Crown question: will this one affect accuracy?

[haertig]

I have a new Shadow 1000 (actually refurbished).  Can anyone tell me if the (pictured) crown on it will significantly affect accuracy and require me to recrown it?  There appears to be a plastic (?) piece on the end of the barrel that is attached by a dent on the outside.  This dent goes through to the inside and is in the crown.

You can also see that the crown does not appear perfectly concentric with the barrel, but it's hard to tell too much about that with this plastic piece in the way.  It looks like the only way to get the plastic out is to grab it with pliers and yank it out, since it's held in place by the dent.  If I take it out, I'm not sure I could get it back in firmly.

Thanks

[Gene_SC]

YES, YES and YES

Gene

[haertig]

In order to get down to the crown past that plastic piece, I'm afraid I just have to yank it out.  I am comfortable doing the recrowning myself - it went well for me on my other airgun.

Since I don't really need a front sight anymore (I have decided to keep this gun scoped), what are my options?  I suspect the plastic piece will be toast after yanking.  So is there something muzzle-brake-looking that I can just slip over the end and onto the knurling?  I don't think I need an expensive real muzzle brake - just something to hide the knurling.  I suppose I could just cut that 1/2" knurled part off the end of the barrel.  But that would disrupt the current setup where the rifling starts back 1/2" from the muzzle.  Would that matter for performance/accuracy? (i.e., if the rifling comes out all the way to the end after I cut the barrel)  I would prefer something to hide the knurling rather than a cut job, but I could probably handle the cut if it's considered an advisable solution.

Thanks!

[PeakChick]

Talk to the man who replied above, he can fix you up with a sweet muzzle brake.

these are the recommendations made by the airgun smith/designer John Bowkett

the crown should be exactly 90degrees to the axis of the bore and the muzzle dished at 30 degrees from the axis of the bore to protect the crown.
"this must be properly cut to an angle of 30 degrees or similar with a crowning or boring tool on a lathe, simple drilling will not produce satisfactory results"
"the optimum way of dishing the muzzle is by having it revolve around a fast turning stone, this grinds away the metal until the correct angle has been achieved"

apparently this method works even better on precharged as it helps divert the blast from the base of the pellet

(taken from the Bowkett file AGW January 1991)

yes i know, doing it is another thing, but you might know someone with a lathe and a lot of skill

i hope this is some use to you

fin

[haertig]

Here are some before/after pictures of my first attempt at recrowning.  On a 1377 Crosman pistol.  I figured it was so bad initially that I could only make it better no matter how poorly I did.  I can now see in the pictures that there are a few scratches in my new crown that I didn't get polished out.  Maybe I'll go back and redo that later.  I just roughed in the new crown with a Dremel tool and a pointed gumdrop shaped grinding bit.  Then I used a #8 brass screw chucked up in a drill to round up the crown, using kitchen cookware stainless polishing powder as my abrasive.  Then I got a second screw and used toothpaste for finer polishing.  I have no idea what the "angles" of my crown are.  Whatever a #8 screw rocked back and forth in a spinning drill gives you!  It may be far from a masterful job, but it's probably better than the original.

[Dave1899]

I'm no gunsmith but that has got to be a bo hunch better than the before pic showed!!!

well done

i love posts like this, methods and solutions using readily available equipment

fin

[howie1a]

If it came from the factory done right their would be no need for us fix their work . Howie1a

[haertig]

howie1a - 4/17/2008  5:44 PM

If it came from the factory done right their would be no need for us fix their work . Howie1a

Initially, I was a little peeved that my Crosman 1377 crown was so bad from the factory.  However, I started thinking later that I only paid $49 for that pistol - new.  What should I reasonably expect?  They could have given me a better crown, and charged $100 for the airgun.  Or I could pay less and put in my own labor to make it better.  I think I like the scenario of "Sell me a diamond in the rough, and let me shine it up" rather than them charging more money to make it that way from the factory.  I would not have bought this pistol had it cost $100, no matter how good the original crown was.  The original crown I received would not have been acceptable for a multi-hundred dollar competition airgun, but the 1377 is not that.

Ditto for the Gamo Shadow that this thread was originally about.  I would have liked a better crown from the start, but I only paid $99 for the airgun (actually, it was free if you consider the Cabela's points I used to buy it).   And I just spent 1/3 the cost of the gun on a new GRT-III trigger.  With a little personal labor on the crown and installing the GRT-III, I think I can have a really really nice airgun for a total cash outlay of $32 (the cost of the trigger, given the gun was "free").  And if I don't, no big deal.  We're not talking a large amount of money by any means.