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[redmoon3580]

Hmmm makes sense. Can this "energy leak" cause the lost of 30 fps?
It looks a little bit too much. I could understand 5-10 fps but 30?

Consider the fact it is at the very beginning of the BBs flight that momentum is taken from it... 30fps actually sounds about right if you understand the concept.
I myself got a hefty FPS boost off of barrel spacers, around 12fps.
And the clay stock mod also boosted my fps, by about 6fps.

[SVT Cobra]

@Fire-Fox, yeah if I have the time, I will try that combination out. I am not sure if I will get to it anytime soon though  .

I agree with redmoon3580 on explaining why the shims help out. Like he said, I think the bb will push up on the hop-up arm when it begins to move. If the shims lock the arm in place, then the arm will be able to maintain its position in the chamber during the shot. This will do two things, one it will apply more pressure over the bucking than if it were to "give away", and two, it will hold the bb back for a tad bit longer allowing pressure to build up somewhat behind it. If I am right on these two ideas, I think 30 FPS should be about correct. I am sure it will vary a little bit from rifle to rifle though.

You did bring up a good point though. Perhaps the TM chamber does have a better fit around the bucking which allowed the PDI o-ring nozzle to seal more effectively. It could have been that the combination of the TM shells, and shims to hold everything in place, is what helped me realize that 30 FPS boost.

However, I do recall one test that confirms that shims helped in boosting FPS. There was a time when I was running an un-shimmed TM chamber and my modified JG hop-up arm. With maximum hop-up, my muzzle fps would average right at 490. One day I decided the shim the TM chamber and test the rifle to see if consistency improved. Well I took a few shots and the bbs would just sky rocket at maximum hop-up. The shimmed TM chamber and JG arm was over-hopping the bbs like never before. When I chrono'd it, the muzzle FPS was averaging at 521. That experiment is where I remember that the shims added 30 FPS. My local field only permitted 500 muzzle FPS, and even with hop-up on its lowest setting, the bbs would still over-hop. I never chrono'd the rifle at lowest hop-up...I wish I had...but I didnt bother because of the over-hop, the arm had to be modified. I compared the TM arm to the JG arm and noticed that the length of the teeth in the JG arm were a bit longer. I believed that if I reduced the length of the teeth, I could lower the FPS and prevent the rifle from over-hopping. I was correct in this idea and was able to fix the FPS/Hop-up issue by filing down the teeth of the JG arm. However, in an attempt to get the rifle exactly at 500 FPS, I ended up screwing up one of the teeth beyond repair. I resorted to shimming the TM arm and trying that out un-modified. To my luck, the TM arm shot exactly at 500 FPS on max hop-up. You have no idea how happy I was lol.

So I know that there were a lot of variables being changed during these trials and I wish I had recorded all of the data. The thing is, I wasn't testing the shims for FPS specifically at the time; that was a discovery made by accident. Further, I am certain that compression does play a vital role in muzzle FPS. However, at least in the example above, the muzzle compression was the same. I noticed the increased FPS when I shimmed the TM chamber with JG arm. It is that observation that makes me certain that shimming alone can increase FPS.

[Excellent]

Cobra would you still recommend glue stick glue like elmers for glueing the shims? the strength seems questionable and the only super glue I was able to get a hold of is the expanding kind, i'm a little worried this will expand the brass in the chamber and throw the whole thing off.

[SVT Cobra]

Cobra would you still recommend glue stick glue like elmers for glueing the shims? the strength seems questionable and the only super glue I was able to get a hold of is the expanding kind, i'm a little worried this will expand the brass in the chamber and throw the whole thing off.

Yes glue stick will work just fine. In fact, its a good option since the removal of the glue it easy. I believe that isopropyl alcohol will dissolve the glue.

Recently, I found that my hop-up arm shim was loose since I used elemer's glue stick sparingly. I re-glued it using super glue (non-expanding) to test its longevity. Super glue is another alternative but may make the shim permanent lol. In my case, I dont mind it being permanent since I am done experimenting with this hop-up unit.

[Excellent]

well i'm probably going to use super glue. I got the thinnest shim stock they had over at ACE and glueing brass on brass then to the chamber walls doesnt seem like the best bond. the stock well chamber is as loose as a tent.

thanks for the response and for posting this thread.

