PP750 Artemis Tear Down and Tune Up

[Back_Roads]

 I just saw another PP750 bottle conversion, seems to be the same setup used on the Notos. I just bought an Air Force clone that uses the same regulator.

[Gerard]

It's been 3 years, but I finally got around to buying a PP750. More than a year into this stage 4 kidney cancer diagnosis thing I'm getting itchy to do something other than take medications, rest too much, and cram in the odd bit of actual work to pay the bills. Modding an airgun for fun will be just the ticket.

I didn't see this Youtube video in the thread, though it's possible I missed it. This fellow goes through all the important power modification possibilities, showing every element quite carefully so as to avoid confusion due to terminology or descriptive phrasing. He doesn't fill in the inlet channel around the barrel as someone in this thread mentioned, and that does seem to me to be a good idea. I'll be marking for alignment and filling the channel with JB Weld steel-filled epoxy, and if one of the two holes doesn't happen to align properly, will drill a third through that.

For someone like me who is very visually oriented, the many pictures in this thread are a huge help... but nothing quite as easily interpreted as a video I can pause and back up at any time. So I saved the video to my computer for reference as I go along. Also wondering about adding a short length of stout 6061 tubing to increase plenum volume, but I'm unclear on the layout, and suspect that may not be possible with this threaded-together installation, though I think I did see a threaded plenum extension on eBay that might fit, not sure. Already ordered a PEEK valve from a hobbyist seller there. And the pistol should arrive in a week or two. Very excited!

[cilami]

Thanks for posting this video. Somehow I missed it. Happy 2024!

[Gerard]

Well I've tinkered and fussed and adjusted my PP750, and have it dialed in at an efficiency level far better than factory settings. Opened up all the ports to 1/8", including the aluminum offset transfer chambers where the hole is at the top edge of one side's hole and the bottom of the other side, using the drill on about a 15 degree angle to avoid touching either inside diameter surface. The objective here was not more power, but a smoothed-out air supply, with which I could then play around at the striker end.

The thing came to me shooting 8.43gr JSB .177" pellets at about 515fps - a hair over the Canadian regulation, silly Snowpeak, seems their 1mm hole in the brass valve wasn't quite small enough. It was LOUD at 515fps! Ridiculously loud. Hence my exploration of efficiency. By the way, adjusting the hammer spring bolt wasn't possible, as the grip frame blocks it from coming further out than flush. I'd have had to cut spring coils off to get it below 500fps.

So with all the guts worked over, thinking of all the successful, highly efficient tunes I've done on a Brocock Atomic, a Crosman 2240 and 2260, a QB78D (all converted to PCP, the last with a Ninja bottle), knowing how a much lighter striker 'tickling' the valve stem instead of bottoming it out (thank you again, Bob Sterne, for the innovation of the SSG, which has given me such great results in a bunch of airguns), I made an aluminum striker. Copied the stock steel one exactly in 7075 aluminum, then bored a pocket in the striking face and drilled and tapped for an 8-32 stainless steel bolt with a large round head, ground that past the slot once the JB Weld was cured, and had my hard striker face. The new striker weighs 8 grams, compared to the 20 grams of the stock steel one. And out of concern for wear on the sear-catching edge, I polished the sear nicely - it was rather rough from the factory, surprisingly. The trigger dropped about half its resistance as a result, from about 7lbs to 3.5lbs. And inspecting the striker's edge after around 50 shots I could see no trace of wear, using a mixture of lithium grease and bike chain oil as a lubricant to keep things smooth in there.

The thing now *sips* air, shoots magazine after magazine with the gauge barely dropping... I've not bothered to shoot it all the way down to regulator level (stock setting is about 120bar from what I can make out - I polished the edges/centres of the bellevilles, so may have shifted this slightly), as I'm too cheap with pellets these days. It's just shooting an awful lot of them, which is great, because the kidney cancer which is spread around in my guts makes running the Hill pump somewhat painful. Hoping the new drug they've got me on will calm that down soon - already improving after three weeks on the awful stuff. Maybe by spring I can pump up my airguns without feeling it for an hour afterwards. Meantime, this Artemis is a joy to shoot, so I'm happy I finally bought one. And I'm happy to report that the *report* of the pistol sounds a little more reasonable for the low power level. Maybe half as loud as factory stock. That's what you get for not using a heavy striker to waste a bunch of air long after the pellet has exited the barrel.

Next up, I just bought an Edgun Leshiy 2 from a guy in another forum. Should ship tomorrow. I won't be needing to modify anything there! Just something I've wanted since it came out, after wanting the original Leshiy since it was in prototyping, and never had the opportunity to buy due to inconsistent finances, or the government ban on the original model, or stores always being out of stock. This one's barely used, in .25", at about 2/3 of retail, so I'm happy I'll finally get to shoot a Leshiy - at least more than the 4 shots I got to try back in 2019 at our monthly HFT gathering. Couldn't miss with that thing at 50 yards offhand. Ridiculously nice gun, and a marvel of engineering.

