Center fire systems parts kit

[dlbard]

While I'm waiting on the camming situation to play out I thought I would do something about the loose stock. With the stock installed on the buffer there was a lot of play I didn't like. At first I was going to make a shim to fit between the buffer and the stock but that didn't turn out to well. So I figured the best way was to make a new thicker flange on the stock cup to fill in the 1/8th inch gap I had between the two surfaces. This would put a load on the threads. First I removed the cup from the stock. Instruction on how to do that I found here on this site. I then turned down the old flange till I was within a 1/4 inch of the cup diameter. I then got a piece of 3/16 4140 scrap I had and bored a hole in it till the buffer slid freely in it. Then I counter bored it till the turned stock cup sat flush and tight in the counter bore.

Next the cup was silver soldered to the new flange.

I next need to turn down the flange till the buffer is nice and snug to take up that 1/8th inch gap I had. This is the amount of the material that I started with before I removal. This is the modified cup in the stock .

This is the outline I traced on the new flange from the buffer end and will contour the shape from it.

Maybe in the next couple of days I'll get it finished.

[42rocker]

Check out the posts on mixing yugo and German stocks and buffers. A 1/8inch gap is normal with a mismatch. Sometimes due to wear but normally not a 1/8 inch gap.
Keep up the good work.

Later 42rocker

[dlbard]

Talked to a friend of mine, a 35+ year machinist, and got his opinion on the camming/trunion section. I told him about my problem with the mismatched pieces and how would he go about fixing it. I said that I could exchange it but I there was no guarantees that the “new” one wouldn’t be a matched pair either. So he came to the same conclusion I had and we would square it up ourselves. I didn't feel like waiting two weeks turnaround time either. We first clamped everything up in a milling vise. With the help of another clamp and about 15 minutes of indicating time, we got everything within .0004 of an inch. All except one leg of the cam that makes contact with the barrel under recoil. More on that latter. He then ran a carbide .250 reamer through the old hole. I forgot what the original size was but the reamer was just a hair bigger. Now everything was right with world.
On to the long leg of the camm. With the camming piece now square and bolted together, I ran it across a surface grinder and ended up removing .020 off the leg on the removable piece. Here is a pic with it all bead blasted and ground. If you look closely the leg on the left at the bottom you can just make out where the grinder didn't grind the whole surface. It is the white looking area. I stopped there because we are only talking about a .0001 or so and I wanted to remove as little as possible.

[TactAdv]

A trunnion is a pair of pins which allow whatever the pins are mounted on to pivot, or a pin on which something pivots.

....so is the extractor in the bolt head a cartridge trunnion then?? ;-)

-TomH (pry open crack, drive truck through)

[DARIVS ARCHITECTVS]

For those who care:

Even though a lot of people incorrectly call the cam piece on an MG42 a trunnion, it is by definition, not a trunnion.

The ramps (cams) inside the cam piece (that's the German term, they should know) cause the bolt rollers to disengage the barrel extension when the locked barrel/bolt recoil. No pivoting is involved.

A trunnion is a pair of pins which allow whatever the pins are mounted on to pivot, or a pin on which something pivots.

Poor John has the sad duty on this board of pointing out every single instance of this misnomer. Don't even get him started on that "clip" versus "magazine" thing. He'll blow a gasket.

Does anyone even know where this "trunnion" name business started?

[dlbard]

I finished my stock cup last week and forgot to post on it. Here are some pics. Everything is a nice snug fit. No slop.

[42rocker]

Nice Work.

Later 42rocker

[dlbard]

For those that are currently building kits and instrested in an AR trigger set up,fcg with spring set at bushmaster $47.90 shipped. Cheaper than dirt was just 5$ more. I'm chomping at the bit to get working on the yugo. Awaiting parts and at a stand still.

[42rocker]

Check the price at cheap than dirt and also brownells then think about getting a wolf extra power spring from brownells or ??
Some times just getting the ar parts that you need is cheaper.
Some folks like the pirate fal or other fal setup better.

Good Luck on yours. I'm waiting to go to the range in about 10 days just double checking the final details.

Later 42rocker

[42rocker]

Something else. Just redid my ar fcg had 2 different types of ar hammers 1st had a rounded top for the bolt to ride on and the 2nd had a top that looked like a notch was cut into it and that was causing some major drag on the bolt. I did not want to round the 2nd one yet because that hammer just seemed to reach the end of the firing pin.

The 1st one that I talked about was from a dpms 4 part hammer group and I can't remember where the 2nd style came from could have been from a dpms complete fcg set not sure.

Good Luck

Later 42rocker

[dlbard]

Thanks for the heads up! I'll let you know which one I get. Last AR I built I ordered a DPMS complete lower kit. When I got it all assembled and did an op check and I could not believe the trigger pull it had! It is no exaggeration to say that it was absolutely the worst trigger I have ever felt. I don't own a pull gauge but it must have been every bit of 10lbs plus and lots of take up! It took some time but after a set screw in the grip screw hole, polishing the sear and over stressing the hammer spring to relax some of the tension, I got things to an acceptable level. I brought this up because I have read several threads about lite firing pin hits with the AR fcg set up. I can't imagine that would of been a problem with that trigger group. Time will tell.

[cz2]

Hi All,
If you have the grip altered to fit the AR parts,consider a Timney drop in F/C for the AR-10. Nice large pins,compact hammer shape,designed to fire the 7.62 round. No high power spring required.
later,czech.

[Mechwarrior]

Dang dlbard, you are a lot father along then me. Nice work on the stock. I don't have any cool guy tools,(lathe/mill). I also have a miss matched camming piece but the holes line up and the bolt locks smoothly so i figured i would go with it.

My understanding of a trunion is, the part that mounts the barrel to the receiver. As the camming piece does not do that, this weapon has no trunion. Correct?

Question, how many parts in this weapon need to be american to be legal? I know about the 20 parts and only using 10 forgien made parts. How many american parts are needed?

Also, does anyone know if the U.S. Made grip panels for this weapon, from rtg, count as 1 of those parts? Just wondering.

If you guys want, i can show you my poor man's milling machine. It might make most of you guys ! LOL

[dlbard]

It is my understanding that this is pretty much a non issue because of the amount of parts that are altered,after which they are no longer considered an import part. You can check this site under 922 topics.

[AaronHorrocks]

How did you get the barrel bushing out?

When putting the new one in, Is it simply pressed, or did you weld it too?