[SVT Cobra]

well i'm probably going to use super glue. I got the thinnest shim stock they had over at ACE and glueing brass on brass then to the chamber walls doesnt seem like the best bond. the stock well chamber is as loose as a tent.

thanks for the response and for posting this thread.

You are very welcome! Thanks for reading!

Let me know how everything works out 

[Excellent]

it didnt work out, lol.

shimming the hop up arm in the TSD/well is a waste because it seems to have a much more pronounced slope. it also comes with a crappy attempt at a shim; the base of the arm was raised slightly on one side. I sanded it completely down.

I just shimmed the sides of the chamber. after having the brass bend alot I said to hell with it and ended up cutting index cards for shims. I dont know about how well they will last in the long run but they fit great and are alot easier to work with.

I think it was Bnoji who said the chamber has the same internal dimensions as the VSR/Bar 10. well after putting in my Laylax barrel and nineball bucking, it was such a tight fit in there that the chamber bulged a less then a milimeter at the seam. all screws went in perfectly fine so this doesn't seem to be a problem other than that I had to sand the two prongs on the hop up block down to make that fit. oddly enough because the chamber is tight around the bucking it acts as an effective ABB system. hopefully accuracy wont be affected. though I could always shave the bucking down, but for now I dont see any issues.

I think I bit off more then I can chew. to get the PDI bull barrel base to fit inside the TSD/Well receiver I had to sand the threads alot and then sand the whole bottom of the base down a millimeter. now I have to dremel the stock of the gun about a millimeter aswell to get that to fit.

my PDI outer barrel looks amazing though... It will go in soon

[SVT Cobra]

Oh wow, I didnt think the TSD/Well variant could cause so many problems! I am glad to hear you are on top of them though.

Index cards is a great idea for shims too! I have a lot of extra shim stock from my first purchase, so using a different material never really occurred to me. I am glad you brought that up though, I am sure the index cards should work well. They should last a while as well as long as you dont adjust the hop-up too often. Personally I just leave my hop-up on maximum all the time.

[DHM78]

Index cards sound good.  I personally like using sheet plastic for shimming.  You can apply it a little thick and sand it down slowly to get the thickness exactly where you want it. 

[Excellent]

Oh wow, I didnt think the TSD/Well variant could cause so many problems! I am glad to hear you are on top of them though

no joke, I wouldnt even say its a clone, more like an imitation. should have just saved up for a TM... modding the gun just to get stuff to fit was way more work than getting the cash to just buy the parts.

I got everything to work but the groupings were even worse stock probably because of the chamber if not the bucking. I have decided to shelf the gun for a little while until I can get a precision chamber. the stock one at this point sucks hard with any sort of mods. also have a M130 spring on the way so I can use the ball bearing spring guide and piston from the upgrade kit. (they wont work with the stock spring)

also I tried the paper spacer mod for use in the PDI bull barrel and again I couldnt get it so that the inner barrel would be perfectly straight in the outer barrel... I honestly dont know how you managed to wrap the paper so tight in the picture on the first post.

and yeah the index card shims worked great. easy to cut, trace for spares and they hold their shape even when cut real thin.

[SVT Cobra]

Hmm that is really odd. Maybe you are rolling too tightly? I didnt add a lot of force when I rolled the spacer in the picture. Could you post a picture of your paper spacer and another of the barrel+spacer within the PDI Bull outer?

I just looked at my rifle and the inner barrel is perfectly within my PDI bull outer, however as someone already mentioned (Lulu?) your inner does not necessarily need to be perfectly centered within the outer. The bbs will still fly straight and all you have to do is re-zero the scope.

[Excellent]

I definitely didnt roll it too tightly, maybe my technique just sucks but I cant get it nearly as tight as in the picture. yours looks machine rolled. both times I have tried it one side is always a milimeter or so thicker.

I have a feeling its because the clear tape is preventing the paper from rolling over it completely flat. how did you roll yours exactly? I put a long strip of clear tape on each side of one sheet length wise and rolled the barrel over each edge at a time.

and I dont want to have to force the barrel into a straight position from the chamber to the endcap because the spacer isnt exactly round, wouldnt it cause the BBs to curve if the barrel isnt straight? I dont know.

I would take pics, but I already tore off the spacer

[SVT Cobra]

I definitely didnt roll it too tightly, maybe my technique just sucks but I cant get it nearly as tight as in the picture. yours looks machine rolled. both times I have tried it one side is always a milimeter or so thicker.

