Post By JRIowa
Alternate material for Carpenter 158
Does anyone know of a "more-readily-available" alternative to Carpenter's Alloy 158?
We are currently making bolts for a very large AR-15 manufacturer. I have had several other smaller firearms companys contact me looking to purchase these bolts. But the material that we are currently using is supplied to us by our customer. The Carpenter 158 has to be purchased in 20,000 Lb lots and is roughly $5/Lb.
So I was wondering if there was another type of material out there that had the same chemical properties as the Carpenter 158, but could be purchased in smaller quantities (i.e. 1000 Lbs?) This is 3/4" dia. round bar stock.
158 is Carpenter's name for P-6 tool steel. Bethlehem calls is Duramold. The problem is that you don't see it as much as you used to. Most of the shops that I deal with use mostly P-20. Try the alloy suppliers in your area. Is your shop doing the heat treat on these parts? You can get a really hard case with P-6.
Carpenter 158 is just ANSI P6 steel. Perhaps look for a P6 supplier instead?
Personally if I was making a new AR-15 bolt I'd go with S7 should handle the stresses of the firing cycle alittle better. But probably also more expensive. Other then BCM and DD I don't think anyone else (except for Colt) makes them using Carpenter 158 anyways. I know there are many on the market that were made with simply 4140. And 8620 has always been a "go to" metal for American arms designers.
Do you know of any suppliers that sell the P6 steel? Does Bethlehem Steel sell directly to the public? I'm having trouble finding contact info for them.
Originally Posted by JRIowa
Bethlehem went broke in 2001. I don't think anybody picked up the tradenames.
Unless you can find somebody that has P-6 sitting on the shelf, you will need to purchase a mill run to get any. As I said earlier, nobody uses that alloy anymore for mold making.
$5/lb for special alloy steel in DCF rounds sound fairly cheap to me. Most of your other tool steels would probably be in the $8-10/lb for that kind of quantity. Others are much higher.
Sounds like a bolt that I know two different shops in Connecticut are making from that same material, Carpenter 158. Nasty stuff, I believe it's 27% nickel.
BTW, I found two different inserts that really perform well in turning that stuff:
Valenite WNMP432 M2 grade 9605, and Walter WNMG432 NM4 grade WSM20.
Which you choose depends upon the depth of cut and desired feedrate. I tested them both at dad's home shop, and found the Valenite one good for up to .100 d.o.c. @ .018 i.p.r., and the Walter works best at .060 d.o.c @ .022 i.p.r. I ran both at 240sfm and got good tool life. Once they start to go however, it happens fast.
P-6 mold steel machines fairly good. It's not high nickel, it's more like a 4110. About 1.5% Chrome and 3% Nickel. Most of the time it's case hardened it's only about 0.1% carbon.
Last edited by JRIowa; 03-11-2010 at 09:41 AM.
I see a couple outfits are touting bolts made with 9310.
IIRC, the original specifications for the GI issue model were for AQ-9310 (aircraft quality). The bolts were supposed to be good for 75K rounds, but most showed signs of cracking after 50-60K. I think that heat treat was changed to nitriding, but the numbers never got up to specificaitons.
P-6 and 9310 are very close in composition. The 9310 has some molybedenum while the P-6 has more chrome and nickel.
Which is better? Don't know, I barely made it through that class. IMO, the heat treat is probably more important than the alloy comp.
Anyone making parts for a large firearms maker can't just switch materials without a long process of testing and engineering approvals. Given that large orders primarily go off to government buyers, there would be risks of liability and, potentially, litigation if a material switched were to fail in any way. Even if no failure, any premature wear or performance issue that made the parts suspect could result in questions no supplier would want to entertain.
At the very least, risking a good contract would not be in anyone's best interest in this business climate.
You think that the 158 is nasty? We are all in agreement at our shop that it machines like butter. I'd love to use more of it if it was more readily available.
Originally Posted by PixMan
Well perhaps it was a different Carpenter alloy the other shops are using for the AR15 bolts then, because the Carpenter alloy I was helping them with was indeed quite difficult to machine and see any tool life.
Any luck in finding the best alternative to the Carpenter 158? Someone told us that Stainless 440C is a good material for M16 bolts particularly for the one piece gas-piston bolt carriers. We have not tried it since I believe it is more expensive but can be bought in smaller volumes. Have you tried this? We are also sourcing for a good alternate metal for the 158 which we can buy in small volumes like 1,000 to 2,000 lbs per order in 50mm diameter round bar.
Originally Posted by Tactical-N8
Hey i am new to this site, I am a AR-15 owner who modifies many AR-15 and other Guns
I use this company for my Carpenter 158 steels
industrial metal sales
it is moderatly priced and they ship quick
give em a try !