392 upgrade suggestions (Mac1 parts?)

[35 shooter]

Yep, felt to the wood on the handle for me!

[Hack21]

Buddy,

Thanks for the confirmation on the felt placement.  It seems like your steroid is treating you well.

Charles,

Thank you for the picture.  I had seen this from Bob's 392 thread a few months back.  Otherwise, I wouldn't have known what adjustment was typical as no instructions were provided by Tim with the kit.  I would liken the pump effort when the cup hits the valve (adjusted this way) to the force required at 2 pumps normally.  So there is a lot of force being applied to the pump cup and valve, but far less than what it will experience at 8 pumps.

I am leaning towards removing 1/8" from the inlet check and reusing the valve spring.  This will reduce the check valve spring rate by 25% and reduce the hammer energy that it can absorb prior to the hammer contacting the valve body by 20%.  There would still be 7.5 lbf applied to the poppet and check.  This should be enough to seal well and allow pumping without first cocking due to the 4lbf that the hammer spring applies to the valve stem. I am hoping I can then back down the hammer spring so that it will only dump 8 pumps as I am more interested in efficiency and longevity on this one than doing a lot of pumps and having a loud report.

[Hack21]

Here are my valve pictures. Nothing earth shattering here. I removed an 1/8" step from the check valve. This reduces the closed force from 10# to 7.5#.  The check valve seat is 0.28", and so the check pressure is reduced from 163psi to 126psi (25% less).  The two spring mod could potentially reduce this much further, but at the compromise of extra complexity and greater likelihood of leaking.

I also packed the valve by adding material to the check valve. I used a #6x1" brass screw and a used check valve for this purpose. The valve volume is now reduced by 10%.  According to some of Bob's plots, this should increase efficiency by about 7% at the expense of loosing 4% of power.  The report should be improved since the residual pressure and volume at the muzzle for any given velocity will be reduced.

The poppet valve is from a discovery. I ground the stem to 0.125" to increase the passage area so that the transfer port is now the smallest passage (which I increased from 0.156" to 0.160").  I ground an angled port onto the valve and lapped the poppet to the seat to remove a nick. The orings are polyurethane.

[35 shooter]

Looking good!

[Hack21]

Results with 14.3gr CPHP:

Pumps / fps / fpe
1 / 294 / 2.7
2 / 430 / 5.9
3 / 504 / 8.1
4 / 564 / 10.1
5 / 607 / 11.7
6 / 643 / 13.1
7 / 673 / 14.4
8 / 692 / 15.2

14.0gr Meisterkugelns 515fps @ 3 pumps
18.1gr JSB 645fps / 16.7fpe @ 8 pumps

I didn't do the third o-ring mod (no lathe) and suspect that would have gotten it to 700fps on 8 pumps with CPHP.

These results are with a Raymond C0300-035-2250-S spring installed for the hammer. It is retaining a small amount of air, but it cocks much nicer with the 5.4# spring than with the factory 7# spring. The lighter spring improved the trigger as well.  It doesn't require cocking prior to pumping and held 2 pumps over night just fine.

It is making roughly 18% more power per pump than when stock mostly through efficiency gains. I can now shoot wadcutters in the low 500s on three pumps.  6 pumps now is equivalent to 8 pumps from the factory.

I compared the results to other published steroid results and these are slightly better at 5 or fewer pumps due to the decreased valve volume. 7 or more pumps and the steroid is still king.  I don't plan on going past 8 pumps with the packed valve and my AS392 HPA is shooting 17.5fpe so the pumper compliments it better at 3-16fpe anyway.

The Mac1 parts are fantastic.  They did add 5.5oz of weight and it is noticable, but not bad and absolutely worth it.  The steel front plug adds 1.6oz at the maximum distance, so if it was a concern for someone, they could use an aluminum factory plug to save weight. 

I am happy with the disco poppet with the shaft ground to 0.125" as a simple upgrade. 

[Tack Driver 10]

Those are great numbers for the mods you've done.
A highly modded valve should get you in steroid territory.

