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garththomas · Veteran Member

My shooting groups were too large and inconsistent for my liking so I decided to check the crown on my QB57. I thought the machining looked kind of rough so I got a round head brass machine screw with a 3/8 diamiter head. I put the screw in the drillpress with some valve lapping compound I stirred the bottom of the barrel around then checked it after a few minutes. The new angle that appeared was uneven so after a closer look I guessed the bore wasn't exactly centered on the barrel and when they machined the slightly curved crown with the barrel in a lath it didn't match the bore. I panicked and thought I had to remove the offensive machining which I did with a file. I had to keep checking my work with a square and it took a few tries but eventually the end was flat and square.
I went back to the drill press until I had a visible angle about 1/32 wide and it looked perfectly even. Then I realised I had to sand the file marks off and that took a bit of time as I was constantly turning the barrel as I was sanding with 400 emery and finished off spinning it by hand on a peice of abraisive pad. Back to the drillpress once more and it looked really good. I have read about using crowning tools and if I had one I would have used it but since I was reusing the factory muzzel brake I figured it wouldn't matter what the crown looked like as long as it was smooth and even. When I tested it out my groups seemed to be tighter although I was using open sights. So anyone have an opinion, have I done a bad thing. Question

SMP · Silver Status Member

No sir doesn't sound like a bad thing. There several different ways to crown a barrel based upon the tools you have at hand and what your application is.

With patience and some care you can apply a really good crown using only hand tools. And based on your description sounds like it turned out well.

Throw up a picture

viper2788 · Member

after using the drill to re-crown, try using only your hands to turn the brass screw and apply very light pressure with the lapping compound you're using. use the same method as with the drill and rotate the barrel every so often. continue doing this for as long as you desire(i gave a good hour). i found this way to really give a fine finish to the crown and it should remove any microscopic imperfections.

garththomas · Veteran Member

Thought I'd try to post a pic

Alstone · Moderator & Site Supporter

The crown from your photo dosn't look bad, the only thing I can think of is that it is a bit shallow, try a smaller screw and increase the angle a bit

Al

garththomas · Veteran Member

I used a 1/4-20 with a head dia. 1/2" to start then lightly again with a 3/16 head dia. 3/8. I'm just about to pull it apart to put in a delrin spring guide and I was thinking of trying a delrin top hat since I heard they would work with a light pistoned gun even if they didn't come from the factory. When I tear it down I'll give the crown another go, thanks for the input.

radar · Silver Status Member

It's beautiful. If you make it deeper it would only be for protection from scratches, right?

SMP · Silver Status Member

That is the crown quandary.

If your trying for absolute accuracy any recess at all has been shown, tested and proven to be counterproductive.

But most rifles are toted around lugged over hill and dale and the recess does provide the true crown with a little protection. This is where the 11deg crown shines.

Given a choice I would go with the dead flat muzzle that has a 0.010" wide crown and I would protect it with a bloob tube or "muzzle brake"

garththomas · Veteran Member

I reinstalled the stock muzzle break and I will keep it just for the open sights as I haven't had much luck with a scope yet.

radar · Silver Status Member

Alstone · Moderator & Site Supporter

Flat is best but achieving it is difficult, the best way is to do it with a tool post grinder using plenty of coolant, any other way runs the risk of leaving very small burrs on the crown.

I have also done them using a dremal in the tool post and a fine emery disk.

What ever you do it will need protecting with a shroud, muzzle break or silencer.

Al

ellerja · Member

how do you get those plastic muzzle protectors off?mine has a set screw which i backed out but still could not move the site/protector off i did not try tapping on it.i only tried twisting by hand.the gun is a airhawk much like the crossman style springers.