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Posted: 8/9/2017 9:49:27 PM EDT
[#1]
Why no nitriding?
What are your thoughts on the Sharps S7 bolts now that they seem to have figured out the heat treat? Btw, I never got your address in our emails. I need to order parts for you to work on. |
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Posted: 8/9/2017 11:18:52 PM EDT
[#2]
Quote HistoryQuoted:
Hope I am not boring you guys. You're putting on a goddamn clinic in here *Bill Burr voice* |
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Posted: 8/10/2017 12:25:39 AM EDT
[#3]
I am no rocket scientist . Everything I have posted is out there if you want to find it. I make all my own parts except plastic. When I take on making a part, I research it to the inth degree. That is what you do when your only hobby is work and building rifles and sleep a little. The bolt is the heart of the rifle. It takes a beating. Trying to build a stronger bolt while staying within the confines of a set dimension is a challenge. My 7.62x39 bolt is a heavy 3 lug. I make my own extension and carrier so I can make it as bullet proof as I want. When doing 5.56 and being compatible with common extensions, it is a challenge. There is 2 choices. Better material or better procedures. There is so much to be gained in a very small dimension change and procedure, I no longer think the super alloys are that necessary. S-7 is not a super alloy. It has been around a long time. If I could heat treat 9310 or 158, I would use it. If a manufacture makes a bolt that goes 4000-8000 rounds, that is a lifetime for most. Even so there will not be complaints that far down the road. Why change? The reason I no longer nitride is because it can fracture. Nitride depth is usually in the .003 to.007 depth. The base under it will be around C scale 52-55. The nitride layer is 62 plus. When flexing, the outer crust can get micro fractures . A fracture never stops. The Mil Spec blueprint says no nitriding. I have a wet mag machine. I have seen it. Craig
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Posted: 8/10/2017 9:14:59 AM EDT
[#4]
Quote HistoryQuoted:
Roller burnishing the filet radius is the way to go. Bolts made from 9310 and 158 would increase life dramatically just by increasing the filet radius behind the lug and roller burnishing. That is where almost all the stress concentration is. Mil spec calls for .020 +0 -.010. .020 is minimal to begin with and .010 is crap. Just by going to .030 is huge. There is enough relief in the extension to do it. Some time every one should take a look at a bolt under magnification. You can usually tell a good bolt from a not so good bolt real easy. A very common mistake is where they cut the lead in angle on the back side of the lug where it first enters into the extension. If they plunge down and go into the base diameter , that puts a sharp corner in the lug filet. That is where it will eventually fail. I was real hot on all the new super alloys for a while. I was going to find that KRYPTONITE. All I really did was drive myself nuts. A couple dimension changes and procedures is real all that is needed.I also got away from nitriding bolts. I am back on planet Earth now. Craig 1) My bolt drawing shows that radius to be 0.020 -.005 inch. Still it’s not a huge difference but with the stresses at this location that extra five-thousandths of an inch are important. And, the 45 degree angle cut on the back corner of the lugs are supposed to have the same 0.020 -.005 inch radius at the base, they shouldn’t be a sharp corner, if they aren't made to print. 2) The diameter of the bolt behind the lugs is 0.550 - .005”, add the two 0.020” fillets, the flat rear face starts at 0.590” dia (MMC). The extension central bore is 0.572 +.005”, and it has two 0.020 chamfers in the inside, so its flat surface starts at .612” dia (MMC). Increasing the fillet on the bolt to 0.030 -.005” will reduce the potential clearance on the flats to a mere 0.002”. And, if there is any abnormality that causes the bolt to be off center by more than 0.003”, which would be just about anything that would put a sharp impact line on the back of the lug, which will defeat the purpose of the increased fillet, if not make it worse. Yes, you are correct, an easy fix to bolt life would be to increase the fillet radius. But, there needs to be a corresponding adjustment to the internal chamfers on the extension as well. The other possible solution is to do what Stoner did when he made the Stoner 63 - make the lugs slightly bigger, and trapezoidal in shape when viewed from the front. Unfortunately, this too, requires a new extension design. |
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Posted: 8/10/2017 9:55:03 AM EDT
[#5]
Quote HistoryQuoted:
Why no nitriding? What are your thoughts on the Sharps S7 bolts now that they seem to have figured out the heat treat? Btw, I never got your address in our emails. I need to order parts for you to work on. I have one and bought one after the recall. |
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Posted: 8/10/2017 11:29:15 AM EDT
[#6]
Quote HistoryQuoted:
. Yes, you are correct, an easy fix to bolt life would be to increase the fillet radius. But, there needs to be a corresponding adjustment to the internal chamfers on the extension as well. . Just burnishing the bolt lugs themselves is enough to double bolt life. |
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Posted: 8/10/2017 12:20:40 PM EDT
[#7]
Quote HistoryQuoted:
According to government testing that's not true. Just burnishing the bolt lugs themselves is enough to double bolt life. I never stated that it was the only possible fix. If you could forward any reports or other documentation on lug burnishing, it would be appreciated. |
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Posted: 8/10/2017 1:29:04 PM EDT
[#8]
I found a Power-Point on LPB of the bolt lugs from RDECOM, that is long on pictures, but short on data. But,I did notice that your “double the life” comes from the testing of ONE bolt.
