MG42 Trouble Shooting Testing Discussion

[Waffentag]

Over the weekend, I will test and try to verify if the problems with my FA MG42 in 308 were solved with the 11mm booster nozzle. Last weekend, I fired short bursts of just a few rounds and closely inspected the cases. Of fifty rounds total fired, no signs if case separation. I did have some FTF where the rounds slammed into the face of the chamber. I attribute this to using the 8mm top cover. So I swapped to the 7.62 top cover for next time.

I will go to the range armed with 7 spare springs, of various strength, an 11mm nozzle, a couple 11.5 booster nozzles, 2 different size BW booster Nozzles (Not sure of size?), old and new style bolt catches, a number of Johns Translated Manuals and a Number of Spare Parts, Also, Lake City, Malaysian, Australian 7.62 Ammo and my reloads.

The plan is to fire a few rounds, and check for signs of case stretching. I will try to find the sweet spot between functioning and ripping apart cases, but trying different Nozzle sizes and spring strengths,

It seems that it runs fine in 8mm? Just need to get it going in 7.62/308?

Any suggestions on how to proceed with testing and what parts to try would be appreciated,

Thanks,

[42rocker]

Wow, sounds like a good plan. Wish I could offer good input but don't own a FA.
Remember a so so day at the range is still better than most. Good Luck!

Later 42rocker

[Waffentag]

A good day at the range with the FA MG42. We took it slow, fired a few, inspected each case for separation, tried different size nozzles, bolt safeties, changed a charging handle that caused light primer strikes from slipping, changed a grip piece that caused problems, a good day, solved lots of problems.

Well, It ran with the 13mm booster without tearing cases apart, longer spring with no signs of sepration. I also used the old style bolt catch which seems to provide a more solid lock up. I tested it with both 7.62 NATO Lake City and Maylasian. It ran great with the maylaisian and Lake City with the 13mm. It would not run reliably with my reloads wtih the 13mm nozzle/booster. But ran the reloads with the 11.5 mm booster.

For my situation, it may be good to have a variety of nozzles, 11,11.5,12, 12.5 and 13? Does anyone else maintain a stash of spare nozzles? What sizes do you keep on hand?

I guess , that if I need an 12mm and a 12.5, I will have to drill them out myself?

[42rocker]

Glad to hear that you had a good day at the range. Sounds like you worked your way thru a few problems, way to go. As far as different size nozzles go I do have a few but shooting the same ammo and only having a semi I don't need them, yet.
Glad to hear about the good range day.

Later 42rocker

[JBaum]

My gun runs in 8mm and .308 with the same nozzle. I swap barrels, top covers and feed trays, and it's ready to run. You're having trouble running .308 reloads in the MG42 because they don't have sufficient powder to make the gun operate. With almost the right load, you'll make the gun operate consistently, but when you really dial it in to the gun, you'll notice the difference about how the gun runs.

Tune the powder quantity to the gun for your reloads. It's much easier to not have to change nozzles to make the gun work when you're running reloads with sufficient powder. For the .308, make 25 round belts with different amounts of powder in 1/2 grain steps, and see which load makes the gun run best. You'll hear the difference in the gun when you hit the sweet spot. If it runs fine on 42.5 grains, try 43 grains. If it doesn't run any better on 43, use 42.5, etc. I did that with mine, and it likes 42.5 grains of BL-C2 (2). It's the same process with other powders.

Don't forget to put a coat of light grease on the bolt rails in the receiver.

[SturmHead]

Is there a way of determining the diameter of the muzzle booster opening other than measuring?

[JBaum]

No. There are no markings on them to identify sizes.

[SturmHead]

Thanks John.
Guess you'll see me with a set of calibers at your neighbors at the next Creek shoot.

[Waffentag]

Thanks guys, I got two more Nozzles from RTG yesterday, one is marked 11, the other is not marked, I got them with the intent of drilling them out. It seems that factory runs ok without tearing off cases with the 13mm. My reloads run fine with 42.5 IMR4064, with the 11.5 Nozzle. I was going to drill one out to 12 to see if I get the reloads to run and not tear factory cases apart?

If not, then I will try 12.5? At that point, I will adjust my powder charge. My Dillion is set to 42.5 because all my rifles like it, but I will change if the 12mm nozzle flops.

[JBaum]

With new brass, I load and then reload for 2 shots total before I start inspecting the brass for stress lines in the sides of the cases. Stress lines appear where the brass will crack/tear if fired again. I've had very few cases that made it past 4 shots total before the darkish lines appeared. When stress lines first appear, that brass goes in the scrap bucket to be taken to the metal recycler.

[waffendude]

I get about 2-3 reloads before the casing becomes questionable. For 7.62 x 51 ~ I use 4895 @ 44 grains. What's weird is that I reload 8mm and shoot it through a Hakim and it seems that it tears the rim off appx every 10th round ~not matter how far I open or close the gas valve ?.
Just my. 02
Waffen

[JBaum]

If that happened with me, I'd reduce the powder load. There is no advantage of having that much power that it tears the brass apart. Also, make sure your chamber is clean.

[waffendude]

I can close my gas valve all the way and it still has way too much power. I think the valve is either broke or just staying in the open position all the time.
Waffen