Machining drawings of Chinese 7,62x39mm ejector block/mag catch??

[TactAdv]

Does anyone have dimensioned drawings of the proprietary Chinese 7,62x39mm Bren conversion ejector block/mag catch (AK mag block) ??

I know it's a long shot, but figured I'd ask first......

I am working up a couple caliber conversions as I await transfer of my Mk II, and am starting on the x39 set up next. I am looking at doing a short CNC run of new blocks. Barring the availability of existing drwgs, would anyone be able to let me borrow an actual block that I will then run through the CMM and produce a new digitized model of, and from that produce a suitable set of .IGES file models to do the CNC run.

If I can borrow the part, I will return the favor by sending you a couple of the new-made 4130 blocks.....or whatever you want.

If I can get the parts made here soon, is there anyone else interested in them?? If I can get a run of >15 pieces, I'll probably make them.

-TomH

Information

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[Peter Laidler]

Seeing how 7.62 x54R works in a Vickers and the closeness of the cartridge length I'm just suprised that you're not going down this road.

The rounds seem to fit and feed in the Bren mags, .303" Bren barrels need just a slight modification to make them work with 7.62mm x54. I know people have made them work in 7.62 x39 but I am one that always tries the simple route first

[TactAdv]

Seeing how 7.62 x54R works in a Vickers and the closeness of the cartridge length I'm just suprised that you're not going down this road.

The rounds seem to fit and feed in the Bren mags, .303" Bren barrels need just a slight modification to make them work with 7.62mm x54. I know people have made them work in 7.62 x39 but I am one that always tries the simple route first

Greetings Peter!,
Wellllllll...YES....I am doing a x54R conversion, as well. If you saw my other posts recently, I am very close to completing a conversion of a 47rd DP-28 pan magazine for just this purpose. I have already done the necessary removing of the old DP magazine well adapter and done the CAD drawings and CNC file conversions to produce a new Bren-sized mag well adapter piece. I should have the new piece "in metal" by the weekend, and then I will TIG it back up under the DP pan, and off we go. My newly designed adapter fits well into a DEMIL'ed parts kit receiver piece I have. Doing the bolt face and barrel rechamber is not an issue. I seriously doubt whether anyone ever thought a DP pan would ever be on a Bren!

I have been reading multiple, numerous, comments on how different the 7,62x54R cartridge recoil impulse is....compared to .303 MkVII ball.....this got to me to investigating things....

I believe the best way to handle the differing "felt" impulse, without resorting to major changes in the angular relationship of the piston-post cam and bolt unlocking cam surfaces, which relationship is really where the issue lies given a specified impulse force, is to simply slightly alter the piston-post buffer dynamics.....re-spec'ing the designed spring there is probably unnecessary, so my take is to install an inner elastomeric polymer buffer, or second interior spring of a suitable rate, to slightly bias the unlocking of the bolt cam by a very slight margin, allowing just a short dwell time longer, or conversely, an impact buffer effect. I'll have to bore the post spring guide, but I've got several to play with, and I am going to start by counter-boring one a fraction of an inch and installing a small polymer buffer "plug" and we'll see where we are.

The 7,62x39 option is simple economics over here.....AK Mags and the ammo are cheap and plentiful. Since the only real effort needed is to clone the Chinese ejector block and ejector and rechamber a barrel, and a little bolt carving......too simple. The ones I have seen pictured seem to work well.

-TomH

[tankhunter]

TactAdv,

Had you thought of simply cutting off a top section/ lips of a .303" magazine. & TIG welding on the underside of your DP pan Mag? Wouldn't THIS be a far easier way to fi it to your gun? You might not have to machine the mag well out on the Reciever then?..............(Keep it Simple)

[Peter Laidler]

Sorry Tac, I come from the KISS school of apprentice training, experience and University. Keep It Seriously Simple - or something like that.

The Bren doesn't lend itself to impulse forces and the likes of other complications. It simply needs a volumme of gas mixed with a dash of simplicity added to a grasp of Boyles Law - and off it goes. The unstoppable Bren. If the remarkable Bren works extremely well with the powerful 7.92, 7.62 and .303 then if you can divert sufficient gas, it'll operate on anything less.

I don't know the economics of things in the US but if this 7.62mm x39 is a bit of as one-off project, then so be it. But if it's for an everyday reliable and commercial shooter, then I would doubt that there's a world shortage of cheap Bren magazines and 7.62 x54r steel cased ammo. But having seen a Vickers - and there's a gun that thrives on bags of wooooooomph generated by powerful ammo - thumping away non stop with 250 round belts of 7.62mm x54R with nothing but a slightly modified extractorway and barrel, then that good enough for me

[Peter Laidler]

Just been told that the 7.62 x54 rim is a teeeeny weeeeny bit large to drop into the .303" rim recess in the bolt but simplicity itself to machine the .008(?) extra diameter. Extractor still works a treat, still tightens up and rolls for primary extraction too.

I mean............. how much simpler can it be..... Same breech block, barrel and magazine to boot..........

[Kev G]

Tom
I have a spare ejector block over here if you can't find one on your side of the pond.
Will PM you.



ATB KG

[TactAdv]

TactAdv,

Had you thought of simply cutting off a top section/ lips of a .303" magazine. & TIG welding on the underside of your DP pan Mag? Wouldn't THIS be a far easier way to fi it to your gun? You might not have to machine the mag well out on the Reciever then?..............(Keep it Simple)

Yes, I immediately looked at that, but the limited strength of the sheetmetal didn't seem inviting. The DP pan uses the milled receiver interface for a reason. It is really no big deal to simply "copy" the concept over to the Bren receiver dimensions.

BTW-I think you may be mis-understanding my process here.....NO receiver mods AT ALL.....just machining a new receiver INTERFACE block, the machined block spot welded to the bottom of a regular DP pan...I just favorably dimensioned a new block to fit the Bren mag well straight across.....I will also figure out a simple front edge suppport/lock down.....not there yet.

I'm having more fun establishing the spot-welding heat range for the sheetmetal of the pan.....it's a weird alloy.... ;-)

-TomH

[TactAdv]

Just been told that the 7.62 x54 rim is a teeeeny weeeeny bit large to drop into the .303" rim recess in the bolt but simplicity itself to machine the .008(?) extra diameter. Extractor still works a treat, still tightens up and rolls for primary extraction too.

I mean............. how much simpler can it be..... Same breech block, barrel and magazine to boot..........

Oh, you'll just LOVE where my mind went this weekend.......and you're spot on, Peter, same breech block, magazine is the BIG attraction.

Let's just say,,,,,,,thinking WAY outside the box with this one.....I think I'll have the measurements and have it all run through the SolidWorks/COSMOS FEA analysis by tomorrow evening.....if it all flows...this is going to make a LOT of people who want to SHOOT their Brens a lot very happy, at least over here I think?? My goals are- Using cheap and VERY available cartridge cases for ease of reloading, using common reloading dies and equipment, availability and economy of favorable FMJ projectiles and ability to use available MILSURP tracer projectiles. I'm pretty sure I've found that combination for Bren applications.

Keeping the original Bren mag and bolt face/extractor is key.....stay tuned.

-TomH

---------- Post added at 09:19 PM ---------- Previous post was at 09:16 PM ----------

Tom
I have a spare ejector block over here if you can't find one on your side of the pond.
Will PM you.
ATB KG

Kevin- Stand by, please, I am still looking at doing this......just got sidelined this weekend with a really promising caliber conversion concept......offer MUCH appreciated, Sir!!

-TomH

[c310pilot]

This has a slightly different profile but looks pretty similar. Any confirmation on what it is?