.38/.357 prototype

[RumRunr]

Well I live between Puyallup and Tacoma. Yeah can\'t miss the Fair. Let me know if you have a minute, maybe we can grab a drink.


Cheers

[Sparky_NY]

Just to prove I have not been totally slacking while you guys make so much progress.

 

Extractors are M16/Ar15 copies I made,   bolts have slot on bottom for ejector pin in pan.   Bolts made from 4140 prehard,  extractors O1.   Holes for firing pins done and rear bushing.   Firing pins are next.

[bruski]

Sparky,

 Your gears, bolts and extractors are looking really nice even your rag looks good with all that shiny on it. Did you use carbide cutting tools on the OD of your bolts or high speed steel?

 

 bruski

[bruski]

Howdy everybody,

 Just in case anybody lost any sleep thinking about the two firing pins that sounded different than the rest of them. It is caused by the .191 diameter drill wandering off its path by a few thousands while drilling to depth. The .186 diameter on the firing pin rubs the .191 bore a little causing a breaking action slowing it down just a fraction before it hits home. I drilled all six bolts with the same drill bit which must have dulled enough to wander a little. The bolts were center drilled from both ends so the small .075 diameter hole on the chamber end is centered but off on the inside. I guess I could just leave it alone and live with the different sounding firing pins or open up the .191 hole a little. If I open up the .075 hole, the primer strikes will be off center.

bruski 

[Sparky_NY]

Sparky,

 Your gears, bolts and extractors are looking really nice even your rag looks good with all that shiny on it. Did you use carbide cutting tools on the OD of your bolts or high speed steel?

 

 bruski

I cheated bruski,   the 4140 prehard was 3/4 diameter,  that is the mill finish on the OD.        I used carbide for all the milling on them.   

[Sparky_NY]

Howdy everybody,

 Just in case anybody lost any sleep thinking about the two firing pins that sounded different than the rest of them. It is caused by the .191 diameter drill wandering off its path by a few thousands while drilling to depth. The .186 diameter on the firing pin rubs the .191 bore a little causing a breaking action slowing it down just a fraction before it hits home. I drilled all six bolts with the same drill bit which must have dulled enough to wander a little. The bolts were center drilled from both ends so the small .075 diameter hole on the chamber end is centered but off on the inside. I guess I could just leave it alone and live with the different sounding firing pins or open up the .191 hole a little. If I open up the .075 hole, the primer strikes will be off center.

bruski 

Can you run a reamer in the tiny hole to true it up?     Otherwise,   I\'d go with the old standard,  If it ain\'t broke, don\'t fix it !

 

      I was REAL worried about drilling out the 4140 prehard I used for my bolts.    I ordered 3 cobalt drills, of each size.   The bolts are 6.204 long so its a real deep stepped hole.      Well, I used only one bit and it was as sharp as when I started.    I did it on the cnc lathe with a peck cycle which no doubt is why it was uneventful.

[Sparky_NY]

Hey Bruski, what did you run on your prototype gun and what would you recommend for a stickout on the firing pin?    

[bruski]

Sparky,

 I have .050 on the chamber end and .430 on the sear surface that rides on the cocking mechanism to the rear end of the bolt. I am not using a cocking switch with this one yet, but might add one later on.

bruski

[bruski]

Has anybody got an idea for a magazine or hopper to feed a .38 or 357 mag. reliably. The heavy bullet on the end of a long brass equals a lot of binding on a stick magazine made out of brass. Maybe if steel is used instead of brass the extra hardness would be slicker for the rims to slide down easier.

bruski

[Sparky_NY]

Has anybody got an idea for a magazine or hopper to feed a .38 or 357 mag. reliably. The heavy bullet on the end of a long brass equals a lot of binding on a stick magazine made out of brass. Maybe if steel is used instead of brass the extra hardness would be slicker for the rims to slide down easier.

bruski

Back on page 5 of this thread, I brought up the bruce feed system.    I am thinking that would be a good magazine for this gun and should hold lots of rounds.   As for the heavy bullet and long brass, well.... its not as long and heavy as the 45-70 that the bruce feed was originally used with !       What would be real cool is if the slide mechanism on the bruce feed could be made automatic when the one column of rounds goes dry rather than manually sliding it over.

