LOL! Seems nobody really read what I posted in my OP.
I even linked to where I bought the 006 rings! (chuckle/sigh)
Thanks again for the replies.
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Tuning Benjamin Fortitude Breech O-Ring .177
- Thread starter BackStop
- Start date
LOL! Seems nobody really read what I posted in my OP.
I even linked to where I bought the 006 rings! (chuckle/sigh)
Thanks again for the replies.
I have no idea how much tension is necessary to maintain a good seal between the probe and the breech, but I suspect the 1.5x4 is for exactly that reason... to seal the breech.
Seems that a 1.5x4.5 might be too liberal and not seal the breech as well. However, I do not know the diameter of the probe itself, so you may be correct.
All I know is that Crosman says 1.5x4, but will not give any further information and I know, from Crosman among others, that the OEM breech seal is easily blown out.
Many thanks again for clarifying some questions I had about o-rings. Damned glad this is only a rabbit hole and not an elephant hole!!! (grin)
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Guilty as charged! Right above it you said you used a spare from a Freedom which told me a metric size, not a dash, so that was confusing. It’s made in China but uses dash O-rings?
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I have been using some I bought from Fastenal I was able to get 43 o-rings for $2.34 (they only had 43 in stock) they have been holding up well for me.
Fastenal Information from receipt
Description: 4mm 70 Duro O-Ring
Part number: 0424100
Fastenal Information from receipt
Description: 4mm 70 Duro O-Ring
Part number: 0424100
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The 177 Fortitude takes a barrel O-ring that is metric. It is 1.5mm CS X 4mm ID. It is the same one that is used on Gen 1 & 2 177 Mrods.
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Wow, okay then. Previously when the M4x1.5 was mentioned, I just couldn’t help thinking it would have a short life. An ID of 0.157” means it needs to stretch 0.020” to pass the head through and then over 0.025” for the skirt. That’s pretty abusive to an O-ring that small. Longevity would be much better if they had sized it 4.5mm and made the bolt 4.6-4.7mm to seal off against it.
But 4mm it is. I think I would go with a 70 durometer polyurethane if possible. Polyurethane to deal with the abrasion, plus it will take a compression set against the bolt to help pellets make it through with less resistance. And the 70 durometer because I think 90 would be too stiff in an O-ring with these proportions. I trust FuzzyGrub will advise if there’s a better combination known.
But 4mm it is. I think I would go with a 70 durometer polyurethane if possible. Polyurethane to deal with the abrasion, plus it will take a compression set against the bolt to help pellets make it through with less resistance. And the 70 durometer because I think 90 would be too stiff in an O-ring with these proportions. I trust FuzzyGrub will advise if there’s a better combination known.
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Jason,
I haven't seen any premature wear on 177 mrod or fortitude barrel O-rings.. Also, don't recall seeing posts with others having that issue. As you said, 70D is fine. The oem is BN, but poly would probably last longer. The probe is 4.5mm, so don't think a 4.5mm ID would provide a good seal, unless the barrel groove was smaller. The 22 Mrod and Fortitude takes a -009, which has an ID of 5.3mm vs 5.5 mm probe.
A larger OD probe would require larger gooves in mag slots which would lead to "sloppy" pellet play/rattle and probably feeding problems. Just my thoughts on that.
I haven't seen any premature wear on 177 mrod or fortitude barrel O-rings.. Also, don't recall seeing posts with others having that issue. As you said, 70D is fine. The oem is BN, but poly would probably last longer. The probe is 4.5mm, so don't think a 4.5mm ID would provide a good seal, unless the barrel groove was smaller. The 22 Mrod and Fortitude takes a -009, which has an ID of 5.3mm vs 5.5 mm probe.
A larger OD probe would require larger gooves in mag slots which would lead to "sloppy" pellet play/rattle and probably feeding problems. Just my thoughts on that.
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Okay yeah I experimented a bit this evening and it's not as concerning as I expected in 70 durometer, provided they're sizing the groove so the O-ring can expand mostly unrestricted. Wadcutters don't inspire confidence but domes seem reasonable.
Other mag-fed guns I've worked with seem to consistently use a breech O-ring that's right on the caliber or slightly larger. A few examples are models from Hatsan, DAR, and SPA. Regardless, if the Fortitude uses the same approach as the Marauder then I really have no reason to question it!
Other mag-fed guns I've worked with seem to consistently use a breech O-ring that's right on the caliber or slightly larger. A few examples are models from Hatsan, DAR, and SPA. Regardless, if the Fortitude uses the same approach as the Marauder then I really have no reason to question it!
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Most of my tinkering involves crosmans, so don't have the breadth of mfg knowledge that you have, Jason. I always appreciate your input.
On Liberty's, they use probe O-rings that have the same OD as the pellet. Two of them, back to back. When I first got one, thought they were going to be eaten up very quickly, pushing them through the mag. Turns out they lasted pretty well. Some of which I attribute to the more rounded edges in Liberty and Gauntlet mags. The crosman mags will fit, but they have sharper edges inside.
OK, back on topic. I live rural, and my closest H/W store is 20 minutes away. While they have a decent selection of standard size O-rings, ziltch on metric. Only 70D BN, though. Never tried at the big box stores, which are twice the distance away. Gas would be more than shipping cost from the O-ring store or other online source.
On Liberty's, they use probe O-rings that have the same OD as the pellet. Two of them, back to back. When I first got one, thought they were going to be eaten up very quickly, pushing them through the mag. Turns out they lasted pretty well. Some of which I attribute to the more rounded edges in Liberty and Gauntlet mags. The crosman mags will fit, but they have sharper edges inside.
OK, back on topic. I live rural, and my closest H/W store is 20 minutes away. While they have a decent selection of standard size O-rings, ziltch on metric. Only 70D BN, though. Never tried at the big box stores, which are twice the distance away. Gas would be more than shipping cost from the O-ring store or other online source.
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For me, they are fewer and farther between than even the big box stores. Maybe the BackStop has some close by.
PS: I have never looked at the HF metric kit to see what sizes are included.
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I have heard of people saying That they buy these boxes of assorted O-rings at Harbor freight. Does anybody know if there any good or not?It seems to me like they would be inferior quality.
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I had low expectations for the assortment I bought years ago but they’ve never once let me down. Most of the large sizes have gone unused but it was worth the asking price the first time it saved me from being down down for days waiting for an online vendor.
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OK thanks. If I ever need any I’m gonna try the nearest hardware store and they don’t have any my friend goes down to Harbor freight now and then and might pick up a box of them.
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I've been meaning to pick up a box of both the metric and US sizes from HF, but I always forget and I don't get out very often.
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FWIW: I took a quick look at the metric HF set. Print was a little hard to read, but do not think it includes a 1.5 X 4mm. It looked like the smallest CS was 1.9mm.
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If I remember correctly, many of the cookie-cutter metric kits are just imperial sizes converted to metric. Limited usefulness for our purposes, though I have on occasion abraded a -0xx O-ring (0.070” cross-section) to an M1.5 (0.059”). And sometimes they work with no modification at all, provided the tolerances and durometer align just right.
In most cases the modified O-rings were to get me out of a pinch or to address a sloppy fit of the OEM size, and are still doing their job years later.
In most cases the modified O-rings were to get me out of a pinch or to address a sloppy fit of the OEM size, and are still doing their job years later.
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