Breech testing continues - Cupped breech inferior

[Daryl]

DP- as to counterbored vents - do you mean WL vents with the 'cup' inside to bring the powder out against the pan?  If so, rest assured they do not foul to become straight holes as a drilled vent.  Whether I've shot 10 shots or 50, when I load, I can see the powder at the vent, not blocking the hole, but inside the vent's 'cup' up against the hole to the outside.  If fouling had turned it into a straight tube, the powder charge wouldn't 'always' be able to come that close to the pan and wouldn't be visible - or would it?  If I suspect I've dry-balled, I merely look at the vent- if I see no powder, I've dry-balled.  It doesn't happen often, but alas, it has happened often enough for me to learn this 'fact'.

[Dphariss]

In actual use the counter bored vents seem to work fine. I have 6 in use right now in my own guns.  When used with a service load the pressure seems to keep them clean. I never put them exactly at the breech face either.
This is the advantage of the small diameter liner, 10x32. The vent can be near the breech without getting into the  breech face and opening the threads to fouling.
A friend used to use SS welding rod and use pipe thread taps and dies to give a gas tight seal for the threads.
I drill a hole in the barrel just slightly larger than the counter bore then counter bore this hole deep enough to allow at least 5 threads. I make the liner and drill the counterbore to a depth that allows me the proper set back for the vent. Usually .030-.050". This will result in much lower pressure on the vent liner as well.
With FFFG there is ALWAYS powder in the counterbore unless something in the bore or a lodged flake of fouling prevents it, but this can occur with any vent. FFG seems to work OK but I seldom use this in calibers under 58.
This is a 15/16 x 50 smooth GM barrel ready for a counterbored liner installation. I goofed the #10 threads and had to make it a 12x32 to clean it up.

Dan

[Larry Pletcher]

Dan,
Thanks for the photo. I think that's a simple, but clever installation.
Regards,
Pletch

[Daryl]

I see what you mean now about a counterbore - great system if the barrel is heavy enough to allow the 4 or 5 threads.

[rich pierce]

Yes, that looks terrific and I can see how it would solve a lot of potential problems: it will lower pressure, you have no trouble with cutting threads through the rifling etc, liner sticking into the bore, must avoid a dozen little ways of snagging patch or tow or collecting gunk.  I'm guessing you need a milling machine to be precise enough with the counterbore depth.

[Daryl]

Careful work with a depth mic. squared drills and bottoming taps will answer.  A milling machine just makes it easier to set up and cut.  I've done a lot of stuff like that in the past - distant past, mind you, using a 3/8" variable speed hand drill long before I got a drill press.  I also used it for milling by hand with the hand drill held in the bench vice - 1/4" to 3/8" end mills & holding the metal in my hands - they cut deeply, by the way - always just a slip away.

[Sam Everly]

You can do some good mill work with a good floor modle drill press and a dividing head with x-y axis . I used one for many years when i first started making rifles . I also breeched many barrels by hand useing the method Chuck Dixon has in his book . It all comes down to how bad you want to do somthing and what you have to work with . I was just a kid and did not know any other way to do it .

[Dphariss]

Yes, that looks terrific and I can see how it would solve a lot of potential problems: it will lower pressure, you have no trouble with cutting threads through the rifling etc, liner sticking into the bore, must avoid a dozen little ways of snagging patch or tow or collecting gunk.  I'm guessing you need a milling machine to be precise enough with the counterbore depth.

Drill press will do it if you have a vise.
A lathe to make the vents is nice too.
I got spoiled while at a gun factory and could not do much without at least a lathe anymore.

Dan

[Daryl]

I've always had a lathe - "variable speed electric drill in a bench vise" - won't hold a barrel, though .  You'd be surprised how much small part 'work' you can do with this setup, using various file shapes and sizes - really!

Now that Taylor's got a real lathe - wonder of wonders - fantastic - what a spectactular machine it is.

[Dphariss]

Careful work with a depth mic. squared drills and bottoming taps will answer.  A milling machine just makes it easier to set up and cut.  I've done a lot of stuff like that in the past - distant past, mind you, using a 3/8" variable speed hand drill long before I got a drill press.  I also used it for milling by hand with the hand drill held in the bench vice - 1/4" to 3/8" end mills & holding the metal in my hands - they cut deeply, by the way - always just a slip away.

I found some piloted counterbores that do good work for this. I grind taps to bottom closer but one must take care not to run into the bottom of the hole and cut into it.
I have a counter bore that with a sleeve on the pilot to increase the diameter cuts a perfect nipple seat in a patent breech. Some have a curved surface for the nipple to seat on and they leak gas when fired, water when cleaning, etc through the nipple threads. I ran into this with a TOW Hawken breech.
Cutting a flat seat square with the threads cures this. Suppose it would work on a drum too.
When you go through a catalog like the one MSC prints its amazing what you find. Then all it takes is $$$.
Carbide drills and mills will cut taps, drill bits and hardened steel parts like tumblers with ease. Takes the headache out of broken taps in blind holes, just run an undersize drill down the center, high speed slow feed, and remove the pieces.

Dan