RWS 350 Magnum while waiting for 300S parts

[AmBraCol]

A fellow member of the local shooting club put a fellow in touch with me.  He's got an RWS 350 Magnum in 4.5 mm (.177) that's "lost power".  Could I fix it for him?  Possibly. Bring it over, we'll give it a looksee.  An initial removal of the buttstock revealed what looked like a strangely compressed spring.  See first file uploaded below.  So I told him, "We're going to need a spring and while we're in there just as well get a seal to go with it." So an order was placed with Air Rifle Headquarters.  Now the waiting begins 'til the package makes its way across the gulf and down to Coffee Country.  In the meantime, just as well get things ready for when it DOES get here.

Today got a bit of time so went ahead and disassembled the power plant.  Zero, zilch, nada, nothing of preload.  In fact, when I backed off the compressor after pushing the pins out leaving slave pins in place my paranoia kicked in and I had to go confirm that nothing else would retain the trigger block in place when the pins were removed.  Once that was confirmed I started tapping on the trigger block to get it to slide out which it did, leaving the spring and piston in place.  A bit of tapping around and got the spring and spring guide and piston to slide on out.  After removing the spring I found that the "strangely compressed" spring was actually a broken spring that had threaded together with the larger piece, the broken ends being concealed so that it looked "strangely compressed".   

Further messing around got the piston liner and a spacer out of the piston.  The liner is damaged, I suppose from meeting the end of the broken spring as the owner continued to shoot it following the initial breaking of the spring.  The pictures are below.  Smoothing out the liner, ie removing the damaged part making sure it's nice and round and not catching on the spring, should not have a negative effect on the function of the rifle, correct?  I'm not sure what the piston liner's supposed to do.  Any feedback on that is highly welcome.

[AmBraCol]

Another thing, is this date stamp indicating June 2002?  Also, is this a T01 trigger?   Still trying to improve my knowledge of these rifles.  Thanks!

[AmBraCol]

Close up of the crown - looks like a bit of polishing is in order...

[Jeff Marshall]

Another thing, is this date stamp indicating June 2002?  Also, is this a T01 trigger?   Still trying to improve my knowledge of these rifles.  Thanks!

That is a T01 trigger unit.

Your pic of the date code is large but blurry. It looks like 02, but if you look at it with a magnifier it could say 92.

Diana started to phase in the T05 trigger in 2000 but there were some T01 guns produced into 2002.

[Yogi]

Piston liners are there to protect against spring to piston inner wall contact.  Metal to metal. 
With a straight spring, secure spring guides they should not be necessary.  An ounce of prevention......
When you install the new spring, make sure to polish the ends.
Good luck with the rebuild,

-Yogi

PS when springs break they often do that, and other than a slight loss of power and a less smooth cocking cycle, hard to tell.

[AmBraCol]

Well, bit by bit - here we go.  Actually, just waiting for a chance to run a few shots, make sure it's all running as it should be then connect with the owner to hand it off.  Here's how it's gone so far.

The muzzle crown was rough as a cob.  See attachment below.  Took it to a friend who has a small lathe.  It chucked up, just barely.  Polished it up a bit and then a touch of cold bluing, it'd been a while so the muzzle didn't do that great.  Still better than bare metal, but just barely.

The compression tube had a bunch of wear marks from the past decade and a half.  It didn't look all that great.  So touched up a bit of roughness with steel wool then degreased and ran several coats of cold bluing - this turned out MUCH nicer than the muzzle crown.  See attachments below.

Finally, to assemble.  Didn't get a picture of this, but sprayed the rear spring guide with some adhesive then fitted a piece of heat-shrink tubing, slipped on the rear shim/bearing then screwed the new, polished end spring on to it, using a bit of moly to give it plenty of opportunity to slip instead of grab.  Since the spring increases diameter as it compresses, this should work a treat to keep it tight and straight during the shot cycle.  Yeah, I'd rather turn a new guide from scratch, but don't have a lathe and my buddy doesn't have the tooling or skills to do it either.

