Bulldog Breach Oring

Silicone grease should have NO effect on the oring, no matter how long you left it in.

I suspect you just got it seated better the last time

I will take a Q-tip and put a little silicone grease on the O-ring . Whenever I go out to shoot 

I recently have experienced this puff of air (across my forehead) coming from the breach of my Bulldog. I first noticed it a few days ago and I thought about this post. I have yet to clean it and I’m approx 320-360 rounds in since purchasing. I have some extra o-rings and expect I’ll need to change it after completing my first cleaning. 


@csbrown5 Crossman recommends doing this with their brand of RMOIL (I think it’s some sort of silicone oil) in the owner’s manual. They also recommend lubing the barrel with Pellgun oil, a petroleum based oil that’s included with the Bulldog. I have read posts, a blog, and a Q&A on Crossman’s site that suggest we avoid using the Pellgun oil in the barrel of PCPs because it’s petroleum based. I believe that I read that this can lead to “diesleing” which can cause ignition of the oil in the barrel. I’ll look for links to AGN posts about dieseling and add some later. 


I’m far from an expert on any of this. Here’s one of the first threads I read that mentioned dieseling. https://www.airgunnation.com/topic/pcp-air-rifles-and-oil/ @Kinetic45 ‘s post is what first brought it to my attention. 

Also read this blog written by Tom Gaylord in ‘07 on mistakingly recommending using Pellgun oil on PCP fill ports to lube inner seals. https://www.pyramydair.com/blog/2007/10/b-b-was-wrong-the-story-of-crosman-pellgunoil/

Looks like the wrong stuff to use on PCPs and the owner’s manual that came with my Bulldog purchased in 2020 still suggests using Pellgun oil to lube the barrel. Could be wrong, but why chance it if there are other options?

Silicone appears to be the way to go. Chemical info on the RMCOIL oil from Crossman’s site https://support.crosman.com/hc/en-us/articles/204509104-Is-RMCOIL-100-silicone-

Here’s a pic of my breach o ring. I’m thinking the nick at the bottom of the o ring is the issue. I’m not quite sure how to replace it just yet. I read that a pick set can be used to remove and replace it. I’ll have to look into this further. Not sure what cause this. I’ve shot some pellets with some pretty ragged skirts. Perhaps they caused this damage to the o ring resulting in the puff of air after each shot. Any thoughts on this?

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The pellet probe may have a burr on it.

The pellet probe may have a burr on it.

Click to expand...

@cmatera Is this something I can visually inspect with the naked eye? If so, what am I looking for? A jagged piece of metal? Hard to get a decent angled pic without further disassembly

The cut in the oring is caused by the curf on the probe, take a piece of emery cloth and run it along the bottom of the probe at the front were the Probe is curved and the to straight edges are. THis will smooth out the bottom of probe also rub silicone oil on the probe on the front all around and put a small drop on oring. This will keep it soft and help the probe slide thru the oring better without nicking it. Put drop of oil on probe every 100 shots or so. You dont have to remove probe to do the emory polish.

@bthurman Thank you for the tip. So far I’d used a cotton swab and food grade silicone oil to lube the o ring. I was thinking maybe the skirts of a beat up pellets nicked the o ring. Some get banged up in transit and I shoot them anyway. I had to back a couple out once when I double loaded. I didn’t attempt to fire. I’d just realized that I’d lost count before shooting and thought it best to remove the pellets. I used the plastic rod and a bore tip that came with the Bulldog to push the pellets out through the breach. Is this a common issue with the Bulldog probes?

Yes it is a common issue that we find for ones that come here to our shop,