Search for better O rings for PMA bore guide

[60723]

Using PMA bore guides. Bought extra red rubber o rings. Oil them slightly before each use. Still having some issues with the rings tearing and leaving pieces in the action. Usually can’t see the pieces unless you scope barrel and look for them specifically. Went to range last week and bullet would not chamber. Tried 5 different bullets. Had shot the same loads the week before. Looked in chamber and saw nothing. Finally FORCED bolt closed and fired one. Thereafter, all the rest loaded and fired normally. Scoped after I got home and saw a red streak where I am sure a small piece of the rubber had melted! Really would like to find a source of tougher o rings for these guides.

 

[Richard Jones]

So I can't help with the o-rings, I thought the red ones were the best. I use vaseline in lieu of oil, seems to me to stick better to the o-ring than oil. Hope you find the answer.

 

[JEFFPPC]

Silicone lube like for a pool.

 

[gary0529]

Silicone lube like for a pool.

Home Depot or Lowe’s in the water filter aisle
Can get a small tube of silicone lube for not much

 

[tmwinds]

Here ya go.

 

[RegionRat]

https://www.parker.com/literature/O-Ring Division Literature/Section VII.pdf

I'll put this link to an o-ring chemical compatibility chart up.

If you don't like chemistry, metallurgy, or engineering, then try to keep your life simple and don't mix solvents, cleaners, and lubricants that your friendly neighborhood chemist didn't specifically warn you about.
YMMV

 

[Chaotik]

I had a similar problem with a Sinclair bore guide O ring. It broke apart and got "lost" in the chamber during cleaning, and with a borescope I was finally able to get all of the pieces out.

 

[Dusty Stevens]

Use a plain black one with bolt grease on there. They last 20 yrs

 

[Bill K]

As for a source for new 0 rings, check out the various one's at Ace or a good parts house.

 

[Old Navy]

The groves are not cut deep enough on some of mine.

 

[Dusty Stevens]

The groves are not cut deep enough on some of mine.

You can take a triangle file and spin the groove against that and keep checking til you get the perfect fit

 

[Old Navy]

You can take a triangle file and spin the groove against that and keep checking til you get the perfect fit

I am going to have my son cut all mine on his lathe. The should have a square bottom to compress properly. Gun lube should not be eating "0" rings.

 

[RegionRat]

Gun lube should not be eating "0" rings.

I wish that were true, but when there are so many strange lubricant chemistries being used, it opens the door to ones that can eat an o-ring. Not to mention the solvents.

Happy New Year!

 

[Old Navy]

I wish that were true, but when there are so many strange lubricant chemistries being used, it opens the door to ones that can eat an o-ring. Not to mention the solvents.

Happy New Year!

Nothing we use should eat Viton rings. They are used in industry for some very harsh chemicals. One of my rods/ring/ grove chewed one up. It was just too tight a fit. The o ring has to have a grove big enough to compress into when you push it all the way in. The two best rods I have are for ARs. The groves are square cut and the rings are a loose fit or floating if you will. Hydraulic valve o rings sit in a square grove and sized to compress 35% for a good seal. Off course we don't need that much.

 

[RegionRat]

Viton

Here is the key word. Viton.
Many guides are delivered with any old o-ring that is at hand (cheap). Fluoropolymer is a more expensive material than a nitrile or buna, but for a little more trouble to find one, the Viton is far more inert.

 

[Old Navy]

Here is the key word. Viton.
Many guides are delivered with any old o-ring that is at hand (cheap). Fluoropolymer is a more expensive material than a nitrile or buna, but for a little more trouble to find one, the Viton is far more inert.

I agree with your post 100%. My point was/is there is a sizing problem. If I can't push the guide in with a thump and pull it out with two fingers it is a fit problem. I kind of used an old Millwright approach on one of mine that came with a Viton ring. It was a tight fit so I just forced it in. I had a hard time getting it out. The ring came off in the action and was chewed up.

 

[RegionRat]

I have bore guides that were made or designed with the wrong groove for their o-ring, not to mention the wrong material...
I dropped the diameter of the gland to have not more than 15 - 20% compression of the o-ring's cross section diameter. After I re-cut the bottom of the gland, I added a negative draft angle to the walls so their section would look sort of like a dovetail cut. That tends to help with pushing in and pulling out without the o-ring trying to extrude itself between the gap.

 

[JMayo]

I have 3. They fit perfectly.
I'd sure check that i used the right one if i had the problem the op has

 

[60723]

Tried contacting PMA but have not received a response yet.

 

[JMayo]

You never said caliber nor action ...
Might could get some help here in which # to use.