avenger pressure question?

[GerrywithaG]

First off, Hi everyone! I am back into the Air world after finishing a 3 year commitment in 22LR Benchrest, and WOW have things changed in a short time!

Anyway, I picked up a wood stock 22 Avenger to have a test rig to re-fit my kit, shop, comprressor, tooling, targets etc. and here's my question. After a refill with the reg closed, my lowest possible setting is @1500psi, and with the reg at 1800 psi and the hammer spring all the way out...left turn..., I am shooting JSB 18.13's at 920fps? Hades 15's are smoking at like 965fps at 1500reg/h.s. full out? I dunno? My chrony could be off, but I don't think so. H&N Cuda 21.14's at 2000reg/2 turns in h.s.are at 890fps. Anyone else have this issue? I mean I can't go low enuf IMO? Thanks, and good to be back in the Air World!
Gerry

 

[Gerry52]

Gerry, welcome back! A LOT has come about in the last 3 years, hasn't it?
Gerry

 

[JimD]

I have a plastic stock Avenger in 25 caliber. I just looked at the gauge on the regulator and it changes from yellow to green about 1500 psi. Is that why you say "the lowest possible setting is 1500psi? The color on the gauge? I am asking because I am pretty sure I changed mine down to 1200 psi initially and then went up from there.

Second question. If you just cannot turn the regulator any lower than 1500 and you are shooting too fast with it at 1800 why not turn it down to 1500? I know that means degassing but once you are low you can go higher if you need to. Initially I degassed my gun without even shooting it and set it to 1200 if I remember right and then checked what the velocity was. I am not at about 2100 and have never shot mine at higher than 2400. It came set to like 2900 and I knew I did not want to shoot it there.

You may also need to find the maximum velocity you can achieve at a given regulator setting with a pellet your gun seems to like. That is important for tuning. You increase the hammer spring until the velocity stops going up and then back off about 5% or a bit less on velocity. I check group size as I go down. You might want to decrease the regulator first unless you want to shoot heavy for caliber pellets, however. Your choice.

 

[GerrywithaG]

Your right Jim, I didn't make that clear enough. If I empty the air chambers fully, close off the reg., fill to about 4200psi, then only crack the reg til air starts to flow, the minimum setting is 1500psi. And I'm talking about cracking the reg open slow and til the reg guage starts to move.

I pulled the reg out and replaced the o-rings, and the bottom gasket looks good. Next I am thinking of opening the reg to clean inspect and lap the plates.

The other oddity is with the reg set at 2000psi, I fire a round, the reg will go down to about 1600psi then slowly work its way back up to about 1800psi what I call the "string" reg setting where you might shoot at a competition cycle time. Seems odd to me?

Thanks for the help!
Gerry

 

[JimD]

I don't remember seeing my plenum fill slowly like seems to be the case for you. One of my pet peeves is the gauges on the plenum, however. I am confident they are very inexpensive (maybe $1) and not terribly accurate. So when you see something funny on the gauge it's hard to say if it is the gauge acting weird or the gun. I would fire a few shots quickly over a chronograph and see if the velocity drops. If it does, then the plenum is not filling normally. There could be an obstruction. But if the velocity stays relatively constant, within 20 fps, and isn't decreasing I would conclude it is just the gauge.

If the plenum is filling slowly then it is probably the seal at the top of the washer stack or maybe something in the small opening it seals. I have not taken my Avenger regulator apart but two others I did dissassemble had a snap ring on the bottom and once that is out of the way I had to put a bolt with the right threads in the end to pull the assembly out. I used a tap the second time just because it was handy and the right thread. One of the regs I took apart was a Huma with globs of silicone grease on the washers. But none on the O-ring sealing the adjustment screw. With that resolved it works great. If you pull the washer assembly out there will be at least one additional O-ring I think. I would just take a picture first so you know how they are arranged and then make sure the washers are lightly lubed and the hole into the washer area is open. I don't know if a light coat of silicone is best or whether graphite might work better.

 

[GerrywithaG]

Well, I got an idea to fix the pressure change happening, so I shot groups with my gamer ammo this morning to establish a baseline. My luck the JSB18.13 shot 2 back to back groups n the .400's at 75yd my best to date. The JSB15.89's are almost as good. A little too much breeze for them,but MOA.

So I went out to the shop and turned a plenum. It ended up being 17.5cc and made from 1-1/2" 7071 Aluminum. What it did was now when I fire a round it goes from a reg set of 1700 down to 1600 and back up to 1700 in less then 40 seconds. I;m good with that! Hopefuly no wind this weekend and I can get some testing done. It looks hopeful!
Have fun,
Gerry