Gamo cf20 mod version any information.

**rovercoupe** · 06-09-2016, 09:37 PM

I recently bought a sorry looking gamo cf20 and it looks like after a bit of research its a mod version with a odd extension on the end of the gun for a different sight and its a low power model. Does anybody know anything else about them and is it possible to get it up on power or is it stuck at 6lbs.

**Phil Russell** · 07-09-2016, 11:31 AM

A CF20 could easily become a 'full power' rifle providing the spring is suitable ... square section monster not needed. Make sure piston washer is OK as well.
Cheers, Phil

**Shed tuner** · 07-09-2016, 12:53 PM

Mine was of the same type... my thread about some improvements here:

http://www.airgunbbs.com/showthread....highlight=cf20

**rovercoupe** · 07-09-2016, 09:44 PM

How bizarre, had a look down the barrel and sure enough the rifling just ends! Chambers has come up trumps with a new spring and seal arriving today and with excitement I replaced the seal and spring and the power was 6lbs..... Put some pennys in the end and no difference. Maybe its just destined to be a low power rifle. Now do I chop the end or leave it as a original as i wanted a hunter and it looks like its going up for sale once the stocks refinished.

**gwyn** · 07-09-2016, 09:48 PM

Originally Posted by rovercoupe

I recently bought a sorry looking gamo cf20 and it looks like after a bit of research its a mod version with a odd extension on the end of the gun for a different sight and its a low power model. Does anybody know anything else about them and is it possible to get it up on power or is it stuck at 6lbs.

Hi , i have one of these ex MOD CF20 Gamos,it was chrono'd at 8ft lb,nice smooth and accurate,at 25yds off a bench rest it would do five shot groups time after time, then the spring broke i took it to a gunsmith and had a new spring and seals fitted,came back returning 9.5 ft lbs but has never matched its old performance,too much power now??

Don.

**rovercoupe** · 07-09-2016, 10:34 PM

This is now twice in a week where a simple seal and spring replacement has caused more issues than a full re seal on my pcp! So it should up the power with a new spring and seal but it has remained exactly the same. To be fair the old seal was scored to hell and was still doing 6lbs so there pretty hardy guns!

**TonyL** · 08-09-2016, 06:41 AM

Originally Posted by rovercoupe

How bizarre, had a look down the barrel and sure enough the rifling just ends! Chambers has come up trumps with a new spring and seal arriving today and with excitement I replaced the seal and spring and the power was 6lbs..... Put some pennys in the end and no difference. Maybe its just destined to be a low power rifle. Now do I chop the end or leave it as a original as i wanted a hunter and it looks like its going up for sale once the stocks refinished.

Can these suffer breech leaking issues with the pop-up port?

**Phil Russell** · 08-09-2016, 08:55 AM

Re breech leak ... I fully expect so. So this could be checked by the wet tissue method.
Also, I have known issues with the breech 'plug' locating properly. It might be worth trying to see if the pellet is moving from loading bay to barrel without hindrance. Maybe by loading and firing into water or whatever to allow the pellet to be examined for scores or tears etc.
Cheers, Phil

**rovercoupe** · 08-09-2016, 09:28 AM

Good ideas, will look into this tonight and see if I can get anywhere.

**rovercoupe** · 08-09-2016, 08:38 PM

Gave it the wet toilet roll test and no leaks from the breech on the top anyway, stripped down again to install a delrin spring guide and still no change. Its not changing when i load some pennys in front of the spring so if something is wrong I dont think its the spring or piston, they were all cleaned and checked before the new parts went in. I did not get round to tring to salvage a round to see if it deformed so thats the next step but if that is ok then I am stumped.

**rovercoupe** · 08-09-2016, 08:40 PM

Just a thought, if I have to strip it down again would looking down the barrel with a torch at the other end show up alignment issues or does a tiny amount out mean big problems?

**Shed tuner** · 08-09-2016, 09:29 PM

is it over sprung ? What was the new spring ? is the comp tube scored / scratched / leaking past the seal ?
Mine does 10FP+ easy

Chopping the non-rifled end of the barrel off and recrowning is well worth it IMHO.

**rovercoupe** · 09-09-2016, 08:44 AM

Its a standard spring and seal from chambers and the internals cleaned up good with no scratches on the internals. The old spring was chopped down by about a inch and it makes no difference on power which one is in it!

**Shed tuner** · 09-09-2016, 05:32 PM

is the o-ring that seals the assembly at the end of the comp tube, into which the pop up breach fits, perhaps perished ?

**rovercoupe** · 09-09-2016, 07:00 PM

Hi i think your half right.... I pulled the old o rings and had a look at testing with some generic ones that fit and i have noticed a scratch where the o ring sits and down the side of the chamber which has turned out to be a crack in the transfer cylinder, to finish off the outer transfer cylinder seal has cracked too.

Time for more parts from chambers and hope this is where the air is going.

I am amazed that the part that stops the piston is plastic, makes sense to never dry fire these!

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