HW30S/JM Kit Quandry

[Oldgringo]

Today, I got around to installing, one of the two recently purchased, JM HW30S tune kits.  Nice shot cycle but the velocity dropped some 30 fps from the original 620 fps using the same AA 7.33 Falcon pellets.  The JM spring is straighter but about an inch shorter than the original spring.  Yes, the rifle was cleaned and lubed in the prescribed manner with JM tar and moly. 

Did I get the correct spring?  My DIY JM kit lube/tunes on my R7 and R9 didn't go down in velocity.  IIRC, the JM springs in those kits were longer than the original springs.  I'm reluctant to "improve" my other (670 fps) HW30s if this is normal for a new JM HW30S tune kit.

 

[Motorhead]

Did a NEW piston seal get installed too ?

[Oldgringo]

Did a NEW piston seal get installed too ?

No, as far as I could tell the original seal was the same size as the original in both height and diameter and neither showed nor felt of any defects.  It has a smooth shot cycle and is as accurate as it ever was - given my 74 year old eyes and original open sights.

You reckon it could be my F! chrony?

[EMrider]

Seems odd. My recollection is that the JM kit springs were longer than the OEM or vortek springs for the R7.

R

[Grover]

My wife's 30 was always a little  lazy..  @ 600fps with 7gr., and it turned out to be the seal.  the bad seal had no visible imperfections. I later installed a kit, and it became and remains our hottest shooting 30s at 700 with 7.33

[Oldgringo]

My wife's 30 was always a little  lazy..  @ 600fps with 7gr., and it turned out to be the seal.  the bad seal had no visible imperfections. I later installed a kit, and it became and remains our hottest shooting 30s at 700 with 7.33

I have replacement piston seals.  I'll hold off until I hear what JM has to say.  Those two springs sure do seem to have a case of the shorts.  That said, this rifle shot 50 fps slower than her sister from the git-go.

Uhmm, anybody have any extra little bitty screws; you know, the one what holds the spring/piston thingies in?   

[Grover]

PA has them.   It's  called a fixing screw.

[Oldgringo]

PA has them.   It's  called a fixing screw.

Thanks Ron.  I'll order a couple    just in case.  I do feel this girl is coming apart at least, "....one 'mo tahm....".

[Motorhead]

Spring Pre-load is a VERY real issue and given piston/breech seals OK, may very well be reason for the slightly soft / velocity your getting.

[Oldgringo]

Spring Pre-load is a VERY real issue and given piston/breech seals OK, may very well be reason for the slightly soft / velocity your getting.

Here's what JM had to say about it.  I'm not sure what he's saying but we'll keep shooting and see if the velocity picks up a bit.  I'm not into killing things just punching paper out to 30 yards and the rifle is still as accurate as I am.  Er,...uhm...what is sring preload?   

Yes, the JM springs for my R7 and R9 were longer than the original springs.

Dear Sir,

All kits require a break in period and the wire size of my spring is bigger than the factory so length means nothing.
You took a factory gun that was fueling lubes with one sloppy fitting spring guide and then you installed a kit with two super tight guides,
put on spring tar and  the moly eliminated the fueling in the chamber. So with that you would not see instant velocity.
That is typical of any new parts. If you ever want max velocity use a loose guide, no spring lube and have some fueling lube on the piston seal.

[Grover]

Preload basically is the amount you have to compress the spring to get the gun together.  In it's assembled & uncocked state, the spring is somewhat compressed...  or "preloaded".  Was there any "preload" when you assembled the rifle?

If it were me, I'd install that new seal.  If that doesn't work, then grab a Vortek kit. 

[Oldgringo]

Preload basically is the amount you have to compress the spring to get the gun together.  In it's assembled & uncocked state, the spring is somewhat compressed...  or "preloaded".  Was there any "preload" when you assembled the rifle?

If it were me, I'd install that new seal.  If that doesn't work, then grab a Vortek kit.