Then the piston liner, it got whacked by the broken spring and was rough with the lip doubled over.  Got out the hand grinder and worked on it a bit, finishing up with some sand paper on a piece of PVC pipe.  It's now got a bit of a U cut into the rear edge, but it's smooth and glides nicely without grabbing anything.

SO after fitting one of Maccari's seals to the piston and checking for proper fit, assembled the piston liner to the piston with a bit of moly where it showed scratches and between it and the heavy washer that was in front of it from the factory.  A bit of moly on the spring where it enters the liner and a bit of heavy tar behind that.  Forgot to measure, but the Maccari spring gave it about four inches of preload upon reassembly.  Also, this apparently was the last of those springs at Air Rifle Headquarters.

Reassembled the barrel to the compression assembly using moly between the washers and the barrel and the tube.  Tightened it "just so" so it's a wee bit stiff upon breaking, and it cocks smooth as can be.  BOY is that thing loud, though.  Didn't seem to be dieseling, just loud.  Will run a few pellets out of it then over the chronograph out of curiosity.  This has been a fun project.   

[Blacktalon6]

Looks good

[AmBraCol]

Looks good

Thanks!  I think the owner's going to be quite happy with it.  He's antsy as all get out and tickled with the pics sent.  He's got a new scope and a Diana mount for it.  Now to find time to run a few through it just to double check it's running OK.  No parts left over.  Well, other than the broken spring and nicked/worn seal. At least, none I can find laying around the place.      

[mpbby]

Just to let you know, from my experience ..  , what instantly damages what you call piston liner ('spring sleeve' for me) is when you try to break the barrel with the rifle disassembled (only without the stock).  Without the guiding groves inside the stock, the cocking shoe goes directly where it shouldn't - the exact point it was damaged in your case. 

[makarov76]

If you can measure the thickness of the piston liner then find a piece of steel shim stock
& you can roll & form a new one’ I only have .003 thick you’re a long ways away
But I would give you a ft or two if you really need it’

[AmBraCol]

Just to let you know, from my experience ..  , what instantly damages what you call piston liner ('spring sleeve' for me) is when you try to break the barrel with the rifle disassembled (only without the stock).  Without the guiding groves inside the stock, the cocking shoe goes directly where it shouldn't - the exact point it was damaged in your case.

Muito obrigado, Marcos!

Yes, cocking out of the stock can have unintended consequences.  In this case, however, the damage was done by the piston liner contacting the broken end of the spring.  Removing the bent piece has it working just fine.

[AmBraCol]

If you can measure the thickness of the piston liner then find a piece of steel shim stock
& you can roll & form a new one’ I only have .003 thick you’re a long ways away
But I would give you a ft or two if you really need it’

Thanks, Jay!  I'd be able to pick some up down here a lot cheaper than paying the shipping, but the offer is greatly appreciated.  After smoothing it out it's running fine.  Am running some pellets through to ensure everything is working fine before handing it off to the owner. 

And thank you to everyone who has participated in this thread!  It's been a fun build for me.   

[WHITEFANG]

PTFE material will work as a piston liners. But the poly bottle material will work. Many thicknesses can be found. Many kick the bottle material to the curb but the stuff works well if installed correct. Makes for a good rear guide tightening also. That crown was terrible.
Did you have JM set the spring? Matters not as long as you got the spring installed. The spring will take set in time. Leaving the gun cocked overnight will set the spring or just a bunch of shooting. Loved the 350 guns.

[AmBraCol]

The factory sights on the 350 Magnum leave a lot to be desired, especially when shooting in bad light, indoors with a black bullseye... But there's 55 pellets through her now and the shot cycle is smooth.  Once the owner gets the scope to me and we can mount and it zero it, we'll see what she's really capable of.  The targets were shot around 5 or 6 meters. (15-20 feet or so) I'm still not sure about where the balance point for the artillery hold is for this rifle, haven't shot it enough yet.  Some of the fliers were due to yours truly shooting from an unstable position, some I'm sure are due to the nature of the wobbly rear sight. 

