technical FAC

[angrybear]

Couple of questions for those who know what they're talking about.

.25 FAC Fast flow currently maxed out at 42fpe.

1/ If I remove the bronze filter do I need to fit a different exhaust spring ?

2/ If I remove both the bronze filter & swap the old valve for a Dr Bob's, will the original spring work or do I need a replacement

3/ Is there any point in a pre-chamber on a fast flow ?

I happen to have both a Dr Bob valve & a pre-chamber (the one off the bay) new & unused, but I'm loath to mess with the rifle because it's great as is, although I'd like a bit more velocity.
Having read that the bronze filters can break up & cause internal damage I want to remove that asap,
when I tried just taking it out the air leaked, I assume because in effect the spring had lost several mm of length ??

[Ca_Varminter]

1/ If I remove the bronze filter do I need to fit a different exhaust spring ?

2/ If I remove both the bronze filter & swap the old valve for a Dr Bob's, will the original spring work or do I need a replacement

3/ Is there any point in a pre-chamber on a fast flow ?

I happen to have both a Dr Bob valve & a pre-chamber (the one off the bay) new & unused, but I'm loath to mess with the rifle because it's great as is, although I'd like a bit more velocity.
Having read that the bronze filters can break up & cause internal damage I want to remove that asap,
when I tried just taking it out the air leaked, I assume because in effect the spring had lost several mm of length ??

1. No, but you will need to have a collar made for the blanking plug.
    to set the spring to the right height and to take the void where the Bronze filter used to be..

2. With the above collar, Yes.

3.Even with a fast-flow, more Pre-chamber volume will help with Power and Consistency !

Yes you will have a problem if you Just take Out the Sintered Bronze filter..
See answer #1

Stuart

[angrybear]

Many thanks Stuart,
but if I would need to have a collar made, a replacement spring would probably be a quicker & cheaper fix.

As I have a pre-chamber, supplied with a longer spring to fit it, I think I'll take the plunge & do a swap.

[Ca_Varminter]

Well if you are doing BOTH at the same time....
Yes a longer spring is needed!
That collar will only work with the Stock Cap!!

Stuart

PS. I checked your profile and email address...... seems OK, but I re-entered it.
Test sent an email... let me know if it shows up!.  Stu

[KevG]

the filter kit return springs are shite.i use a proper spring plus a disc spring guide to keep the spring central and stop it from buckling.
KevG

[KevG]

heres one I did with extension chamber
KevG

[angrybear]

Ah, wish I'd seen that before I reassembled it, I'd have taken a pic of what I've got  Yours also looks way nicer so I might be asking after one of them complete.

Anyway it's the pre-chamber as listed on the bay at the moment, the spring supplied looks remarkably like a hammer spring with a brass spring guide to fit over the valve stem.

I was actually surprised just how different the valve & spring are with the bronze filter, I assumed they'd use the same valve.

It also surprised me how much swarf & debris was inside  enough to get out a can of brake cleaner spray & give it a good hose out 

1 other thing I expected a larger barrel port for the FAC barrel (24") but it's a straight 4mm hole, same as my "MFR" sub 12.

Now I just need to find a battery for the chrono & see how it's doing 

[angrybear]

Right well that failed miserably 
shot 1 - 875fps - 43.2ftlb, 
shot 36 - 815fpe - 37.5ftlb
Previously gave 50+ consistent shots around 865-860 fps, it's also now Very VERY loud !

did the tissue test & no blowback at the breach/mag so must be wasting air behind the pellet 
I suspect it's that valve spring.

The now removed chamber, spring & guide (Dr Bob's stem)

[KevG]

fac should be 4mm can also have a 6mm countersink on mk2 type .12 ftlb should be 4mm stepped down to 3mm.though some are stepped down to 2.5 mm
KevG

[Dr Bob]

 That's a standard stem. Have you tried the Hi Flow?

Bob

[etiam viviens]

mine has a RAW power valve, no regulator.
first time i filled it to 200 bar and it is was doing 295 m/s about 73 joule.

could not find a lot about the RAW power valve on this forum but it seems to work
https://luchtbuks.com/nl/rawtheoben-high-power-valve-house-stem-cpl

[angrybear]

That's a standard stem. Have you tried the Hi Flow?

Bob

Hi Bob,
I thought your valve was for both sub-12 & FAC ?
So No, not tried the hi flow, I can't try either until I can get a replacement valve spring & the cap to fit it, as the cap for the bronze filter is different.

If you can supply the required parts; Hi flow valve, spring & cap I'd like to buy them.
Steve