What Causes a Breech O-Ring to Blowout?

[Ezana4CE]

Put 120 pellets through my Bantam Sniper on a single fill. I was trying to push the bottle to see how many shots I could get on a fill and it wasn’t completely full to begin with. On my last shot I heard a moderate “pop” from the breech and the bolt was pushed half-way out.

First I thought I’d double loaded pellets. Then i realized that I pushed the rifle to the point where the pressure was too low for the regulator setting. However I wasn’t expecting the o-ring to come out. It still looks good. I may re-install it and test it to see if it will work properly. If not I have more. Is this what happens under these circumstances? If you’re familiar with regulated rifles I’d appreciate your input. Thanks y’all. 

 

[Odoyle]

You probably didn't close the bolt all the way home and down.

Complacency at work...

 

[nervoustrig]

The bolt flying open explains it...if the bolt doesn't stay closed during the shot cycle, it's not supporting the O-ring and the blast of air caused it to dislodge.

It has nothing to do with being regulated or continuing to shoot below the regulator's setpoint.

 

[Ezana4CE]

Ok cool. So it seems that it’s just a matter of the air pressure escaping through the path with least resistance, right? I was mainly concerned that I may have damaged something. From what you guys are saying I shouldn’t have much to be concerned about, right?

 

[Bobbybeef]

When mine blew out it was because it was not all the way forward and once it came out it stretched and would pop out on every shot after i replaced no problem i just careless i make sure the bolt is closed now

.

 

[L.Leon]

@Odoyle, and @nervoustrig, answered you. I have shot thousands of pellets through my Bantam Sniper HR all on the original breech seal. Make sure that bolt is closed.

 

[Ezana4CE]

@L-Leon I get that and thank you all. Now my only other concern is knowing whether or not this can cause any other sort of damage. Anyone think I should be concerned about any type damage on the rifle as a result?

 

[L.Leon]

@ezana4ce, no damage, just replace breech seal and continue to enjoy that sweet gun.

 

[Ezana4CE]

@L-Leon That’s what I was hoping to hear. Thanks. I do enjoy shooting it. It shoots very well! Now if I can only work my skills up to the level of the gun’s capabilities.... 

 

[Bravo1956]

I did the same thing when my Bantam HR was new, now I make sure bolt is closed and down if I dry fire. Thousands of rounds now and has not happen again.

 

[Beezer]

Just like in a firearm, there should be a sear disconnect that does not allow an airgun to fire unless the bolt is fully turned down. One day I forgot to unset the set trigger on my CZ 527, and when I chambered another round, the rifle fired when I loaded another round and turned down the bolt. The bolt did not blow open as the striker cannot be released until the bolt lugs are mostly engaged. I got a bit of a scare, and luckily the rifle was pointed downrange on shooting bags. I adjusted the set trigger to a higher pull weight until it would not fire when the trigger was set and I aggressively operated the bolt 6 times, as the magazine holds 5 rounds and I wanted a small margin of safety. Problem solved, and the set weight trigger pull weight increased only slightly. The CZ rifles with single set triggers are not for those who forget to unset them if not taking a shot immediately. I never fail to unset my trigger if not taking a shot immediately after that day. I also did the same with my CZ 550 as CZ seems to adjust the pull weight too lightly as they come from the factory. Anybody with a CZ rifle with single set trigger should do what I do and operate the bolt aggressively a few times with the trigger set and see if it fires. The adjustments were no more than 1/8 turn of the adjustment screw. I occasionally retest the trigger to see if the adjustment has held.

I also had the bolt blow open on my BSA Lonestar .25 as the probe catch was only slightly engaged. I did not lose the probe o-ring, but somehow the pellet blew out backwards and was stopped by the rear scope mount. If the open sights had been used, I would have had a pellet in my face or eye. I solved the problem by pushing forward on the probe TWICE and making sure the probe catch is in the full upward position. The incident had never reoccurred, and I make sure I have shooting glasses on when I shoot the Lonestar. I would advise anybody with a Lonestar, Hornet or similar type BSA with the push probe/MMC system to MAKE SURE the probe catch is fully engaged as there is no sear disconnect if the catch is not fully seated. Especially important if using open sights as there is no rear scope mount to deflect the blast from your eye.

 

[Ezana4CE]

@Beezer I’m not familiar with set triggers. I’ll have to look that term up. Thankfully the tank pressure was just about as low or lower than the reg when my incident occurred. The ring landed where it is in the photo. The pellet went down range and hardly deformed as the others usually do. I think I recovered it protruding out of the cardboard behind the target when I removed them. Having a projectile blowback out towards your face is alarming. The closest I’ve seen to that is stacking so many pellets in group tight enough for lead to bounce off of lead causing some to ricochet out 10-15 yards towards me seated at 25 yards. That’s occurred several times shooting 10 shot groups. 

 

[Elbowgrease]

Really spicy curry can cause that sort of blowout.

 

[Ezana4CE]

Really spicy curry can cause that sort of blowout.

 

[Ezana4CE]

Thanks for pinpointing the issue guys. Watched this video, 



https://m.youtube.com/watch?v=3AO1NZuWM_s&t=3s grabbed



then grabbed a pick set, hex wrenches, silicone oil, and gloves and reseated the o-ring. If it pops out again I have others and now that I know what to do. Took about 30 mins trying to situate the o-ring. First I pinched the ring and inserted it, next I used the tip of a pick to gently guide the o-ring into the groove. 

Rail and barrel put back together and it looks like I’m back in business!

I’m beginning to feel like I can confidently tackle minor fixes and maintenance on my airguns. The AGN community has been a great help. Many thanks. 


*Side note -The “Brocock Official Handbook” is super vague. I didn’t find much help at all. It’s like a quick start guide with photos. Then there’s a few pages of schematics with numbers corresponding to the various parts, but no part names or numbers in the handbook. Then they posted a digital version of the same thing on their website. Shoutout to Airguns of Arizona for posting helpful tutorial videos. 

 

[MaineJim]

Good job,you might want to use brass picks so you dont scratch the chamber though.

 

[Ezana4CE]

Good job,you might want to use brass picks so you dont scratch the chamber though.

Duly noted. I’ll look for some. Thanks. 

 

[Quad82]

Forget the picks and use a wooden dowel. Pinch the o ring and shove it into the breech. Slide the dowel down the barrel while holding your finger over the breech hole. Pop. It’s that quick.