Low FPS?

[nateious]

Today when I was shooting my CFX I noticed I was able to see the pellet through the scope, normally I can't so I got out my chrony and fired a few rounds.  They were fairly consistent, all clocking in between 605-615fps.  I know the CFX doesn't typically shoot near the advertised 1000FPS but I'm pretty sure I've suffered a drop in velocity.  I'm shooting the 7.9 grain Crosman hollow-points, the CFX is about a year old.  I had only used the chrony once before and I think it was clocking in around 750-850, I can't remember just that the Crosman quest I have was about 100fps faster and that one is clocking in at 950 today.  Unfortunately I don't have a spring compressor so I can't open it up and look at the spring any other ideas of what might cause this?  Thanks for any input!

[RatRacer]

Check the easy one first, the breech seal, by draping a tissue over it during firing cycle.

[nateious]

Ok, I've tried that, it seems ok, the tissue didn't move so I presume it's not leaking.

*Edit*
It hasn't been cleaned in a while (~1000-1500 pellets), could that account for such a large drop?

[sobyo1]

My Stoeger did the exact thing after only 500 pels or so. Could see it going down range with a definate delay. Opened it up to find the lips on the piston cup seal compressed and not touching ID of tube. When I tipped barrel piston fell right out! Put JM seal after a de burr and some moly and its back lighting fast/

[s10gto]

By friends CFX was shooting low FPS too. Found the seal like this. Its a .22. Was shoothing high 500's. Now shoots high 600's with a JM Tesla seal.
Dustin

[nateious]

I should probably add that this is the .177 version of the CFX.  I'm not sure how to take the seal out, I'll poke around and see if I can find a thread with directions.

[Jay]

You can't check seal without a compressor nateious(you all ready said you don't own one), but it does sound like the seal is shot or your spring is broken, have you taken the action out of the stock an done a look in the slot at the spring to see if you can tell if its broke?

[nateious]

You can't check seal without a compressor nateious(you all ready said you don't own one), but it does sound like the seal is shot or your spring is broken, have you taken the action out of the stock an done a look in the slot at the spring to see if you can tell if its broke?

Not yet but that much I can do as I did it before when I put in the GRT-III.  Guessing it's time to look into making a spring compressor.

*Update* I don't know how much of the spring I can see but I don't see any breaks





Going on the assumption that it's the seal, and the fact that I'll need a spring compressor either way, I am now thinking about if it's worth replacing the spring at the same time.  I remember reading about someone who put a gas ram in their CFX.  I also think I read about a better than stock spring but can't remember the name of it.  In any event are the seals the kind I am likely to find at a Home Depot or a Lowes or am I going to have to order it from someone?

[Bullit]

You'll have to order the seal from an airgunner supply.  JRH offers piston seals only, as well as Gamo tune kits with seals, spring upgrade lubricants.

Here's a link for the tune kits page.
http://www.airrifleheadquarters.com/page/page/251488.htm

Hope this helps.  Good Luck.

[Jman]

You can't check seal without a compressor nateious(you all ready said you don't own one), but it does sound like the seal is shot or your spring is broken, have you taken the action out of the stock an done a look in the slot at the spring to see if you can tell if its broke?

Not yet but that much I can do as I did it before when I put in the GRT-III.  Guessing it's time to look into making a spring compressor.

*Update* I don't know how much of the spring I can see but I don't see any breaks





Going on the assumption that it's the seal, and the fact that I'll need a spring compressor either way, I am now thinking about if it's worth replacing the spring at the same time.  I remember reading about someone who put a gas ram in their CFX.  I also think I read about a better than stock spring but can't remember the name of it.  In any event are the seals the kind I am likely to find at a Home Depot or a Lowes or am I going to have to order it from someone?

My Big cat began shooting low 700's in .177, and my spring looked perfect like yours until I opened it up, and the break was on the side I couldnt see, 2 coils from the back. I have bets on the spring...

