Pardini bolt o-rings

Anybody know what size these really are?  From measuring in inches and converting to mm the best i've come up with is 1.9mm CS X 2.1mm

Scott

O-rings are measured (as a standard) with a cross section (CS) and outside diameter (OD).  With a OD of 2.1mm and a cross section of 1.9mm, there would be no hole in the O-ring, so something is not quite right.  Taking the 2.1mm as an ID and 1.9 mm OD, that would give a standard o-ring dimension of 1.9x5.9 mm. 

Based on standard aerospace specs (AS568), a 1/16"x15/64" o-ring (AS568-005) should be a suitable substitute (if not the correct replacement size).  Most hardware stores in the US should have one.

Edit: I looked at the o-ring store listings, and a "1.9mm x 5.8mm Metric O-ring - Buna-N 70 (JIS P6)" is available.  They are $0.06 each but the order will cost ~ $10 in total.  A local hardware store may have that size.

The O-Ring store dimensions are defined by cross section and inside diameter.  Closest I can find there is 1.9mm x 2.4mm.  Im gonna take some old ones to Ace Hardware and see if I can find any that visually look correct.  The o-rings from Pardini are $4.59 each and it takes 13 of them.  I'm looking for a slightly cheaper option for next replacement.

Your right, I had that backwards.  My bad.  Carry on.

If you decide to go with the o-ring store, it may be worthwhile to order a couple of sizes over and under.  By that I mean to order a 1.8x2.0 mm, a 1.8x 2.24 mm, and similarly a 2.0x 2.0 mm might get you what you need along with the 1.9x2.4mm.  I've measured o-rings with a Nikon measuring microscope and even then, the measurements are 'close'.  Good luck!

Greetings,

Are these the rings that go underneath the plunger at the rear of the bolt?

If so, do consider that there are several materials and hardness used for o-rings.

Most likely they will be a Metric size o-ring.

Some o-rings are attacked by gun oils and cleaning solutions.

Different hardness (durometer value) may result in a modified recoil effect (malfunctions)

Good luck with your reverse engineering.

Cheers,

Dave

I took the old rings out of the back of the bolt.  The 13 old rings were 1.5mm shorter than the 13 new ones so they were definitely wore out.  I was told not to soak the bolt in mineral spirits because it would damage the o-rings so that gives me a clue as to what they are made of.  I'm gonna buy several sizes from The O-Ring Store and give it a try.  At $.06 a piece from them I'm not gonna be out much if they dont work.

Scott

SMBeyer wrote:I took the old rings out of the back of the bolt.  The 13 old rings were 1.5mm shorter than the 13 new ones so they were definitely wore out.  I was told not to soak the bolt in mineral spirits because it would damage the o-rings so that gives me a clue as to what they are made of.  I'm gonna buy several sizes from The O-Ring Store and give it a try.  At $.06 a piece from them I'm not gonna be out much if they dont work.

Scott

 
What was the total length of the 13 new rings?
What is the diameter of the bore they go in?

The size of the rings should come easy after that.

Something to consider on the o-ring compression, and they being worn out.  Generally, o-ring seals (which is what I have experience with) have a compression set.  It's normal.  If the o-ring is cracked, torn, or has no compression then it is either the wrong o-ring for that application or needs replacement.  13 o-rings, with a 2 mm CS, having a compression set of 1.5 mm is ~ a 6% compression and  doesn't sound too bad (if my math is right).  At ~ $5/o-ring I would also be examining alternatives.  However, in the big picture scheme of things that is a $65 replacement spare part for a $2k pistol.

Bullseye_Stan wrote:Something to consider on the o-ring compression, and they being worn out.  Generally, o-ring seals (which is what I have experience with) have a compression set.  It's normal.  If the o-ring is cracked, torn, or has no compression then it is either the wrong o-ring for that application or needs replacement.  13 o-rings, with a 2 mm CS, having a compression set of 1.5 mm is ~ a 6% compression and  doesn't sound too bad (if my math is right).  At ~ $5/o-ring I would also be examining alternatives.  However, in the big picture scheme of things that is a $65 replacement spare part for a $2k pistol.

the o-rings looked bad compared to the new ones and the shorter length makes the plunger too soft and therefore the bolt cycle too fast.  I agree $65 once a year or so isn't gonna keep me from shooting its just the paying $65 for 65 cents of product seems extreme.  Unless I cant find a suitable replacement and then $65 will be a bargain to get my gun functioning again.

