Anti-Tamper Removal Guide

HW100 Tuning and Anti Tamper Removal

HW100 Tuning and Anti Tamper Removal Guide (UK)

DISCLAIMER: Carrying out modifications on this page will void your gun warranty - the author accepts no responsibility for damage to your Gun by using the information on this page - continue at your own risk.
Anti Tamper, Tuning Power and the Law:
Before reading this page you should fully understand the implications of current UK Firearms Law regarding Anti Tamper and Power adjustment.

1) The power of an Airgun (Firearm) in the UK is the sole responsibility of the owner/possessor. The maximum power for a rifle is 12fpe (12 ft. lbs.) and 6fpe (6 ft. lbs.) for a pistol. Breaking these laws will result in very harsh penalties including time spent at Her Majesties Leisure (Prison). Again - The power setting is YOUR responsibility, no one else's.

2) It is completely legal to remove AT (Anti Tamper) from a UK Airgun (or add it for that matter). There is no or has ever been any Law or Legislation regarding the fitting or removal of AT. It would *seem* that AT was invented by airgun manufacturers and other airgun top brass to line their own pockets - these people claim it was forced on them by the Home Office but can provide no proof and what's more when asked the Home Office deny this in WRITING. This is highlighted by Daystates recent reverse on their policy and are now offering to remove AT from their guns - albeit at a hefty price tag! (making money from us again). So if the Home Office were behind Anti Tamper then how can Daystate suddenly remove it????? Answer - we've been had!

Having mentioned no 2 it is however still prudent to only share this information with people you feel are responsible and of a legal age to carry out the modifications. We have enough idiots ruining the sport as it is, we don't need to encourage more.

DO NOT ATTEMPT THIS TUTORIAL WITHOUT AN AT REPLACEMENT KIT (see the bottom of the page for details)
This guide assumes the reader has working knowledge of the HW100 e.g. how to remove the stock from the action etc

The purpose of this guide is to show how to remove the Anti Tamper (AT) from a Weihrauch HW100 Airgun and replace the AT with new parts that will enable the owner to keep the rifle running UNDER the 12fpe UK legal limit. It is a commonly known fact that many HW100's have a liability of running over the UK legal power limit during their "running in" stage. This is due to Weihrauch using quite a thick grease in the hammer assembly, this grease thins with time, heat and use causing the hammer to move more rapidly when fired. A quicker moving Hammer assembly "can" cause a power increase in the Rifle, this increase can be small but has been known to be well over 1fpe - AGAIN: ANYTHING OVER 12fpe IS ILLEGAL IN THE UK. Obviously any increase in power is a serious situation and before AT was introduced it would be a simple case of the owner adjusting the Hammer spring on his/her HW100 and testing in on a Chronograph to ensure the rifle was below the UK legal limit. However with the addition of the AT system the user has no choice but to send their gun back to Hull Cartridge, direct or via their local Registered Firearms Dealer (RFD). This takes time and money for something that is very simple to do for yourself.
Step 1: Strip down
Remove the scope and scope mounts (if attached), remove the magazine (making sure the gun is not cocked and is empty) then remove the action from the stock. Next remove the pressure bottle (buddy bottle/tube).

Following the 4 pictures below remove the 2 hex head bolts that release the trigger mechanism.
Strip Trigger 01 
 Strip Trigger 02
Strip Trigger 03
Strip Trigger 04
Remove the rear plate. Then remove the small cocking latch that the red arrow is pointing to.
Rear Plate 
Cocking Plate
Next is a slightly fiddly, potentially really annoying bit - removal of the cocking lever. The cocking lever hinge pin is located in the first picture, pointed to by the red arrow. The second picture shows the line of the cocking pin, you'll instantly notice that the line is not straight when accessed through the hole in picture 1. We need to find something to poke down the access and gently tap with a small hammer to knock the pin almost out (we don't need it all the way out, just enough to remove the cocking lever). I found that the best way is to get an old wire type coat-hanger and cut 3-4 inches out of a straight bit, the wire is very strong but can be bent enough at one end to slide down the access hole nicely.
Below is a picture of mine - it had a white paint coating on, that is why the end looks gnarly. It's just the paint coming off. You'll notice the slight steady bend in one end. Place the bent end in the access hole and tap gently, the pin should start to come out. Continue until the cocking lever comes clear. At this point the whole Hammer assembly and cocking lever should slide out easily and should look like the second picture below.

