Gauge Blocks

[Doc Sharptail]

Cover is coming down fast where I hunt, and I'll soon be able to take grouse and rabbits with the air rifles.

Finally got around to getting the leaking gauge and block out of my 3 K psi D/V disco tube. Replaced them on a temporary basis with the units out of my 1701-P. Huge differences in both the gauges and gauge blocks.

The P-rod block is blued steel of some kind with an air passage through it that is way bigger than the hole in the aluminum Discovery block.
The gauge probe ends are different too, with the Discovery gauge having a bronze wire coming out of the probe end. The P-rod gauge probe end appears to have two tiny s/s buttons in it, well below the probe surface.

It's currently in .177 right now, and I'm expecting a bit of an increase in power. I'll partially fill it tomorrow, and see how well it holds air.
The valves are different too, with the P-rod valve just having one beefy o-ring, instead of the Discovery's two slender ones. I think the P-rod valve is aluminum that is anodized a gold colour. Was sorely tempted to switch out the hammers while I was at it, but I'll leave well enough alone for now, with the home made by me motor shaft hard stainless hammer. It's quite a bit heavier than the P-rod hammer.

I'd really like to drill out that tube to take the P-rod riser breech and valve, but none to sure about how to do it. I get antsy thinking about drilling into that curved tube surface, even with the breech as a guide. Factory job looks like it was done with a tiny end mill cutter. The holes look milled, rather than drilled. Any advice on doing this would be more than welcome...

Looking forward to getting it up and running.

-D.S.

[jckstrthmghty]

You are trying to enlarge a current hole? I'm not sure what tools you have available but at least a drill press? If you are enlarging a metal hole it would really help to have something to guild the drill bit. Something like a piece of hardwood drilled to the outer diameter of the tube, cut in half down that length of that hole, then drilled on the inside of the convex curved portion with the new hole size. That can be lined up on the tube and clamped. That would stop the drill bit from wandering when it hits metal. The tube itself should be placed in a v grooved rest and clamped or you could use the other half of the wood and clamp it with your guide around the tube. Goes without saying you have start with a square piece of wood and to be able to drill and cut square.

Easier if you are drilling a new hole. Center punch, clamp, then drill.

[rsterne]

When "drilling" at an angle to the tube surface, I always use an end mill....

Bob

[Doc Sharptail]

Dunno how enlarging holes got into this discussion. It wasn't me, I swear

I'll have to get down to Luke's sometime this week-end and find out how small and long those end mills come. My do-all 1/4" is on a very stubby shaft.... those square shouldered mill holes certainly look nice on an air rifle tube.

What I'm considering doing is modifying a Discovery pattern tube to take a Marauder pistol riser breech and valve.

-D.S.

[wesb2007]

Cool project!

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[Doc Sharptail]

Lookin good so far on the switch over. She's held 1500 psi for the last 4 hours.

Gonna get her out to the gravel pit Friday for a full bore test, starting around 2400, and take it from there.
Couldn't resist a couple of test shots with no pellet, and it sounds quite a bit louder than previous with the rva all-in.

We shall see!

-D.S.

[Doc Sharptail]

Got a nice curve at 2400-2600 PSI.... with the RVA 4 turns out from coil bind.
9 C today, and quite windy.

10.5 Gr. Crosman Ultra-Mag

1.) 802.9 (2600 PSI)

2.) Err 2

3.) 825.5

4.) 843.0

5.) 844.9

6.) 843.4 (2100 PSI)

7.) 857.1

8.) 861.0

9.) 865.7

10.) 861.6 (1800 PSI)

11.) 873.3

12.) 872.1

13.) 859.4

14.) 864.5

15.) 845.3 (1300 PSI)

Both the transfer port seal, and the tiny o-ring on the bolt that serves as a breech seal need to be replaced. There's a slight air puff on the firing cycle.

Got a couple of pix to follow. Just need a few hours of calm wind to get this laser properly zeroed.

-D.S.

[Doc Sharptail]

For those who wonder what such a creature looks like

P-rod grip frame and trigger, 3 K Discovery pattern tube by Derek Vineyard, 4-12X 40mm Vortex Diamondback, and a lot of accessories from scopes and ammo....




1701-P gauge showing today's start point

-D.S.

[wesb2007]

Nice!! Thanks for sharing! That is a long looking tube!

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[Doc Sharptail]

The Discovery valve stem in it went frappe de flooey today- it went braappp on 3 consecutive shots, which completely emptied the tube, and now it won't hold air.
Wasn't pushing that hard either- last fill was to 2400 psi, and 6 1/2 turns out from coil bound on the RVA...
Too busy hunting right now to do a tear down to see the extent of the damage. Switched to the .22 pcp'd A/R 20-78 for a hunting air rifle for the time being.

-D.S.

[wesb2007]

Dang hey! Hopefully an easy fix anyway besides having to tear it apart. Good luck hunting! Grouse? My Dad has shot a bunch with his (mine actually, lol) 22 lr, but he got a couple with the 1322 as well. No ruffed grouse down here on the Prairie, pheasants I think but haven't seen any.

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[Doc Sharptail]

I actually went through this before with the pcp'd A/R.
Think I have a delrin stem for the A/R that could be modified to fit this thing.

IIRC, the earlier disco's topped out at 2K psi max. Kinda surprised 2400 would blow one (valve stem) though...

That'd be Hungarian Partridges and Sharptails around you out in the open country Both are fine eating!

-D.S.

[rsterne]

Not sure why a failing valve stem would cause severe hammer bounce as you describe.... I have run Disco poppets up to 3000 psi without a failure.... although now at those pressures I typically substitute an MRod poppet, by bushing the valve stem hole down to 1/8"....

Bob

[Canadianguy]

I was on GTA earlier this week and seeing a pic of this guy's BnM breech drilled just like this prod breech your talking about. He said you need a end mill as you guys said.

Would love to get mine done.

Like to see how this goes for you Doc!

[Doc Sharptail]

Hi Bob.

When the A/R stem went, the little "seal" insert in it popped out, and split, lodging the poppet open.

With the current gun and valve, I'm suspecting the poppet return spring climbed up over the shoulder stop, or the spring is broken. Won't know until I get it apart.

Not too sure when I'll get around to the breech switch. I still have to investigate mill cutters, and find the proper size for the job.
The more I think about it, the more it makes sense to get the P series valve into it~ I may save myself a bit of effort in going that route...

-D.S.