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Old 09-12-2022, 03:57 AM
NMC_EXP NMC_EXP is offline
Join Date: Jul 2010
Location: New Mexico
Posts: 320


You are very welcome.

For 5 years I worked o-ring problems. They were #3 on the corporate warranty list and kept me real busy.

Anyway, Parker Hannifin O-ring Division was a great supplier. Parker supplied a gadget to dealers called a "cone" and that is what it was. Drop an o-ring on the cone and you could read the approximate inside diameter.

As to the cross section diameter AS568 specified standard CS diameters. Rather than putting a caliper on the cross section and squeezing, I'd recommend setting the caliper to a certain gap then seeing if the o-ring will slide thru the gap. If not, open it up a few thou and try again until you get a little drag as it slides thru.

I'd be guessing on durometer hardness for this app. But I'd guess not very hard such as maybe 40 to 50 durometer. For frame of reference 90 durometer is hard as a rock.

As to material type: I'd recommend EPDM rubber but mostly you will find "Buna-N" aka nitrile rubber which will work.

If anyone has a Unertl parts list they may show a "dash size" for the o-rings. For example, "-072" or "dash 072". In that case you are home free as to size (I pulled the 072 number out of the air - don't mean nothing).

Like I said if I was still working I'd do a full analysis on sample o-rings for you and the rest of the Unertl world. I shoot a 20X Unertl on my 40XB samllbore rifle.

Good luck.
“After all is said and done, successful rifle shooting on the range is nothing more than first finding a rifle and lot of ammunition which will do precisely the same thing shot after shot, and then developing the same skill in the rifleman.” ~ Capt. E. C. Crossman (Book of the Springfield)
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