Please note
how the small spring and stopper are connected to the cocking lever/pellet probe as you will need to put this back when re-assembling.

Also note where the two pins on the cocking lever/pellet probe interact with the Hammer/AT adjuster. The smaller red arrows show where the pins slide into the Hammer/AT assemblies (this becomes apparent when putting them back together - it does honest).

One other thing you will notice is that the Hammer and AT Assembly are joined together by a rod that goes down the centre of the spring (Hammer Spring) - This is what we need to change/modify.

At this point you should get some kitchen roll/old rag and thoroughly remove all the thick grease on and around the hammer and cocking lever.
Now we are getting somewhere: We need to remove the AT assembly, this can be done one of two ways:-

AT Removal Method 1) Cut the AT assembly off at the green line in the first picture below, this is by far the easiest way to remove the AT assembly, the only problem with this method it is very easy to damage the Hammer spring and that is not a good idea. Once cut off you are left with the Hammer similar to the second picture. Notice there's approx 6 - 7mm of the rod still sticking out of the Hammer, this serves as a spring guide.
AT Removal Method 2) This is the potentially harder but safer way of removing the AT assembly.

HEAT is the key - using a blow lamp or perhaps even your gas cooker ring, heat up the area around the grub screw in the picture and remove it (it's a 1.5mm Allen key). With heat it will come out very easily, without heat it's almost impossible.
Next with a Dremel cut a slot in the top of the AT Assembly, then heat up with blow lamp/cooker and screw in/out the inner screw with a coin/screw driver/whatever you can find. Don't be frightened of damaging the AT Assembly *IF* you have managed to source an AT Replacement Kit  (see bottom of the page for details) as this part will be discarded anyway.  The pictures below should speak a thousand words.
AT Mod 
 AT Mod
AT Mod
AT Mod
Once that is completed it should look something like the first picture below. Now we just need to cut off the AT threaded section at point A in the second picture (once again being careful of the spring). Once cut remove the spring and cut at point B, leaving approx 6 -7mm as a spring guide . Now you will be at the same point as in Method 1. You can probably see why this way is safer e.g. there is a gap you can safely cut off the Hammer Bar with little risk of damaging the spring.
AT Cut 
AT cut
AT Replacement Kits  - ************** Actual kits are now slotted heads instead of a hex head because the hex head varaints are no longer available from the manufacturers due to the very high cost. (It would have added an extra £6 to the cost, eek!)
The replacement kit consists of a new threaded adjuster and a matching shuttle. The units are expensive as all the threads have to be machined and are Extra Extra Fine (as the original weihrauch ones). Below are a couple of pictures of the kits (please note the spring is NOT included). Although I can get them from Germany and they are very expensive).
Below is a picture of the unit assembled with the Hammer spring inserted.
You will need:
1) A good light gun oil - I used Birchwood Casey Synthetic Gun Oil with PTFE. Using a light oil will make the gun a lot more consistent, especially during changes in temperature .e.g. it will be more or less the same power in summer as winter. This is because the oil will not get thicker and harder in the cold or thinner in warmer environments.

2) Some Loctite 248 thread-locker medium strength (or similar) - this does not set really hard and is perfect for holding the adjuster on place.

At this point you can remove the very small grub screw if you wish - it's been reported that Hull Cartridge have starting removing the grub screws and they aren't really needed - your choice really.

Put a small amount of Loctite inside the shuttle and screw in the adjuster so that the end is flush with the chamfered end of the shuttle (you don't want it sticking out like in the above picture.

Next if you have the grub screw in place then take it out for the moment.

Insert the Hammer guide (the bit you left on) into the other side of the spring, it will now look like the below picture again the only difference will be that the bar down the centre of the spring is not continuous and the adjuster now has a hex insert in the top to allow easy adjustment.
Lightly Oil the parts where you removed the thick grease (the Hammer and the Cocking lever internals and reassemble in reverse order, EXCEPT leave off the rear plate, stock and scope.

Now get your chrono and test the power, screw in the adjuster with an Allen key clockwise to increase power an anti-clockwise to decrease power.

Once the correct power level has been established then you can put in the grub screw to lock the setting (better to leave it out in my opinion as the Loctite does an ample job) fit the rear plate, stock and scope. (remember 12fpe for UK legal limit)

Hope this helps.
For information on general HW100 tweaks, Regulator testing and Hammer balancing please see:

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