Artemis/Snowpeak/Diana/SMK M-16A

https://i.postimg.cc/MZ4C2w2Z/3.jpg

Backstory here is simple really. The local vendor that i do jobs for had a few of these laying around in 25cal.. and they´re to be phased out. So a deal was struck and i ended up with yet another 25cal PCP.
That simple.

For those not in the know the M-16A is a kind of budget to mid range PCP that sports a regulator as kind of a key feature. The Artemis line of chinese made PCP guns range from ultra budget (Stormrider) to the auto loaders like the M40, and the P15 to P35 as in between bullpups and what have you not. I´ve been waiting for their new M-60 "FX Impact look alike" to surface.. to no avail yet.
Anyways.
M-16A

https://i.postimg.cc/4Nq68WF3/6.jpg

IMO to call it a pretty gun would be stretching it. I believe the intent here was a basic regulated PCP rifle, one that sports a barrel length just as the Stormrider. Sports a shroud stock, and we´ll get into that.. adjustable trigger and what have you. Regulator is to be adjusted from the outside btw while the stock "buddy bottle" has no provisions in form or shape of check valve or similar.

Like the Kral and Reximex guns the Artemis offerings are often rather accurate in comparsion to much out there IMO. That´s to be said as i see it. So i expected this M-16 to shine in that dept..

https://i.postimg.cc/ZYjjLFS9/2.jpg

Shroud. Right. As the thing comes out of the box the shroud simply does not work. Point being that it´s a tube that rides atop the barrel and that´s about it. What´s more the diffusor that rides at the muzzle of the barrel carries some sort of funky thread that i´m sure was a good idea to someone at Artemis/Snowpeak but.. whatever.
As that thread´s larger than the industry standard 1/2"UNF though.. i just recut that and threaded it.
Then. To make the shroud functioning i cut back slightly on the flange and then cut an o-ring groove into it. In this manner the shroud is sealed vs the diffusor, which hands that all gas that´s expelled behind the bullet is free to move down the shroud and the shroud to pull it´s fair share of work muffling the piece.
All good then?
No. The other end of the shroud tube there´s a series of holes for "venting" the shroud. Completely uncalled for as the air will just bounce back need be.. and them holes make the shroud omit.. noise.
I just did a McGyver on that one and wrapped the tube with some elastic black electricians tape, adding one layer on the inside of the shroud tube as well to keep rattling to a minimum where it comes to a stop on the guns separate breech piece.
So.
At that point all content and ready to accept a moderator of choice. More on that further down...

https://i.postimg.cc/VNyFNKjh/3.jpg

The M-16 is a regulated gun. That brings lower running pressures than if not, why i from the onset decided on opening the transfer passages up. In this case for starters to 6mm flat. At that rate the one of the two stock allen grub screws in M5 is out.. cause i drill that passage on one of the bench drills.. with the valve seat body set into the main block while at it, handing me absolute fit between the various opening when done.
That also brought that i in turn had to drill what you see there in the picture to 6,5mm to accept an M8 tap.

The poppet on most Artemis guns is rather small and light. Works off of a 3mm spindle. Opted to cut the center of said spindle, which works within the main valve exhaust port, back to 2,5mm on the lathe.

Future mod, if needed, will be to open the valve seat through hole incl the space beneath it to 7mm flat. Need be.

https://i.postimg.cc/d3Q6YD8t/1.jpg

Hm. Yet another point where this gun sure isn´t "done". Why is that? Anyways. It sports a barrel that threads into a breech piece. For whatever reason that part of the barrel that sticks into the breech bottomed out where it´s absolutely at its thinnest, within the breech, instead of at the flange so intended (in picture).
What´s more..
There´s two o-rings for the transfer passage between the block and barrel. All good. There´s an o-ring to seal vs the probe. Again all good. But there´s nothing to keep it air tight between the barrel and the breech piece?
So.. barrel on the lathe to cut an o-ring groove and then countersink the opening for the barrel on the breech piece.
NOW it seals 100.
To make that there happen i had to cut back 0,8mm on the piece that sticks into the breech, which in turn handed that i needed to cut back 0.6mm on the shroud tube - to make it all come together.

