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.38/.357 prototype


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#21 Sparky_NY

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Posted 31 May 2018 - 01:31 AM

Half inch diameter for the bolts does seem on the small side.    The .22 versions are roughly 7/16 and look at the difference in the diameter of the ammo.    A bigger diameter, 5/8???, bolt would give more room for the pieces.

 

I know there are hardly any posts on the forum these days BUT.....  I look daily and have a lot if interest in your project.    I have the barrels and plan on a .410 shotgun, 6 barrel gun build next.   As I always do, I expect to shamelessly steal your ideas.     Your gun design elements should apply to any center fire version and ideas for those are a rare find.

 

I am fighting the temptation to inquire with Cutter about that extra set of 38/357 barrels he has.  

 

George


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#22 Cutter

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Posted 31 May 2018 - 05:02 PM

Half inch diameter for the bolts does seem on the small side.    The .22 versions are roughly 7/16 and look at the difference in the diameter of the ammo.    A bigger diameter, 5/8???, bolt would give more room for the pieces.

 

I know there are hardly any posts on the forum these days BUT.....  I look daily and have a lot if interest in your project.    I have the barrels and plan on a .410 shotgun, 6 barrel gun build next.   As I always do, I expect to shamelessly steal your ideas.     Your gun design elements should apply to any center fire version and ideas for those are a rare find.

 

I am fighting the temptation to inquire with Cutter about that extra set of 38/357 barrels he has.  

 

George

Go ahead George, pull the trigger, it's risk free for 30 days


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#23 Cutter

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Posted 31 May 2018 - 05:48 PM

And by the way, the Carrier model in an earlier post
uses .875 diameter Bolts


#24 Sparky_NY

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Posted 01 June 2018 - 01:49 AM

 

And by the way, the Carrier model in an earlier post
uses .875 diameter Bolts

 

After cramming in the flat firing pin, hammer and extractor into the bolts for my DE hybrid, that sounds huge !  


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#25 Cutter

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Posted 01 June 2018 - 02:02 PM

My plan was to move the Bolt rapidly on the
helix to close the chamber. The pick up point
for cocking would be a radial move.
I would like to hear feed back , – or +

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#26 Cutter

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Posted 01 June 2018 - 02:24 PM

After cramming in the flat firing pin, hammer and extractor into the bolts for my DE hybrid, that sounds huge !  

 

 

The RG-G bolt compared to 7/8 diameter bolt

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#27 Sparky_NY

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Posted 02 June 2018 - 10:06 PM

 

My plan was to move the Bolt rapidly on the
helix to close the chamber. The pick up point
for cocking would be a radial move.
I would like to hear feed back , – or +

 

I am trying to digest what you are saying.     I think closing the bolt rapidly is just a matter of the cam profile and to make feeding more reliable, if I follow you correctly.    What I don't get is the radial move for cocking,  how is what you are thinking any different from the RGG approach?       Are you saying that it would cock after the bullet is fully chambered somehow?


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#28 Cutter

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Posted 03 June 2018 - 04:10 PM

I am trying to digest what you are saying.     I think closing the bolt rapidly is just a matter of the cam profile and to make feeding more reliable, if I follow you correctly.    What I don't get is the radial move for cocking,  how is what you are thinking any different from the RGG approach?       Are you saying that it would cock after the bullet is fully chambered somehow?

 

 Sparky,

The cam profile for a more reliable feed, and to prevent

the problem Bruski had with the recoil dislodging a feeding cartridge.

The RG-G picks up the cocking switch on a combined

radial/helical move at 90 deg. clockwise, putting pressure

at the cam and follower tangent point / hard cranking.

I think pulling the spring straight back is easier  



#29 Sparky_NY

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Posted 03 June 2018 - 06:20 PM

 Sparky,

The cam profile for a more reliable feed, and to prevent

the problem Bruski had with the recoil dislodging a feeding cartridge.

The RG-G picks up the cocking switch on a combined

radial/helical move at 90 deg. clockwise, putting pressure

at the cam and follower tangent point / hard cranking.

I think pulling the spring straight back is easier  

Ok, now I follow you.   Do you have a mechanism in mind to pull the pin straight back?    The only parts that move in a linear fashion are the bolts so rotary motion will have to be changed to linear motion to get that straight back pull on the pin.   

 

Interestingly,  the RGG gun uses 2:1 gear ratio while the DE gun uses 3:1.   I did not notice anything that I would call hard cranking but that may be due to the gear ratio.   I noticed in the first post, Bruski used a set of DE gears,  I wonder how he feels the cranking effort is?


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#30 Cutter

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Posted 03 June 2018 - 07:06 PM

Ok, now I follow you.   Do you have a mechanism in mind to pull the pin straight back?    The only parts that move in a linear fashion are the bolts so rotary motion will have to be changed to linear motion to get that straight back pull on the pin.   

 

Interestingly,  the RGG gun uses 2:1 gear ratio while the DE gun uses 3:1.   I did not notice anything that I would call hard cranking but that may be due to the gear ratio.   I noticed in the first post, Bruski used a set of DE gears,  I wonder how he feels the cranking effort is?