For reference, here's 2 steroid 392 results from the web:

#1:
CPs 14.3 grn:
4 pumps 565, 569, 563
6 pumps 658, 658, 660
8 pumps 728, 732, 731
10 pumps 762, 778, 772
12 pumps 814, 819, 814
14 pumps 840, 841, 840

Gamo Rockets 14.2 grn:
4 pumps 553, 552, 546
6 pumps 645, 644, 644
8 pumps 727, 725

JSBs 15.9 grn:
4 pumps 548, 547, 555
6 pumps 629, 638, 638
10 pumps 748, 757
13 pumps 812, 808

Daisy wadcutters 13.6 grn:
4 pumps 573, 573, 565
6 pumps 664, 665, 667

#2:
After the upgrade you'll get slightly higher velocity per pump but the gun can also be pumped to as many as 14 pumps without wrecking the gun (like you do with stock ones) and more importantly it will dump all the air with the shot (which stock won't) meaning you can nearly double the delivered energy to the shot. IIRC using heavy pellets and 14 pumps you get way past 20 fpe. You can make 20 fpe (800 plus fps) with normal 14.3 grain pellets like CPs if you like that kind of stuff.

2pumps-418fps
3pumps-494fps
4pumps-564fps
5pumps-599fps
6pumps-650fps
7pumps-687fps
8pumps-707fps
9pumps-723fps
10pumps-757fps
11pumps-772fps
12pumps-783fps
13pumps-799fps
14pumps-812fps

[Hack21]

For reference, here's 2 steroid 392 results from the web:

Ron,

Thanks for the data. That #1 set is hotter than I had seen elsewhere. The #2 set is closer to the others I had seen.

Tim says the inlet check valve is the weak link and Bob's calcs determined the valve retention to be appropriate up to 1200psi with the factory retention. Since I kept the factory check and packed it to have higher pressure per pump, I was only planning to go to 8 pumps.  The steroids address this with greater valve volume and a better inlet check (and possibly lower margin than Bob was aiming for).  I don't think my back yard would tolerate the sound of 14 pumps from a steroid!  I will probably do most of my shooting at 2-5 pumps and occasionally go higher.  It would be interesting to know how much gain that the additional o-ring would have yielded.

I am very impressed with Tim's pump kit. It is rock solid and very smooth and surprisingly much quieter on close up.  If anyone prefers to diy and is on the fence, I say do it.  Probably using Tim's inlet check and a disco poppet could be a good option for steroid-like results (with porting, pump kit, and o-ring). 

[Tack Driver 10]

The Mac1 steroid parts are top shelf for sure.
I put one of his billet arms in a 312 awhile back and it's one hot tamale.
Has a smaller valve volume than the 392 but strong up to 10 pumps.

I started modding a 342 that will be a similar build.
Should start posting it here in a few days.

Here's the 312 mod:
https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.0

I don't have a 392 but picked up a few valves to mod.
This one is a FT with a 1/8" Delrin stem, concave seat, ported TP, light spring etc.

[Psipumper]

For reference, here's 2 steroid 392 results from the web:

Ron,

Thanks for the data. That #1 set is hotter than I had seen elsewhere. The #2 set is closer to the others I had seen.

Tim says the inlet check valve is the weak link and Bob's calcs determined the valve retention to be appropriate up to 1200psi with the factory retention. Since I kept the factory check and packed it to have higher pressure per pump, I was only planning to go to 8 pumps.  The steroids address this with greater valve volume and a better inlet check (and possibly lower margin than Bob was aiming for).  I don't think my back yard would tolerate the sound of 14 pumps from a steroid!  I will probably do most of my shooting at 2-5 pumps and occasionally go higher.  It would be interesting to know how much gain that the additional o-ring would have yielded.

I am very impressed with Tim's pump kit. It is rock solid and very smooth and surprisingly much quieter on close up.  If anyone prefers to diy and is on the fence, I say do it.  Probably using Tim's inlet check and a disco poppet could be a good option for steroid-like results (with porting, pump kit, and o-ring).

The third o’ring would be 12 fps more at the speeds you have at 8 pumps.
Tim may  be referring to the old style check valve from the 1960’s as a weakness.