[Gerard]

Spoke too soon on the sear marring the aluminum striker - after about another 70 shots I pulled it apart and found some slight rounding at the edge where the sear slips past, so obviously not going to last very long.

Found a thick stainless washer of decent hardness in my parts bins and turned the middle out to a press fit, snugged that up against the flared end after turning down about 2.5mm of aluminum to make room. Then drilled 4 x 1/16" holes around it and put short sections of finishing nail into them, required hammering them in against a drill shaft then hammering some more to flare out both ends flush and keep the pins in place. That should do the trick.

[Vlada1911]

Did anyone tried to polish the tube where the hammer slides? Is is made od steel or aluminum?
I polished the hammer but I noticed the tube surface is pretty rough, too. Might benefit from polishing?

[Gerard]

I doubt the finished inside surface is causing any significant friction on the hammer. A trace of some lubricant ought to be enough to ensure the hammer drops easily and consistently. My measured velocity strings show very small variation shot to shot, easily accounted for by the need for the regulator bellevilles to wear in and become smoother, even though I polished them at contacting areas. And this is with my aluminum hammer, less than half the mass of the original steel, where friction would show up as a higher percentage of velocity change compared to the steel if it were an issue.

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I made a small modification to the buttstock, as it bothered me that leaving a magazine in the receiver meant either firing a shot, or leaving the gun cocked. I'd rather have the full 9 shots available. And carrying magazines... where? In a pocket? Sure, for extras, but for the one I will want to use first? So I drilled and carved the aluminum of the butt plate and used tape on a magazine, coating it with a beeswax/mineral oil paste that I use for lubricating zippers on instrument cases, so that it would not stick to the JB Weld steel-filled epoxy I used to fill the voids in the plastic and make for a neat fit. Pushed in a small neodymium magnet to retain the magazine. Works great, can't fall out but is easily lifted out by tilting from one edge, and doesn't get too close to the grip when closed, even though I replaced the big steel knob with a small bolt to allow the stock to close an extra 1/2".

Oh, and I found a neat little scope on eBay for $75, shipped. The size seems right for such a small airgun. It's a 3.5x prism scope, with 3-colour illuminated turret. 3 brightness levels each on red, green, and blue, with no illumination (off) between each colour on the dial. Should be handy for any sort of lighting situation. Next up - figuring out an adapter to get my infrared monocular/illuminator thing to fit to it for ratting.

[Vlada1911]

I doubt the finished inside surface is causing any significant friction on the hammer. A trace of some lubricant ought to be enough to ensure the hammer drops easily and consistently. My measured velocity strings show very small variation shot to shot, easily accounted for by the need for the regulator bellevilles to wear in and become smoother, even though I polished them at contacting areas. And this is with my aluminum hammer, less than half the mass of the original steel, where friction would show up as a higher percentage of velocity change compared to the steel if it were an issue.

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I guess you are right then. So, how satisfied you are with aluminum hammer now that you sorted the galling issue?

[Gerard]

I'm rather happy with this setup. Efficiency of 1.15 fpe/ci isn't hugely successful compared to something like my hyper-efficient QB78D where I get 1.87fpe/ci, bur for a short barrel like this it isn't terrible.

Bob explains efficiency here for anyone not familiar:
https://hardairmagazine.com/ham-columns/pcp-efficiency-what-is-it-what-changes-it/

[rkrr20307@comcast.net]

Here is my PP750 with bottle mod- 16 inch .177 and .22 barrels from WES at AIRGUNARCHERYFUN - custom barrel band with pic rail from HOTSNOTS and custom side lever made from aluminum angle and hand tools. It right now in .177 is shooting 10.5 at 855 FPS.

[stergios]

Should I buy the 10.5" barrel? How much more fps?

[Barr]

 I seen some where it makes difference for the good and speeds it up. I got the 10.5 barrel from Wes but have not tried it yet. I need a Crony to test, up here in Canada we need to stay under 500 fps so no help. but I did learn that the torque is hand tight and a bit. And that’s why I joined GTA so welcome to the GTA.

[stergios]

I'm waiting on the 10.5 barrel from Wes. Here in Greece we have no fps limitation. Thanks for the reply.

[Barr]

Very cool you will not be disappointed, Wes is the Best, I bot a muzzle brake and it makes my pp 750 look complete. I still need that crony so I can’t do mods yet. Maybe for Christmas? Let us know what you think when your done testing your Mods. Happy air gunning.

[stergios]

I would also like to buy the gauge blocks when they become available again. I can't see how accurate the regulator setting is.

[Barr]

Ya Wes has to work his butt off to get stock but it will come. The gauge on the block look like a standard 0 to 300 bar or you can change it I think, ask around I am no expert be safe thats why I joined GTA. I think it’s bin about a year, not that I have the funds and I am saving of that crony first hehe. I want to stay within the law don’t want mess up are sport it’s hard enough now. but yes I will try one if I can get my hands on one. I would like to add a moderator or silencer but for now we can’t. Are speeds here is a bit low and the tree rats can hear them coming so you have to be extra sneaky, look like a tree.  Also they look cool. Happy air gunning.