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KJW Ruger Mk1 NBB Pistol Mods


Mike 8-{>

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I posted a comment about a mod I had made to the KJW Ruger Mk 1 NBB pistol in this thread in the General Discussion area. I was going to post the following there but figured it would be better to post it here in the Just Handguns section.

 

There are three parts to this:-

  • Barrel stabilisation mod
  • Hop rubber mod
  • Hammer spring mod
Barrel Stabilisation Mod

 

I have several variants of the KJW Ruger Mk1 now. 2 originals, the SOCOM Gear Gemtech Oasis and the ASG carbine. All suffer from a poor fit between the inner barrel and the breech block. This allows the inner barrel to move around as it is pulled back against the magazine seal. I figured making the barrel fit better would stabilise it and make the shot to shot consistency better.

 

I found a thin walled brass tube in a local model shop which is a much better sliding fit over the inner barrel and is thin enough that the breech block can be reamed/drilled out and the tube fitted to it. 

 

Some numbers:-

Inner barrel OD = 7.95mm

Breech block ID = 8.4mm

Breech block to Inner barrel clearance = 0.45mm

Model shop brass tube OD = 8.9mm

Model shop brass tube ID = 8.1mm

Model shop brass tube wall thickness = 0.4mm

 

How to do it:-

 

The pistol itself

 

gallery_81613_2225_256925.jpg

 

Remove the grub screw which retains the outer barrel to the breech block.

 

gallery_81613_2225_243436.jpeg

 

 

The outer barrel removed

 

gallery_81613_2225_221834.jpeg

 

 

Unclip and remove the retaining pin clip assembly.

 

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The retaining pin clip assembly removed.

 

gallery_81613_2225_210909.jpeg

 

 

Remove the pistol grip / trigger assembly from the upper body.

 

gallery_81613_2225_297837.jpeg

 

 

Remove the breech block and inner barrel from the upper body by sliding it backwards and out through the bottom of the body.

 

gallery_81613_2225_16107.jpeg

 

 

A close up of the breech block which will need drilling / reaming out to accept the brass tube.

 

gallery_81613_2225_184371.jpeg

 

 

Close up of the inner barrel installed in the breech block showing the large clearance around the inner barrel.

 

gallery_81613_2225_53089.jpeg

 

 

The inner barrel with the brass tube fitted over the top of it.

 

gallery_81613_2225_283922.jpeg

 

 

The brass tube offered up to the breech.

 

gallery_81613_2225_182008.jpeg

 

 

You need to cut off a piece of the brass tube approximately 50mm long. If possible part it off with a lathe to ensure the tube has square ends. If you dont have access to a lathe then saw it with a fine tooth saw and file the ends as square as you can. Remove any burrs from the ID and OD of the cut ends.

 

gallery_81613_2225_232912.jpeg

 

 

You will need to bore out the breech block to accept the tube. Again if possible do this on a lather by either drilling or reaming the ID of the breech block out to 8.9mm. Ideally this will be a gentle press fit for the brass tube in to the breech block. At the very least try to use a drill press / pillar drill and ensure that the breech block is square to the drill. If you have to drill by hand be as careful as you can be to drill the hole straight and true.  Remember to measure twice and cut once. Double check the dimensions of the tube you have and drill / ream the hole to suit. Below is the tube fitted in to the breech block.

 

gallery_81613_2225_85019.jpeg

 

 

Another view of the fitted tube.

 

gallery_81613_2225_276517.jpg

 

A view in to the breech block. Ensure that the tube is flush with the inner face of the breech block and that it doesnt extend in to the block. If it does the pistol wont function!

 

gallery_81613_2225_191458.jpeg

 

The barrel refitted in to the modified breech block. As you can see it is a much better fit now. Brass being self lubricating it will slide smoothly without the need for any additional lubrication.

gallery_81613_2225_153425.jpeg

 

Reassemble the pistol by reversing the dismantling process. This is most easily done with a magazine in the pistol grip. The trickiest bit is usually refitting the pin and getting the hammer operating pin back in to the pin clip assembly. I find it easiest to point the barrel upwards and "jiggle" the pistol a little to get the hammer pin to drop in to place.

 

 

 Hop Mods

 

The Hop unit on the Mk1 doesnt seal terribly well and the original hop rubber patch may not be the best. It is possible to use the G&G (or other) Tanaka M700/M24 Hop Rubber kit as a replacement. I found wrapping the hop rubber with PTFE tape helped a little too which you can see in this close up of the hop unit. By the way another "gotcha" when reassembling is getting zinc allow collar on the left upside down. As shown is the correct way up. The pistol wont function if you try to reassemble it with this part rotated around the barrel 180degrees (upside down)

 

gallery_81613_2225_241572.jpeg

 

The G&G kit packet for reference.

 

gallery_81613_2225_224343.jpeg

 

 

The contents of the kit. You only need the square patch on the right.

 

gallery_81613_2225_328613.jpeg

 

 

A close up comparison of the original KJW hop rubber at the top and the G&G Tanaka M700 rubber at the bottom. As you may be able to see the G&G is slightly wider and needs carefully trimming down, best done in situ on the inner barrel, with a scalpel or other sharp knife. Watch your fingers!!

 

gallery_81613_2225_110067.jpg

 

 

The original KJW rubber in situ.

 

gallery_81613_2225_119216.jpeg

 

 

The G&G rubber in situ showing the over hang of the slightly wider rubber.

 

gallery_81613_2225_168512.jpeg

 

Once trimmed wrap the rubber with ptfe tape to help pack out the hop unit and improve the seal.  Reassemble the pistol and see how it performs for you.

