Steel and Heat Treat for Falling Block

BruceS · May 1, 2020

This is an Idea, something that I can make.

But....every time I build a wildcat, it ends up being a 375 H&H or more powerful.

I have a Ruger and Falling Block Works "J". I need one just slightly bigger than the "J".

It uses a 3/4" x 1" block.

My original intent was to use 4140 pre-hard, but that was for 30/06 class cases.

This is for my own personal use, it will have a seam down the sides.

The front, drop block can be machined with a custom end mill.

So, my question is, Is 4140 pre-hard strong enough.

I have a professional heat treat only an hour away, if needed.

Suggestions Please.

Retired Tool and Die Mold Maker

Doug W · May 1, 2020

4140 has been used since the 30s?? for receivers and bolts.

4140 PH is usually in the 28-32 Rc range and usually down at the 28 end. Only the odd piece is near 32.

For my homebrew bolt action receivers I use 4140 hardened to 36 Rc.
The bolts are a bit harder, 42 ish.
I have the local HT place harden, temper then I machine. So it is PH, just not PH off the shelf.

Harder has more tensile strength and less 'stickiness', yet 36 is still machinable even with HSS.

BruceS · May 1, 2020

Doug W,Thank You!

That is what I found out also, that most of the pre-hard is 28.

I have been doing some searching about hardness of steel. I found Viscount 44, pre-hardened H13. Forgot about that! I use to machine it when I worked at the Mold Shop.....nearly 40 years ago. HS can cut it, but it was tough.

36RC sounds just about right.

Do you finish your bolts, then harden them?

john.k · May 1, 2020

I find with single shots that the harder the block the better ....soft blocks can jam from the opening force being non straight line .....this only happens if there is no lube on the sliding faces ,which does happen sometimes with guns.....Which is why I have generally sprung for the little extra for case hardening to a high hardness......Not the"pretty colour " jobs ,proper vacuum case ,ends up dull grey,but you dont need to worry about shrinkage and distortion.

DanielG · May 1, 2020

john.k said:
I find with single shots that the harder the block the better ....soft blocks can jam from the opening force being non straight line

Makes sense, having a decent hardness delta between them would minimize the risk of galling.

Doug W · May 1, 2020

BruceS said:
Doug W,Thank You!

That is what I found out also, that most of the pre-hard is 28.

I have been doing some searching about hardness of steel. I found Viscount 44, pre-hardened H13. Forgot about that! I use to machine it when I worked at the Mold Shop.....nearly 40 years ago. HS can cut it, but it was tough.

36RC sounds just about right.

Do you finish your bolts, then harden them?

So far all my bolts are store bought from PTG, but I have plans for making my own. I am just not there yet.
I would probably rough them out, harden and then finish.

I asked PTG what their bolts were hardened to, as I recall it was the mid 40s.

Here is a thread on broaching the lugways with HHS broaches.
https://www.practicalmachinist.com/...ya-someone-had-do-349085/?highlight=broaching

Actually got better broaching finishes with 36Rc than 28Rc.

ronan · May 2, 2020

There is a company in New Zealand who makes falling block rifles, cannot think of their name off hand. They used P20 steel for their actions. Just another option you might want to consider.

Edit; Its Soroka rifles. Technical Data - Soroka

BruceS · May 2, 2020

john.k said:
I find with single shots that the harder the block the better ....soft blocks can jam from the opening force being non straight line .....this only happens if there is no lube on the sliding faces ,which does happen sometimes with guns.....Which is why I have generally sprung for the little extra for case hardening to a high hardness......Not the"pretty colour " jobs ,proper vacuum case ,ends up dull grey,but you dont need to worry about shrinkage and distortion.

What steel are you using, and how hard is it before case hardening?

Just talking with my brother, he suggested hardening everything. Then when finished, have the drop block Ion Nitrated.

That way, I can fit all the parts, and just have minor fitting on the block if needed. The whole receiver will be 36 RC....other than the block.