 

Yes Sir,

You are correct , there will be radial motion

while pulling back the shear


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#31 Sparky_NY

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Posted 03 June 2018 - 10:41 PM

I was wrong on the gear ratios,   RGG is 1.5:1 and DE is 2:1,   concept remains the same.



#32 bruski

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Posted 05 June 2018 - 04:13 AM

The DE gears seem to work ok with 6 bolts, but my springs are not much heavier than the RG-G bolts.

 

I have noticed that the aluminum carrier is a little bit on the soft side when it comes to the bolts sliding back and forth. The aluminum wants to gall up if not properly oiled which is a magnet for dirt. Maybe a little polishing of the bolts is needed on the bottoms.

 

 The steeper cam angle solved the problem with the chambering cartridges jumping out of alignment from the recoil of the firing barrel. I am not grasping the hammer cocking that cutter has in mind. Unless what you are saying is the steeper cam angle is the straighter pull on the hammer. That makes sense because I really don't even feel the hammers cocking on the 357 gat. with the steep cam angle.

 

bruski


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#33 bruski

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Posted 05 June 2018 - 04:16 AM

Cutter,

 What type of extractor are you planning to use with that 7/8 diameter bolt?

bruski


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#34 Cutter

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Posted 05 June 2018 - 02:38 PM

Cutter,

 What type of extractor are you planning to use with that 7/8 diameter bolt?

bruski

 

 

 

I like this one shown in the picture
of the bolt from a 1877 Colt Bulldog replica.
Heavy duty

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#35 bruski

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Posted 05 June 2018 - 05:10 PM

I was awakened in the middle of the night with a clear picture (subject to correction) of what cutter is talking about on the cocking subject. The cam that opens and closes the chambers does just that only. After the bolt is closed around 4 or 5 o clock position a second cam surface catches a tab on the firing pin hammer and cams it rearward just a little bit needed to fire the round. This second cam could be the piece needed behind the bolt to absorb the recoil. While it holds the bolt closed on the front end of it, the back side of it cams the firing pin rearward and then releases it at BDC. The spring would need to be a heavy stiff spring for this to work with the shorter cocking distance.

bruski  


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#36 Sparky_NY

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Posted 05 June 2018 - 08:21 PM

I was awakened in the middle of the night with a clear picture (subject to correction) of what cutter is talking about on the cocking subject. The cam that opens and closes the chambers does just that only. After the bolt is closed around 4 or 5 o clock position a second cam surface catches a tab on the firing pin hammer and cams it rearward just a little bit needed to fire the round. This second cam could be the piece needed behind the bolt to absorb the recoil. While it holds the bolt closed on the front end of it, the back side of it cams the firing pin rearward and then releases it at BDC. The spring would need to be a heavy stiff spring for this to work with the shorter cocking distance.

bruski  

If the separate cocking cam operates over a far shorter crank rotation, I would think it would make cranking erratic.   Smooth and easy then a stiff area while it cocks then easy again until the next sear engages.   The original design spreads the cocking effort out over a larger crank rotation and gives more mechanical advantage,  also a bolt is always engaged so crank effort is constant.  

 

Could be wrong, its just my thoughts.



#37 Sparky_NY

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Posted 05 June 2018 - 08:51 PM

The DE gears seem to work ok with 6 bolts, but my springs are not much heavier than the RG-G bolts.

 

I have noticed that the aluminum carrier is a little bit on the soft side when it comes to the bolts sliding back and forth. The aluminum wants to gall up if not properly oiled which is a magnet for dirt. Maybe a little polishing of the bolts is needed on the bottoms.

 

 The steeper cam angle solved the problem with the chambering cartridges jumping out of alignment from the recoil of the firing barrel. I am not grasping the hammer cocking that cutter has in mind. Unless what you are saying is the steeper cam angle is the straighter pull on the hammer. That makes sense because I really don't even feel the hammers cocking on the 357 gat. with the steep cam angle.

 

bruski

Aluminum is a decent bearing material.    Briggs and Stratton and others use aluminum connecting rods in small engines with no bearing insert, the rod runs directly on the crank.   I would use something like a silicone, teflon or moly spray lube that dries after the solvent evaporates.   The bolt surface can't be too polished either.  



#38 Sparky_NY

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Posted 05 June 2018 - 08:57 PM

 

I like this one shown in the picture
of the bolt from a 1877 Colt Bulldog replica.
Heavy duty

 

The 45-70 has about 3 times the muzzle energy of a .357 round.   (approx 1200 vs 3600 ft lbs)     7/8 seems like gross overkill.   Also, that replica gun is built from the original drawings I believe, they didn't have the material or machining options in those days that we have now.



#39 Sparky_NY

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Posted 05 June 2018 - 09:03 PM

 The bolt carrier and rear barrel plate are T 6 aluminum and the bolts are 1/2 inch cold rolled.
bruski

 

attachicon.gifpost-93-0-66992600-1419801742.jpg

From previous research,  4140 seems to be a very popular material for center fire rifle bolts.     For bushing type bearings and shafts, the norm is a soft bearing material and a hard shaft material, never soft/soft or hard/hard,  that is a recipe for galling/seizing.



#40 Cutter

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Posted 06 June 2018 - 03:33 PM

Hey Bruski,
You are a been there done that guy.
What changes would you make or suggest on the 357 build ??





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