Dynamic .25 cal PCP - First Impressions and Observtions

[Gertrude]

I assume that the cap screw at the top of the trigger is not an adjustment point but just holds that block in place?

You assume correctly. That block will get polished on the face, as it is what engages the Sear for second stage.

[Wayne52]

Ron have you measured the length of the barrel yet?  My DAR seems to be shooting much more accurate with my cast pellets than my Mrod does.

[Gertrude]

Ron have you measured the length of the barrel yet?  My DAR seems to be shooting much more accurate with my cast pellets than my Mrod does.

Have not removed shroud or barrel yet. I think they may have used a gallon of locktite on it. 😒😱😞
Will try to get it apart today after it cools down some here.
Yeah, I'd say mine shoots at least as well as my Mrod too.
Pretty impressive performance considering the price point.

[Gertrude]

Ron have you measured the length of the barrel yet? 

Barrel is 17" from leade to crown.

I was fairly surprised to see how heavy the barrel is. It is .585 OD, and unchoked.
 (I still have not checked the twist rate, sorry).
 The TP is machined into the side of the barrel and measures .221
 The barrel is sealed to the breech using a o-ring forward and aft of the transfer port.

 On the muzzle end, the last 1" of barrel is .355 OD to allow for the slip-on Shroud Support. It does not have a traditional "Air Stripper". It is more of a Vented Shroud Support, that allows air flow between the barrel and the shroud.
As the pellet passes through the first baffle, it would basically be doing the same thing as a typical Air Stripper.

[Gertrude]

Here' some more pics of the innards,




The Regulator looks to be well built and is externally adjustable for output pressure.
  I will be adjusting this for a little greater output pressure before reassembly. Unfortunately, I do not yet have a test rig yet for setting output pressure, so I wont know the actual pressure I change it to, and will just have to rely on chrony readings and shot strings. Maybe Bob will be able to apply some mathematical wizardry once I get those numbers to compare to the first shot strings.



The Plenum is a simple straight piece of anodized(?) aluminum.
 It measures .830 ID and is 1.570 long

[WiseGuy]

Great work so far Ron, keep it coming brother...once you figure everything out, I want one too!  That valve looks like a Cricket one...very similar. Nice work and great pictures too.

[TleVta]

I want to buy one and put a 13 c.i. Ninja bottle on the air tube. But I gotta finish my motorcycle project, first. Then again, I could wait until the .25 Gauntlet comes out. Bike may be finished by then..

I do like the DAR since it has a side lever, and the Gauntlet does not.

[rsterne]

Thanks for the pics of the internals.... It looks like the regulator fits inside the plenum a short distance, maybe 0.2"?.... That would result in a plenum volume of about 12 cc.... Do you have any idea how much volume there is inside the valve, or the back of the regulator, which would add to that plenum?.... That's pretty small for a .25 cal, IMO....

Bob

[Gertrude]

Thanks for the pics of the internals.... It looks like the regulator fits inside the plenum a short distance, maybe 0.2"?.... That would result in a plenum volume of about 12 cc.... Do you have any idea how much volume there is inside the valve, or the back of the regulator, which would add to that plenum?.... That's pretty small for a .25 cal, IMO....

Bob

Yeah, I'd guess about 0.2 .
 Unfortunately, I put the gun back together tonight before seeing this post, so I cant measure it right now.
 I'll be shooting it tomorrow to test out my polish/lube job on he trigger, as well as my adjustment to the reg.
 No doubt, I'll be taking it back apart after this weekends testing, so I'll try to get you those measurements next time it comes apart. I did feel the plenum was a tad small too, once I saw it.
 
Here's some picks of the valve before I put it back together.

Upon removal of the valve, I did find the Brass Pin Guide to be loose, as well as the Retaining Cap for the Poppet Spring (on the opposite end of the valve). I will be using some blue loctite on reassembly to prevent this happening again.
 The exhaust port is pretty big, measuring .223 - .224 . Next time I have it apart,I will do a little Dremel work to radius the bottom of the port to the throat of the valve.

 The valve slides into the monoblock, it i sealed with 2 o-rings, and is held in place with two indexing screws on the lower side. One screw doubles as the Stock Mounting Lug. This makes the port alignment to the monoblock a easy no-brainer. The port in the monoblock meas. .223, and the port in the barrel meas. .221




The hole on the "shoulder" of the valve is a pressure bleeder for Degassing. It has a grub screw plug.



