Gamo "Smoothbore Rifled" barrels

[Shed tuner]

Looking at the newly acquired (thanks Al) CF20 I've been setting up for my son today...

Done a basic tune on it, got rid of the twang, bit of weight in the piston, shoots pretty nicely at 10 FP with a weak spring (really easy to cock), but around 1" groups at 30 yards. I'd put this down to pop up breach alignment, until today, when I was removing the ugly plastic lump that protects the crown...

...the bore was smooth... no rifling marks/crown at all.... Hmmm...


Then I looked more closely... the barrel actually was rifled, up to about the last 10mm, which was then smoothbore Dowhat ? What were they smoking when they decided that would be a good idea ! I'm not talking a larger counterbore like on a BSA springer - this was actually the bore of the barrel. Within about 3 minutes of discovering it, the offending piece of barrel was on my garage floor, and I was filing square and doing a "brass roundhead screw in a drill with polishing paste" recrown job on the end of the rifled bit...

Results - groups now down to around 1/2" at the same range

But seriously, what were they thinking

PS As a bonus, the protruding section of muzzle was just the perfect size for threading 1/2" UNF, so I did; screwed on a neat little ally muzzle finisher to protect my new crown

[Hsing-ee]

Looking at the newly acquired (thanks Al) CF20 I've been setting up for my son today...

Done a basic tune on it, got rid of the twang, bit of weight in the piston, shoots pretty nicely at 10 FP with a weak spring (really easy to cock), but around 1" groups at 30 yards. I'd put this down to pop up breach alignment, until today, when I was removing the ugly plastic lump that protects the crown...

...the bore was smooth... no rifling marks/crown at all.... Hmmm...


Then I looked more closely... the barrel actually was rifled, up to about the last 10mm, which was then smoothbore Dowhat ? What were they smoking when they decided that would be a good idea ! I'm not talking a larger counterbore like on a BSA springer - this was actually the bore of the barrel. Within about 3 minutes of discovering it, the offending piece of barrel was on my garage floor, and I was filing square and doing a "brass roundhead screw in a drill with polishing paste" recrown job on the end of the rifled bit...

Results - groups now down to around 1/2" at the same range

But seriously, what were they thinking

PS As a bonus, the protruding section of muzzle was just the perfect size for threading 1/2" UNF, so I did; screwed on a neat little ally muzzle finisher to protect my new crown

Glad I gave it to you, I would NEVER have discovered that astonishing fault. Sounds like quite an accurate rifle now, certainly beats the Chinese alternatives. Maybe the smoothbore was for the spigot of some kind of rifle-grenade practice round issued only to Cadets...

[Shed tuner]

Glad I gave it to you, I would NEVER have discovered that astonishing fault. Sounds like quite an accurate rifle now, certainly beats the Chinese alternatives. Maybe the smoothbore was for the spigot of some kind of rifle-grenade practice round issued only to Cadets...

If you saw and shot it now (sitting in a slightly chopped CFX stock) I think you'd be quite impressed
Drop by when you next get some time now you know where I'm at...

Thanks again !

[TonyL]

Excellent result; nice one.

[combatpanda]

Hi guys. Sorry to jump in on this thread. Just got a cf20 to rennovate as a project.
Was wondering if the cf20 will fit straight into a cfx stock?
Hope u can help.
Thanks

[Shed tuner]

Hi guys. Sorry to jump in on this thread. Just got a cf20 to rennovate as a project.
Was wondering if the cf20 will fit straight into a cfx stock?
Hope u can help.
Thanks

yup....

[evert]

Bringing this topic up from the deep..

Because I have some thoughts on why they do the counterbore. Upon inspecting the muzzle end of the CFX, theres some quite heavy machining done to the outside of the barrel. While the machining on the CF-20/30s I have had the front sight off have had less aggressive machining done on the muzzle, there still is some splining done for the front sight to sit on.

Could the counterbore be a way to remove imperfections in the bore caused by the machining operations done to the muzzle?