So. There i was.
Rifle now shoving "34 grain" (i use that phrase loosely) pill downrange at a reasonable 950-960fps (even saw 97o).
But.
That IS stonewall if we´re to use some sort of reason here. Mind you, at this stage i had ALSO weighed the stock hammer of a mere 19 grams down to approx 34 grams by "leading" it (melting lead into the cavity of it) and in turn replace the stock hammer spring with one for an FX Impact.

So what´s the issue then? Welp.. regulated guns in essence NEED what´s known as plenum volume. Ie; an entity AFTER the regulator that only sees regulated pressure. This plenum is what the guns to draw from as the valve opens, and if not there.. the reg sure becomes a bottle neck to keep up with the pace we´re talking here.
Issue is that the M-16 plenum is of a mere 11cc´s... We normally say that 10cc´s per 10fpe is a good rule of thumb..
So what i´ve done is look into this, in more ways than one.
Where we´ll end up is anybodys guess as of current, but that it WILL happen and it WILL show the results to go with it.. you can take that to the bank.

Anyways. Shooting.

https://i.postimg.cc/SQTXtVsm/12.jpg

The M-16 sports what i´ve come to call a "semi weighed" trigger group. As there´s plenty of direct contact in there, while other parts of it is spring loaded. Like the sear for instance (hidden by the frame work in the pic).
No matter it´s kind of neat that it sports an entirely stand alone trigger group as i regard it.
Anyways. Shooting.
So the trigger can be adjusted for 1st to 2nd stage slack and then sear engagement too. This via two separate adjusting points holding M3 allen grub screws.
I adjusted the trigger... and it wouldn´t hold after a few shots. Adjusted again.. repeat n rinse.. sorta.

Tracked that down to that the adjusting screw for sear engagement was way to loose in its threads...

https://i.postimg.cc/8cVy8Dwr/10.jpg

Indeed. Took the trigger assembly apart and handed that pesky little screw some blue Loctite and done deal. Since that was let to cure.. trigger is downright wonderful.

https://i.postimg.cc/wM0DWdrz/11.jpg

In turn. Me i like VERY light 1st stages and as can be seen in the picture of the entire trigger group there´s a small spring to act on the trigger for the first stage. Replaced that.. very happy.
Sear adjustment in turn is such that there´s no creep what so ever and i´d say that after cutting the angles of the sear as i see fit i´ve got a trigger pull somewhere around 1-1,5lbs approx. Real happy with that.
Actual trigger blade holds the safety too btw. Completely useless..

Then today.
No pics, coming up.. But anyways, i sanded that god dreadful stock down. For some reason Artemis/Snowpeak friggin DIP their stocks in pore filler which hands a rather "plastic" feel to them, albeit wooden stocks. So fact is ALL my Artemis guns has undergone this. Have treated it with some dye and in turn linseed. Will revisit the dye come tomorrow.
While at it.. that "forend" is simply to much. So i took the saw to it, getting rid of approx 1" of the absolute bottom of it.
WAY WAY WAY better... now it looks like a "normal" rifle at least.. But i´ll get back to you on that.

Do keep us posted on your progress. You are the only Airgun Smith we've got here so your posts are informative. So I detect some of the "Queens English" coming thru your posts. Are you in the UK?

Keep in mind we are all Colonials over here and by definition not nearly as sophisticated as you "Continentals."

Randy

Thx.
Nah. I´m a half breed, thus i guess my both way to build a sentence as wording and what not gets clustered?
U tell me.
Live over here in Europe since ages though. When you hear me speak tho.. there´s no mistake :mrgreen:
Ill in my case and then as an adult back for Az and Mr Cooper and what not for a while. So.. have moved around a bit, which sure marks my speech i bet.
..and for the sake of argument, yeah. A language or two doing so.

I´ll be happy to!
What i "really" do is pull loads of work as far as old original BP firearms though, this whole PCP bit came out of us getting rat infested at the shop. (Don´t ask..)
As i keep three muts all in all poison was sure out, one thing led to another.. why i came to opt for PCP´s. As the shop of mine is in a "semi" downtown area i can´t use firearms sans permission while a moderated and shrouded air gun carries no such limits.
Ergo..
Then.
Have a past with motorsports and that kind of brought that there.. "jack of many trades, master of none".. kind of.
Been at it with the old original black powder guns for a number of years now and compete as much as time allows. On various boards and what not over here.

