How to access Gamo muzzle for recrowning?

[haertig]

In one of my other threads, "Crown question: will this one affect accuracy?", Gene mentioned that I should recrown.

So how do you gain access to the muzzle?  I've gotten the sight off, but there is a piece still blocked muzzle access.  I though it was plastic in my earlier post, but it is not.  I tried to yank it out with pliers this morning and found that it is metal, and SOLIDLY attached by that dent that holds it in.

[edit] My first error in the above paragraph was thinking that this piece was made of plastic.  My second error was thinking it was a separate piece held in place by that dent.  I now see that the barrel is all one piece, machined to this configuration.  The wonders of what close inspection with a  magnifying glass will tell you that your naked eyes trick you on.   The "dent" is most likely a setscrew drilling attempt by the previous owner, gone awry (this gun is a refurb).  [/edit]

So, do I need to hacksaw this part off to recrown, of is there something I'm missing?

Thanks!

[Machinist]

haertig:
Have you considered taking this project to a gunsmith?

[haertig]

Machinist - 4/19/2008  9:44 PM
Have you considered taking this project to a gunsmith?

No, I would like to try it myself.  The recrowning itself I don't expect to be any problem.  It was easy, I enjoyed doing it, and it came out well on my Crosman 1377 pistol.  The Gamo rifle has a bit more complexity on the muzzle end though.  Before recrowning, there's a piece that needs to come off that's blocking my access to the muzzle. I was looking for advice from people experienced with getting that piece off.  Possibly, all Gamo rifles are recrowned by professionals that have lathes that can gain access to the muzzle even with that piece in place.  I don't know.  But I'd like to do it myself if possible.  Even if that means hacksawing off the end of the barrel by about 1/2" to "force" access for recrowning.  Unless hacksawing is terribly ill-advised.  I do not need to reattach the original sight, and as best I can tell that extra piece and the knurling on the end of the barrel are only there for the front sight.  I'm hoping some experienced people will answer my questions so I can intelligently decide what my options are.  I'm afraid that shipping the gun off to a gunsmith to have the work done would not be affordable for me.  I am just a new shooter who wants a reasonable gun for fun - not a top of the line target/showpiece model.

Thanks!

[haertig]

Thanks for the info.  Especially for that tip about checking for choke at the end of the barrel before deciding to cut it.

Maybe I will shoot this gun more before deciding on recrowning it.  I haven't shot it all that much yet, and I'm not a very good shot anyways.  I also just added a GRT-III trigger and need to go shoot with that in place.  My point being, rather than assuming that I'll have an accuracy problem due to that dent in the crown, I should verify that in fact I do.  That means I need to go do some serious shooting and eliminate all other causes for low accuracy before hacking on the barrel.  I haven't really shot this gun for accuracy yet - mostly plinking so far - I was assuming that I needed to run several hundred pellets through it before worrying much about how accurate it was.  I haven't been particular on pellets yet either, just trying to get a good quantity of anything shot through it to get it broken in (probably not necessary since this is a refurb airgun).  On the other hand, I was also trying to get all the known "accuracy killers" dealt with early on, and it seems like crowns and triggers are near the top of that list (ignoring the shooter for the moment!)

Thanks!

[Splash]

My S1K doesn't have it either. Since it's a refurb, someone probably drilled the dimple for a set screw, on a muzzle brake. I think your gonna find that it's gotta go.
Mike

[haertig]

I also think my "bump" is due to some previous owner of this refurb trying to drill a setscrew location to mount something.  The Shadow did come with the stock front sight however.

If I attempt the recrowning myself, my plan was not to try to work down the bump.  My plan was to cut the barrel behind the bump and start over trying to create an entirely new crown from scratch.  That stepped down diameter of the barrel (where the knurling is) is between 1/3" to 1/2" long.  The second stepdown is another 1/3" long.  I do not know the purpose of this second stepdown, it's i.d. is much larger than a .177 pellet.  Cosmetic possibly?

I was thinking of cutting the barrel down right at the stepdown from the main diameter - totally removing that knurled section.  That should be fairly easy since I have the nice bug shoulder to guide me for a straight cut and touch-up filing.  Which brings up another question.  I can see that the rifling stops a little bit back from the muzzle.  If I cut as I planned, that rifling would probably come all the way out to the muzzle.  It is difficult to tell exactly how far the existing rifling is set back, but my best guess is "not as far as I'd be cutting the barrel".   Would this present a problem?  I have not done the pellet push-through test yet to check for choke near the muzzle.

[johncedarhill]

AT the risk of a stupid idea--what about drilling the hole all the way through and then deburring the edges?
THis would save the problem of cutting the bump and recrowning.

[Splash]

The rifling going to the end of the barrel, will not cause a problem. You can use a pipe cutter and cut the barrel most of the way though, just be sure you have spare cutter wheels. Then cut it off, on the waste side with a hacksaw and you'll have a straighter shoulder to file down to. This will choke the barrel too tight and you'll need to crown deep enough a pellet will pass through. I cut 4 1/2" off one of my barrels this way and it worked real well. I crowned it just deep enough for the pellet head to pass, when pushed with a weed trimmer line. After you crown it check the crown with a Q-Tip, if no fibers are left behind, you should be good to go.
Mike

[haertig]

Actually, I was planning on cutting it behind the flutes, so that after cutting, the barrel would be one o.d. from breech to muzzle, with no "stepdowns in diameter" for lack of a better term to describe what I mean.  Since the dent is right in the middle of the flutes there is no way I could cut out the dent without cutting out the flutes too (maybe I could leave about 1/16" of flutes remaining, but what would be the point of that?  I don't see any reason to leave the flutes there.  AFAIK the only reason for these it to attach the front sight, which I don't need to do.  Cutting along the shoulder would serve as a guide for a nice straight barrel cut.

[haertig]

fix - 4/22/2008  5:09 PM

now i understand..your gonna chop it after the bump but before the rifle flutes??
if thats so i see no problem..as long as its cut in an area bigger than the actual bore.
go for it.

I don't understand what you mean "...as long as its cut in an area bigger than the actual bore..."  Sorry for being so brain damaged.

[rkr]

Your barrell bore is also off the centre in relation to the recess so it would indeed be a good idea to cut it off.

[DanoInTx]

.....grab hacksaw, cut off barrel where ever you'd like anywhere between 8" from the breach and the damaged end of the muzzle, recrown, done.  Don't know of any stock Gamo's with a choked muzzle, shouldn't hurt a thing, may improve accuracy, and since you don't want the front sight it will probably look much better.  I've cut the ends off of barrels before with a hacksaw, then squared it up good and recrowned.  If you take your time and do it correctly it should shoot just fine when done.  The operation usually takes me 10-15 minutes and I have always been pleased with the results.....but remember, if it shoots good now then there's no reason to redo it unless you just want to get rid of the hideous knurling:)  I think there's a simple barrel recrowning procedure in the Library here on the Gateway.  Good luck!