Rammed out! Which spring??

[leetrenchard]

Using lockdown time to go through all my airguns not working properly.

Got to my errant Remington Thunderjet, bought this to have a cheap fiddle with gas rams and got what I wanted.

The gun is weak despite me taking it apart for a good clean up and relube. The piston seal is a bit tatty looking but can't find a replacement.

The ram itself is 300mm in length with a diameter of 19mm. Gone through my old springs and found a Weihrauch one that is 19mm o/d and about 255 length.

This has worked with 14mm of slip washers in the piston end, the spring sits on top of the trigger block as its too big to slip into the block as the ram does.

It cocks and fire smoothly, with the ram it was at 645 fps average/7.67 ftlbs with superdomes (.177), with the spring and absolutely minimal preload its at 735 fps/10ftlbs

So, can anybody recommend a spring? needs to be 19 o/d and 300mm or more? hopefully the 19 will fit inside the trigger block and not rest on the top, will make a guide for it when I can borrow a lathe.

[TonyL]

Hi Lee, I'm not au fait with your rifle. Looking briefly at images of it, it looks like it may be based on the Gamo platform, as shared with a few other guns originating from China?

Have a look at the Mainspring Data Thread in the Useful Section. Go to the last page. You'll see an excellent post by Phil Russell giving spring stats of many springs. And also an updated one for Titan springs posted by Pete, "look no hands". Alternatively, you could try Tony Wall at SFS with your required dimensions.

If it is based on the Gamo design, take a look on the Welsh Willy site to get an idea of the spring guide design required.

Hope this helps a little and be sure to shout up for any further help.

P.S.....The stock looks nice on the Thunderjet.

[leetrenchard]

Was coming to similar conclusions on origin of it.

Ordered a titan 006 for it, would be useful to find a spring guide. It does look similar Internally to a meteor Mk7, are they Chinese too?

[TonyL]

Hi Lee, no, the Meteor is not Chinese, but these later Meteors are Gamo based (Gamo now owning BSA).

I like many of the characteristics of the Gamo action. But they are renowned for being very twangy, due to the spring guide being a loose fit on the spring. Usually, to rectify this, one would drive out the guide section that is set into the rear portion of the guide and replace this with one that is a better fit for the spring. So, if you can make your own, that's why I mentioned having a look on the Welsh Willy site to view the design of the guide. If you can't, I don't know if Will (he's a lovely and very helpful chap) would supply you just the guide and top hat? I'm not familiar with the innards of the gas ram version and whether the rear of the action is the same, or if you'll need to first buy the standard type springer guide?

Don't know if anyone on here may have the dimensions for the guide for of you wanted to make one. It's a stepped design and needs to clear the trigger unit / sear arrangement.

Once suitably tweaked this action provides very polite firing manners.

Ooh, just another thought......Lyn Lewington (venoman on here) runs ARC Tuning which specialises in tuning the Remington springers, so he might also be an excellent port of call?

[Neil54]

Your thunder jet is a Chinese copy of the Gamo Hunter series of rifles. SMK XS19, remington pest controller, many crosmans and the Turkish kral devil all use this platform.

I have an old rear spring guide I can give you the dimensions of. I also had two gas ram rifles, one with the ram facing forwards and one with the ram facing rearwards.

[leetrenchard]

That would help.

The trigger is in a cast rear section that pins I to the rear of the cylinder. It has a 19mm hollow in it where the ram/spring guide goes.

So the spring guide would have to have a short 19mm section tapering down to the guide rod to fit in a 19mm o/d spring.

[TonyL]

The ram itself is 300mm in length with a diameter of 19mm. Gone through my old springs and found a Weihrauch one that is 19mm o/d and about 255 length.

This has worked with 14mm of slip washers in the piston end, the spring sits on top of the trigger block as its too big to slip into the block as the ram does.

It cocks and fire smoothly, with the ram it was at 645 fps average/7.67 ftlbs with superdomes (.177), with the spring and absolutely minimal preload its at 735 fps/10ftlbs

So, can anybody recommend a spring? needs to be 19 o/d and 300mm or more? hopefully the 19 will fit inside the trigger block and not rest on the top, will make a guide for it when I can borrow a lathe.

