full length main spring conversion

[rocky]

semi 42 running an O.E. main spring with no problems. feeds great. a little crazy ? yes I bored the wood stock.
But looks stock.

[rocky]

Ok, Herrmueller helped me with is crazy idea . I will try to get him to post prints after the long weekend.

[TOM R]

so will this also work on the bakelite stocks?

[rocky]

1.5 OD on tube . I think bakelite stock might be to thin . I don't own a bakelite to measure.

[none123]

What are you using for a inner spacer for the buffer bolt boss, and what are you doing to gain access to the bolt pin. Off hand i'd think some 1/2-3/4" od tube would work for the spacer and some 1/2" holes would give access to the pin.

[rocky]

Very thin wall tubing .Buffer boss build in to rear section ,which is pressed in and welded . No more bolt pin ,
blue lock tight. Had to gut the stock and cut the stock tube. I'm going to shorten stock screw and drill/tap tube.
It will hold the stock in place. I should of took more pics before it was welded together.

[HerrMueller]

Hi Guys..I have prints. but they are hand written. I can try to scan them and post them up on the Index.This mod. is not for the backyard smashshinest. Your going to need a well equipted machine shop with some good equipment. It can also be fairly dangerous if you don't know how to properly run a lathe or a bridgeport miller.
The buffer Mod consists of three parts. The buffer , the extension tube , and the ejector extension pin.
The material for the extension pin and is 1018 CRS. The extension tube is dom tubing from Online metals.
First and foremost I measured the length of the ejector spring in the buffer, from the upper edge of the buffer to the top of the spring and also from the top of the spring to the bottom of the buffer(inside). I then made a hand written print of those dims.I then removed the cross pin that holds the bolt in the buffer and counted the turns it took to remove it. The reason is once the assembly is put together with the new tube i'm going to Loc - tite it with permanent Red. I guess you could bore a hole thru both sides but I felt that i could try it with Blue thread locker and when I had it working just remove it and make it permanent.I'll give you an explanation of what i did.

I took the buffer and put it in a Bridgeport Milling machine , using a V Block I plunge milled out the threaded web where the ejector spring was threaded using a 4 flute 3/4 inch Carbide endmill.Don't bother trying to use HSS tools,The parts are case hardened and will destroy HSS tools. I then used a boring head with a carbide boring bar and bored the hole out to with- in about .030 from the I.D of the buffer.

Then I put the buffer in a lathe using a three jaw I.D chuck and indicated in The I.D as well as I could. Its not perfectly round.This is the dangerous part. You do not have much to hold on too. Take lite cuts and go slow.You want to bore the hole out so you match the I.D inside the buffer.

Before you break down the set up bore the I.D out and additional .100 thou. by .100 thou deep. (i'm working off memory so don't start cutting until I post the prints!!!!! ) this is for the extension tube to fit in for welding.So now you should have a buffer that has a thru hole all the same dia. except for the last .100 thou. which should be .100 larger. Another point I need to make. Your buffer needs to fit SNUG in your Receiver. If it is loose you need to fix it. Mine was loose so i put it in the receiver and useing shim stock figured out how much material I needed to add. I used a mig welder and added material to the two ears of the buffer. Then , when I had it chucked up , I turned the thickness of the ears to what they needed to be to tighten up the fit.It worked perfectly. Again, Go easy!!

The extension tube is DOM tubing from Online metals. You can also order it from Wicks Aircraft supply.(GREAT PEOPLE!!! )
1.500 O.D with a .187 wall. I cut the tube to the length of the tube that I added to the back of my MG-42 Bolt PLUS .600 thou. it was 3.600 inches over all.Make sure the ends are faced true to the O.D.
I bored the I.D to the same Dim. as the I.D of the buffer. I then turned the O.D on one end to fit into the buffer where the .100 by .100 step is. You want this to fit SNUG. When I post the prints it will be clearer what I did.

The pin is made from 1.500 O.D 1018 CRS. I turned the pin down to about .015 thou below the Dia. of the ejector spring.I had to single point I.D thread the pin for the bolt to thread in. 11mm X 1.0 is the thread size. I think I went .875 deep.I don't have the prints in front of me so I can't give you accurate Dims. for the length. I left .500 of the over all Length of the pin to press into the Extension tube. I turned the O.D to .0005 oversize to press into the tube.I then turned about 3/16 of that dia. to .0005 below the I.D of the extension tube. This allows everything to align before the press fit starts. This has to be done accurately or the pin will be crooked and the spring will hit the bolt extension. All the numbers had to match up and put the Spring in the same position so the gun would eject the case. I don't remember all the numbers so you'll all have to wait till I get home.I'll post everything for you guys and field any questions.Please be careful.!!! If you don't have good GOOD machine skills go to a couple machine shops until you find a fellow shooter or hunter.He will be glad to help you out.
I'm lucky. I can work during my lunch and my boss is a shooter and a fellow Online gamer. Of course having a million dollar machine shop to myself 6 days a week is cool too.. LOLOLOLO Sorry I know I know ..STFU!!!

[rocky]

not to scale...

[js412000]

Rocky,
How well does your gun work with the full power mainspring?
Do you have trouble with slamfires and doubling?

[rocky]

Feeds great in 308 with m13 links .Have not shot any 8mm yet. No slams fire or doubling. Ejects fine. I just
parked the mg42 and its going back together. Then off to range burn up some belts:) .

[rhw1225]

Thanks for the pictures and explanation. looks like a good solution.

One question though. Since you had to bore the hole through the buttstock, how did you modify the buttstock latch to keep the buttstock from turning?

[blckwlfny]

guys, im trying to head off difficulties in an SA that is being built now:
Sorry for the ignorance, but what does this modification achieve that shortening the recoil spring does not?
thanks

[none123]

what does this modification achieve that shortening the recoil spring does not?
thanks

a spring that retains all of it's strength.


Keeping all of the springs strength is important. and remember the spring also has to pull the charging handle forward in a S/A. not so in the F/A

[rocky]

Drill stock ,cut metal collar inside stock ,cut stock pin and weld to bent washer. Epoxy collar and pin in place.
stock held in place by modified caridge bolt (made to look oem.)

[TOM R]

what is the big buffer spring attatched to ?

[boss429]

Accoring to shots build the semi bolt extension is 2.5" long, so that is how much the buffer tube needs to be extended--in Rocky's buffer tube extension it seems more like 3.175" was added to the spring travel length which is .675'" longer spring travel than is stock. Is this by design or ????

[PvtJoker]

So, has anyone given any thought to making this as a kit yet?

[RaccoonRough]

Yes I was wondering the same thing. Is anyone out there willing (if given the parts) to do this conversion for a fee?

RR

[URAR1004]

Who wants to make some Full Length Main Spring Conversion Kits??? I'll take 2!!! Could someone explain what the Main buffer spring is attached to? And how to keep the butt-stock locked in place? Thanks

[Bil]

Maybe it is time to really look into this.Has anyone else used mthis set-up? And I know what happened to the pictures,but is there anyone that saved them,or can they be re-posted? Thanks. ---bil