Superstar\ RB2 .25 rotary breach

[gary_c_ham]

does anyone know the allen key size for the grub screw that fits in the rotating breach on a superstar? are they loctited from the factory? is there a knack to getting them out?

[edbear2]

does anyone know the allen key size for the grub screw that fits in the rotating breach on a superstar? are they loctited from the factory? is there a knack to getting them out?

Take great care with making a note of the exact distance it is in, and also use Loctite 243 when re-fitting if this is the grub that protudes into the air passage transfer as per RB2 Airsporter.

I re-built a RB2 (which had never been apart since new) a few years ago, and removed the grubscrew and neglected to measure exactly how much it stuck out into the airstream, I then had several times to strip the gun as it would not make more than 8 ft/lb despite all my efforts.

I left the screw in the position that seemed to make the most power, which was just over 9 I think, but was at a loss, all new inside etc.


I spoke to Jim Tyler about this and he said "air leak"......I said "what....down past a grub screw????"

I had not Loctited the screw.......I used number and letter drill shanks to measure the screw height into the transfer, then removed it, re-fitted it to the correct position with Loctite and left 48 hours........It went straight to 11.3 foot pounds

So if you are thinking it will alter the power, you may be right, but you may also be giving yourself hours of grief.

ATB, Ed

[gary_c_ham]

thanks for the reply. Any idea what the allen key size is?

Take great care with making a note of the exact distance it is in, and also use Loctite 243 when re-fitting if this is the grub that protudes into the air passage transfer as per RB2 Airsporter.

I re-built a RB2 (which had never been apart since new) a few years ago, and removed the grubscrew and neglected to measure exactly how much it stuck out into the airstream, I then had several times to strip the gun as it would not make more than 8 ft/lb despite all my efforts.

I left the screw in the position that seemed to make the most power, which was just over 9 I think, but was at a loss, all new inside etc.


I spoke to Jim Tyler about this and he said "air leak"......I said "what....down past a grub screw????"

I had not Loctited the screw.......I used number and letter drill shanks to measure the screw height into the transfer, then removed it, re-fitted it to the correct position with Loctite and left 48 hours........It went straight to 11.3 foot pounds

So if you are thinking it will alter the power, you may be right, but you may also be giving yourself hours of grief.

ATB, Ed

[edbear2]

thanks for the reply. Any idea what the allen key size is?

Sorry, too long ago..... I looked at Chambers drawings but the breech block is just a single part number, It surely is just a case of trying different allen keys till one fits?..

ATB, Ed

[gary_c_ham]

1.5mm seems too small, 2mm too big.....

Sorry, too long ago..... I looked at Chambers drawings but the breech block is just a single part number, It surely is just a case of trying different allen keys till one fits?..

ATB, Ed

[Phil Russell]

You have me puzzled. I recently stripped and resealed a Superstar in .177 and do not recall having to remove a grub screw or whatever on the breech with a hex key to do so. To get at the rotary breech you need to strip the piston out then remove the breech lever ... it just comes out with a bit of leverage but watch out for a small flat spring there. The rotary breech then slides back down the cylinder just like the piston does and exits at the back of the cylinder.
Or do you refer to removal of the end block that is secured by a trigger guard screw from underneath and another screw from on top etc
Cheers, Phil

[SRV1]

Mmmm...As per Phil Russell, I have stripped and rebuilt a few Superstars, but did not come across any grub-screw in the RB block. I would assume the Airsporter RB block would be identical?

[edbear2]

1.5mm seems too small, 2mm too big.....

Sounds like 1/16'' Imperial then, that's about between the two, Invest in a good set of imperials I would say, ATB, Ed

[edbear2]

You have me puzzled. I recently stripped and resealed a Superstar in .177 and do not recall having to remove a grub screw or whatever on the breech with a hex key to do so. To get at the rotary breech you need to strip the piston out then remove the breech lever ... it just comes out with a bit of leverage but watch out for a small flat spring there. The rotary breech then slides back down the cylinder just like the piston does and exits at the back of the cylinder.
Or do you refer to removal of the end block that is secured by a trigger guard screw from underneath and another screw from on top etc
Cheers, Phil

Hi Phil......You don't need to remove it to rebuild the gun, I assume they are factory set. If you look through the roatating block you will see the point of the grub screw protruding into the transfer port. The gun I was rebuilding was a Bell league gun and was not happy with AA Fields, the control pellet.

I noticed the grub screw, and being clever.....Thought it may be an idea to back it out a bit to regulate the power, thats how my saga started.

If you wander through the photos here, I think one just shows the position of the tapped hole, It is photo 16.

http://anotherairgunblog.blogspot.co...ar-part-2.html

As I said, the gun was bought new in the 90's and had never been apart with one owner from new, so 100% factory.

ATB, ED

[Phil Russell]

Fine ...but I have to say that I did not see one on the Superstar I worked on and during the fettle I removed / replaced the rb maybe 3 times.
Maybe the design changed over the years.
Cheers, Phil

[Mikeymoo]

Was wondering if anyone on here has a .25 RB2 Airsporter ?

[Shed tuner]

not all RB2 breech blocks have the screw... not sure if it's just some calibres, some years, some markets, or just a transitional change and it depends what was in the parts bin.

it simply resitricts airflow thru the transfer port within the roller block. See my Airsporter RB2 thread (just the first post) for a brief comment on the size and length of the TP.

[gary_c_ham]

Its just the .25 ones that have the grub screw to keep the power down with the larger calibre.

not all RB2 breech blocks have the screw... not sure if it's just some calibres, some years, some markets, or just a transitional change and it depends what was in the parts bin.

it simply resitricts airflow thru the transfer port within the roller block. See my Airsporter RB2 thread (just the first post) for a brief comment on the size and length of the TP.

[SRV1]

Interesting thread - A wealth of knowledge from wise contributors in this most excellent forum who have revealed what the grubscrew was all about for certain model. Never knew it existed and as far as I know, not listed anywhere/parts diagrams?

Seasons greetings to all.....

[Shed tuner]

Its just the .25 ones that have the grub screw to keep the power down with the larger calibre.

I don't believe this is correct, as i have seen it on two different .22s - one was an airsporter the other I believe a s-star