FWIW, there are o-ring material testers: https://www.marcorubber.com/o-ring-material-identifier.htm which work on the rebound (i.e. elasticity) properties of the compound.  I'm not sure buying the o-ring tester is worth $97, but it's good to know how it works.

From the description of non-compatibility with Stoddard solvent (mineral spirits) and high elasticity, EPDM is a possible candidate material.  The closest size o-ring is a  2mm x 2mm (a standard o-ring size), which is likely a reasonable substitute for a 1.9mm x 2.1mm.  Since a minimum order from the o-ring store will cost ~ $10, adding some variety in materials would be cost effective.

what model are we talking about?

Toz35m wrote:what model are we talking about?

Mine is a SP new Bullseye.  Bought in 2015

I will definitely buy several different sizes and flavors from The O-ring Store.  As cheap as they are I'm not out much.

Forgive my ignorance, but where exactly are these O-Rings located? I have an SP-22 from 2011. I have replaced a Firing Pin, chasing the locking pin across the floor in the process, but have never seen any O-Rings. If they are back behind the bolt in the receiver cavity, I'll need a flashlight to find them. Digging out my translated piss-poor Manuale Di Istruzioni I see part #771 on the exploded diagram (page 38). This looks like "maybe" it is an O-Ring setup? Not that the diagram is useful to this idiot, as some fools put the diagram in the manual and conveniently forgot to describe each listed piece. Makes me wonder how a company that produced this fantastic shooting machine can't employ a tech writer that speaka de englis. Looks like a Chinese Christmas light instruction manual.
Thanks!

Greetings,

The newer Pardini SP Bullseye models have a different bolt.

At the rear of the bolt, next to the head of the firing pin, there is a rod protruding. This rod is a "buffer". The normally installed mushroom shaped buffer is not installed in this model.

The older SP pistols have the mushroom buffer.

Cheers,

Dave

Dave,
I dug through a ton of old parts in my gun closet, and found a Pardini invoice for my SP-22. I asked Pardini to provide common replacement parts when I purchased the gun. I had found out the hard way with my Izzy that lack of parts support was a serious issue. The invoice has a bunch of parts bags attached. It includes part #771 Damper O'Ring and there are 2 o-rings costing $4.77 each, so I assume my bolt has these. Seems a little expensive for a 2mm O-Ring  
I'll get the pistol out and check out the bolt, now that I know about it. If the O-Ring Store has them, I would buy a box and change them often. Otherwise, Pardini may sell me a set every year or two. Thanks to all involved for bringing this issue up for review. The SP-22 is just one of those few pistols I have that I rarely take apart. It just goes on and on, never FTF or FTE, and makes lil round holes at 50 yards

I just measured the o-rings in my 2014 SPBE. Looks like the ring is 1.77 mm thick and 5.5 mm OD. The closest metric o-ring is -004 or 1.78x1.78. 

Now the hard part. (pun intended)
What is the material and durometer?

Is that measurement from the old rings or a new ring?

They are the original o-rings. 

The next size up in ID is 2.57mm which would be an OD of 6.13mm which wouldn't fit in the space they go into (5.5mm). The next size width is 2.62mm which wouldn't fit since that's 10.92mm longer for the stack of 13.

Please see if the pics that show a new SP O-ring match your sizes. I have set up my Starrett caliper to just barely hold the O-ring, so as to not deform it. This O-ring has never been used. The pistol the O-ring belongs to is a 2011 SP.
Thank you.

Amanda4461 wrote:Please see if the pics that show a new SP O-ring match your sizes. I have set up my Starrett caliper to just barely hold the O-ring, so as to not deform it. This O-ring has never been used. The pistol the O-ring belongs to is a 2011 SP.
Thank you.

Yes.

Went down to the local hardware stores today. Found some tiny O-rings, but none small enough in diameter to use, no matter US or Metric type. If anyone locates a match, hope they will post size and business to purchase from

McMaster Carr
https://www.mcmaster.com/#o-rings/=1ar80v2

Dr.Don-
Nice selection, but has anyone figured out exactly which size to use?
Thank you!

I don't have a Pardini.  I just figured that if you can't find a size that works from McMaster Carr, you probably won't find one ..............

It seems to me if you keep these from getting any solvent on them they should perform for a long time.  My 2015 model does not seem to have any issues.

I think once you replace them you should be good for several if not many years.  I only wipe down my bolt to remove the grunge from it to keep it clean.