I have a feeling its because the clear tape is preventing the paper from rolling over it completely flat. how did you roll yours exactly? I put a long strip of clear tape on each side of one sheet length wise and rolled the barrel over each edge at a time.

I am a little confused here. Its been a while since I made my spacer and I cant exactly remember how I did it. I do know that I did it a total of two times. My first technique made a good spacer but was a bit sloppy for my liking. The spacer worked just fine however. The second attempt was from scratch again and I implemented a new technique which resulted in a much nicer looking spacer. This spacer is the one shown in the photograph. If I remember correctly, I would tape 2 sheets together using one long piece of clear tap and attached it along the long edge of the paper. Then I would roll those two sheets onto the barrel tightly (but without using excessive force) and taped them down with one long piece of tape. Next I prepare another 2 sheet piece and tape the first edge on the side opposite to the last piece of tape. I repeated this process until the spacer fit snug within the outer barrel. A few quick measurements told me the final spacer was uniform through out.

and I dont want to have to force the barrel into a straight position from the chamber to the endcap because the spacer isnt exactly round, wouldnt it cause the BBs to curve if the barrel isnt straight? I dont know.

You definitely do not want to bend the barrel within the outer as that would cause curving. However, as I mentioned before, the position of the inner within the outer has no impact on the performance of the gun. In fact, to some extent, it can be said that the outer barrel provides no functional purpose. The outer is there mainly for aesthetic reasons and perhaps to add some protection/support to the inner barrel and hop-up chamber. In other words, I could rig my rifle so that it didnt have an outer barrel and with a thicker barrel spacer, my performance would remain the same.

Now if your inner is not entering the end cap, you have a problem. However this issue could also be caused by the receiver-outer barrel meshing and not necessarily the barrel spacer. It could also be an alignment issue with the hop-up block, hop-up chamber, and outer barrel. Just some food for thought.

I would take pics, but I already tore off the spacer

[Excellent]

I am a little confused here. Its been a while since I made my spacer and I cant exactly remember how I did it. I do know that I did it a total of two times. My first technique made a good spacer but was a bit sloppy for my liking. The spacer worked just fine however. The second attempt was from scratch again and I implemented a new technique which resulted in a much nicer looking spacer. This spacer is the one shown in the photograph. If I remember correctly, I would tape 2 sheets together using one long piece of clear tap and attached it along the long edge of the paper. Then I would roll those two sheets onto the barrel tightly (but without using excessive force) and taped them down with one long piece of tape. Next I prepare another 2 sheet piece and tape the first edge on the side opposite to the last piece of tape. I repeated this process until the spacer fit snug within the outer barrel. A few quick measurements told me the final spacer was uniform through out.

and this i'm positive is why mine would come out uneven. my method was taping one long piece of clear tape on each side of a piece of paper, have the sticky side up and then roll the barrel over the piece of paper. the placement of the seams of tape wasnt accounted for like in your technique. I'll definitely try and make another with this in mind especially since the ID of the PDI bull barrel front is so small, it shouldnt take long.

You definitely do not want to bend the barrel within the outer as that would cause curving. However, as I mentioned before, the position of the inner within the outer has no impact on the performance of the gun. In fact, to some extent, it can be said that the outer barrel provides no functional purpose. The outer is there mainly for aesthetic reasons and perhaps to add some protection/support to the inner barrel and hop-up chamber. In other words, I could rig my rifle so that it didnt have an outer barrel and with a thicker barrel spacer, my performance would remain the same. Now if your inner is not entering the end cap, you have a problem. However this issue could also be caused by the receiver-outer barrel meshing and not necessarily the barrel spacer. It could also be an alignment issue with the hop-up block, hop-up chamber, and outer barrel. Just some food for thought.

I actually bent the stock 512mm Well barrel with the first paper spacer. both times with the well in the stock barrel and the Laylax in the PDI they didnt slide into the endcap without adjustment, but it might have been issues with the Well chamber in the PDI outer bull barrel.

thanks for all the info, I'll try to make another spacer when I get the precision chamber. you should update the first post with your technique.

[SVT Cobra]

Awesome thanks for the feedback! Let me know how your new spacer turns out once you make it again.

Yes definitely take into account not only the total thickness of the tape, but its placement as well. Good luck!