 

 

The Trigger / Hammer Spring Power Mod

 

You may well have seen this elsewhere so apologies if you have but for completeness...

 

If you remove the pin, indicated, which holds the clip release lever in place you can access the spring. As well as being the spring for the clip the spring is also the hammer spring. By either pre loading it, clipping it (you may need spacers) or replacing it with a spring of the same diameter which is softer or stiffer you can adjust the force with which the hammer hits the magazine gas valve. 

 

Take care when removing the pin. Releasing the spring can cause the detent ball bearing for the retention clip to shoot off and disappear as only spring driven ball bearings can. Also make sure you replace the hammer spring follower which sits at the other end of the spring the right way round. As I did this some time ago I dont have any pictures of this disassembled currently but can do if people would like to see some.

 

To increase the spring force it is possible, although not ideal, to us a full or half BB as a spacer.

 

gallery_81613_2225_4229.jpg

 

 

Two assemblies showing different springs. The original spring is shown in the bottom photo.

 

gallery_81613_2225_315223.jpeg

 

There you go. I hope this is useful. The improvements in consistency and accuracy arent huge but they do make a difference.

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Instead of using the M700 rubber, I find Marushin designs work best with DIY fabricated hop rubbers made from tire interiors. Basically you just get some tire interior that's about 1mm thick. Cut a square the same size as the original hop rubber. Cut a circle using a punch for paper fasteners. Roughen one side of each then glue together with a little cyanoacrylate and make sure to wipe off excess glue squeezing out the sides. Install and enjoy your concave flat hop. No need to seal with tape either as the punch is just a hair oversized making it plug up the hole in the barrel better.

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Thats a good idea. By "tire interiors" I suspect you mean "inner tubes"? The taping in my case isn't to seal the hop window. More to seal the rest of the barrel end in to the metal hop piece. With the hop rubber only being a square it doesn't wrap the whole barrel like an AEG/VSR style rubber does. Unless of course you made a strip to wrap around the whole barrel end? That might be worth trying... I have a few bicycle inner tubes left over from trying out the BAMSE diy airsoft "grenade." ;)

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Yup, same inflatable tubes. Can't wrap around the rubber as practically all Marushin designs (of which the KJW is copied) have a collar hugging over the square patch. You'll need to modify that piece but I find that it isn't altogether necessary. Why I specifically mention getting a tube in 1mm thickness is that it's slightly thicker than stock which is about .8mm. The added material helps keep the square patch snug like the oversized circular patch making up for a better seal plus keeps the collar from moving around. It does need a bit of coaxing to get on, but not entirely difficult.

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With my KJW MK1, I found the stock rubber perfectly good once bed in and coupled with heavy ammo. Due to the fact I wanted it as quiet as possible with the custom suppressor I made, I actually reduced the power to ~340fps to reduce the escaping gasses. I did it by replacing the hammer spring with a lighter one. This lightened the trigger pull a lot, from that I then replaced the valve springs for lighter ones and reduced the hammer spring again.

 

I now get lovely range and accuracy as well as MK23 levels of noise.

 

Good guide btw and thanks to RC for the rubber idea.

 

Gotta love the MK1

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With my KJW MK1, I found the stock rubber perfectly good once bed in and coupled with heavy ammo. Due to the fact I wanted it as quiet as possible with the custom suppressor I made, I actually reduced the power to ~340fps to reduce the escaping gasses. I did it by replacing the hammer spring with a lighter one. This lightened the trigger pull a lot, from that I then replaced the valve springs for lighter ones and reduced the hammer spring again.

 

 

Where did you source the springs?

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Spares box, I've been a tech for AGES and have tons of odds and ends. just trial and error with a chrono 'til you hit a winner.

 

Bugger. Thought you might say that.

 

 

Nice guns BTW. Love the vintage assassin look on the pistol.

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Regarding springs I have found that buying sets, kits or just random bags of springs has proved a worthwhile investment over the years. Google, Ebay and Amazon can provide useful results. I have got bags of random assorted springs from Proops (http://www.proopsbrothers.com/) the past but it seems they have gone from being really budget and have got fancy, their website has finally joined the 21st century, with it they have lost some of the things they used to do. A possibly useful site all the same. Otherwise searching for "Assorted springs" or similar can bring up things like this:-

 

 http://www.amazon.co.uk/dp/B00D3MRZ00/ref=pd_lpo_sbs_dp_ss_2?pf_rd_p=569136327&pf_rd_s=lpo-top-stripe&pf_rd_t=201&pf_rd_i=B0062MGJ5U&pf_rd_m=A3P5ROKL5A1OLE&pf_rd_r=0N0WVFSZPN2H0KWXAD1X .

 

Also Maplin http://www.maplin.co.uk/p/150-part-spring-assortment-n06ct , Screwfix http://www.screwfix.com/p/hilka-pro-craft-extension-compression-spring-assortment-200-pieces/63863 and others can do kits of compression, extension and torsion springs. 

 

Just acquiring random springs can prove surprisingly useful to rummage through at some point in the future when you need a stiffer or softer spring or one has pinged off never to be seen again.

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Don't know. Cant find the Majestic part available in the UK http://www.majesticarms.com/store/ however these may be available

 

http://www.brownells.co.uk/........=Mark+II

 

Particularly

 

http://www.brownells.co.uk/epages/UK.sf/en_GB/?ObjectPath=/Shops/UK/Products/09958746102001/SubProducts/746102001

 

Have recently bought some other real steel bits from Brownells which appeared promptly and worked well. So for less than a tenner might be worth a look. Also as they aren't a part in contact with any pressurised parts there shouldn't be an issue buying them.

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