Big Cat has a Big Hairball

[preez]

Does anyone know what is going on with my rifle? See pic. The nail on top is where I aim and it spreads pellets vertically all over the map! Pellet: CPHP distance: 25-30 yds off-hand, kneeling. And yes, that is my shed door I'm shooting.

I'm not the greatest shot, but I get much better results with my CFX.

Thanks for all your help.

Chris

[CharlieDaTuna]

Looks to me like you may have a power plant problem Chris. The fact that it is fairly in line on a verticle axis it would appear that there is a velocity problem. You didn't point out the shots by number but I'm assuming that they are moving up and down at random.

It can very well be that the seal has some damage and that lube is weeping by causing either excessive combustion or maybe even detonation. That causes extreme shifts in velocity and impact the verticle accuracy.

[preez]

Yes, they move up and down at random, and then group few shots at the same elevation and then shift again. I posted on another occasion a pic of breech seal that was shredded on the bottom. I will perform tissue paper test, maybe that's the cause. The rifle is new, not even a 1000 shots through it.

As per detonation, I don't hear anything, no smoke either, just the twang... much noisier than the CFX though.

Should I send it back to Gamo?

P.S. Your triggers are fantastic, made a lot of difference, even for a noob like me.

[leftcoast1]

Being that it was not an exspensive gun save your pennies and send it to CDT for a tune it will make a difference look what they did to the Whisper. If you send it to Gamo no doubt that they will fix it but the problem may surface again.

[CharlieDaTuna]

The way to test to determine whether or not the breech seal is leaking is to cock the gun, put a pellet in the barrel, insert a small piece of wax paper (not tissue paper) in the breech and carefully close the breech. Then safely fire the gun. Open the breech and look at the paper. You should see just a small hole in the paper. If so, it is not leaking. If it has a hole blown out the side of the paper, then it is blowing past the seal. I doubt it will be leak.

[vinceb]

Scope or open sights?

With the gun cocked and the breach closed, does the lock-up feel right, or is there some play in it?

[preez]

Thanks for all replies! I will definately try the wax paper.

Vince, scoped with BSA 3-9x40 that came with the gun with 1 piece Accushot. There doesn't seem to be any free play at lock up. That was one the first things I checked. Is it possible that the scope would not hold zero vertically only?

Just to mention, I was able to originally zero it in with no problem, it was shooting well for a while.

Cheers
Chris

[shadow]

My big cat get's hairball's but I got this stuff that I feed her, oh wrong subject sorry hehe. Had to say it   Ed

[preez]

Well, I was going to attempt a lube tune on this one to get rid of the twang anyways. I guess I'll crack her open and take a peek at the piston seal. I assume there's an upgrada available from JM?

[preez]

First, let me thank the Master Himself, Charlie da Tuna for his terrific DYI tune guide. I must have read that thing about 100 times before I even started. I know it's probably only 30% of what he does in his tunes, but it helped me and my rifle tremendously!

So I finally got brave, got the lubes and seals from Jim Maccari, made a spring compressor (ugliest I've seen yet, but works great) and home tuned the Big Cat. I followed Charlie's directions (almost) to the letter. Changed the seal, deburred, polished, honed, lubed and put it back together. What a difference! Rifle cocks smooth as silk, no seal squeaking or spring twisting sound at all. Firing got much better too, twang almost gone, so is most of the vibration, just a "thwack" noise and more linear recoil. I'm very happy with the outcome.

However, it did not fix the problem! Tested it at 25 yds with similar results as I started with, vertically it's all over the place.

Next we take a look at barrel lock-up and breech seal. While I had everything apart I polished the area around tranfer port as it had some weird grooves from machining process.

Learning about this stuff is really fun!

Chris

Congrats on the successful operation, Chris.

If you have access to a different scope, I'd be tempted to mount it up in place of the current one and see if that makes any difference (since there ain't open sights on the Big ol' Cat ;~). As I understand it, it's not out of the realm of possibility that the vertical adjusments on a scope could go bad, and string the shots vertically, while the horizontal could be just fine-- I'm not an expert by any means, but that might eliminate one possible cause of the shot stringing.

Hope that helps.

Bryan

[PeakChick]

I would have to agree, it sounds like it is far more likely to be the scope and or mounts.

[preez]

Thank you for replies, testing in progress as we speak (type)

Chris

[preez]

Nope, the scope's not it. Here's the scan of "group" I shot at roughly 10yds. I numbered the shots.

[DAMAGE]

Check the inside of the barrel could also be a chunk missing I had this happen to me and it caused the pellets to tumble and I got patterns like that also.