So hereI am just sitting and thinking .........

[Missed-Em]

Ok, I'm just slightly frustrated with my Diana Stormrider.  Sure it's a cheap PCP at $200 but I'd hoped for better than "just squirrel head accuracy" as my Urban at about the same price is much more accurate. So, as I said I'm just sitting here thinking and what pops into my mid but "I don't have a .25 cal.".  So today's dumb question is what's involved in converting a SPA PR900 from .22 to .25cal?

[Ribbonstone]

Did notice that SMK (in the UK) has or had a single shot version of the co2  CP1 in .25....never saw the single shot version in the US.   So evidently, at least a single shot .25 can be built on that sized action.

As for your rifle, barrel and new bolt.  No factory mags in that caliber, and don't really think converting a .22mag to .25 would be easy (they are tiny little mags, without a lot of "extra" room).

Would likely go single shot...which also means the new made bolt could carry the o-ring rather than cutting an internal o-ring seat for an o-ring inside the barrel.

Wouldn't be too expensive if you can do yourown barrel fitting and bolt making.

[KnifeMaker]

How about massaging the barrel you already have. Polish the bore, re-crown. Nothing to lose if not happy with that accuracy you are currently getting.

Knife

[cobalt327]

I'm guessing a lot of different pellets have been tried? If so, I tend to agree w/Knife- going over the barrel, checking fasteners, smoothen/lighten trigger pull might net better results.

[Missed-Em]

How about massaging the barrel you already have. Polish the bore, re-crown. Nothing to lose if not happy with that accuracy you are currently getting.

Knife

This is the direction I'm headed but I have heard barrel is difficult to re-install.  Want to polish the throat to ease chambering, as well.  I still hate the magazines but the single shot tray is nice.  But at .25?  Dreaming is always fun!

[Rob M]

How about massaging the barrel you already have. Polish the bore, re-crown. Nothing to lose if not happy with that accuracy you are currently getting.

Knife

This is the direction I'm headed but I have heard barrel is difficult to re-install.  Want to polish the throat to ease chambering, as well.  I still hate the magazines but the single shot tray is nice.  But at .25?  Dreaming is always fun!

I converted my plinkster to 25 cal , and several guys have converted the varmint to 25 and 30 cal single shot.. I machined an npxl barrel to fit ( 19 dollars from crosman ) , leaving a mighty thin wall at the breech area, which wasn't a huge problem because you still have the barrel band as support. The probe, lead in , and bolt area in general were the only challenge. I later built a custom breech from scratch in order to make it 9mm , but that's irrelevant and NOT needed for 25 caliber,.the loading area of the breech was very tight for 25 cal as someone mentioned

[Ribbonstone]

Suspect that he's not real comforatable with airgun work (YET), and likely doesn't have the equipment for lathing/fitting a barrel.   Maybe I'm wrong and he has a whole hot-rod shop's worth to tooling at hand....but I suspect not.

If you just want to massage the barrel, don't really have to take the rifle apaert...just get the barrel off, and work on it by itself...no take down.

Actually, other than manybe needing to replace a barrel o-ring, getting the barrel off isn't really all that hard.  Are some PCP's where the transfer port interlocks with a recess in the barrel....this isn't one of them so you can get the barrel off without a full take down.

 DO NOT TAKE DOWN ANYTHING....this will go easier if it's left all as it is.  De-scope, undo the 3 little set screws on top of the front end of the breech, remove the barrel band cross screw, and it should pull stright off (by still being in the stock, the barrel band is kind of locked in place, so it won't slide as you pull the barrel).

The muzzle brake/LDC is also held by little set screws, but sometimes they lock-tited them...sometimes they aren't.   If the screw won't easily unscrew, I'd apply a bit of heat.  Rather than heat the whole LDC (as there is some plastic inside)...find a good size nail...heat the nail until it is hot-hot (like just strting to glow), and hold the tip of that nail directly on the set screw.  May have to do that more than once, but the idea here is to get the sealer to let go and not strip that tiny little screw.

Yeah...likely at least one of those three  little set screws that holds the barrel on will be kind of loose and feeel like the hole is stripped.  At least on mine, the problem was the little set screw was "wrong" not the hole.  BUT, if you didn't screw up the LDC set screws, can try one of those in it's place (which worked for me).

