Check your MG34 "booster cone" ...a possible warni

[jimdvan]

I checked mine and it, too, was 9.5mm. I bought an 11mm jobber length drill bit from McMaster-Carr and chucked the booster in my 4 jaw chuck. I have an Enco 9x20 lathe. As I was testing the speed of the spindle I accidentally turned the switch to reverse. The chuck unscrewed a couple of threads and was stopped by the booster hitting the drill bit. The only damage done was it chipped my brand new $25.00 drill bit on each front cutting edge just in from the sides. I still was able to drill the hole cleanly then cleaned up the burrs with a needle file. I only wish my lathe would turn slower than 130 rpms.

[Barrel26]

The MG34 booster cone was originally made of steel and not stainless steel as used during WWll. Any cone made of SS is of a post war manufacture...which incidentally is not a bad idea.

[Barrel26]

And BTW, one of my cones measures 9.1mm and the other measures 8.01 ! Extremely close tolerances...almost approaching bullet diameter. Go figure...

[geladen]

checked mine, i bought a replacement for the one on the right from numrich. the damaged one is 9.1mm and the new one is 8.7mm. ill have the damaged one opened up. could these have been "fitted" to the gun by the builders?

[rocco1911]

WOW I will have to check on my kits to see what size they are?

[MGMichael]

The standard MG 34 duse orifice is indeed about 11mm and the duse is usually unmarked. These can measure from 10.75mm to 11.25mm depending on the amount of encrusted metal fouling deposited on them (which varies greatly according to the ammunition used) and how often they have been scraped clean, which tends to open them up. The smaller ones that are original WWII (I know nothing about the aftermarket semi-auto versions) measure around 9mm; some of these came out of MG 34/41s or MG 34Ss (the Schnell guns), though the possibility remains that they are BFA constrictors. The small ones are to be avoided when using ball ammo, as they beat up the guns unnecessarily, but some variation in the larger ones does not seem to make much difference in functioning.

The new-made stainless steel examples offered by Allegheny Ordnance have an 11mm orifice, and are a marvelous idea, as they are very easy to chemically clean without scraping.

Some ammo, notably the "Canadian" clandestine 7.9 stuff made for The Agency, atomizes a heavy copper deposit onto the duse that has to be chipped out with a pocketknife. Ugh.

M

[dwmmg08]

I just did a lot of work on my MG34, and I've had an 11mm cone in mine for years. All of the parts kits I've bought and the gun when I got it came with smaller diameter cones. i am very curious about the source for the 11mm comment now, as almost all of the parts kits or guns I have inspected appear to have a smaller diameter cone than that.

My problem was, with the Romainan 150 grain (steel core?) 8mm ammo, the gun would run well, but would run away occasionally. I had already replaced nearly all the parts and springs in the action. So I tried the smaller diameter cone to see if that was it? It was. Worked like a champ.

I'm not sure these cones are that rare, as nearly every parts set Iv'e ever seen has one in it. I'm wondering if it has something to do with the rounds used, and they probably were fitted to the gun. They certainly do not seem to have anything to do with blanks; with the blank adapter barrel, (2 piece) my gun runs ok even with the 11mm booster cone!

[schaubel777]

My S-243 TNW build was mostly matching with the cone at slightly less than 9.5mm. It runs great now but does sling the empties out with seemingly unneccessary force. My old 275 dollar FAC kit came with an 11mm booster and I'll be using that from now on so long as it cycles the bolt reliably.

[TactAdv]

There is some pretty well placed, though still anecdotal to this point, evidence that the 9,0-9,5mm booster nozzles are original wartime German issue, but for a very refined purpose.

Despite the huge metallurgical and machining technology advances that the Nazi's enjoyed in making their weaponry, they were still confronted with the same serious issues that everyone else was when it came to having access to suitable high quality weapons lubricants. For the most part, they spent the war like almost everyone else, with a less than ideal lubricant situation in that they always used petroleum-based, or later synthetic esters (coal oil using Bergius hydrogenation process/Fischer-Tropsh process/or PAG-polyalphaolefins) which all still performed like petro's in the environmental aspects. In very, very cold weather.....like that found auf die Ostfront, all petro's became unsuitable due to thermal viscometric properties that basically turned the lubricants into glue. The only solution was to continually heat the metal surfaces....any way possible......or, simply run the guns absolutely bone dry, sans any lubricant. German war time lubricants were generally used uninhibited, and no inhibitors or additives were used in almost all cases, the one major exception to this was in weapons lubricants where two purpose-designed additives were employed regularly. The first was the common "flowers of sulfur" which was nothing more than finely powdered sulfur that when added to the oil bonded to the metal as a metal sulfide coating adding a measure of anti-scuffing protection. This was abandoned with time as a more modern and refined version known as "Mesulphol" which was a synthesized product that was (usually) combined with a competing-action anti-corrosive substance additive known as KSE (korrosionschutzester). Despite the radically improved lubricant properties, these lubes were still at the mercy of extreme low temperatures and their attendant problems.

One of the measures taken to alleviate sluggish running was to increase the available system energies in the recoiling parts and this was ostensibly documented to be the source of the smaller diameter booster nozzles. Currently, the only sources for this information seem to limit the discovery of these parts only in guns issued, or found later, in areas where fighting took place in extreme cold conditions. Guns known in Finland, the Baltic States and Ukraine have been shown equipped with the smaller booster nozzles, as discovered. The theory seems to be consistent with the notion that the smaller nozzles were intended to impart a starting energy that was significantly higher as to overcome any tendency for the lubricated surfaces to resist movement, or alternately, for any un-lubricated surfaces to adhere from frosting. Once running, available heat from combustion and friction was probably generated to warm the larger surfaces sufficiently to keep the gun functional for a reasonable duration.

