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View Full Version : how to make Yugo M53 ROF same as MG42


open ear shooter
August 16, 2015, 07:30
a long time ago i had a friend who claimed that some German Soldier's during WW2 would file down the bolt carrier to gain higher ROF in their MG42s

25 yrs on i learnt that there where 3 or so different weight carrier's that the MG42 had avalible which would alter the ROF, currently i have a M53 and wish to make it's ROF the same as WW2 MG42 so my question is what parts do i need i.e. light carrier,stronger recoil spring etc
do the lighter carrier have special codes ? or is this "light carrier" opinion fiction

BigBoy1
August 18, 2015, 06:55
Why would one to increase the rate of fire of an MG42?

From an engineering point of view, not a good idea. The parts were designed for the forces and loads generated by the required cyclic rate. Increasing the cyclic rate would increase the forces and loads on the gun parts, pushing them close to the breaking point. Without having the engineering specifications, one does not know how much margin of safety was designed into the MG42. Would an increase of 100 rpm be the failure point or would it be 500 rpm?

The WWII MG42 manuals I have see make no mention of different weight bolts. The post-war MG3 had a heavy bolt (950 grams) made for it and it required the recoil spring to be replaced with a hydraulic buffer. Also, the MG3 had a rate reducer which fit inside of the standard bolt.

On my MG42, with the standard bolt the rate is between 1150 and 1200 rpm. By adding the MG3 rate reducer inside the bolt, the rate drops to about 950 rpm. With the heavy bolt and hydraulic buffer, the rate is down to 600-650 rpm.

Abominog
August 18, 2015, 07:36
The MG42 ROF was variable gun-to-gun. I was just reading some study, forgot where, and the ROF on tested guns varied over 200RPM.

The heavy/ light bolts were experimental. Standard production all the same.

What is the ROF of your M53? It may well overlap with the MG42 ROF already. If your goal is to make it faster, check the weight of your bolt against an MG42 bolt. There are other factors as well such as recuperator shape, rail conditions, spring strength, etc.

open ear shooter
August 18, 2015, 17:40
Why would one to increase the rate of fire of an MG42?

From an engineering point of view, not a good idea. The parts were designed for the forces and loads generated by the required cyclic rate. Increasing the cyclic rate would increase the forces and loads on the gun parts, pushing them close to the breaking point. Without having the engineering specifications, one does not know how much margin of safety was designed into the MG42. Would an increase of 100 rpm be the failure point or would it be 500 rpm?

The WWII MG42 manuals I have see make no mention of different weight bolts. The post-war MG3 had a heavy bolt (950 grams) made for it and it required the recoil spring to be replaced with a hydraulic buffer. Also, the MG3 had a rate reducer which fit inside of the standard bolt.

On my MG42, with the standard bolt the rate is between 1150 and 1200 rpm. By adding the MG3 rate reducer inside the bolt, the rate drops to about 950 rpm. With the heavy bolt and hydraulic buffer, the rate is down to 600-650 rpm.

Why !? Historical accuracy and i like iconic barking sound a true MG42 make's

open ear shooter
August 18, 2015, 17:44
The MG42 ROF was variable gun-to-gun. I was just reading some study, forgot where, and the ROF on tested guns varied over 200RPM.

The heavy/ light bolts were experimental. Standard production all the same.

What is the ROF of your M53? It may well overlap with the MG42 ROF already. If your goal is to make it faster, check the weight of your bolt against an MG42 bolt. There are other factors as well such as recuperator shape, rail conditions, spring strength, etc.

at a guess the ROF on the M53 is about 850-900 its just not hitting the right beat of a 1100-1200 MG42, im going to start with changing the Bolt out then look at stronger spring

amafrank
December 12, 2015, 16:49
If your gun is running 800-900 rpm then something is wrong.
First thing to check is the recuperator. This is the tube that runs down the lower left side of the receiver. If the springs are broken or weak it will allow the barrel to slam into the trunnion which will damage both the trunnion and the receiver over time. With the barrel hitting the trunnion a lot of energy is lost and the rate of fire will go down.

Next thing to check is the buffer spring. This is the piece sticking out of the buffer housing that the buttstock attaches to. It is a big flat wire spring that returns energy from the recoiling bolt to the bolt in order to speed up the rate of fire. These springs sometimes crack or break and the rate of fire will suffer.