Reminder: there is a little o-ring INSIDE the rear end of the barrel.  YOu can't work on that end with the o-ring still in place.

If you're not use to this kind of work, my advice is that It's much harder to screw up a barrel if you work by hand-power.

To do a simple polish, cleaning up any roughness or burrs, use your hands. With enough little bits of round wood (dowel/chop stics/BBQ skerwers/ etc.), shaped to whatever seems best, and fine grade abrasive paper glued to the shaped parts of the wood, and run by hand....would be hard to "go too far" and regret it.

From here...if you're willing...can get into some other things that may or may not help.

[Missed-Em]

Offline Ribbonstone

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Re: So hereI am just sitting and thinking .........
« Reply #6 on: Today at 12:23:04 PM »

    Quote

Suspect that he's not real comforatable with airgun work (YET), and likely doesn't have the equipment for lathing/fitting a barrel.   Maybe I'm wrong and he has a whole hot-rod shop's worth to tooling at hand....but I suspect not.
    Unquote

-----------------------
You nailed it right there and I really appreciate the "how to" info.  I'm OK with removing and replacing but don't have machining equipment or skills. 

I've been to the Library but can't find a thread on barrel polishing - can someone provide a thread or tutorial?

[miksatx]

Never polished a barrel. But I've polished a lot of agate, semi precious rock, silver and gold. Diamond polishing paste from 50,000 mesh clear down to 220 grit. Maybe felt pellets they use for cleaning mounted to the end of a cleaning rod. preferably one that twist with the rifling as you move in an out. You can get mineral oil. To soak in the felt and then add diamond paste to felt pellet dab it around with your finger. Then go to swabbing the barrel. I buy most my diamond paste and mineral oil off eBay. Not really that costly

[Ribbonstone]

We (that would be the "royal we") tend to forget how much of a"hoot" it was to take down/reseal/put togeter a Crosamn 2240/3350/3360.  Which is retrospect, its about as simple as a co2/PCP gets.  Then we (again, th "royal" we) tried our hands at a somewhat morte complicated m air rifle (like a QB 78 or a Disco/Maxi).

You gotta start somewhere... and the riddle at hand (so far as barrel adjustment) is not too big a challenge.

[KnifeMaker]

Good advice Rib's has given!

One thing that helps a lot of barrels is a re-crown. A simple round head brass wood screw larger than the bore, and coated with a good polishing compound works wonders. If nothing else, fine valve lapping compound and a follow up with a fine metal polish works very well.

Many low cost, an high dollar airguns need a crown polish, and the transfer port is a common place to look from a burr that can cut the pellet when pushing home with the bolt. Check it as well.

A cotton swab, (Q tip) is very valuable for checking both. insert it into the breach and pull out over the port. Any cotton fuzz of threads pulled by it? Same for the muzzle crown. Look for fine threads or fuzz pulling from the tip.

Use Rib's advice to smooth the transfer port.

If you wish to polish the bore, before the crowning , use flitz or start with JB bore paste, put on a tight fitting patch and use the same method you would use for cleaning the barrel starting from the breech. do this about 1000 stokes changing the patch every 20 or less strokes. Finish with flitz or other fine metal polish.

 Don't go out the muzzle. Only within 18-3/16 inch of the crown or muzzle. You don't want to widen the bore at the muzzle.

Knife 

[Ribbonstone]

If the poster gets there...would treat crowns as a sepate item (with lots of YourTube vids to watch).

'Ugly" crowns can shoot great.

"Pretty-polished" crowns can shoot like "carp".


It's not so much "art" as practicality....even/smooth transitoon at the muzzle seems to be the "winner".....muost of the"fancy stuff" is just "fluff".

[KnifeMaker]

 

True That!

Knife

[Missed-Em]

Thanks guys, looks like a fun project.

[Ribbonstone]

Lets do it in pictures.

Fixing a transfer port burr.

Basically, thin abrasive paper...a rod (in this case brass, but a wooden BBQ skewer would work)...glue to afix the paper to the rod.  Hand power.





Cured the burr...polished the rear "ramp" of the barrel...and didn't enlarge anything.


BUT...in my limited experience (2 rifles and 1 pistol on the same action), getting the set screws to actually clamp down hard did more good than anything else.