Tuning Benjamin Fortitude Breech O-Ring .177

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BackStop

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Crosman has always used dash O-ring sizes, at least until recently when they added the rebranded imports. The Fortitude preceded that.

If you have some calipers, measure your bolt probe. If it's close to 0.176", use a -008. If it's close to 0.208", use a -009. Go with either either polyurethane or Buna-N. 70 durometer is the safe bet.
 
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Crosman has always used dash O-ring sizes, at least until recently when they added the rebranded imports. The Fortitude preceded that.

If you have some calipers, measure your bolt probe. If it's close to 0.176", use a -008. If it's close to 0.208", use a -009. Go with either either polyurethane or Buna-N. 70 durometer is the safe bet.
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No calipers here. Although 1.5x4 is the specified 0-ring, it doesn't say anything else. So... I don't know exactly which o-rings to buy and I hate paying the prices for o-ring "kits" when all I need (for now) is the breech o-ring. Buying specific o-rings by the 50 or 100 pack drives the price down CONSIDERABLY! (grin)

In any case, I can still continue using the 006 o-rings I bought for the Freedom because they do work and I have more than 90 of them left. The breech o-ring seems to be a problem for the Fortitude. It is easy to blow it out of the gun, apparently. My Fortitude came without one to start with and Crosman sent me 2 for free, but I would like to have a lot of spares as it seems to be a problem for many folks with this AG.

Thanks
 
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Nervous Trigger O-Rings...

Screenshot_2020-11-11-16-57-202.1605150028.png
Screenshot_2020-11-11-16-56-312.1605150028.png

 
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I guess I simply don't understand how 1.5x4 translates into the sizes shown in previous posts. That has been the problem in finding these breech o-rings.

All that is ever stated is "1.5x4", but nothing else. No cross-section, etc. Seems like a conspiracy to force people to pay exaggerated prices for something that should only cost a few pennies each.

In any case, thanks for the replies. Maybe I am just too dumb to understand...
 
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I guess I simply don't understand how 1.5x4 translates into the sizes shown in previous posts. That has been the problem in finding these breech o-rings.

All that is ever stated is "1.5x4", but nothing else. No cross-section, etc. Seems like a conspiracy to force people to pay exaggerated prices for something that should only cost a few pennies each.

In any case, thanks for the replies. Maybe I am just too dumb to understand...
Click to expand...

You can use what you have and very carefully don't overdo it clean barrel with alcohol only at the empty o-ring breech and dry and use Shoe Goo to make the o-ring stay put.

That 1.5x4x7 might work but that's a whole lot of o-rings.
 
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A 1.5x4 metric O-ring has an inside diameter of 4mm with a cross-section of 1.5mm. That means the outside diameter is 7mm (4 + 1.5 + 1.5 = 7).

If indeed it is a metric size, the 4mm is probably 4.5mm instead because that's the caliber (4.5mm = 0.177in). A 4mm would wear prematurely since it has to expand twice for each pellet being chambered.
 
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A 1.5x4 metric O-ring has an inside diameter of 4mm with a cross-section of 1.5mm. That means the outside diameter is 7mm (4 + 1.5 + 1.5 = 7).

If indeed it is a metric size, the 4mm is probably 4.5mm instead because that's the caliber (4.5mm = 0.177in). A 4mm would wear prematurely since it has to expand twice for each pellet being chambered.
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Thanks


 
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Is it a breech O-ring (in the barrel) or a bolt O-ring? If it is in the barrel, M4 makes no sense...too small and will wear quickly. If it's on the bolt, it makes perfect sense.
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I wish it was a bolt o-ring. That makes more sense to me and I have never had a problem with those.

The Fortitude uses a breech o-ring, not a bolt/probe o-ring. I think the Marauder Pistol uses the same method? The 006 o-rings I have work, but wear out fast and I can feel the friction every time I use the bolt to cock and reload. Easy to replace, but I am not sure that they are actually sealing the breech properly as I still get some aberrations in fps and accuracy.

I would simply like to buy the "correct" breech o-ring for the Foritude .177 in quantity because I know if I can identify the correct size, for what it would cost me to get 2 of these o-rings from Crosman (plus shipping) I could have 50 or 100 for the same price.

While I am at it, I would like to fix my Nova Vista Freedoms, but since I was banned from GTA several months back, I forgot who was making the poppet for them. He is in California and his name "may" be "Dinh" or "Duy" on GTA, but I don't remember.

The Freedoms were VERY accurate/precise from 10-60 yards with Crosman CPUM 10.5 pellets and I had the option to go from ~12fpe to ~20fpe at the turn of a knob.

I was limited to 60 yards for pesting then and now I am limited to ~35 yards for pesting. New neighbor built a privacy fence that blocks my longer range and although he is OK with my pesting, I can no longer shoot in that direction even if the privacy fence was not there.

Oh well, many thanks for the replies!

Kerry


 
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Oh! A -006? It has an ID of .114" which is WAY undersized. I suspect what you call "feel the friction every time I use the bolt" doesn't quite do it justice. The nearest dash size that would generally be used for .177 cal is a -008, two steps larger than the one you have in there now...and a world of difference in terms of fit down at the bottom end of the sizing spectrum.

But since Crosman is apparently using metric, I would order some M1.5 x 4 and some M1.5 x 4.5 in 70 durometer and try each one.
 
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