Canadian Airgun Forum

Hey there!

I bought a QB78 .177 the other day after reading it's mostly positive reviews and after a few hours of zeroing it in I found it to be super accurate and super fun to shoot. Unfortunately yesterday after only a week of shooting (maybe 315~ shots) I noticed it started to make a funny "ping" sound when it would shoot. A sort of vibration sound. After putting some pellets through it it seemed to stop but as I continued shooting I noticed a weird odor coming from the breech. I took a few shots trying to pay attention to the breech and muzzle and noticed white puffs coming from the breech but what was more worrying was the foot long flashes coming from the muzzle. I decided to leave it overnight and check it in the morning.

Next day I did some research on common leak issues and tests. I dry fired the rifle and it still shot large clouds. I filled my sink with a small amount of water and submerged the barrel about 2~ inches into it and saw no bubbles.

But once I wiped it down and went to dry fire it to remove any water from the barrel the smoke stopped and began shooting the same as it did straight out of the box. I put a light piece of tissue over the breech and it showed no signs of leaking there. I shot some pellets through it and performed perfectly.

The gun has always had pellgun oil run through it, I always wiped the rifle down and would go out of my way to keep it clean and away from debris. The gun wasn't left in the sun, warm places, cold places. It still has a replacement warranty so if it is a leak I can trade it back in for another.

My Question is what could have been causing what I assume was it running "rich" on co2? Was that bit of moisture enough to maybe "hide" the smoke for a short period of time?

Thanks in advance for any help!

I would assume the diff is how you hold it. Meaning the valve has gas or liquid in it, or some liquid. Liquid would be a waste and no doubt less powerful. So for a few seconds after the shot there would be liquid in the Xfer port and barrel turning into gas, which you'd see and smell. I don't own a QB but I did have some CO2 guns as a kid and I remember the liquid thing. I also recall putting cloth over the barrel and when it was a liquid shot there was a frozen and smoking spot on the cloth. I believe I used my pant leg, so a double layer of Denim. Since I only had CO2 pistols, the cartridge was low and pointed up. In a rifle where it's horiz I'd assume you're blowing liquid a large % of the time? Maybe the way the valve and passage is setup it minimizes that, but I'd imagine if pointed upwards it would have no choice but to shoot liquid. I dunno, shoot several shots keeping it pointed down at all times, then several pointed up and see the diff. CO2 has a funny smell, which I'd imagine you'd recognize it from sody pop?

I'd agree it sounds like co2 spraying out, but why it started then got better is a bit mysterious, though Chevota's theory makes sense about which way it had been sitting.
QB guns have too powerful of a hammer spring in them and if you take the back end of it apart after taking the stock off you can get at the hammer spring and cut some coils off. You won't lose velocity and will gain a lot of shots, and it should make the gun quieter with less visible co2 coming out of the barrel.


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wesb2007: I didn't know about the spring being too strong in those. I was wondering if you/anyone has done the "Bstaley Mod" on that gun? Seems like it should work? And ideally with a weaker spring rather than cutting it? I dunno, I'd have to see it apart... Fyi I tried that mod on my MRod and it certainly helped. Not a cure but worth certainly the effort.
I'm curious to see what the OP has to say too. Been a week....