[QUOTE=skires;222562]Specifically the S10 0.177.
All the usual ... shoots heavies best ... blah de blah.
As a few others have mentioned it has a tight area at the breech and then goes slack all down the barrel and then tight again at the choke at the muzzle end.
Bigtoe, and now my local RFD Keith M, has commented that the tight bit at the breech can't be doing me any favours. The pellets will be being sized down during transit through that bit and then enter the main length of the barrel undersize. Possible that compressed air will get past the pellet, cause instability blah de blah.
Let's review some facts about what you were told about machining the exterior of a barrel:
Button cut barrels tighten the bore when machined externally, Cut Barrels usually are not affected considerably to cause any issues and while I don't have much hands on experience with hammer forged barrels I know for a fact that they shrink when externally machined...So button barrels grow, hammer forger shrink and cut barrels are not usually affected.
Having said this, check what kind of barrel you have so you know what to look for if there is some machining somewhere....Here are some tips that I have used over the years.
My advice would be to first "Gauge" the Bore...Put a pellet in the breach and push it to the end and see in you feel more resistance...If you do this is positive, if the resistance goes from more to less this is a bad sign (loose bore) and can not usually be corrected...
Introduce a pellet at the breach and push it backwards with cleaning rod and measure it, compare to the pellet you pushed all the way out (previous paragraph)...If breach pellet is larger diameter than pellet pushed all the way out, then you are OK but may then have other issues...Bad crown, burrs around lands/grooves requiring POLISHING (Don't lap), maybe you need to cut a new crown or polish the one you have, etc...Flitz and similar light metal polishing compounds work fine...Go gently, keep in mind that those lands/grooves are very shallow in airguns.
Shoot a pellet or two at a bucket full of water and retrieve the pellet and inspect with a 10 -15 X magnifier and look for skirt/head markings or damage...
Last edited by azuaro; 18th January 2016 at 04:06 AM.