.25 R3M breech o-ring size?
Was out shooting my R3M after adjusting the regulator and got a puff of air to the face… the breech o-ring decided to follow the pellet down the barrel.
I didn’t get any spare o-rings with my rifle so now I’m hunting for o-rings. If anyone received a spare breech o-ring with their .25 R3M I’d appreciate the measurements, for now I’m going to try to find something close enough to keep shooting…
Measurements of the breech, breech bushing, & bolt are as follows:
0.394″ breech housing ID
0.250″ bolt probe OD
0.068″ recess between brass lead-in bushing and rear of breech block
Based off those measurements I have narrowed it down…
AS568A-010 o-ring, 0.239″ ID, 0.379″ OD, 0.070″ thick
However, it may also be:
6.1mm (0.240″) ID, 1.6mm thick (0.063 thick, 0.366″ OD)
6mm (0.236″) ID, 2mm thick (0.0787″ thick, 0.394″ OD)
I’m guessing the 6mm x 2mm is the correct one, the OD matches the breech ID, the ID matches the bolt/probe OD, and it’s slightly thicker than the o-ring recess in the breech so when you install the brass bushing it will compress it slightly to retain it.
Again, I’d appreciate if someone could measure either their actual breech o-ring or the spare if they received one.
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Viewing 9 replies - 1 through 9 (of 9 total)
Ok, after finding a local supply of 6.0×1.5mm Oring, I measured the one that came out of my 25 cal r3m and its 6×1.62. Not 6×1.5. Od is 9.3mm. Does this mean they put the wrong Oring in at factory or what?
Ernest
It’s not just a good habit, it’s correct o-ring sizing. As you said if the o-ring is too large it will “bunch” in the groove and will not have an even compression all the way around the circumference. An oversize o-ring is much easier to cut or pinch during installation as well. The slightly oversize o-ring installed on the regulator is certainly the wrong size and will be susceptible to leaking in the future. Next time I have the regulator out I will install the correct size o-ring.
And Peter– yes, the brass insert sits completely flush with the rear of the breech. There is a groove machined into the brass ring that centers on the setscrew that retains it in the breech housing.
I already have an o-ring kit I got from Tedd a couple of years ago but obviously it does not contain the new o-ring size needed for the R3M breech.
I did some digging in the garage and found that I had a package of Viton 75A durometer AS568A-010 o-rings on hand (they’re used on the bendix of the starter for my RC turbine helicopter, have to love overlapping hobby inventories.) The -010 o-rings are 0.239″ ID, 0.379″ OD, 0.070″ thick. That works out to 6.07mm ID x 9.62mm OD x 1.78mm thick. They fit into the breech perfectly, you can feel the nose of the bolt engage the o-ring when you close the bolt and they pass the “tissue paper test” to check for a breech o-ring leak.
For now it looks like panic averted, I’m back in business. However I will order a package of the 6.0mm x 1.5mm o-rings to have on hand.
Regarding the regulator, my .25 R3M was shooting 945 +/- 4 fps for 54-55 shots out of the box. That’s the best “out of the box” regulator tuning of any of the 4 Edguns I’ve owned in terms of consistency even if the velocity was a little high. It was pretty accurate at 945fps but not as accurate as my old single shot R3 at 915fps and the single shot at 915 got about 70 shots per fill. Now that the R3M has 1200 pellets through it and the springs & o-rings have worn in I removed the regulator to drop it to about 900-910 fps. Unfortunately by the time I found the replacement breech o-rings and got the gun back together it’s now too late in the day to go out and Chrony and adjust the HST and verify the new regulator setting, I have to stay inside and help get things ready to have people over for Christmas tomorrow. 😕
Regarding the regulator housing o-rings, I noticed that they seemed to be a little oversized on my R3M too.I had to carefully compress them when reinstalling the regulator. They don’t leak though.
Was QA inspector on board UUS Dixon, a submarine tender. we use a repair instructions the size of a holly bible just to repair one 5″ haul valve that penetrate the people tank, well one of the check for the oring is to insure that the new oring doesn’t rotate freely on the inside ID of the oring (for proper equal compression), well been inspecting that requirement for 5 years—> so it became a good habit that’s hard to brake.
Ernest
If you remove magazine and look at the brass insert. Does it stick out at all? It has to sit pretty much flush.
Maybe you can take a pic from the side.
-peter
Thanks Ernest.
I already have an o-ring kit I got from Tedd a couple of years ago but obviously it does not contain the new o-ring size needed for the R3M breech.
I did some digging in the garage and found that I had a package of Viton 75A durometer AS568A-010 o-rings on hand (they’re used on the bendix of the starter for my RC turbine helicopter, have to love overlapping hobby inventories.) The -010 o-rings are 0.239″ ID, 0.379″ OD, 0.070″ thick. That works out to 6.07mm ID x 9.62mm OD x 1.78mm thick. They fit into the breech perfectly, you can feel the nose of the bolt engage the o-ring when you close the bolt and they pass the “tissue paper test” to check for a breech o-ring leak.
For now it looks like panic averted, I’m back in business. However I will order a package of the 6.0mm x 1.5mm o-rings to have on hand.
Regarding the regulator, my .25 R3M was shooting 945 +/- 4 fps for 54-55 shots out of the box. That’s the best “out of the box” regulator tuning of any of the 4 Edguns I’ve owned in terms of consistency even if the velocity was a little high. It was pretty accurate at 945fps but not as accurate as my old single shot R3 at 915fps and the single shot at 915 got about 70 shots per fill. Now that the R3M has 1200 pellets through it and the springs & o-rings have worn in I removed the regulator to drop it to about 900-910 fps. Unfortunately by the time I found the replacement breech o-rings and got the gun back together it’s now too late in the day to go out and Chrony and adjust the HST and verify the new regulator setting, I have to stay inside and help get things ready to have people over for Christmas tomorrow. 😕
Regarding the regulator housing o-rings, I noticed that they seemed to be a little oversized on my R3M too.I had to carefully compress them when reinstalling the regulator. They don’t leak though.
Yes, shows tighter groups. didn’t do in-depth accuracy testing. I was mostly in side tuning and getting oring measurement’s. I notes it used 3mm X 25mm oring on the reg OD body–they where loose on the bottom sealing surface, didn’t like that so I change it to viton 3mm X 24mm perfect fit and been holding for two weeks.
Ernest
Ernest;
what about the accuracy? have you noticed any difference in accuracy when the power was on 940 fps and lowered to 890 fps?
1.5 X 6mm
I have a hard case kit containing 80 orings 10 orings per size with grease available, PM me
Mine was shooting 940fps with kings so lower it to 890fps. (lowered reg pressure to 120B) got more shots and quieter.
Ernest
its:
1.5 X 6mm
I have a hard case kit containing 80 orings 10 orings per size with grease available, PM me
Mine was shooting 940fps with kings so lower it to 890fps. (lowered reg pressure to 120B) got more shots and quieter.
Ernest
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They could have used a lube that swole them up a little.