Gunsmithing Rockwell hardness levels - in real life?

[ProudKiwi]

Hi all,

Firstly, I freely admit that I am a noob at this sort of stuff so please ignore any incorrect terminology etc

I've got a bit of a project going and I have been reading lately about the suggested differences in hardness between the bolt face and barrel to reduce/eliminate galling.

Now I understand that ideally there is at least 5 points of difference between the two but my question is - how big a difference is 5 points in real life?

I have had my barrel/reciever (it's a Blaser R8) tested and it's apparently 36. The material I'm looking at using (17-4 ph) is about 41. Is the 5 points a massive difference or would I be better to get someone to anneal it down to 36ish before commencing the machine work?

Also, I assume that the bolt is usually harder?

Thanks in advance.

 

[turbo54]

Re: Rockwell hardness levels - in real life?

what is the 17-4 going to be?

Annealing 17-4 is a huge PITA, by the way.

 

[ProudKiwi]

Re: Rockwell hardness levels - in real life?

The recieved will be made out of 17-4. The plan is to screw a barrel blank into the end of it.

I did not know that about 17-4! Ideally I would like to leave it as it comes which is what prompted my question in the first place. Is the 5 points between 36 and 41 huge?

One of the challenges with the Blaser is I can't hardness test the bolt as its a collet.

 

[turbo54]

Re: Rockwell hardness levels - in real life?

I'm still confused what you're actually asking about.

Yes, conventional wisdom says locking lugs on the bolt should be a different hardness than the lugs on the receiver/barrel extension/breeching ring/whatever. The two surfaces that touch, locking the bolt is what we're talking about.

Not the barrel.

Does it really matter? Don't know. My Win70 has been salt bath nitrided, nd both bolt and receiver surfaces are ~70Rc and they're doing just fine.

Are you making both a bolt and receiver?

17-4 is a fine material, why not just buy it at the hardnesses you desire (41 bolt, 36 receiver)? Or, just treat them differently (H900 bolt, H850 receiver)?

 

[romanleader]

Re: Rockwell hardness levels - in real life?

Kiwi, you'll be fine leaving it as it comes in at 41rc.

Good luck with the project!

 

[ProudKiwi]

Re: Rockwell hardness levels - in real life?

Turbo - Its hard to explain unless you are familiar with the Blaser line. Basically they dont have an action/reciever in the way a Remington does for example.

At the chamber end of the Barrel there is an extension (its all one piece from the factory)that has a recess cut into it. The bolt, which is a collet, opens up into this recess. Im proposing making the 'reciever' end out of 17-4 and threading it to take a barrel blank.

I just want to avoid galling hence the question relating to hardness.

Romanleader - Thanks for that

 

[pcschwenke]

Re: Rockwell hardness levels - in real life?

ProudKiwi,

17-4 is prone to galling. I've seen an engineer install a 3/8-16 stainless steel fastener into a tapped through hole with his fingers. The bolt never came back out without the use of a Milling machine. This doesn't happen every time but 17-4 wouldn't be the best choice if galling is to be avoided. Our company makes parts from 17-4 everyday up to 22" in diameter. Your Rc41 hardness tells me it' most likely heat treated to the H1025 condition. Machining as mentioned above can be a PITA but, with the proper tooling, it's not bad. Be sure to use carbide tooling everywhere possible. Carpenter does make a project 70, 17-4 material. It has similar properties but machines easier and is less prone to galling.

 

[LRI]

Re: Rockwell hardness levels - in real life?

416 or 15-5ph is a more popular choice for receiver material.

17-4 will work harden very easily. even in the H1150 solution annealed state unless your tooling/speeds/feeds are jonny on the spot.

Getting 416 to 41-42 can be tough so I'm told. Better have a lengthy conversation with your heat treater. I'd send a sample coupon first and have them harden it, then test independently afterward to ensure.

Also, HOW the receiver is quenched is important when dealing with air quench steels like 15-5. It's not as simple as putting a fan in front of it. Where/how the air hits it can have a big impact on tolerances moving around.

Nesika found this out the hard way after Garrett and I left in 06/07 when attempting to substitute 15-5 for 17-4. The receivers warped.

You'd be wise to talk to Jim Borden. He's a wealth of knowledge/experience and he uses a particular grade of SS that seems to work really well. He has a particular recipe of steel that he uses that yields some really good results.

Good luck.

C.

 

[JJones75]

Re: Rockwell hardness levels - in real life?

I machines alot of 17-4 as well as some other semi exotic and exotic stuff and for the most part its a pain in the ass and 4340 could do the same job thrength wise and is easier to heat treat and machine.

Another problem with 17-4 is that is galls bad. I made a suppressor (legal form-1) 100% out of 17-4 and it turned out great , super strong pretty light weight but i could have likely made one a couple ounces heavier out of 316 or 304 that would be just as strong and way easier to make

What is your particular reason you want to use 17-4?

 

[ProudKiwi]

Re: Rockwell hardness levels - in real life?

PCSchwenke - Hmmm, galling is less than ideal, especially in a collet type bolt arrangement. Thank you for your feedback.

Chad - I was hoping you would chime in especially given that it was you that made me aware that galling could be a problem in the first place. The intention is to get the metal to or as close as I can to 36 Rockwell as that is what the factory "receiver" tested out too. I was planning on having the round bar stock treated before machining to aviod any movement. I am certainly open to other suggestions re the type of metal used. 17-4 is what was suggested to me by the engineer.

JJones - As above, I am absolutley open to suggestions other than 17-4 if you think there is a better way to do it.

Thanks in advance.

 

[LRI]

Re: Rockwell hardness levels - in real life?

416 or 15_5ph would be my choice.

The 17 stuff is just a bit gummy and that means it wants to booger up. 15 is better, but still suseptible to it. The 400 series seems to be the ticket.

Chromoly is worry free if your willing to address the corosion.

C.

 

[Ring]

Re: Rockwell hardness levels - in real life?

have it nitrided, it will be RC 60 to 70 when done...

www.blacknitride.com will do it cheep, ask for shade, tell him Ring sent you from SH...

 

[turbo54]

Re: Rockwell hardness levels - in real life?

If material cost is of little consequence, consider some ALLVAC C350.

Exceptionally strong, excellent impact toughness, great corrosion resistance, and machineable.

It will end up being 5+ points harder than your bolt, rather than 5pts softer.

 

[pcschwenke]

Re: Rockwell hardness levels - in real life?

I'd use 416 if it were me. The two precipitation hardening materials 15/5 & 17-4 are very similar in properties. In transducer development, 17-4 is much better. 15/5 is sometimes used but can have other issues. We've found that it warps more do to internal stresses more often than 17/4 but again, that's our companies experience of being in business for over 50 years. I'm not knocking 15/5 as it is a great material. Machining of 416 would be much easier than that of either materials listed above.

 

[turbo54]

Re: Rockwell hardness levels - in real life?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pcschwenke</div><div class="ubbcode-body">I'd use 416 if it were me. The two precipitation hardening materials 15/5 & 17-4 are very similar in properties. In transducer development, 17-4 is much better. 15/5 is sometimes used but can have other issues. We've found that it warps more do to internal stresses more often than 17/4 but again, that's our companies experience of being in business for over 50 years. I'm not knocking 15/5 as it is a great material. Machining of 416 would be much easier than that of either materials listed above. </div></div>

My family is in the force transducer industry. 17-4 is the gold standard for that application.