[mpbby]

Scopes lifespan on a D 350 may be a problem. Btw, when the scope doesn't actually 'break', but loses its consistency (doesn't hold zero) it may be a nightmare.

Scopes are more resistant to recoils when the adjustments are close to the center.  The D 350 usually has a barrel droop, then, when zeroing, you may have to abuse the vertical adjustment, and the scope becomes more fragile..

People do some things to avoid the perfect storm.. Are you aware about this?

[AmBraCol]

Scopes lifespan on a D 350 may be a problem. Btw, when the scope doesn't actually 'break', but loses its consistency (doesn't hold zero) it may be a nightmare.

Scopes are more resistant to recoils when the adjustments are close to the center.  The D 350 usually has a barrel droop, then, when zeroing, you may have to abuse the vertical adjustment, and the scope becomes more fragile..

People do some things to avoid the perfect storm.. Are you aware about this?

Yes, I'm aware of the issues.  The owner's bringing over a new UTG scope (usually very recoil resistant) and a Diana Zero, or whatever it's called, "shock absorber" scope mount.

In the meantime, I got to playing with the old scope.  It was missing part of the scope mount, hadn't noticed before as he handed it to me dismounted.  So a one piece base was borrowed from another rifle and the BSA 3-12X44 scope was mounted.  Here's one 5 shot group, shot from standing at about 6 meters.  Not too bad, this rifle seems to want to shoot.  We'll see how it does with the new mount and scope when he comes in a little while.

[dtdtdtdt]

A suggestion on the 0.003" material needed.  Don't know how big a piece you need but I find a convenient source of well-known thickness small pieces is a feeler gauge set used to gap spark plugs and other similar uses.

Cheap, convenient.  Makes good scope shims if you need them for anything!!

Also, regarding the scope mounting.  You mention that he has an RWS mount to use.  If you are lucky it will be the droop compensated single piece mount.  I use a Wheeler FAT (torque wrench) to mount scopes and to tighten things in general.  If you have something like that it makes life much easier.  (A good Christmas/Birthday present if they as hard to find down there as I suspect.)  The torque for screws into rings to hold a scope are 15-18inlb or 20inlb with a thumper like the magnum springers.  Mark the scope so you can detect slippage (pencil mark works).  To hold the bases to the rifle using the RWS rail, torque the cross bolts to about 35inlb and mark the base so you can detect slippage. Use a slippage pin (recoil) to keep everything in place.

[mpbby]

Very good news!  Besides absorbing recoil, the Diana Bullseye ZR mount (ZR = "zero recoil") has a fixed built in compensation (inclination) for barrel droop; just remember the white arrow pointing toward - the muzzle..

Btw, the ZR is a great idea.  When you pull the trigger, the rifle goes backwards and, by inertia, the scope tends to remain still; so, it pushes the ZR's spring a bit.  While pushing, the piston reaches the end of its course and generate the 'huge' recoil.  The idea is that, at this very moment, the scope doesn't have a (rigid) point of support, and doesn't suffer the 'impact'.

Judging by me..  when seeing the ZR for the first time  , it helps to understand where the white arrow has to point, and what is the actual function of the spring.

[dtdtdtdt]

Just saw the comment on the Diana ZR base.  That is really nice!  I have one on RWS 54 that appears to hold zero extremely well and is definitely droop compensated.  I also have the older (cheaper!) style on another RWS 54 that also works well.

The white arrow points to the muzzle.  If you have micrometers, the front of the mount is about 0.025"  (0.63mm) lower than the back end. You can measure it from a reference position (put it on a table without rings) measure the distance from the surface to the bottom of the rings. 

The scope mount itself slides on the two smooth steel rods and are returned to position by springs inside the base.  if you are familiar with the old external adjusting target scopes like the Fecker, Unertl, or Lyman that were used for many years by target and varmint shooters.  The scope tube was protected by the recoil spring and sliding of the scope tube under recoil.  The spring returned the tube to its ready-to-fire position. Artillery pieces have a similar mechanism to absorb recoil too. 

The ZR mount works the same way!

Comments on torque apply there too. 

Dave