[Hack21]

Here's the 312 mod:
https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.0

Ron,

I remember following that thread. Great build. Your machining capaciities and skills far exceed mine. My 392 enhancements were executed on a drill press and with a dremel.  I was going for enhanced, simple, and durable. Your builds are a few tiers above that!

Tim told me the later 342 models are the best out their. He said all of the Racine tooling was new and they are top notch. The later models have a taller front post and provisions for the williams peep.  If I could justify a second brass/wood pumper I would probably be looking for a 347. 

Thanks.

[Hack21]

The third o’ring would be 12 fps more at the speeds you have at 8 pumps.
Tim may  be referring to the old style check valve from the 1960’s as a weakness.

Thank you Charles.  I am not surprised that you know the answer to this.  I probably would have made a careful attempt at cutting the o-ring groove on my drill press if I hadn't done the porting and seat lapping first. At that point I felt like I had too much time invested to start over. It also looked like it needed to be placed close to the valve retention screw threads go keep a proper cross section. 

You may be right on the check valve. It seemed very slick and I thought maybe PTFE? Maybe I will get brave and chrono 9 pumps. Tim's pump parts are certainly good for it and the disco poppet should be also.

Thanks again.

[Tack Driver 10]

Here's the 312 mod:
https://www.gatewaytoairguns.org/GTA/index.php?topic=166841.0

Ron,

I remember following that thread. Great build. Your machining capaciities and skills far exceed mine. My 392 enhancements were executed on a drill press and with a dremel.  I was going for enhanced, simple, and durable. Your builds are a few tiers above that!

Tim told me the later 342 models are the best out their. He said all of the Racine tooling was new and they are top notch. The later models have a taller front post and provisions for the williams peep.  If I could justify a second brass/wood pumper I would probably be looking for a 347. 

Thanks.

I'm not sure specifically why Tim says the early 312/342s are not a good candidates for a steroid mod.
I know the early 312s had 2 small screws securing the front plug instead of a roll pin that could shear off.
My 342 has roll pins so much stronger, same as the 312 I modded.
Perhaps the smaller valve volume?

If you would like to road test the 392 valve above in your gun I can send it to you.
You can replace the FT with your stock top valve half.
I'd like to see what difference it makes.
PM me if you're interested.

The guts of the valve were from an early version.
Here's the innards currently in the valve.
It has a reduced volume as you can see.

[35 shooter]

Eric,

Nice no’s. for what you did!

[Hack21]

I have been meaning to wrap some things up on this thread, so here goes...

I stated that Tim had told me that he believed the later 342 models to be the top of the heap.  I scoured some of his old posts and found the following.  His reply #18 to the following thread gives some clarity. In addition, he had told me that all of the Racine tooling was new.  https://www.gatewaytoairguns.org/GTA/index.php?topic=96487.0

Also, I found a post that confirmed that the inlet check valve weakness was on earlier models than the 392.  In fact, I found a post of his that seemed to say that the Steroid inlet check valve is made from the oem part. 

After putting most of a tin of pellets through my updated gun I ran it back across the chrony.  Surprisingly it is making 5% more power now than immediately after the reassemble.  I would think the pump cup and o-ring have taken a set or are making a better seal?

Pumps / fps / fpe (14.3 CPHP)
1 / 301 / 2.9
2 / 435 / 6.0
3 / 515 / 8.4
4 / 576 / 10.5
5 / 622 / 12.3
6 / 666 / 14.1
7 / 690 / 15.1
8 / 711 / 16.1
9 / 732 / 17.0

All shots were with a dry fired valve before pumping.  I also put the factory hammer spring back in and confirmed that the velocity was unchanged versus my lighter spring. In fact, I polished and lubed the hammer, bolt, spring, and guide and set the softer spring to reduce it's length by 1/8" and it is still making the same velocity with 18.1gr at 8 pumps but now is much easier and smoother to cock with the only resistant coming from the 90 durometer bolt probe o-ring that I installed as it enters the breech. The trigger benefits as well and the shot cycle is smoother.

Does anyone know where to get a new "Sheridan Hand Guard" for one of these?

Thanks.