ARrrgh, I give up… wait maybe not

Carving up a breech for the .308 project and everything going ok… then remember I HATE cutting O ring grooves. Made a small tool from an old allen wrench, but it was too flimsy so got a section from another allen wrench, much bigger, and welded them together so they’d be stiffer. Seems to work now… cut the groove for an R6 ring, .093 width by .050 depth… insert O ring; insert barrel end (thin end that goes through the breech) hmmm, some resistance… then plop, it comes through; and the end of the barrel poking out through my new breech is wearing a part of the O ring like a mustache. Crap. Put in another R6, put lots of lube this time; plunk, it tears that one too. Take out barrel, recut the end to put more of a taper on the very end so it gently swages the O ring as it goes past… sand, then polish the new end… insert new O ring; plop, another busted ring. Hmmm, maybe the groove is too shallow; put the breech back into the lathe and cut the groove .002 deeper; okay, long story longer, half a dozen O rings later and maybe another .005″ deeper and it’s still busting O rings. Now the groove is so deep that the O ring is playing around in there, impossible to line it up properly so that it stays centered, and with a sinking feeling I know this breech is scrap metal. MUTHA FFFFFdkkddknsfniewioe1828374@@!!! That was hours spent on that stupid breech and now I gotta scrap it???? Then my old breech caught my eye and bingo, light comes on, I can still save it, maybe. Use R8 ring, which is thicker but same outer dimensions… quick scribbles on notepad to calculate new dimensions…. .080″ depth and now .140″ width… couple of cuts later, lube new R8 and insert barrel; plop; holding my breath…it comes out clean!!! No mustache!! Yayyyyy, the good guys get to each lunch.

Now, if only this one holds the O rings…. last breech was fine, except…. the groove was cut with a very slight taper to the walls and about half the time when firing, the O ring would climb OUT OF THE GROOVE and announce its presence with a huge BANG!!! Really, really uncool. In a .22 or .177 that’s kinda ok, but in a .308, it’s not fun.

aloha,
walt

langnasen

Participant

January 19, 2009 at 9:19 am

quote The Machinist:

An oring cutting tool made from a allen wrench??
Why would you make one from a allen wrench? what material are you trying to machine? I did see Mcgiver weld a aluminum connecting rod together once with a pair of jumper cables and a quarter… 😆

I have a number of cutters made from allen-keys, for cutting plastics, brass and alu. I use them for grooves and tapers and they work very nicely. 😀

love-my-talon-ss

January 19, 2009 at 7:26 am

Episode #25 (just kidding) 😆

the-machinist

January 19, 2009 at 4:12 am

shrpshotr28

January 19, 2009 at 2:48 am

quote walt_in_hawaii:

Simple explanation…. I like it. And you’re probably right. I’ll check it when I have it apart again.

Please share what you find out.

My experience pales compared to you and some others here and I continually learn from you all. I can say from my own experiences though that as I get comfortable with a process, it becomes taken for granted and it becomes easy to overlook the obvious. Seems I learn more from my mistakes than my successes.

Don

walt-in-hawaii

January 18, 2009 at 7:56 pm

January 18, 2009 at 7:36 pm

Walt,

possibly the operation of cutting for the oring is raising a “burr” on the edge of the oring groove that has gone unnoticed. My “allen key” oring tool leaves a VERY sharp edge after cutting the oring groove which I have to carefully clean up by hand afterwards.

look forward to seeing how your .308 shoots.

January 18, 2009 at 7:08 pm

Nope, the edge is fine on the barrel, I made sure it’s nice and polished, with a gentle taper.

I am running very, very tigh tolerances between my barrel and breech… not even 1 thousandth of an inch, if there’s oil in there they slide next to each other with a silky feel…. you WOULD NOT BELIEVE how small a space an O ring can squeeze through. Just a tiny, tiny space and out it comes. Of course, I’m using a much larger O ring than a standard barrel uses; this is a .308 build, and using CygusX’s 600+ fpe valve, which also uses a larger tophat. On his breech, he used a double O ring at the back; so I’ve just modified my breech and put in another O ring so there are 2 at the tophat end… I assembled it last night and fired it… empty it worked just fine, but when I put in a pellet and fired it, it developed too much backpressure and BANG! the tophat O ring popped out again, so I pulled it apart again and cut the extra O ring groove. Haven’t tried to test fire it yet as it was dark and it gets quiet around here after dinner time. I’ll know this morning some time.

I don’t think the tolerances are that critical with smaller O rings because the groove is small it turns qiuckly, so there is an inherent stability. The larger the O ring, the straighter the wall sections become, so they behave more and more like a string in a groove rather than an O ring. I may have to just see if I can find harder O rings. I bought the ebay kit for $12 and they probably have the softest and cheapest ones. I’m not sure if doubled small O rings are better than a single thick O ring. But Cygus had a doubled ring design, so that’s what I’m trying.

January 18, 2009 at 1:08 pm

That’s odd Walt, I didn’t think the tolerances were so critical, having done a lot of stabbing in the dark with my breeches. The one I’ve just done for Pablo has a 4mm (2mm groove depth) on the barrel-end and a 3.5mm (1.75mm groove depth) on the tophat end. There’s a lot of resistence on the 3.5mm end but it does go through without anything tearing. And these are quite soft X-rings. Are you sure there’s not a nasty edge on the lip of the barrel’s breech?

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