My road to regulation - warning - long post

[curlyjim]

Hello everyone. I've been on the Yellow for a short while now, but just registered for this site a few days ago.

I've been shooting 10m air pistol for a couple of years, but started shooting air rifles late last spring. Mostly I shoot powder guns, but since I can shoot air guns up to 40 yards in my back yard, it's really nice to just step outside and do some shooting. My interests are mostly in target and field target, although there are no field target matches around where I live (SW Utah) that I know of.

I have a gen 2 Marauder in .177 that I've been tinkering with for several months. Boy, there is a lot to learn about air guns. I got it shooting pretty well using both the A-team method and the bStaley approach, but was still curious about how it would do with a regulator. There is a lot of info on this site about installing regulators, but a lot of it involves machining valves and otherwise permanently altering the gun. I wanted to see how much performance I could get without doing anything that was irreversible.

So, I started a new project to put a regulator in my Marauder without doing anything that wasn't reversible. I thought I'd post what I accomplished in case others are thinking along the same lines.

My goals were:
1) maintain 16 to 17 fpe power level
2) increase the number of shots per fill
3) decrease the velocity spread across a shot string (previously 25 to 30 fps)
4) maintain or improve accuracy

I started by watching a number of the Robert Lane videos on Youtube and by searching the forum for posts on regulating an air rifle. Lane has a LOT of info out there on regulators. Also, major kudos to everyone here who likes exploring the boundaries of performance and shares what they have learned. It's an outstanding resource.

I decided to put a regulator where the pressure gauge block was and use the gauge hole in the air tube as the vent hole. I bought a Lane regulator with an integral standoff that positioned the vented area across the gauge hole and provided some additional plenum space behind the regulator. Mr. Lane set the regulator to 120 bar as a starting point and this is marked on the regulator so I can return to it if I want.

The first configuration follows:
1) .177 caliber gen 2
2) stock valve (internal volume is 3 cc and counts toward the plenum volume)
3) transfer port screw 4 1/2 turns out with plastic tube mod. (a 9/64 inch drill just fits into the valve port hole and barrel hole, so the port diameter is about .140 in.)
4) stock hammer and spring
5) Lane regulator set at 120 bar (standoff volume is about 4 cc)
6) Estimated plenum volume is 7 cc
7) Estimated reservoir is about 212 cc as the regulator is not much bigger than the gauge block it replaces.
8) 3000 psi fill pressure per my Hill pump gauge.

The first tests gave me a maximum velocity of about 940 fps with JSB 8.4 pellets. No amount of hammer travel and spring preload would increase this. I backed the hammer energy down to the minimum needed to get that velocity and got a shot string of 52 shots with an ES of 23 fps. There was a hump in velocity where the gun came off the regulator which added a little to the ES and showed that the regulator pressure was too high. Ending pressure was about 110 bar.

I figured that there was probably a lot of hammer bounce and Lane recommends a lighter hammer when using a regulator. The stock hammer is very heavy (about 76 grams). I read about Motorhead's development of a lighter weight hammer so that seemed like the next logical step. I also figured that some factor was limiting the power I could get, i.e. transfer port size, plenum size, or constriction in the valve. So I ordered a 28 gram hammer and figured out that I could also increase the plenum size by 1.8 cc with some additional standoff.

I installed the new hammer and standoff and had to adjust the hammer spring to 6 1/2 turns cw to get a maximum velocity of 925 fps with JSB 8.4 pellets. But I did get 80 shots with an ES of 20 fps. There was also still a hump as the gun came off the regulator and I thought 6 1/2 turns on the spring was somewhat high and a bit harsh.

Motorhead had mentioned in one of his posts that the valve spring in the gen 2 Marauders was a lot heavier than in the gen 1 guns. So I thought I would try to remedy this.

The gen 2 valve has a threaded plug that retains and compresses the valve spring. It was a simple matter to drill and file a washer that would shim the plug and reduce the spring compression. I used a metal washer I had on hand and it turned out to be .065 inches thick. This was used to shim the plug and the amount of force needed to unseat the poppet was considerably lessened. I also decided to reduce the regulator pressure to about 115 bar to see if I could reduce the hump.

Changes for the third configuration are as follows:

1) 28 gram hammer and stock spring
2) additional standoff adding 1.8 cc
3) .065 shim under the valve plug.
4) Estimated plenum volume is 8.8 cc
5) Estimated reservoir is about 210 cc
6)Full hammer travel and start at 6 1/2 turns cw on hammer spring

As luck would have it, this was a pretty good guess. I could now get about 950 fps with JSB 8.4 pellets. At this point I decided to switch pellets and adjust the velocity to coincide with data Motorhead had posted on one of his .177 regulated tunes. That way I could do a direct comparison and see how I was doing. I switched to JSB 10.3 pellets and eventually backed the hammer spring down to 3 1/2 turns cw from full out. This gave me an average velocity of 855 fps and kept me above 16 fpe. The hammer strike was also much less jarring.

The first shot string I did, starting at 3000 psi gave me:

JSB 10.3 pellets (unsorted)
98 shots
avg velocity 855 fps

ES all 98 shots – 16 fps (1.9%)
ending pressure about 1500 psi
65 deg. F.

The string still has a slight hump after it comes off the regulator, but things are looking good. I might be able to improve the tune, but this is pretty good for now.

I did check the accuracy using a 12 shot string using an OnTarget TDS target. Accuracy with the 10.3 pellets seems a little better than the pre-regulated accuracy of the gun. I'll do some testing at longer distances when the weather warms up.