[Roller]

Sparky,

 

The description of the Bruce Feed in the patent documents states that the cartridge carrier would swing over to the loaded side as the initial track was emptied.  

i tound out that .22 shorts won\'t do this. I manually slide it over.

 

Frank

[bruski]

I have been studying the patent also. I think that the spring tension on the magazine bottom has to be just right along with the heavier cartridges make this automatic swinging happen.

 

The grooves where the rim of the cartridge slides looks to be quite a bit wider than the thickness of the rims, I mean depth wise doesn\'t it? This means that the rims will be over lapping each other and tilting down a lot. It seems as they would be binding up more than sliding down like they should. In the beginning of this project, the stick magazine that I made had close tolerances and the cartridges would not always slide smoothly down to the bottom. So I guess I will try the wider looser grooves out and see what happens.

bruski   

[Sparky_NY]

I never realized the original bruce feed switched automatically.

 

Bruski, I had problems with the 22 magazine feeding until Cutter suggested making the T slot deeper, enough so the rims can overlap.   That cures my feed problems 100%,  it will feed as fast as I can crank, about 800 round/min.

 

I always think of some of the most reliable guns made, the 1911 45 auto, the AK47,  both are loose as a goose in their fits.    Tight fits are great for accuracy but loose wins for reliability.

 

No gat gun work this week, got the bridgeport head torn apart changing it over to a poly-V belt drive both for quietness and to get higher rpms.    I am waiting for the electric motor shop to call that they finished dynamically balancing the motor armature and its large pulley.    The noise from that head at high rpms was driving me crazy.   Pretty sure I will be good to 6500 rpm now which will be so nice with those tiny endmills.

 

I did work on the entire design in Fusion 360 though.  Have to nail down a lot of sizes before more chips.    The bolts are done, bolt carrier is next.

[bruski]

Does any body know the trick on how to machine the radius feed lip on the bottom and to the left of the star wheel where the cartridges feed onto the pan? Keep in mind that there is no access from the front or rear, just from the top (Fig. 10) or the bottom.

bruski

 

 

 

 

[Sparky_NY]

Is the radius even needed for our guns?   The pan in the patent drawing has a sawtooth shape, our guns feed straight down.   Once the bruce is down to a single column it should feed the same as any other mag from that point.      I wonder if the star wheel is needed also?

 

IF the radius is needed for some reason,  two pieces silver soldered is what I would probably do.  

 

Maybe Roller will chime in,  he built one for his gun.

[bruski]

You are probably right about the need for a radius on the lip as straight down would work on ours. I am thinking about trying the star roller because the patent said that it keeps the nose heavy cartridges from landing on the pan front end first then jamming the pan to a halt. If any body wants to read about the patent, go to google patents then type in the numbers 247,158 and pick the \"cartridge feed for machine guns\". Any other searches turned up nothing.

bruski  

[maccrazy2]

Out of curiosity, did you guys scale down from an original or up from a 22 and switch to centerfire? Or, is this a figure it out as you go project? Thanks.

[bruski]

HI mccrazy2,

 This is a build as you go project. I don\'t think that any of us have the same measurements with exception of maybe the barrels. If you decide to build one of these prototype 357\'s, keep the maximum OD of your receiver 4 inches or smaller. I am having a hard time locating some brass pipe or tubing large enough to cover my box cam that is 4 1/2 inches OD. I know that cutter and sparky are drawing there parts in Cad so they can make models of some parts if not all of them first which is great for cnc machining.

 Good luck with your builds,

bruski

[maccrazy2]

Thanks Bruski. I’m going to get my feet wet with a 22 first. It would be cool to do one of those someday

[Sparky_NY]

Hey Bruski,   how is the bruce feed investigating going?       Also, have you come up with any solutions to the problem of finding stock for your housing?