RWS 38 & 24 questions

[ayerstg]

New poster here...  4 AGs (three relevant to this forum):  M38 dom 04 85, M24 dom 11 91, Winchester M363 (Diana M6) dom 11 69 (IIRC I bought it new in 72 or 73) and original Sheridan Blue Streak (Second owner; I had it re-built in 1969 or 1970 by the original factory in Racine, WI).  Original owner of the the three RWS / Diana AGs

I have to put new seals in the M 363 - my dad used it for many years and returned it to me with the seals about shot a year or so ago.  Not the topic of this post...

My M38 is as-shipped except for a trigger hone I did, uh, a long time ago - it has a superb trigger.   It used to be extremely accurate, but has been driving me nuts to the point that I have rarely shot it the last few years.  Have the bug bad again and so I'm going to tear it down and tune it.  (Yes, I have a spring compressor I built a couple of years ago for tinkering with a Chinese ag and helping son #1 with a Shadow Sport he was given).  At the moment, Vortek site is down for maintenance and I haven't been on that site previously.  So opinions on - JM parts or Vortek parts / kits?  Accuracy #1, but up to a point, more power is also welcome.  I already have JM lubes on hand (Moly, Velocitar, Heavy Tar, Clear).

I blew the gears out of both my mini-mill and mini-lathe (don't ask - it was the same project - grrr) so until I get around to ordering and installing new gears, I'm at the primitive end of power tools, with a drill press with x-y table as my most "precise" machine tool.

Parts/kits?  Seals? O-rings?  to button or not to button?  Links to happy-camper diy tunes?  Not interested in having it done for me; it's important to me to do it myself.

Same questions for the M24, except it shoots fine.  Was the kids ag growing up (OK - they squabbled a bit over the Sheridan as recently as yesterday... it's a great shooter and awesome hunter for younger eyes).  Maybe my "indoor" ag and certainly the one my wife prefers to shoot.

Fire, er, twang away with answers, please!

Tom

Edit: Hmmm.  Maybe I should re-post in the shop talk forum?

re-Edit: I think I dragged out everything I needed to know from the shop talk forum, bit-by-bit.  Wish they would finish up the site maintenance on Vortek's site...

[Mark 611]

I personally like the Vortek Products because their a straight drop in kit 99% of the time and VT piston seals require no sizing unlike most of JM seals, the Vortek kit don't need all the lubes you just have to put moly on the seal, VT kits come 80% lubed with just a dab to add to the spring in the kit, Tom's kit don't need all that junk in them to make them work! Their super smooth noise free and have lots of power, adding lubes only slows down your rifle, as said VT kits do not need all those lubes to make them function correctly, and to me having to buy extra lubes is added expense to make something work is foolish to me.

[RedFeather]

I don't believe Vortek makes a kit for the 24, if that is what you are asking.  Those benefit greatly from a lube tune.  At the low power level, the spring should last forever.  If yours does not have the adjustable trigger (going by the date) I wouldn't fret over it.  Both of mine are direct sear but seem pretty decent as to pull weight and predictability.

[Rocker1]

 I am sure the RWS 24s  have leathers seals to. Thanks David

[RedFeather]

Gee, I'm not sure about that.  I will have to ask over on the DWC.  Both of mine are about ten years old.  I should have thought Diana transitioned to synthetic seals by the 90's.

[ayerstg]

I'll let you know when I take mine apart, but IIRC from another discussion years ago, I'm pretty sure mine has synthetic piston seal.

[Rocker1]

 Could be so the one I had was from the 80s  1984,  and I  know  its has a leather seal so does my rws 45.Thanks David

[ayerstg]

Got the M 38 done.  Was dark, so no chrony numbers.  New piston seal and JM spring kit (not the civilized one).  Breech seal is OK, although I may go ahead and change that anyway.  Used velocity tar on the spring.  Old spring was pretty good but small kinks in two plains.  Compared to the factory spring there was a scary amount of preload with the new one - no way it would have gone in without a spring compressor.

Had de-burred it years ago so only inspected and lightly touched that up.  Never was much de-burring needed.  Honed/cross-hatched the compression tube - very lightly.  Original finish was mirror-smooth.  I burnished in some moly before re-assembly and left it with only the "plating" - no visible moly.  Moly paste from JM on the appropriate places.  Tiny assembly gouge in the original piston seal and the new one was a really tight fit.  It smoked a little the first 3-5 shots but no detonations and no perceptible smoke after the first few shots.

It cocks about the same as before (probably a little harder, but not remarkably so).  Makes a lively "thunk" sound now with zero spring noise and I cannot detect any torque offhand.

I'll wait until I have a tin of pellets thru it and chrony it, but I think I may cut the seal diameter down a little.  As I wrote, it was a tight fit and suspect it may be robbing me of a little energy at that fit.  I would be purely guessing at velocities right now, but it *feels* and sounds like it may favor heavier pellets now.  Heaviest I have on hand are 9.3 gr, so I'll have to get some 10.5 gr and try those again.