Nothing exotic going on inside, standard Poppet and Spring.
I will say, the Poppet Spring in this thing is SERIOUSLY STIFF ! ! ! (too stiff IMO), but we'll mess with that at a later time.
 The Retainer Cap (valve inlet) has 4 (small) holes. I think they can be opened up a little more, which we'll also do later.
  I did notice the Retainer Cap does not have any sort of pin/groove/shoulder/etc. to keep the Poppet Spring on center. I see this as a potential problem as it allows the Poppet Spring to go off-center, and thus, applying a side-load to the head of the Poppet.
 This could be something that needs to be addressed in future models.




Here's a nice little feature,
The hammer tube in the monoblock, is "lined" with a hard plastic/delrin(?) sleeve. This prevents the steel hammer from touching the aluminum monoblock. Pretty cool, I think. No internal "marring" or damage to the monoblock, and very slippery slide for the hammer.

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[Wayne52]

Thanks for great pictures and excellent descriptions Ron !!!   I wasn't even aware that this had a delrin() sleeve in it, that's pretty darned neat, you'd never need an MDS hammer on this one.  I might add DO NOT DRY FIRE THIS GUN without air because through my experience of doing just that I damaged the brass bushing for the valve stem, I ended up removing the mushroomed part (I.D.) where the hammer hit it with a jewelers rat tail file.   That actually happened soon after I bought the gun and hasn't been a problem since but it was still a PIA. All in all it really is a fantastic gun for the price, they need to be tinkered with though.

When I think about just how many non members (a lot) that read these threads on this forum it makes me wonder just how many of them buy these guns.

I might also add from your measurements it appears that the ports on this gun are already above being 85% of the bore, that also is really nice to know, it's something I never measured when basically I was more worried about sealing the gun up at the time, the 25's really do generate some great energy. 

On my 177 the barrel port is .133 and it could probably be opened to .150 but for now I'm happy with it, it's slinging the 16 grain stuff very well.

[Gertrude]

Ok, next installment,
So I did some minor polishing of all contact surfaces in the trigger group. Big improvement on making it feel smoother, but still very heavy second stage. I will be taking it apart again to do an even better polish job, and I will look for a lighter spring to install for the second stage.

While I had it apart, I adjusted the pressure regulator by 1/4 turn to increase the output pressure. I do not have a test rig set up, so this was a complete guess and I would only be able to test the results over the chrony.




 (Prior to me adjusting the regulator), it was pushing JSB 25.39gr at 885-890fps , and 33.95gr at 760-765fps with a 3000psi fill

 After adjusting the regulator and reassembling the rifle on friday evening, I filled to 3000psi and shot the 33.95gr at 898-901fps. I loaded up the truck to meet the guys on Saturday morning, and left 3000psi in the gun.
 Saturday morning, I set up a different chrony, and duplicated the same 900ish fps for 3 sets of 10 shots.
  We got busy with several different guns and I set the gun aside for the rest of the day. I did not shoot it again until Sunday.

 Now this part may be my ignorance of typical regulator behavior, or it may be something else (?), I dont know.

  Sunday, I shot a few more 33.95gr at a 3000psi fill and found it had dropped about 100fps ! (?)
 I found that strange since it had done 900 over 2 separate chrony's already.
 Could this be what is referred to a the reg is " settling in " ? ? ?
 I decided to start at a little higher pressure to better determine where we were coming off of the regulator.
 Here are the results for both 25.39gr and 33.95gr (after adjusting the reg output).





By the time I got done with the chrony work, the winds had picked up to 13-15 mph, and I could see no sense in trying for more 50yd groups in that much wind. I'll see if conditions are better next weekend.

So can anyone here explain why I dropped 100fps after letting the rifle sit overnight ?
 Is this the regulator "Settling in" ?

btw, I did not replace any of the o-rings upon reassembly. I used the original factory o-rings, and to my surprise,... No Leaks ! YAY !

[nervoustrigger]

Ron, generally a new regulator will not shift downward in pressure, the obvious exception being that the adjustment screw self adjusted somehow.  It's more likely to shift upward as the seal wears in against the valve seat.  That is, it becomes indented or takes a compression set.  What is happening is the spool (or piston if you prefer that term) is having to travel further before it meets the valve seat, thus the air pressure must build to a higher level to compress the spring by this additional amount. 

