Repairing Hammerli 480K Air Pistols?

[Gwhite]

The team I help coach has twenty one Hammerli 480K air pistols. Before Larry Carter passed away, we had then all converted to use the skinnier AP40 style cylinders, which are still available to meet the 10 year rule. The original regulators had issues, and the conversion also included a replacement based on the AP40 design. They are still excellent pistols, and we had one student who finished third in the 60 shot qualifier with one at the Collegiate National Championship last spring. 1st & 2nd went to members of the US Olympic team...

One by one, the pistols are slowly dying. Larry provided the repair work we needed, but since his death, we have been unable to find anyone who can work on them. I think we have eight out of commission now, including four that were waiting for service at Larry's shop. The most common symptom is a breeze blowing into the trigger area from the regulator. Based on the diagram of the AP40 regulator, I'm guessing the regulator piston seal/O-ring is blown. I know there are special tools needed to do things like adjust the regulator pressure, but they have not been located in Larry's estate. If all I have to do is replace dead O-rings, I should be able to fix quite a few.

Does anyone have any information or experience on repairing these? One problem is that I don't have any documentation of the conversion process. I don't know which parts are from the original 480K, which are AP40 parts, and which are custom parts to adapt the the AP40 bits to fit the 480K. I don't even know how to disassemble the resulting hybrid. I may have to risk sacrificing one to find out...

Any info or suggestions welcome.

Thanks!

[David M]

Manuals and parts dia. from Walther
https://carl-walther.com/download-area?q=AP40&lang=en
To pull the regulators apart you may need to make the tools.
I have done a couple of Walthers and FWB, "o" rings and Belleville Springs
available from china.
Contact Walther, they may have additional drawings of regulator internals.

[spektr]

Hi Dave..... Have you blown synthetic oil thru the gun. A lot of times the seals "come back" as they absorb the oil and tighten things up........ You lose nothing for the attempt.......

[Rover]

Hi Dave..... Have you blown synthetic oil thru the gun. A lot of times the seals "come back" as they absorb the oil and tighten things up........ You lose nothing for the attempt.......

In all my years of shooting, I have never heard this (though I've done it on a couple of SSPs). Certainly worth a try!

[Gwhite]

I have tried blowing oil through all of the misbehaving pistols, without any success. The information David M linked to provided some info I didn't have. I could have sworn I saw an AP40 manual that had an exploded diagram of the regulator, but all of the manuals on the Walther web site show it as a fixed "reduction valve complete" assembly. If I can buy those (and figure out how to swap them out), that may be a quick (but probably expensive) fix.

[David M]

Here are the doc's I have for both LP200 ans Styer pistols.
If you can get the old regulator apart, measure the seal sizes (hope they are only "O" rings
not propriety seals. Also measure the spring washers, they may or may not require replacement.
The Belleville washers in the LP200 were shot and needed replacement. The exact spring was not available
in blue steel but in stainless. I had to change the pile arrangement to get the pre-charge right by trial
and error on the range with a chronograph and a good pressure gauge on a big air bottle (3-4 Hrs).
These may help you understand the regulator.
The spring pile load is what adjusts the pressure reduction.
Increasing the spring pile load will increase the pre charge pressure.

[Gwhite]

Thanks! As long as we haven't gotten wet air from a compressor system at another college, the springs should be OK. Supposedly a couple Benelli Kites we had serviced a number of years ago had rust in the regulator from bad air. I can get replacement springs from McMaster Carr in any event. My assumption is that if I carefully note the spring orientations when it comes apart, that I can get close enough using the same setup.

Steyr actually sells a pressure gauge that bolts onto the back end of the regulator. As our collection of Steyrs increases, I may invest in one. So far, I haven't had to rebuild a regulator, but we have 8 of them now, so the day will come...

[fc60]

Greetings,

Check out Judith's website.

https://schiesssport-billharz.eu/LP-480-K

She is shipping to the USA again.

Note, most parts may have Walther part numbers along with the Haemmerli part numbers. This may be good suggesting that Walther is still making parts.

Also, contact Walther and explain the situation. Maybe they will send you technical documents on advanced repair.

Cheers,

Dave

[Gwhite]

Thank you! That is an excellent resource! The regulator assembly we may need is ~ 80 Euros, but that's still worth the expense.

I will contact them and see if they can help with repair advice as well as parts.

[ShootingSight]

If you decide to sacrifice one, send it to me after you are done. I specialize in taking things apart, and occasionally get them back together with few parts left over (apart maybe from ones I judge probably weren't necessary in the first place). Plus, I have a machine shop if we need to make tools.

I have zero expertise, so I might not be your number 1 choice, but if you are to the point of experimenting anyhow ....

[Gwhite]

Art: thanks for the offer. I will keep it in mind.

I've been studying the diagrams, and it may be that the regulator assemblies are OK. At least in the AP40, they are held into the frame with a set screw that mates with a dimple on the bottom. There is a small hole in the middle of the top that must be the low pressure port. I couldn't figure out how that would seal to the frame, but there is a very small O-ring that appears to go on top. If the regulator piston seal isn't blown it may be that the tiny O-ring is the culprit. It may even be that the set screw that holds the regulator in place has worked loose.

AP40 Regulator & O-ring.jpg (30.13 KiB) Viewed 3615 times

I'll let folks know what I figure out. I have several queries out, and a couple more sources to check with next week. It appears I can get whatever standard parts I may need, I mostly need to understand the details of the 480K to AP40 conversion hardware.

[Gwhite]

The plot thickens... I found some information of the contents of the conversion kit. It turns out the regulator assembly used for converting the 480K's to use the AP40 cylinders is not just a normal AP40 regulator.

The part number for the conversion regulator is: 274 46 08
The part number for the regular AP40 regulator is: 274 48 60

I also found a part number that I believe is for the complete conversion kit: 273 34 12

I will contact Neal Stepp at ISS and see if either of these are still available.

[ShootingSight]

I used to take apart and rebuild my SCUBA regulators, and never died following reassembly. There is very little movement of parts inside a regulator, so I would not expect wear failures for any of the components, if they have an issue it would be corrosion or crud buildup. Most often, o-rings and seals needed replacing. Springs could potentially fail, but spring life is driven by the number of cycles at high stress levels. While 10,000 cycles is expected life for springs that cycle up near their maximum displacement, as stated the motion they see in a regulator is very small, so I do not see that as an issue.

[David M]

The biggest killer of the "springs" appears to be leaving the tanks screwed on the pistol and the springs under load all the time.

[Gwhite]

I don't know the history of these pistols, but I make sure the cylinders are backed off, and the trigger "fired" before they get stored every summer. I don't know how essential either is, but it certainly can't hurt.

[ShootingSight]

Plastic parts can take a set because of long term storage, but steel springs do not lose strength by being stored under load or in a compressed state, unless you heat them to above about 450F. Springs degrade due to cycling.

[Gwhite]

In theory, and to first order, perhaps. Reality is different. "Relaxation" in steel coil springs at lower temperatures does exist:

https://www.rockfordspring.com/relaxation-of-springs

I've seen a lot of pistol springs that come out of an old pistol that are shorter than when new. Whether it's from initial "set", over-stress due to poor design, excessive compression cycles, or relaxation is impossible to tell. It's also not just the spring that is a concern; the spring is being held by other parts. Here's what happens when you leave Benelli MP95E's cocked for many years:
.

It doesn't hurt anything to leave expensive target pistols in an un-cocked state when stored for long periods of time. The older the pistols, the more difficult is is to get parts, so I choose to treat them as gently as possible.