Gamo Big Cat 1250 Bunch 'O Questions.

[reservoirdogs12]

So I recently bought a Big Cat 1250 and mounted a Leapers 3-9x40 AO scope on it. Went out shooting today and was able to zero it in at 20 or so yards. After about an hour in 12 degree weather (I live in Minnesota) I was shooting about a foot low all of a sudden consistently. I tried making minor adjustments to elevation but that didn't seem to do anything. Is it possible that the spring lube got really cold and significantly effected velocity to the point where the pellets would drop so far so quickly? I did notice my scope mount traveled back maybe the diameter or a pencil somehow (considering I tightened the stop-bolt).

On that note, I bought the gun for an excuse to be outside in the winter so I'm thinking I should probably convert from a spring to a nitro piston and add a trigger from charliedatuna while I'm at it. Could someone give me the part numbers/source for the conversion and a proper tune? And recommend a particular spring-compressor setup that would fit my needs. I don't want to ship it to pyramid air or a stranger when I feel I could do this myself in less time.

Thanks.

[cooter472]

your POI is most likely due to the scope moving, now for the N2 conversion theirs more to it than you think. I would recommend you get ahold of Oletomcat(Al), he has lots of knowledge with these and can fix you up alot cheaper & modify the for way less than you think.

[OleTomCat]

That gun isn't easily converted to a N2 ram, Crosman rams are too long and off the shelf 100mm rams are too short, so either you have to order a custom cut ram (~$100.00) or do some machine work to make a longer ram fit.

The lube can get kind of thick in cold weather but that probably isn't the source of your problem.

Give us some details on the shooting conditions: What weight pellets were you shooting at what distance?

Did you clean the barrel before shooting?

Did you check the screws that hold the action into the stock?

[reservoirdogs12]

That gun isn't easily converted to a N2 ram, Crosman rams are too long and off the shelf 100mm rams are too short, so either you have to order a custom cut ram (~$100.00) or do some machine work to make a longer ram fit.

The lube can get kind of thick in cold weather but that probably isn't the source of your problem.

Give us some details on the shooting conditions: What weight pellets were you shooting at what distance?

Did you clean the barrel before shooting?

Did you check the screws that hold the action into the stock?

I was shooting Gamo Master Point Energy pellets with 7.56 grams. 20~ yards distance. The ammo shot fine at first then all of a sudden went consistently low. I did a very brief clean of the barrel when I got it about a week prior with a Gamo cleaning kit. (Which I now know is a mistake because of the wire brush, brake cleaner, and metal rod). 

I'll locktite the stock bolts tonight. Good idea.

And based on what you're saying maybe a better solution (cheaper anyway) would be just to tune the gun and replace it with a better spring (if one exists) and temperature-flexible lube. Thoughts?

[OleTomCat]

That gun isn't easily converted to a N2 ram, Crosman rams are too long and off the shelf 100mm rams are too short, so either you have to order a custom cut ram (~$100.00) or do some machine work to make a longer ram fit.

The lube can get kind of thick in cold weather but that probably isn't the source of your problem.

Give us some details on the shooting conditions: What weight pellets were you shooting at what distance?

Did you clean the barrel before shooting?

Did you check the screws that hold the action into the stock?

I was shooting Gamo Master Point Energy pellets with 7.56 grams. 20~ yards distance. The ammo shot fine at first then all of a sudden went consistently low. I did a very brief clean of the barrel when I got it about a week prior with a Gamo cleaning kit. (Which I now know is a mistake because of the wire brush, brake cleaner, and metal rod). 

I'll locktite the stock bolts tonight. Good idea.  Replace the OEM ones with good quality Gr 8 Button Head cap screws

And based on what you're saying maybe a better solution (cheaper anyway) would be just to tune the gun and replace it with a better spring (if one exists) and temperature-flexible lube. Thoughts?

That is exactly what I do.....

[OleTomCat]

For tuning suggestions there is the kit from Air Rifle Headquarters that includes either the Tarantula or E3650 spring and two seals...

Get some Ultimox 226 from Ebay....

GRT IV trigger blade replacement.....

Look in the Library for a spring compressor build...

[reservoirdogs12]

For tuning suggestions there is the kit from Air Rifle Headquarters that includes either the Tarantula or E3650 spring and two seals...

Get some Ultimox 226 from Ebay....

GRT IV trigger blade replacement.....

Look in the Library for a spring compressor build...

So I started looking into your suggestions while still going out and shooting it everyday. It's still inconsistent. Then I noticed this gap:

(sorry for the blurry picture)

I have a very bad feeling about this. Is this normal at all? There's an inner rubber ring around the barrel but it only slightly protrudes out where the gap is, and doesn't look like it seals. Come to think of it, the gun seemed a lot louder when I first purchased it as well...

It's way too late to return the gun, and I have the patience to repair it myself.

[OleTomCat]

The easiest way to test the breach seal(that rubber ring that seals barrel to compression tube) is to take a piece of toilet paper and drape it over the breach and shoot the gun if the paper blows away or gets a hole blown in it the breach seal isn't sealing, new ones can be ordered from Gamo USA or you can try to flip it over or shim it out with dental floss.

[neras]

For tuning suggestions there is the kit from Air Rifle Headquarters that includes either the Tarantula or E3650 spring and two seals...

Get some Ultimox 226 from Ebay....

GRT IV trigger blade replacement.....

Look in the Library for a spring compressor build...

So I started looking into your suggestions while still going out and shooting it everyday. It's still inconsistent. Then I noticed this gap:

newbielink:http://s919.photobucket.com/user/reservoirdogs12/media/gap.jpg.html [nonactive] (sorry for the blurry picture)

I have a very bad feeling about this. Is this normal at all? There's an inner rubber ring around the barrel but it only slightly protrudes out where the gap is, and doesn't look like it seals. Come to think of it, the gun seemed a lot louder when I first purchased it as well...

It's way too late to return the gun, and I have the patience to repair it myself.

this Intrigues me also:on a well tuned rifle should there be contact  or be a gap , to ensure the rubber gets permanent compression and if so how big?, or just follow the paper test

[OleTomCat]

There will always be a slight gap normally not noticeable, the paper test tells you if the seal is actually sealing....

[reservoirdogs12]

Well, tried the TP test for the breech seal and didn't notice anything. But this weird pattern has emerged: I zero in my scope, am fairly accurate for about an hour or so, then I suddenly can't hit the broad side of a barn. At first I thought it was the scope moving backward after a number of shots, but that wasn't an issue today. I read about scope tube float from over adjustment, but don't think I am doing this either.

Is 20*F and lower just too cold for springers after a number of shots?

I also feel like this could be a broken/defective scope. When I first received the scope (leapers 3-9x40 AO TS) I twisted the elevation turret too much and the knob became disconnected and wouldn't click. I used the allen key slot and was able to re-seat it fine. (POI moves with laser bore sighter with adjusments). Maybe things are too loose now...

[Bullit]

That sounds like your problem.  Turning it out that far relieved the spring pressure.  So there's nothing holding the erector tube in place when fired. I hope the damage hasn't already been done.   
 You probably have "droop".    Look into a droop compensation mount, and some good 4 screw scoperings.   Leapers/UTG makes good ones.
Invest in the GRT trigger upgrade...if you wanna lite pulling trigger.