Nope, the new spring just laid there.  It went in about the same distance as the original came out.  I just came in from miking the two springs.  The original was .108" and the JM was .117" in diameter.  While out back, I hit my spinner spoons 3 for 3 at 30 yards with the original open sights and that tickles me.

Five bucks plus S&H for one of those those little-bitty fixing screws strikes me as exorbitant.  Anybody know what size and thread they are?

[Grover]

Preload basically is the amount you have to compress the spring to get the gun together.  In it's assembled & uncocked state, the spring is somewhat compressed...  or "preloaded".  Was there any "preload" when you assembled the rifle?

If it were me, I'd install that new seal.  If that doesn't work, then grab a Vortek kit.

Nope, the new spring just laid there.  It went in about the same distance as the original came out.  I just came in from miking the two springs.  The original was .108" and the JM was .117" in diameter.  While out back, I hit my spinner spoons 3 for 3 at 30 yards with the original open sights and that tickles me.

Five bucks plus S&H for one of those those little-bitty fixing screws strikes me as exorbitant.  Anybody know what size and thread they are?

I meant when you inserted the rear plug/trigger housing --  how much was rear plug sticking out of the tube with the spring inside? 

You could just make a spacer (washer) and put it in front of the tophat.  That plus a fresh seal should get you to healthy velocities. That's a fix for any budget.

[chardosmith]

JM kits.  Another reason new kits from JM can be slow and pick up speed is the tightness of the guide.  A tight rear guide limits vibration and twang,  but can cause drag.  This drag slows the velocity, but with use, the spring and guide break in and velocities increase.  If you want max speed,  use JM's spring on a loose factory guide and very little tar.  It will twang, but shoot quickly right away.

[Grover]

My money is still on that seal. It was tired before the new spring and it's tired after the new spring.

[Oldgringo]

Thanks everybody.   

I'm gonna' shoot her a bit more and if the velocity doesn't come up about 10%, I'll take her down again and change out the seal AFTER I get a couple of those little "fixing screws".  ITMT, she has a sweet shot cycle and is more accurate than I am.   

[Grover]

Thanks everybody.   

I'm gonna' shoot her a bit more and if the velocity doesn't come up about 10%, I'll take her down again and change out the seal AFTER I get a couple of those little "fixing screws".  ITMT, she has a sweet shot cycle and is more accurate than I am.   

did you lose it or bugger it up?

[Oldgringo]

Thanks everybody.   

I'm gonna' shoot her a bit more and if the velocity doesn't come up about 10%, I'll take her down again and change out the seal AFTER I get a couple of those little "fixing screws".  ITMT, she has a sweet shot cycle and is more accurate than I am.   

did you lose it or bugger it up?

It did take me a while to find it after I dropped it and it might've got boogered on the reassembly.  The 30S was much more difficult to take down and put back together than was my R7.       Inasmuch as I may be doing the other 30S......?   

You mentioned washers in front of the top hat in a previous post.  School me on washers if you please. What kind/size/number, etc., etc.

[stija]

JM sells plastic spacers for 1-1.5 on his site with various OD. I attached a pic. I am sure you could find some something similar to work at Ace Hardware or your local friendly hardware store. Place them one by one on top of top hat until you reach desired power levels.

[SpiralGroove]

Hey Greg,
Understand your quandry,
After I tuned my HW30S using a JM spring, piston seal and homemade top hat, it shot at 678 fps for about the next 100 rounds.  During that time the gun was so accurate, it shot like it had been touched by the hand of God.  Then, however, the gun noticeably started loosing its magical accuracy.  I thought at the time, I had just lost my edge and needed a break?

Later, when I cronied the gun, the velocity had dropped to the upper 590's up to 615 fps?  I haven't had time to look into it yet, but yearn for that "Magic" accuracy again.  I know the gun must have been dieseling or something, but need to crack her open to investigate.   

I can make/add spacers as others have suggested, but don't want to trade off with a harsher shot cycle and diminished accuracy.

We'll see ........... Kirk