Having done some low-cycle fatigue testing in my career, having the number of cycles to failure that increases by a factor of two between the low and high side is not uncommon, so was this one bolt on the high side? Low side? Or, was it average? As of that report they were testing six of each type (LPB and standard) to determine the real safe fatigue life of the bolt.* So, the life increase is “yet-to-be-determined”. Depending on the exact amount of residual stress imparted by the burnishing, you might get more, I am pretty sure you will get a significant increase in any case. _____________________ * Which is shorter than you think, it usually runs 1/3 of the average number of cycles to failure, so if the average number of cycles to failure is 15,000 rounds, the safe fatigue life will be around 5,000 rounds. The reason for this is fatigue is not very predictable, and the ‘safe fatigue life’ is set so that no part will fail due to fatigue before the official retirement age. |
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Posted: 8/10/2017 2:02:11 PM EDT
[#9]
Quote HistoryQuoted:
Yes, you are correct, an easy fix to bolt life would be to increase the fillet radius. But, there needs to be a corresponding adjustment to the internal chamfers on the extension as well. |
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Posted: 8/10/2017 2:50:35 PM EDT
[#10]
Quote HistoryQuoted:
Isn't this one of the purported advantages to the ARP Superbolt, but without any extension changes? You could reduce the lug root diameter and move the radius away the from the extension lug, but then would the taller lugs make a difference? You could model it and see. Me, I'll just look for cracks periodically. |
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Posted: 8/10/2017 3:44:50 PM EDT
[#11]
Thank you @BlackRifleJuju and @CMSENGINE
Great thread!!! There are times I wonder why I hang around here and times I'm astonished at the knowledge to be gained. This is definitely the latter. |
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Posted: 8/10/2017 4:18:22 PM EDT
[#12]
Quote HistoryQuoted:
Probably, but what happen if you get the Maximum Material Condition (MMC) and the extension pounds a notch in the radius? You could reduce the lug root diameter and move the radius away the from the extension lug, but then would the taller lugs make a difference? You could model it and see. Me, I'll just look for cracks periodically. |
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Posted: 8/10/2017 4:35:54 PM EDT
[#13]
Quote HistoryQuoted:
Ironically enough it looks like it won't matter anyways since the Army is in the process of replacing the M4 with a .308 rifle. 
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Posted: 8/10/2017 4:59:05 PM EDT
[#14]
Lysander. You are correct that some extension may have an issue with increasing radius to .030. What I have found is that if you also undercut the radius into the base diameter by .005, the extra radius far out weighs the reduction in diameter. Because S-7 is touchy, I always make one extra bolt each batch(we are talking only 10-15 bolts at a time). I built a bolt destruction press and I see how it stands up. I do the same with the extension. I do not know any other way to test it. I assume that all the batch will be consistent. What say you? Craig
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Posted: 8/10/2017 8:18:33 PM EDT
[#15]
Quote HistoryQuoted:
Lysander. You are correct that some extension may have an issue with increasing radius to .030. What I have found is that if you also undercut the radius into the base diameter by .005, the extra radius far out weighs the reduction in diameter. Because S-7 is touchy, I always make one extra bolt each batch(we are talking only 10-15 bolts at a time). I built a bolt destruction press and I see how it stands up. I do the same with the extension. I do not know any other way to test it. I assume that all the batch will be consistent. What say you? Craig If all the bolts are made from the same piece of stock (or at least the same run of steel) and are heat treated in the same batch, your assumptions are pretty good. |
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Posted: 8/10/2017 8:21:18 PM EDT
[#16]
CMSENGINE, and lysanderxiii, please enjoy your new Team Memberships.
Thank you for your contributions. |
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Posted: 8/10/2017 8:32:51 PM EDT
[#17]
Quote HistoryQuoted:
CMSENGINE, and lysanderxiii, please enjoy your new Team Memberships. Thank you for your contributions. 
