it's done right.

[dpvu]

Once you have the basic shape down I think you can sandpaper it smooth.

[RacingManiac]

Can you use a counter sink bit on a lathe?

[m102404]

Make sure it's square. I used to do it by hand, but it takes a while. I use a bench sanding disk machine now.

Once it's square, you want to debur the inside of the barrel. The key is to do it evenly and keep the entire bevel 90deg relative to the axis of the barrel.

How shallow or steep the bevel is doesn't really matter for airsoft (matters a lot more for centerfire rounds).

I use a large diameter drill bit and turn it with just finger pressure. You're not aiming to "cut" matterial away...brass will come off fast enough on it's own. Just focus on keeping the barrel and the drill bit in-line (or else your crown will be cock-eyed).

With just a couple of turns you'll end up with a decent crown. Then the inner edge of the crown has to be deburred. I use 1200 or 1600 grit sandpaper, twisted into a cone shape (like a pencil) to simply "rub" that edge. Pretty much like sharpening a pencil, but just with no force.

Take a magnifying glass and inspect under good light....and you're done.

Takes about 5min (if you have a way of getting the barrel cut square to start with).

[BloodSport]

Styrak if you swing by MJ tomorrow afternoon I can show you the proper dremel attachment to use.

[coach]

Originally Posted by RacingManiac

Can you use a counter sink bit on a lathe?

if you have a lathe, I don't see why not. turn it slow or you'll take too much material. you'll still have to go in after and possibly touch it up by hand.

[Qlong]

There was a post before where someone stated that they had better performance with a non-crowned inner barrel?

[Styrak]

Originally Posted by BloodSport

Styrak if you swing by MJ tomorrow afternoon I can show you the proper dremel attachment to use.

I'm not driving 2 and a half hours to find out how to crown a barrel!
Lol, I'm not coming down to Claybank until Saturday morning.

Thanks, I'll try the drill bit idea with sandpaper.

[m102404]

The crown itself does nothing except protect the 90deg edge of the inner barrel.

With real rifles, the bullet is actually touching the inner surface of the barrel. As it leaves the barrel it needs to leave contact with the barrel around it's whole circumference simultaneously. Imagine that the barrel was cut at a 45deg from the longitudinal axis...the bullet would basically tip as it came out since one side of it get's "touched" for longer than the other side.

So if the barrel is simply cut off square, and doesn't have any burrs, then it's fine.

But people bump their barrels...so barrels are crowned (basically indented) so that the non-bullet touching edge of the barrel ends up dinged and the "ever so sensitive" inner surface remains pristine.

An 11deg crown is a convention...there was some thought that it was the ideal angle to have hot gases vent evenly/away from the base of the bullet resulting in it's maximum stability...but it's kind of hard to prove. Consensus from gunsmiths was that an 11deg crown was a good balance between easy of machining, durability and excellent consistent results.

A lot of this stuff is from a mix of field shooting and benchrest shooting...benchrest guys are pretty fastidious, field guys are more practical.

A clean 90deg cut off will work just as well in airsoft...because there is a whole other outer barrel protecting the inner.

I can't believe that any blow past forces at play in an AEG system would have any significant effect on AEG accuracy (which already sucks in comparison to real steel)...crowned barrel vs. not....as long as the cut is nice and the inner edge pristine.

[BloodSport]

Originally Posted by Styrak

I'm not driving 2 and a half hours to find out how to crown a barrel!
Lol, I'm not coming down to Claybank until Saturday morning.

Thanks, I'll try the drill bit idea with sandpaper.

bah I was going to include beers, but thats your loss.

[Styrak]

Well I solved my own problem. I used a small sanding drum with a fine grit slip on paper, and went at the end of the barrel at an angle and pressed the sander and barrel together while twisting the barrel around with the hand holding the barrel. So it does have a proper crown now (and as you said m#, it doesn't really matter the angle.)

Seems very smooth, even fixed my first botched job. Only a shooting test will tell if it's completely deburred.

[medhatboy]

i just used the de-burring tool from my reloading kit for case necks, worked fine.