Ratatatman's build with notes on construction.

ratatatman · Post by **ratatatman** » Mon May 21, 2007 9:02 am

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First off I want to express my appreciation of this forum. There is a lot of good information to be found here. However, there appears to be a lot of flailing around to find what works and what doesn't work. I have pretty much found out what doesn't work or what works marginally after rebuilding my brother-in-laws BRP semi and building my own semi 42.

The first thing I found is that the gun really needs a full length spring for reliable operation and to have enough energy to strip a round out of the belt and load it in the chamber and there is a good sticky on that build. Remember that you have extra resistance riding over the hammer for the semi fcg that the full auto gun doesn't have. One thing that I did in addition to the extension was to grind down the buffer pin (the part that strikes the ejector) and the spring OD as small I thought I could get away with to prevent the post from binding when passing throught the bolt extension.

The fire control group - There is only marginally enough energy to make a AR-15 fcg work & every thing else has to be right for good primer ignition. I used Pirates FAL gripstick conversion for my build and recommend it to everyone that is haveing problems with light primer stricks. Also, your gripstick needs to lock or pin in solidly so that there is no movement causing loss of energy.

The bolt - I went through modifying three bolts before I came to a satisfactory design that really worked good. In my final design for the feed roller I used Panacea Beach Bum's roller and stub. I machined my own extension from 1 1/2" bar stock and made the rear portion mirrow the appearance of the back end of a non-modified bolt. I added a window to the top of the extension to enable seeing what and where the hammer was actually hitting and to allow an additional amount of clearance for the hammer. On the bottom of the bolt I completely removed the full auto nubs and milled the bottom of the bolt flat right down to the main body section. I made up my own design firing pin using .209" diam drill rod, drilled out nuts for stops and the original firing pin in the front.

Bolt hold open- You almost have to have one or a second person to load the belt or any time you just want the bolt open. I found that all that is really required is to add one small bump to the ratchet plate. Due to the design of the charging handle it will hold open on the bump and close when the handle is pushed foreward.

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a-kmanator · Post by **a-kmanator** » Mon May 21, 2007 5:34 pm

nice work ratatatman,i like the wood grips ,did they come with your kit?...kman

ratatatman · Post by **ratatatman** » Mon May 21, 2007 5:43 pm

I cut the wood grips from a 1" thick piece of rosewood. Used the plastic grips as a pattern, traced one side out on the wood and cut both pieces out together with a bandsaw, then split them in half on the table saw. After that used the angle grinder with a sanding pad to rough finish then hand sanded to final finish.

Post by **bolex** » Mon May 21, 2007 5:48 pm

The bolt extension appears to have a duplicate of the rail guides that were currently on the bolt carrier. Do these engage/disengage the rails when the weapon is fired and the bolt travels into the buffer?

Keep Up The Fire · Post by **Keep Up The Fire** » Mon May 21, 2007 6:13 pm

Whats up with the funny looking cross on the butt stock? Almost looks like a half donkey swasitka!

Post by **JBaum** » Mon May 21, 2007 6:28 pm

Milling the top of the bolt extension was a wise choice. The mass of the bolt is increased a lot with the extension, and milling it out, as well as removing as much of the bottom of the lug area reduces the power required to get the bolt to cycle. Any idea about how close to the original bolt weight your modified bolt is? A few relief cuts in the sides of the extension might help too, provided it wasn't overdone to the point of losing stiffness. I'd think that keeping the bolt weight as close as possible to the original would be a good goal.

Having to cut the hammer down a bit reduces the force of the impact on the firing pin, so avoiding having to grind off some of the hammer for clearance is a good thing too. A stiff/stiffer hammer spring, and maybe adding a little weld to increase mass of the hammer (if there is room) would also be a good thing to do to the hammer, as light primer strikes are also a problem.

A big ATTA BOY! is in order here.

ratatatman · Post by **ratatatman** » Mon May 21, 2007 6:30 pm

The bolt extension does engage the rails in the rear. But the purpose of doing that is to allow maximum possible metal around the end of the spring. I have experianced several examples where the spring has split the back of the bolt extension from being forced to seat into to small an area.

The funny looking half ass swasticka was carved into the stock by the previous Yugo owner/operator and I saw no reason to sand it out.

Post by **Bil** » Mon May 21, 2007 7:49 pm

Very nice job-very nice post.Thank you for telling of your experiance on what works for you.It is good to see a finished gun,and some new methods,too.Thanks again. ---bil

Post by **gdmoore28** » Mon May 21, 2007 8:46 pm

Keep Up The Fire wrote:Whats up with the funny looking cross on the butt stock? Almost looks like a half donkey swasitka!