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Posted: 8/11/2017 3:35:15 AM EDT
[#18]
Quote HistoryQuoted:
NICE.... |
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Posted: 8/11/2017 7:27:45 AM EDT
[#19]
Quote HistoryQuoted:
I think you should have more ar's and not worry about breaking or wearing one out |
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Posted: 8/11/2017 2:20:22 PM EDT
[#20]
Quote HistoryQuoted:
Doesn't look like the changes have been applied yet. I'm not seeing that bronze star. I hope I didn't do it wrong. |
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Posted: 8/20/2017 3:04:20 PM EDT
[#21]
SRC has their S7 DLC bolts for $45. I decided to buy 3 as replacement / backup bolts.
http://store.srcarms.com/product-p/xpb.htm |
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Posted: 8/20/2017 4:46:46 PM EDT
[#22]
The Diemaco bolt carrier groups as pictured on page one have an excellent reputation. I am building something to put one in.
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Posted: 8/20/2017 7:26:06 PM EDT
[#23]
We need to start lobbying for roller burnished bolts.
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Posted: 8/20/2017 7:46:52 PM EDT
[#24]
Quote HistoryQuoted:
I know some will say it's just bling but I love my Toolcraft with Cryptic coating. I have never really had a problem with any but the CC really doe's just wipe off. |
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Posted: 8/20/2017 10:31:52 PM EDT
[#25]
Thank you for the Team membership. I do appreciate it. Craig
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Posted: 8/21/2017 12:05:14 AM EDT
[#26]
Quote HistoryQuoted:
SRC has their S7 DLC bolts for $45. I decided to buy 3 as replacement / backup bolts. http://store.srcarms.com/product-p/xpb.htm |
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Posted: 8/21/2017 5:24:23 AM EDT
[#27]
Quote HistoryQuoted:
Why use an unknown as a backup? I've got a couple rifles that see a decent number of rounds and 50k 5.56 to use up. So I'll probably need a bolt or two, especially since a couple cycle at 1200rpm or so. Even if they ended up not working right I've got multiple spare rifles. |
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Posted: 9/3/2017 12:36:35 AM EDT
[#28]
I have to resurrect & slightly hijack here.
Over the past few years I've noticed an abnormal amount of wear on some cam pins, are there any hardness & materiel specs for the cam pin? Who makes the best one? I've never had an issue with using old surplus (probably Colt) cam pins that I purchased decades ago, but some of the ones that came in a few newer guns seem to wear fast! PS: Outstanding thread! This thread is a great example of the high level of expertise possessed by the members here. |
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Posted: 9/3/2017 12:48:31 AM EDT
[#29]
Quote HistoryQuoted:
I have to resurrect & slightly hijack here. Over the past few years I've noticed an abnormal amount of wear on some cam pins, are there any hardness & materiel specs for the cam pin? Who makes the best one? I've never had an issue with using old surplus (probably Colt) cam pins that I purchased decades ago, but some of the ones that came in a few newer guns seem to wear fast! PS: Outstanding thread! This thread is a great example of the high level of expertise possessed by the members here. http://damageindustriesllc.com/store/index.php?route=product/product&product_id=308 Generally I just inspect cam pins while cleaning and swap them out if they show heavy wear. I don't recall many reports of broken cam pins. I've heard of more bolts cracking at the cam pin than than broken pins. |
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Posted: 9/3/2017 10:42:47 AM EDT
[#30]
I have always focused on getting my bolt from the same company as the barrel and found that to be more important as bolts are generally good for some time. The only bolt I have ever had a issue with was a AA one and it was promptly replaced.
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Posted: 9/3/2017 10:56:04 AM EDT
[#31]
Quote HistoryQuoted:
It seems a bit difficult to find cam pin specs. I decided to try these cam pins as they're on sale and have free shipping this weekend. http://damageindustriesllc.com/store/index.php?route=product/product&product_id=308 Generally I just inspect cam pins while cleaning and swap them out if they show heavy wear. I don't recall many reports of broken cam pins. I've heard of more bolts cracking at the cam pin than than broken pins. I suspect it was due to Hydrogen Embrittlement. |
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Posted: 9/3/2017 11:50:15 AM EDT
[#32]
Quote HistoryQuoted:
I had a DPMS cam pin snap, it was a Hard Chrome cam pin that only had 400 rounds through it. I suspect it was due to Hydrogen Embrittlement. |
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Posted: 9/3/2017 12:40:56 PM EDT
[#33]
DS Arms sells Nickel-Teflon bolt parts including the cam pin.
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