That would help.

The trigger is in a cast rear section that pins I to the rear of the cylinder. It has a 19mm hollow in it where the ram/spring guide goes.

So the spring guide would have to have a short 19mm section tapering down to the guide rod to fit in a 19mm o/d spring.

Ah, just thinking, although without the benefit of having all the parts to hand.......The gun will obviously work with the spring anyway, so no issues with anything interfering with sear operation? So, maybe, the "fix" might be even simpler? Guessing it's the 25mm bore Gamo base as opposed to larger. The trigger block (and maybe a "boss" within?) is held in? How about a nice, substantial plain 25mm diameter polished washer ahead of the trigger unit. About 3mm thick? Then the guide can be either a one or two piece affair, with the "flange" section being 25mm and the guide portion to suit the spring id? Even a TX one could be used then. Or is this too simplistic?

Just thinking; hope this helps and/or gives food for thought.

[TonyL]

I've just been looking at some images of the Gamo IGT trigger unit online. Guessing the above idea might work okay providing the combined depths of the spring guide and the washer to support it aren't too close to the nook of the sear?

Wish I had another Gamo to play with as I enjoyed the Vipermax that I had. Once things open up I might look to sell the Mercury S I have, or trade it in, as I really do prefer the Gamo. Some would say this is madness, but I really think the Merc is overrated, as opposed to the Gamo being underrated.

[TonyL]

Thinking out aloud a little more. For the rear guide "bearing", how about a "reversed top hat" arrangement, id of 19mm allowing insertion into the trigger unit casting, with the od of 25mm?

[Neil54]

Here is the standard layout.

The black plastic bush is a sliding fit over the spring guide.

On a springer, you keep the back block, knock out the spring guide tube, replace the black bush and guide with one made of delrin or similar. You could add a locating pin on the rear of the new guide to locate it in the back block but most kits don't.

Here are the dimensions.

The end of the stepped block (19mm) has to go inside the piston. Dry fit all new parts with out the spring to make sure it will cock, just in case the guide and top hat touch.

[leetrenchard]

Thanks all for the info.

Have it working better than before with a slightly bodged in spring thats not quite the right size.

Correct spring coming next week as well as a length of 20mm delrin. Will borrow a mates lathe when I get it.

The picture of the steel spring guide from Neil is what it needs, will have to be 19mm at the fat end to fit in the trigger block.

If I can workout how to load pictures I'll put some on.

Its not possible to have anything on top of the trigger block as the sear is very close in to the block itself.

Ps the piston is quite large, 29mm if I remember correctly, would really like to know what piston seal fits this, it does look v similar internally to one of the Gamo rifles on tw Chambers diagrammes.

[TonyL]

Hi Lee,

Yes, looking at those images earlier I did wonder if clearance forward of the trigger unit may be marginal re the sear.

I think the Gamo 1250, and related variants thereof, have a 29mm bore. I also still wonder if it might be worth talking with Lyn to see if he has tuned any of these and if he has any spares / goodies for them?

[leetrenchard]

Hi Tony L

Thanks for Info.

Is it just a forum name "Lyn" to contact this member?

Would really like to get a good piston seal for this rifle.

Thanks.

Lee.

[TonyL]

Hi Lee,

Lyn runs ARC Air Rifle Tuning. I'm hopeless at links and such like, but if you were to search ARC out I think you can contact him through faceberk if you're a user.

He is known as "venoman" on here. A search should find him and you could send him a pm. All round nice and knowledgeable chap. He used to be an approved V-Mach fitter and has specialised in the tuning of the Remington rifles for a good few years now.

Hope this helps.

P.S. I've just had a quick search on the 'net for you. Even if you're not on that social media platform, Lyn's contact details do temporarily show up. Have a quick look and have your pen and paper handy.

[leetrenchard]

Trying to add photos, asked for forum help!