This carving was covered in another post. Apparently it is a "Serbian Cross." Here's the link:

http://panzer46.net/mg42board/viewtopic ... bian+cross

It was carved on one of my buttstocks, too.

GeeDeeEmm

Post by **tony** » Mon May 21, 2007 9:15 pm

so does having the rail guides in the bolt extention help keep the bolt from canting down in movment? Seems to make sense since your adding length and weight to the bolt.

RaccoonRough · Post by **RaccoonRough** » Mon May 21, 2007 9:19 pm

Thank you very much for sharing your accomplishments and also your trials. I too agree it is nice to see a working finished gun.

Enjoy it.

RR

Post by **Abominog** » Mon May 21, 2007 9:45 pm

Sweet! Some great mods that give reason to consider...

Thanks for posting!

ratatatman · Post by **ratatatman** » Mon May 21, 2007 9:46 pm

so does having the rail guides in the bolt extention help keep the bolt from canting down in movment? Seems to make sense since your adding length and weight to the bolt.

The rail guides do keep the bolt straight which really was a bonus to what I was trying to achieve.

doit659 · Post by **doit659** » Mon May 21, 2007 11:25 pm

I am impressed with your understanding and physical abilities to build one of these projects.

At the same time, I am somewhat worried that this type of project is really for an advanced hobbyist or professional.

I really don't want to spend a ton of money and realize that the tools and talent outdistance my abilities.

I have been around this site, but does anyone know about a thread that discusses the tools and skills needed to realistically undertake this project?

Thanks in advance.

Post by **Bil** » Mon May 21, 2007 11:46 pm

Welcome aboard! Have you read'Pirates build'? That covers a lot of what you can expect.You will need to have some welding skills or the assistance of someone that does.Basic hand tools-screwdrivers,etc.A dremel tool or the like.Patience.[you can't buy this]. There isn't a lot to spend if you can do the basics,or are willing to learn.The hardest part I have found is deciding which way to do it,there are several and I am still working on them.I think you should have a real interest in the project.I have gotten discouraged at times,but I really want to get the project finished.It also depends on your definition of 'tons' of money.I am sure you can build one cheaper than you can buy one,if you can find one.I started out without any gun-building skills,and am almost at the point of finding out if it works or if I need more work on it.Minimum investment,lots of fun.There are enough folks here that have finished theirs that I feel it is a good, do-able project that you can have fun with without spending tons of money on.Hope this helps you out. ---bil

doit659 · Post by **doit659** » Tue May 22, 2007 1:11 am

Thanks, Bil. Your reply does help give me perspective.

My father is a WWII veteran, and I have always been interested in this period.

In part for that reason, I have made an effort to get non-museum quality examples of the most popular rifles of the period. As you know, some are inexepensive and in great condidtion.

On the other hand, parts kits like the MG42 have become more difficult to even find, let alone convert to semi-auto.

But I think I'm going to take the plunge and give it a try.

Post by **bolex** » Tue May 22, 2007 7:39 am

Bil, has the right idea. I have built ARs which were basicly a kit in my opinion, AKs are a little more fabrication if you use an 80% receiver (the pistols are a blast if you are willing to do even more fabication work). The MG42 is still a work in progress for me. To build one it appears to me that the easiest way would be to start with the demil receiver and weld it back together if you have good skills as a welder. The advantage is that you know that the parts fit and worked at some point in time, and you are trying to put something back together as opposed to starting with a blank 80% receiver. The 80% receiver has never had these parts fit before so a lot of fitting and layout of holes and slots is involved. The up side is that welding skill level required is a lot lower. With the new 80% receiver you can make the welding joint tight and therefore a lot easier to weld. To weld the demil receiver together you are filling in 1/4" gaps or larger and still trying to keep eveything lined up and not warped. I once read somewhere that you can't weld air.

Just my observation.

Post by **Bil** » Tue May 22, 2007 4:06 pm

I agree about the original receivers.I have nothing against the new ones,and they certainly fill a big hole in the hobby.But I like knowing that the pieces actually worked at one time,in addition to the historic factor.Look in any custom or hot-rod magazine,they are full of cars built by guys like us that have chopped the tops and done numerous modifications with skill levels comparable to most of us,ranging from beginer to professional.Believe me,a top chop is a lot more complicated that a receiver re-weld.And if you get part-way through and decide that it is not for you,you can always sell it,try that with a car without a roof!

---bil

MGW LLC · Post by **MGW LLC** » Tue May 22, 2007 7:02 pm

WHat was your work around for a full length main spring?

ratatatman · Post by **ratatatman** » Tue May 22, 2007 7:50 pm

http://panzer46.net/mg42board/viewtopic.php?t=2781

full length mainspring conversion.