Next thing is the booster cone. This is the cup inside the booster assembly on the front of the gun. You will find cones with hole sizes that vary from about 11.5mm in dia to 14.5mm. If you're outside this range it will affect reliability of the gun and also can reduce the rate of fire.

In reality the guns from WWII up to the MG3 or MG74 of today vary in rate of fire. The range is about 1100 to 1300rpm in 8mm and 1000 to 1250 or so in 308. The weight of the bolt has very little effect on the rate of fire unless you do something drastic. The mainspring has little effect on the rate of fire but it will affect reliability.
The bolt catch which is sometimes called a rate reducer is in there to prevent the bolt rollers from moving out of the locked position in the barrel extension. It has absolutely nothing to do with the rate of fire. If installing one in your gun makes a difference in fire rate there is something else wrong. There is a harmonic in the bolt which causes the bolt rollers to bounce in and out of lockup and the spring loaded bolt catch damps the bouncing by smacking into the locking piece and absorbing some energy. It is only there to damp the harmonic and any weight it adds is of no account. The germans in WWII found that primer timing could cause the round to fire when the rollers were not locked and this blew the barrel door open in most cases and could destroy the gun. It is firing unlocked when this happens. There are a few different variations on the catch and one of them can be installed in a manner that preloads the locking piece in the bolt. This does not keep the rollers out as you might assume and merely causes more wear. The bolt catch should be installed in any of these guns and it should rattle back and forth as you shake the bolt. If you don't use this in your gun you're asking for trouble. Its not an optional part its a safety related piece.

There are basically 3 different weight bolts used in the MG42, MG3 and MG74. The bolt heads are essentially the same on all of them and all are interchangeable. The only real difference is the way the extractor is held in place.
The first is a 550gram bolt which is the earliest type and the one used in all the MG42's and M53's. The bolt body is cast.
The next version is the MG3 standard bolt used in both the MG3 and MG74 from the factory. The bolt body is the only difference and these are forged. They have a flat top and bottom and spring loaded feed roller so that you can close the spring loaded top cover with the bolt in any position. These weigh about 600-650 grams depending on when and by whom they were made. They won't affect the rate of fire at all compared to the very slightly lighter MG42/M53 bolt. Some call these the heavy bolt or the heavier bolt but they are really just the standard bolt used by almost all of the MG3's in the world.
The last type is the 950gram bolt developed by Piettro Beretta for the MG3's used by the italian army. You will find all the heavy bolt bodies are marked PB with a date, usually 1981. Italy for some reason wanted a lower rate of fire and by combining this bolt which is about 1 pound heavier with a buffer that absorbs recoil energy rather than returning it to the bolt they managed to get it down to about 700-800 rpm. If you use this heavy bolt with a standard buffer your rate of fire will be more like 1000-1100rpm and you will damage the receiver. I've fixed a lot of these because at one time the bolts were readily available but buffers were not. Now neither are readily available.
The rate reduction affected by the heavy bolt and its matching buffer was tough to do and does wear the gun more due to the weight of the recoiling mass. As far as I know the only ones to use this setup were the italians. The italians also made up a .223 conversion for their guns in order to reduce training costs. I've not seen one in person but have seen pictures and videos. The conversions appear to have not been widely adopted or reliable.

There is a lot of myth and mystery attached to the series MG42/MG74 but its not that tough to figure out. The bolt catch is a safety feature not a rate reducer. Rate of fire isn't changed by a few grams difference in bolt weight.

So back to your issue.....
make sure your recuperator springs are ok, Bob Naess of Black River Militaria replaces them. I'm not sure of the cost.
Make sure your buffer spring is ok. RTG parts has new and used buffers. The housing for the MG3 should fit the MG42 or M53 but not the other way round. This is due to the longer recuperator housing used in the MG3/MG74.
Make sure your booster cone has a hole diameter less tha 14mm and greater than 11mm in dia. Smaller means better reliability and more wear. Larger means less reliability but less wear (if it won't run it won't wear right?). Smaller also beats the gun more so that is where the wear comes from.

Hope something there helps


Frank