Will tackle the Win 363 next - the M24 is shooting fine and all I would do with it is lube tune and check seals anyway - it can wait.

[Mark 611]

Sounds good! Keep us up updated.

[ayerstg]

Rebuilt the M 24 today using the original spring, which was in very good shape.  Spring measured 8.8" long, 29 coils of about 0.105" wire at approx 0.725" o.d. and 0.501" i.d.  The factory rear guide was a good fit and I reversed the washer to get a clean face.  Polished spring ends, new Apex seal and new breech seal.  De-bur, cross hatch, etc.  Apex seal was VERY tight. Moly paste usual places and Vel tar on spring.  Good clean on barrel with Balistol, brush, patches, and dry patches.  After about 50 shots, put the chrony 1 foot ahead of muzzle and fired 2 sets of 10 shots seating pellets flush with my thumb, then 2 sets of 10 shots seating pellets deep using a Fisher Space pen (point retracted).  (Wish I knew what became of my Beeman Pellseat...)  Pellets were CPLs (7.9 gr).  I think the seal is too tight and robbing a little energy, but open to knowledgeable comments:

M 24 lube tune + new Apex seal (very tight) and new breech seal. Original spring.                     
   Pellets thumb seated      Pellets uniformly deep seated      
CPL weight   7.9      7.9      7.9      7.9
                     
Shot 1   505      489      474      471
Shot 2   492      504      478      473
Shot 3   500      491      485      479
Shot 4   495      505      483      473
Shot 5   507      500      477      480
Shot 6   490      490      478      473
Shot 7   495      503      470      474
Shot 8   499      493      480      480
Shot 9   487      495      475      476
Shot 10   487      479      487      478
Average   495.7   494.9   478.7   475.7
E.S.       20      26      17      9
Std. Dev.   7.01      8.21      5.21      3.33
Ave. FPE   4.3      4.3      4.0      4.0

OK - that's about 100 fps / 2 fpe less than I expected.  Interesting to note that deeper seating improved the Std. Dev.  More testing later.  Meanwhile... any comments about the seal tightness?  Or should I post that query on the Shop forum?

The M 38 has me REALLY perplexed, as you will see.  I ordered the GRT Mk2 tune kit, new Apex seal, did a normal tune and lube, etc.  This seal also was very tight.  I have about 100 - 150 pellets through it and put 20 CPL 7.9 gr pellets over the chrony - reversed order this time, with first string seated deep as above and second string seated flush using my thumb:

M 38 tune, Apex seal, and GRT Mk2 tune kit         
Pellets seated   Deep      Thumb
CPL weight   7.9      7.9
         
Shot 1   750      839
Shot 2   746      840
Shot 3   753      841
Shot 4   755      842
Shot 5   745      840
Shot 6   758      840
Shot 7   750      837
Shot 8   761      841
Shot 9   740      836
Shot 10   739      841
Average   749.7   839.7
E.S.      22      6
Std. Dev.   7.30      1.89
Ave. FPE   9.9      12.4

OK - I am flabbergasted by the E.S. and Std. Dev. of string 2.  And the 90 fps increase in velocity is good, too.  BUT - this reads like low factory or GSX tune kit numbers, NOT GRT numbers!  What gives?  Again - could this be a consequence of having too tight a seal?

I am perplexed.  Comments invited.

Tom  

[ayerstg]

More numbers on the M 38 in weight order high to low (all ten shot statistics)


H&N   11.57 gr
652.9 fps
14
4.95
11.0 fpe

H&N   10.19
700.2 fps
29
10.20
11.1 fpe

Gamo   9.4 gr
737.6 fps
44
12.19
11.4 fpe

CPL    7.9 gr
839.7 fps
6
1.89
12.4 fpe

H&N   5.56 gr
1036.0 fps
12
3.94
13.3 fpe

This is shooting slower than it was before I tuned it.  Don't have the numbers handy, but by way of example, the lightweights were going loudly supersonic before and now they are subsonic.  My top two thoughts are:

1.  Tight seal is robbing energy or
2. Somehow I got a GRX kit even though I ordered a GRT Mk2 kit

I hate to tear the gun down again, but I could drop the factory piston seal back in and try the chrony again.  Or (less work) - drop the factory spring and spring guide back in and hit the chrony, leaving the new seal in place.

Suggestions?

Tom

[ayerstg]

I've moved the quest to the Shop forum but will report back here any significant changes.  While I remember... the M24 has synthetic piston seal and adjustable trigger, in answer to earlier questions.  It's a sweetie to shoot - that + size is why my wife likes using it.

[Mark 611]

If your piston seal is tight its killin your power! JM seals need to be sized 99% of the time to fit the tube of the rifle its being used in! As I read in your post in the shop talk you got too much tar in the rifle? if so tar will kill your velocity if not used correctly thats why I don't use it at all and its nasty and sticky, I use other lubes that work just as well and don't lose velocity, just my 2ct