Factors which may aggravate this are:
a.  If the valve seat has a raised lip.
b.  If the seal material is soft and/or prone to take a compression set.
c.  If the rifle experiences a major temperature increase.  For example, if the rifle was last fired at a modest temperature (70F) and then subsequently left in direct sunlight or a hot car, the plenum pressure increases and more forcefully presses the spool against the valve seat and deforms the seal material.

Therefore...

If this sort of "settling" has occurred with your rifle, you may need to bump up the hammer spring tension to bring the velocity back up to where it was.  That is especially likely if you had adjusted the hammer strike to not be wasteful of air.

[Gertrude]

Jason,
Thank you for the very I formative explanation. I am certainly not an expert on internal regulators.
(I've never taken one apart to see the internals), but will probably do so soon.
Judging from your explanation, I suppose the temperature may have had a factor, as well as the possibility of a soft seat.
The first time I got 900fps was in the evening at about 75 to 80 degrees. The following morning when I saw 900fps again it was about the same temp.
When I then set the gun aside in the rack, it did see so.e sunlight and the day did get up to maybe 90 to 95 degrees, so if it was directly in the sun, it would have gotten even hotter. Follow that with sitting through the night with whatever pressure it had climbed to.
So I suppose a seal may have changed shape under heat and pressure (?).

Also, I had already noted how incredibly stiff the poppet spring is inside the valve. Waaayyy stiffer than it should really need. So with a very stiff poppet spring AND increased reg output pressure, it stands to reason the need for more hammer strike.
But, then again, that would not explain the first two rounds of 900 fps. Hmmmmmm.

I do have an assortment pack of various springs. What do you think about me trying a lighter poppet spring in the valve, before trying to increase the hammer spring tension ?

If I get some time tonight, I may try to take the reg out and do some disassembly and home ed-u-ma-kate-shun 😜.

[nervoustrigger]

Don’t waste your time with the valve spring.  Even a very stiff one has very little effect compared to the air pressure holding the valve closed. 

Do it with the hammer.

Sorry so brief, not much time.

[Gertrude]

Don’t waste your time with the valve spring.  Even a very stiff one has very little effect compared to the air pressure holding the valve closed. 

Do it with the hammer.

Sorry so brief, not much time.

Aye aye Cap'n, will try it.
Thank you

[Gertrude]

just a little update,
I've not had time yet to take the gun back apart, due to other obligations. Once I do, I will be trying Jason's suggestion of increasing the hammer spring tension. I will also be looking for a conical spring for the poppet to provide a straight tension/push  for closing the poppet. Other owners have stated they already have a conical spring, and that it should help to prevent a broken or bent poppet head.

Earlier today, I learned that the other 4 rifles my group has ordered, has arrived and we will be testing them this coming weekend.
 I guess I better get off my tail and get busy. The guys I shoot with will be expecting me to have this stuff all figured out.
They can be pretty brutal and find no greater pleasure than to pick on me and hurt my sensitive and tender feelings              
Bwa-hahaha !

It will be very interesting to see how many of these next 4 rifles will have any (or all) of the leaking (or other) issues that some folks have already experienced.

 I wish I had a trigger weight scale to measure trigger pull weight, but I don't own one. Maybe one of the guys do, and we can get some comparative numbers going on that area of interest too.

[Rat Sniper (AKA: PaulT58)]

Bring a bag of #117 Dura 90 o-rings and a set of hex keys with you, that should fix most if any issues they may have.  Besides replacing the o-rings check that both ends of the valve assembly are tight, those two thing pretty much fixed my air leaks.  I'm looking forward to hearing how things go, have fun!

[Lastdog]

Just joined the group. I have a DAR 22. Knock on wood every thing is working good. Thanks to you guys I bit the bullet and bought one. For me it was a great deal. Been shooting it about a week and I love it.Thinking of giving it to my son and getting the 25. Holding back to see how the 22 holds up. I would be more inclined if I could get at least extra mags. Anyone been able to buy extra mags yet?

[Gertrude]

Per a recent communication with Aim Sports, the mags did not come in from China as they were expecting. They said that the mags are currently on the slow boat, and should be available in about 3 to 4 more weeks. Nothing they can do to get them any faster from China.

[Wayne52]

Ron the only other option would be Fedex like SPA does but that's much more expensive.  It would be cost effective if a person ordered a dozen of them direct from China factory but that too is unknown right now.  When SG sent me a Fedex return deal for my 25 I thought to myself, yeah and start over again, I don't think so.  I should have told Ryan about my crack magazine too but didn't think about it at the time when I sent the email about the barrel band and corroded stuff.