Dunno if you´re into it at all, but over the yrs i´ve come to end up with the occasional boom stick or two that´s.. rather fabled.
So.
Albeit this the air gun forum here goes (as an exception)

https://i.postimg.cc/J0hpFpdb/16.jpg

https://i.postimg.cc/Dyxb1DYc/36.jpg

Here a basically mint Enfield P-53 "Export". IOW the exact same gun that got delivered for the CW. Yep. In essence new.

https://i.postimg.cc/022gJJGw/8.jpg

https://i.postimg.cc/rpZkrzFF/23.jpg

An original London proofed 3d model Dragoon is full working order (and used such.. :mrgreen:)

https://i.postimg.cc/prdsCz1N/6.jpg

Business end of a Cape RIFLE. A 500 Express made in ZA way back.

https://i.postimg.cc/pLW2MtvJ/19.jpg

Here my 8mm Kropatschek. This is a permit gun to me though (most of the others are not due their age)

https://i.postimg.cc/PJ6hz7px/75.jpg

Merrill carbine..

https://i.postimg.cc/PJMXkh8Q/13.jpg

...basically mint 1858 Army...

https://i.postimg.cc/BQK8jKrD/50.jpg

...a Swiss Milbank hybrid carrying one of the most beautiful tiger striped walnut stocks i´ve ever laid eyes on...
Due a mishap (before me) i came to chamber the thing for 45-90 shells using 43" pills.

https://i.postimg.cc/G2drJmcS/41.jpg

A 45 cal Westley Richards rifle. A so called Monkey tail. Was this one EVER a trainwreck as i got it!

https://i.postimg.cc/15hL109n/4.jpg

1865 Rogers&Spencer

https://i.postimg.cc/nhRr5Y8B/73.jpg

Yet an 1858, one where the ship had sailed for real so i restored it and since use it for CAS.

https://i.postimg.cc/ZRJPWY0d/7.jpg

Starr cap n ball carbine in very good working order. As we CNC cut our own molds.. yeah. The one for this one is a bore-rider with its driveband at a full ,555" diameter.
Although i own a Sharps -59/-63 rifle too.. i´ll be damned if i don´t hold this Starr higher actually.

https://i.postimg.cc/JhwJRFRk/100.jpg

https://i.postimg.cc/5y0ww5Fq/127.jpg

Yes. An original Whitworth 451 Military match. We not only cut our own molds but play around with making swaging setups too on occasion.

This just a few.. but as you can gather, yep. Find PCP tech very interesting and carrying a lot of potential.
Uhu. Compete using "modern" guns too (time permitting. Ended up 2nd place this sunday at a rifle match actually)
...but more than anything it´s about the "ol´uns" to me.
Mind you, the really old stuff.. not so much. I kind of got excited due what Whitworth and Purdey arrived on there back in the 1850´s, where "modern" accuracy was born.

Understanding PCP tech that said, not all that much of hazzle to me and as i´ve got the "guns" part already.. it was mainly about melting them two together, and here we are.

https://i.postimg.cc/76TnHFrt/15.jpg

Back on track. Took about an inch off of the bottom of the stock, making the thing way more prone to "normal" rifle looks IMO.
Hue on the other hand, not so sure. That can always be changed though.

Performance.
We´re aware the thing is regulated from the factory and that reg actually works semi decent TBH. Like all regs it takes bit of time for it to "settle" which i guess mainly is about the inherent belleville washers working up against each other.
However.
That reg has a mere 11cc´s worth of plenum chamber downstream, and that simply won´t suffice for where i´m headed so extra plenum volume is no doubt needed.

I´ve debated "inletting" an approx 70cc steel cylinder that heads into the stock placing of the pressure gauge (which reads regulated pressure), and.. might very well revoke to that all said...
But.
As the reg is on there i thought to myself that why not simply move the reg way more up front? 70cc´s added, then a freshly made reg housing.. before the bottle.
Yes. This would no doubt add length to that part of the rifle but all said and done the bottle and so forth are a rather far cry from the end of the muzzle as is.
In short, i dunno what that "iteration" would come to look like, why i´m exploring it.
Then again, it will keep the gun more "compact" if i just use the steel plenum i´ve already made and install that to the utmost rear underside of the stock bottle.
But?
Won´t that look kind of cramped?