This way, you still have hard rubbing on softer steel.

BruceS · May 2, 2020

Option #2 is to make all parts 36 RC, then Ion Nitride the Falling block.

#1 is to heat treat the block to 42 after machining. Ion nitride the contact surfaces only. Main body 36 RC.

Any other ideas?

Doug W · May 2, 2020

The heat treater I use has a cost per lb and a minimum charge.
If I recall 42 cents/lb and $90, that was for non atmospheric controlled.
The scale wasn't an issue since all my machining was after heat treat and tempering.
And there is an extra charge if they have different final hardness values in your lot.

My solution and biggest bang for the buck was bringing down enough material so that I met the minimum at 42 cents a lb.
So I have plenty of PH material for receivers and shop projects.

So if you start using different methods of heat treating the costs go up significantly.

If your breach block is a simple design w/o a lot of complex machining, I would just harden it to 42Rc and machine it.
Of course I would bring enough other material for breech blocks or whatever to meet the minimum.

BruceS · May 2, 2020

Kind of a rough sketch to show what I am trying to do.

Hope you understand it.

4575wcf · May 3, 2020

How will you be permanently joining the pieces? I have a similar project in the planning stages I am thinking 8620 and welding, then surface hardening the high wear surfaces.

BruceS · May 3, 2020

With a 30 degree taper, I am hoping to make a press fit in what I call the 'taper lock'.

Thinking that 30 degree on one side may work, may have to go to 45 degree. Or a true 30 degree dove tail.

But in reality, there will be a small pin in the 'taper lock'.

And, there is a 'key' in the rear halves, just to keep them even. Hoping to use the stock bolt area as the key.

ronan · May 3, 2020

Can i ask for what purpose you are making the receiver from four pieces of steel rather than one ? I made a square hole for my falling block receiver reasonably easily, i see you are a tool and mold maker, if i can do it you certainly can.

BruceS · May 3, 2020

ronan said:
Can i ask for what purpose you are making the receiver from four pieces of steel rather than one ? I made a square hole for my falling block receiver reasonably easily, i see you are a tool and mold maker, if i can do it you certainly can.

I couldn't come up with an easy way. My plan to have then cut with wire fell thru. Care to share how you did it.

Iv'e had several ideas about broaching the corners out, but hadn't found one that I like.

Doug W · May 3, 2020

Alphawolf over at home gunsmithing forums did his falling block mortise with a file roller jig.

Basically the file was guided by 2 rollers so you couldn't file out of plane.

His falling block was a work of art!

BruceS · May 3, 2020

Without a casting, I think that machining the inside will be easier with the three pc design.

I had thought of a round hole and broaching out the sides.

Doug W · May 3, 2020

The Mueller single shot book that village press sells, Mueller used the quill on his BP to single point the mortise, ala a vertical slotter.

I believe he made a simple clapper box.

I have done it with files and guides, it wasn't that hard.

MilGunsmith · May 3, 2020

Remember that you are building a 150 year old design, it could be made then with old school tools. Use a file after drilling and milling the majority of the material away. Old school apprentice work.

john.k · May 3, 2020

Work is the operative..hard work......I simply get someone with a wire EDM to cut a hole to 002" accuracy,and yes ,I have drilled and slotted, Ive also daily driven a prewar truck......now I have a couple of bucks ,I pay for the hard part done easily as possible.....Here s another tip for those without a Haas....its easiest to get alignment of the block hole etc if you do the barrel tenon first operation ,finished threaded ,and make up a dummy barrel stub that can be easily held for alignment ,especially if the action profile isnt a regular flat box.

Steel and Heat Treat for Falling Block

Aluminum

Hot Rolled

Aluminum

Diamond

Stainless

Hot Rolled

Cast Iron

Aluminum

Aluminum

Hot Rolled

Aluminum

Aluminum

Aluminum

Cast Iron

Aluminum

Hot Rolled

Aluminum

Hot Rolled

Stainless

Diamond

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