Odd screw needed for Ljungman

[DanM]

I want to do the gas block mod to my ljungman, but can't find the right screw. A simple mod, that allows the gas flow to be adjusted by inserting a longer screw in place of the existing one on top of the gas block. The factory thread is a M4x0.50, which is very hard to find. On line, I find only European companies that list it. Our local specialty fastener company is no use. At our hardware store, we deal with Midwest Fasteners, but they don't carry it. Length needs to be 10-12mm, so I could cut it down to exact needed length, but would try one as short as 8mm. Also need a bottoming tap sized M4X.050, but might be able to do the job without cutting deeper threads if I turn some of the threads off the new screw. I have been advised to use a common 8x32 screw and retap for that but would rather not ruin the factory threads. Maybe someone here has already gone through this process, and has some advice, or extra screws?
BTW....An allen head set screw would be ideal, but a cap screw might be OK.

[jmh54738]

OK Dan, maybe only you and I think about these kinds of things. I didn't like the way the ejector was beating up the rims of my 6.5x55 brass. I made a replacement, the length of which I regulated to give positive functioning with j bullet loads and 4895 powder. The one that came with the rifle I use for cast bullet loads. You have the size correct, The pitch of .5mm ( .019685) is so close to 50 TPI, pitch .020, that I turned up a new screw with 50 TPI. The error would be .000315 per turn. With 6 turns on the screw, the total error would be .00189, which is insignificant. Only one of my lathes would let me do this, a 16" swing Heavy Duty LeBlonde, in which I had inserted a 1:2 reduction in the gear train, thus, set at 25 TPI, it would cut 50 TPI. I imagine that all of the recent import lathes have metric capability and would cut the .5mm pitch directly as will my German Weipert lathe. However, at the time, I did not have the Weipert, and additionally, it is a 33" swing. The centerline angle of the bevel under the head of the screw is 60 degrees, 120 included angle. I wish that I could tell you that I had a supplier for a ready made screw, but I can't and I don't. Do you have a friend with a lathe? By the way, it worked out great, no more beat up brass.
John

[jmh54738]

I did more searching, MSC/JL has the taps @$4.70 and a die @$12.17.
John

[DanM]

John....Well, I am glad to find someone who has done this mod! Seems a simple job except for finding the tap and screw. Are you thinking that I should get the die and thread some 4mm rod stock? I guess that would mean experimenting with the depth of the new screw and then locktiting it in place. I was hoping to make an adjustable set up with a locking nut on top. I will keep looking for the right screw as time permits. Thanks for the tip. Only suppliers I have found were in the UK or Europe. What are you sizing your cast bullets to for the Ljungman? Mine is a LOT tighter than the M96...DanM

[jmh54738]

Dan, from the first sentence of your original post, I figured that you just wanted to replace the screw with a longer one. Your last post suggests that you want an adjustable set-up. But if you locktite it in place, it is no longer adjustable. What is the object of your modification? Is your brass getting beat up like mine? Does the rifle throw the brass 25 feet, like mine? Can I assume that your screw has a .242 diameter slotted head with the 120 degree bevel like mine? I started with 1/4" stock which I turned to .156, added the thread, cut it off and added the screw driver slot. You have a lot of options, now that a tap and die have been located. With the tap and the die you could make up a threaded rod, and with the tap you could make a lock nut for the adjustable set-up. With the die alone, you can make the screw with simple lathe operations and modify the length to get the desired results. I'm cheap, so I just went out to the shop and single pointed a new screw, cost, $0. I have an SAFN in 8x57 that has an adjustable sleeve that allows complete control of the gas system by just turning the sleeve. Neat!

[DanM]

John, yes I want a longer screw to limit the gas flow. Sorry if there was some confusion, but I know just enough about machine work to get me in trouble. I may have found a source for the right screws on fleabay of all places. I found an assortment of metric cap screws that includes m4x0.50. I could use cap screws and cut them to different lengths as needed. No locktite. Your opinion on this idea would be appreciated. I just bought this rifle, and yeah, I hate what it does to my cases with full power loads.
What are you sizing your cast bullets to for the Ljungman? Mine is a LOT tighter than the M96...DanM

[jmh54738]

Dan, glad that you found the cap screws that you need. My only concern is that you will not have the angled seat under the head of the screw to seal the high pressure gas from escaping. The port pressure could be in the range of 9000-12000 PSI. This could cause gas cutting of the threads or the beveled screw seat. Just my opinion, I could be all wet. My bullets are sized .2677, I just measured some. In checking my records, my Ljungman is bored .2564, with .2667 grooves. My Mausers are very close to being the same, one being .2560 x .2665 and another at .2563 x .2664. Not a lot of difference to write home about. The only mold that I have is 266469.
If you look at the rear sight, you should be able to pull out a retainer clip and reverse the elevator, as it had two different cams, one for the old heavy round nose bullet, and one for the spitzer. Very cool.
John

[DanM]

John...I did not notice any special shape to the factory screw head, thanks for the tip. I will remove the new screw and examine the threads after the first few rounds. If there is a problem, I should be able to seal the threads with some high pressure pipe dope, ot maybe antisieze compound would do the trick.
I do need to slug the bore and do a chamber cast before going much further. All I know at this point is that my .268" boolits make for some very short rounds. They don't reach the lands at all, but are stopped in the throat.
Very cool about the rear sight. These rifles are engineered to the hilt. I did order the front sight set from SS today. Also very cool how it adjusts for windage....DanM

[jmh54738]

Dan...what bullet are you using? My Lyman 266469s are seated out of the case .800" for an overall cartridge lenght of 2.980. I use a slow burning powder so that the port pressure is sufficient to cycle the action at reduced velocities. Something must be amiss if your loaded rounds are short. All of my rifles have long throats. Keep me posted.
John

[Buckshot]

..............I made that mod to my Ljungman also. I also bought a spare gas tap since I was going to alter the existing one.

http://www.fototime.com/AFB8DC2EE04ECFB/standard.jpg

As shown I simply D&T'd to 8-40. Works well.

..............Buckshot

[DanM]

Buckshot....I wondered when you would jump on this thread. Maybe a point on the end of the new screw would work as well as the bevel, and would not have to be aligned with the exit hole? Do you have any trouble with gas blowing out of the new threads?
Has anyone thought about buying a spare safety gadget and mounting an improved rear sight for a better sight radius? Very little play in it, and it could likely be shimmed if there was too much movement for the new sight.

[Buckshot]

Buckshot....I wondered when you would jump on this thread. Maybe a point on the end of the new screw would work as well as the bevel, and would not have to be aligned with the exit hole? Do you have any trouble with gas blowing out of the new threads?


...............Nope. None at all. It's not shown in the drawing but I have a nut on the sockethead screw to lock it in place. I don't know if movement might have been a problem as the lock nut has been on there since the git go. You can adjust the gas so it just unlocks the action when using cast, and you manually extract the empty and reload.

.............Buckshot

[Dutchman]

I've been looking for the photos I had of the conversion.

Best tactic is to buy a new gas block from Springfield Sporters and save your original.


http://images47.fotki.com/v1399/photos/2/28344/6456804/eklund1-vi.jpg