Well. Give it a moment to sink in.. cause see, what this gun ALSO lacks is some manner in which to put a bi-pod and what not on there.
So what i´m entertaining here is the idea of what i did to the bottle/cylinder on the Artemis CP-2 i made into a PCP gun. Weld the bracket needed to the plenum (in this case) and thereby.. i´m not so sure the final product would look all that funky when done?

You guys tell me. That plenum is on a diameter of like 35mm or so (1,37")

No matter which i NEED plenum volume to push on..

https://i.postimg.cc/NFsFD6JT/18.jpg

Yeah, ok. So things have progressed a bit.
First up. Moved the entire shop of mine, one MASSIVE undertaking. In short the surroundings are going to look a little different hereon.
Gave LOADS of thought how to implement a plenum "for trials". Being all to aware of the difference to be had..

https://i.postimg.cc/NMYjG8wV/19.jpg

No. Not the most ideal of solutions, but truth be told one of the few that let me do this "for trials". I simply removed the pressure gauge for regulated pressure and took it from there.
The pressure gauge then being reset to the front of the plenum. This extra plenum coupled with the stock 11cc´s handed me about 90cc´s total. Should be more than ample for the task at hand.

https://i.postimg.cc/28ttQZD6/20.jpg

A temporary setup or no i fabbed a sorts of bracket to keep things in check out of aluminium.

So.
First hit. Yep. At first i reached the same energy levels as on the stocker now using a mere 130-135bar on that stock Mickey Mouse gauge.
That done i turned the screw of the pressure regulator aaaaand....Now i saw an easy 1020 or so using 33,9´s and this at a way more sane 160 bar vs before.

In short, that plenum sure did what it was supposed to. However. I didn´t get the increase i thought upping the pressure even more, when i dawned on me that the porting job i had done on the piece.. so long ago i couldn´t recall where i left off dimension wise!
So apart the thing came. Indeed. Porting job was far from finished, and this time out i arrived on a "full port" job. Ie; 6,5mm transfers.
Now.
There´s a caveat, sorts of, to this and that´s that the valve body housing is placed such on the main block (same for the P-15 and P-35 btw) that at 6,5mm you´re really pushing it.
As it turned out, more then i cared to realize.

Yep. All of a sudden all that wonderful pressure just... went AWOL.

https://i.postimg.cc/nhh21zbh/22.jpg

Right. So the valve housing is one thing right. It seals vs the main block via an o-ring. Nothing strange there.
The issue at hand is that the transfer port of the main block is placed so close to that o-ring that already on 6,5mm transfer port diameter the "upper" part of the support structure for the o-ring collapsed under pressure, ripping the o-ring apart in the process.
So what i did was turn a "helper" shim out of steel. In short this "shim" goes down first thing in the cutout for the valve assembly and thus becomes a support for that there o-ring to seal the valve body vs the main block.
I´m here to tell you it works golden, so back together with the gun right.

https://i.postimg.cc/zvW66dFv/23.jpg

https://i.postimg.cc/zDRsyBYN/24.jpg

The bracket for the picatinny i welded to the plenum. Bad move as it simply places the entire thing to "low" and due that makes the bi-pod sit such that it turns the rifle a bit to high.
So since i just relocated that to a clamp that sits on the actual bottle instead, way better. In turn that Harris copy rides WAY higher than an Atlas so guess what.. LOL.

The now more mainstream ports did their fair share. I now had them 33.9´s out the muzzle at an easy 1050-1060 and seeing the rather short barrel i wouldn´t be surprised if ME´s rise even more using 40 grain pills. Just haven´t gotten around to that yet...

Happy n content then?
Not quite just yet. I´ve dialed the thing in reasonably and it shoots well and shoots hard, for an airgun pellet/slug rifle. Going to pull yet a few stunts before calling it done though... This entails both increasing throat diameter of the seat as well as a new design moderator and what not. Going to investigate a more "designed" rate hammer spring and then in turn a SSG setup. The latter mainly to increase efficiency.

On a general whole however this little story tells a thing or two on the importance of plenum chamber volume as power goes up for any given PCP as far as i´m concerned.
That power jump i´m absolutely positive will end the north side of 120J which in short tells that on THIS gun for a given pressure there´s approx 30J to be had from added plenum volume alone. Fairly stiff numbers IMO.
It is often said that one should calculate for 10cc´s worth of plenum for every 10fpe increase in power. As to how that holds water or not it´s still a testament to the importance thereof.