[Bullit]

The CFX is a different critter from breakbarrels, so I wouldn't assume anything.
I personally think a CFX is well worth working on, and a tune kit would be worth it.  You may also wanna replace the Breech Orings while your at it.  There's info here at the GTA for tuning, etc.
Best of Luck to You.

[s10gto]

Here's a nice kit.

http://www.airrifleheadquarters.com/catalog/item/251488/7718385.htm

Dustin

[nateious]

So I found a few different spring compressor build guides last night and I picked one posted up on youtube that looked a bit easier to follow. (at least in comparison to the others.  I spent a good chunk of this afternoon getting supplies and working on it.  Hopefully I'm doing this correctly as I've never done anything like this before.  I've got some pics of my progress so far.

Here is the youtube link:





The bit I'm not sure about is the guide called for 1/2 inch bolts to hold the C-clamp unfortunately i lack a drill that can accept a 1/2 inch bit (and a 1/2 inch bit) I was able to drill 2 3/8 inch holes in the clamp.  Does anyone know if 3/8 inch bolts would hold the clamp under tension? I could always drill a 3rd hole and use 3 instead of just 2, if not I'm going to have to see if I can find someone with a bigger drill.

[Jman]

The pressure on the clamp is really not too much, heck I think a strong man could hold the spring in..don't try that tho!

[nateious]

The pressure on the clamp is really not too much, heck I think a strong man could hold the spring in..don't try that tho!

Heh, don't worry I won't   I'm probably going to finish this up tomorrow as I need to go either get 3/8 inch bolts or borrow my friends drill and 1/2 inch bit.  After it's finished up I'll take the CFX apart and try to figure out what's wrong.  I'll update this thread when I know.  Thanks for the links / advice everyone!

[tom96]

The pressure on the clamp is really not too much, heck I think a strong man could hold the spring in..don't try that tho!

im 14 and ive done it a few times when tuning my RWS34 its pretty easy so are the 350s and crosman springers

[Jman]

and the parts are self explanatory to get back together. Only thing that could be hard is trigger group.

[ayerstg]

Does anyone know if 3/8 inch bolts would hold the clamp under tension?

Absolutely.  Have fun - you're opening up (pun intended) a whole new world.

Tom

[nateious]

I can't wait to get home from work and finish this thing up.  I'm sort of hoping it's the spring as I'm highly considering the Theoben gas ram, especially with the E3650 spring being out of stock on that other link.

[nateious]

Sorry for the double post but I managed to finish up the compressor tonight and take out the spring (and the rest of the bits)  I'm so glad I took some pictures of this thing before I started because I'm afraid I've already forgotten where some of the bits go. Here is what I've found:

The spring seems to be intact, though is slightly bent, I am not sure but I think I read this happens if there is an issue with the spring guide?


The o-ring on the rotating breach is broken, however that might have snapped when I was pushing it down the end of the barrel, or when the breach popped out and dropped to the floor, I'm not sure.  That thing seems rather tiny and fragile for the pressure it must have to withstand.  Either way I'll need to get a new one.


Onto what I think this was the real cause of the problem (sorry that the 2nd image is blurry, my phone camera doesn't do well with closeups.


As you can see there is what looks like a fair sized nick in what I assume is the seal (it's the yellowish plasticy looking bit)

Finally there are what looks like 2 more seals, one on the end of the rotating breach and one in the barrel of the gun, I don't know if they come out or not so I won't touch them for now, but they appear to be intact.



So I have a few questions:
Does anyone know if the bent spring is a issue enough to warrant a replacement (I'm really leaning towards that Theoben gas ram if I do replace it)
Assuming I am correct and the yellow plasticky party is the seal, how should I remove it?
Lastly (and I'll also google this, just haven't had a chance yet) does anyone had any ideas on that o-ring?  I'm thinking I might be able to get it from gamo, though I'm wondering if anyone has heard of maybe a better quality replacement.