JSB 10.3 unsorted pellets
855 fps
10 yds indoors (winter here now)
12 consecutive shots, 2 shots as called fliers
1.367 moa for 10 shots
width 1.242 moa
height 1.328 moa

So, I'm very pleased. All goals met.
Thanks to Mr. Lane and to Motorhead for excellent products.

[Motorhead]

Takes a bit getting there .. but given the tweak time you done good !
Under 2% for 98 shots at that power ... AWESOME !

[SHOOTINIT]

if you are just shooting paper i would drop the fps..i get around 200 shots at 650..

[RayK]

You should try the AA 10.34 grain pellets.

At least in my 177 M-rod with stock barrel, they are *very* consistent - more so than the JSB pellets of the same weight.

Or you could upgrade to an LW barrel which seem to prefer the JSB pellets.

Ray

[curlyjim]

Motorhead - Thanks. It helps a lot when others have blazed a trail. I got pretty lucky on the valve shim thickness.

Shootinit - 200 shots would be tempting and would probably feel like I was shooting forever on a fill. But I think I want to keep it set up for FT so I can practice for a bit. It tends to be windy here, so velocity is a plus.

RayK - I have a couple of tins of AA 10.34 pellets. I'm going to do some careful testing of promising pellets. Mr. Lane mentions in one of his videos that a gun may change it's preferences after being regulated. Time to have a look-see.

Curlyjim

[sr1sws]

Hmmm... I may steal the shim idea for use on my Gen II SynRod in .177.

I have the AGE Huub regulator in mine with a Motorhead lightweight hammer. It's spitting JSB 10.34 grain 'heavies' at about 710 fps. Regulator is set to about 1600psi. I get 50 shots from 2100psi fill (I fill from SCUBA, so low fill pressure is one of my goals/desires/constraints). I have 4 magazines, so I usually just shoot 40 shots.

Right now, it shoots the JSB heavies the best. I do have some AA heavies too. They shoot to a slightly different POI. I have not evaluated if the JSB or AAs group best. Offhand, I'd say they are about the same.

I need to re-chrony and see if anything has changed/drifted since I set it up about 3 weeks ago. I have not really tested for velocity consistency as I was pushed for time when I got it set to where it is now - and I guess I've been too lazy to re-test.

Unfortunately my normal backyard range is only about 50' and my longest possible is 60', so no long range accuracy testing for me.

I guess it's time to tinker with it some more

Steve

edited to state velocity as 710 fps instead of 850 fps. It shoots about 710 for 10.34gr heavies, 850 for 8.4gr 'mid-weight'.

[curlyjim]

Sounds like your setup is a lot like mine. I would definitely try the valve shim. I think the stock spring is too heavy for the light hammer and it just won't perform as well as it could. The lighter valve spring balances things better. Also, the hammer spring tension will be a lot less. For me that meant a lot less jarring of the rifle when shooting it.

My rifle likes JSB 10.3 pellets pretty well. The AA 10.3 pellets shoot just as well, at least at close range. It also likes the JSB 8.4 pellets, perhaps slightly better than the JSB 10.3. My vote goes to the AA 10.3 because they're cheaper. I'm going to do some longer range testing when the weather improves.

My fill pressure is 3000 psi. The shim improved the shotcount a lot. I don't know how much you might improve yours. I'll have to try filling to about 2100 psi and see what I get so we can compare.

Curlyjim

[sr1sws]

I finally made a shim to reduce the Gen II valve spring tension. I made it from delrin and it is about .070" thick.

Today I re-tuned the gun for about 13fpe. My SCUBA tank is low, just below 2000psi, so I just tethered for the tuning. The AGE/Huub regulator is set for about 1500psi. I also have a Motorhead lightweight hammer in the gun.

I started from 'zero' on the adjustments. I wanted about 755fps using JSB 10.34gr 'heavy' pellets. With settings at zero, shots were running about 738fps. One turn of the 1/4" (hammer spring) got me too fast (sorry, didn't record the fps) - adding 3 turns of the 1/8" (stroke) adjustment got me to 755fps.

I then continued with the 1/8" hammer stroke adjustment to improve efficiency. Velocity climbed a bit and then settled back at 751fps with 6 turns of the stroke adjustment.

Prior to the shim, I was able to fill to 2100psi and shoot for at least 40 shots before coming off regulation. I un-tethered with the gun filled to about 1950psi and shot for 40 shots and was still on regulation. I need to re-test, but it appears efficiency is up and with ES at 13 or less than 2%, I'm pretty happy with the tune at this point.

Steve

[curlyjim]

Super. Glad the shim worked out well for you and thanks for confirming the .065 to .070 thickness. I would have used nylon or delrin for a shim too, but I didn't have one handy. 40 shots with a low fill pressure is great. One of the nice things about a regulator is that you can fill to any pressure up to 3000 psi and get more shots without anything else changing much. At 13 fpe you should be able to get over 100 shots from full pressure.

curlyjim

[sr1sws]

Yup, pretty happy with it.

I started with a Disco and fill from SCUBA, hence the "low pressure" fill. I have 4 magazines, so it's easy to keep track of my shot count/refill point at the lower pressure too. Yeah, I'm wasting air from the hose (I don't believe it's a microbore) by refilling more often, but the air is very cheap in comparison to the pellets.

Got my tank filled at lunch... probably won't be able to test after work since it's pouring here.

Tinkering is fun

Have a great day!
Steve