Other combatants generally, particularly the Finns, ran their weapons completely dry in arctic conditions preferring the accepted levels of wear over tendencies to fail to fire. The Soviets went in the other direction and completely went away from petroleum based lubricants and even HC synthetics, and developed a wide range of excellent animal fat based synthetic lubes, to the extent that almost all Soviet vehicles never saw a drop of petroleum oil or grease, ever. The Soviets issued no weapon-specific lubricants; one used what was available so probably everything imaginable was used, some with good results, some bad.

It seems now entirely probable then that these 9,0-9,5mm booster nozzles were completely normal issue in certain areas for assisting with functioning when faced with a still vexing issue of less than perfect weapons lubricants. There does not seem either, to be any records extant that document this as logistical fact, only the guns themselves so equipped survive to tell their story. And since so many of the "parts kits" guns came from these areas, it should some as no surprise really to find these smaller booster nozzles in many of this origin of kit gun.

-TomH

[mossie]

Brand new member,just joined today.
Question..
Noticed in some older post.Booster cone should be 11mm in dia.
Mine is 9.5mm.
Where might I fine the correct part?
Best to the group.
Mossie

[tomcatshaas]

Mossie,

most just ream it out to the correct size. Use a carbide reamer as the cone is hardened.
TC

Brand new member,just joined today.
Question..
Noticed in some older post.Booster cone should be 11mm in dia.
Mine is 9.5mm.
Where might I fine the correct part?
Best to the group.
Mossie

[pryotex]

Reading over this thread, I have two cones, both are 9.1mm I will throw one of them in my annealing oven and machine out to 10mm and then re-harden / temper it. Then I will see if there is a difference. I do have 10mm 10.5mm 11mm and 12mm endmill and then the cross with the standard sizes so I might play with what works well with the my gun.

Great info here, Love it.

[landser]

my booster cone is stamped 9.5 on the side of the cone.i drilled it out to .440 dia. or just under 11.25mm
Jeff G

[mg42jamesw1]

After reading this and previously checking my booster cones on my MG42, I thought I better check my MG34 booster cone hole size. It is a good thing I did as I have not fired the gun in quite a few years and it needed cleaning like no tomorrow. Anyway, I measured the booster cone size as close as I could with a dial caliper and it came out as 8.9mm. Since I also have a 308 conversion kit for this gun, I thought I might have mixed up the cones. After the better part of 4 hours searching for the conversion kit, I measured the 308 booster cone hole size it was 8.65mm +or- .05mm as the hole size was not perfectly round. The 308 booster cone appeared to be a hard chromed steel unit. I noticed AA is still selling the 11mm stainless booster cones so I ordered one today. I remember this gun always seemed to have, what I thought was excessive recoil and an excessive rate of fire. More like my MG42 with the light WW2 bolt installed. Now I might know the reason why. I'll try the 11mm cone when it comes and if need be I can modify my 8.9 cone to somewhere in between. Maybe I'll even enjoy shooting this gun again.

[haak48]

my booster cone is stamped 9.5 on the side of the cone.i drilled it out to .440 dia. or just under 11.25mm
Jeff G

The 9.5 stamped cones are for use with the l.s. ammo (86 grain, aluminum core) not that common. JH

9.5 mm cone for l.s ball.jpg (4.62 KiB) Viewed 4810 times

[mg42jamesw1]

I'm not sure why the booster cone that came with my pre-86 DS MG34 has the hole size so small (8.9mm). Maybe the previous owner had cycling problems and this covered it up. Either way, this is now my new project gun so I'll try the 11mm cone for 8mm ammo and start checking all the other parts to see if they are within specification. By the way, what hole size is most common with the 308 conversion units. I'll also ask BRP if they know as they are still selling a booster cone for the 308 conversion. The 308 conversion unit that I have is an early prototype with a cut and welded feed try and welded piece on the feed pawl and apparently a drilled out cone as the hole is not perfectly round, and a nice barrel. I remember the gun cycled fine in 308 but it will definitely be looked at further. Does anyone know if there are 308 calibrated sights for the MG34? Any more MG34 8mm feed trays around? I like BRP's 308 conversion for the feed tray better than my cut and shortened one. It would be nice to be able to mount a drum to the tray.

[mg42jamesw1]

In talking with BRP, they indicated it is not the hole size but the volume size of the 7.62 booster cone that allows the 7.62 cone to give the greater back pressure needed.

[HauptfeldwebelGVF]

I just got my TNW and it had a 9.3 mm cone. It seems they haven't cared to fix that problem. I'll be buying an 11 mm soon!

[Abominog]

There are at least four cone sizes from 9.5 to 11.5. Not withstanding the evidence that the 9.5 was to specific ammo, that multiple sizes exist may be indicative that the cones could be used to tune for conditions. For example a gun heavily used in running battle (eg Kursk) could have been made to run better without thorough cleaning with a 20 second cone swap. This is only theory as I’m unaware of gunners kits containing multiple cones. Even if it were not practiced in wartime it is practical for contemporary shooters.

[shooterike]

When using full power 7.9mm (8mm) ammo you should check the booster cone. The WW2 German soldier method was to slide a regular 7.9 x 57mm cartridge into the small diameter end it should go past the shoulder and it should stop somewhere before the rim. If it totally falls through, the MG 34 will not function properly.