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Thread: Bolt issue from ramping

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    Registered User y2k87k2000's Avatar
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    Bolt issue from ramping

    I recently machined and ramped my bolt and now after test firing some of the bolt material has deformed and is now interfering with the hammer contacting the firing pin and is leaving marks on the bolt itself.

    Anyone know how to harden the bolt so I can stop this? Thanks!

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    Registered User MG34_Dan's Avatar
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    It's been said many times before:


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    Registered User y2k87k2000's Avatar
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    This is what I got, some scratching further up the new ramp and I removed the material that was in the way of the firing pin

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    The cheap way is to use a rose bud oxy-asetolene torch. Heat the striped bolt cherry red and drop into a bucket of used oil. Carbon from the oil will case harden (give a couple of thousands of harder steel on the surface) which will help with wear. There are also companies that do Nitride coating services. It is a very similar process in that carbon in the steel is chemically brought to the surface to case hardened the steel object without heating the object which could cause deformation. So with both processes there is a hardened high carbon surface that would resist wear. The nitride surface tends to be smoother.

    My guess would be that the ridges that go across the bolt were made from the sharp notch from the top of your semiautomatic hammer. Ramping helps but the sudden recoil of the blowback system shoves the hammer back so quickly that the hammer hits the hardened disconnector so hard that recoils back up and the sharp notch at the top of your hits the bottom of your bolt. I would also look at the back of your hammer and disconnector. Even with hardened fire control parts, such pounding can deform those. There is a technique to "V" notch the back of the hammer and fit the top of the back of the disconnector and trigger to give more throw to the hammer.

    Sorry to say I am not a heat treating expert. Personally I don't think that some kind of case hardening will solve your problem. Case hardening will help with wear, but it doesn't change the strength of the material. I have had several Colt factory bolts ramped. I even had a local to me Smith ramp a bolt while I watched. The material that the Colt 9mm bolt is made from is very tough. There was no case hardening needed when a factory bolt is ramped because the steel bolt is made from is so tough. Of course that also makes the bolt much more expensive to machine.

    If you made the bolt yourself, congratulations. You have a skill that I wish I had. Maybe a heat treating expert could save your bolt. What that would cost would more than likely be more than buying a brand new Colt factory 9mm bolt. I don't think that a couple of thousands of harder steel will stop the softer material underneath from being deformed. But I am not an expert.

    What are you using for a buffer? The blowback system needs a certain amount of mass to hold the bolt closed during the high pressure phase. I was at a shoot where someone was using a "H" buffer in a carbine stock with the Colt 9mm system. There was not enough mass to hold the bolt closed. The shell moved back far enough during the high pressure phase that the side of the shell ruptured. Luckily for the shooter the brass shrapnel sprayed inside the upper instead of out the port door and into the face of the shooter. We looked at the shell casings on the ground that had been fired. All of them were bulged. The Colt 9mm carbine buffer is around five ozs. A "H" buffer is only 3.8 ozs.

    I sincerely wish you luck with your 9mm bolt project. Please update your progress. Inquiring minds want to know.

    Scott

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    Registered User y2k87k2000's Avatar
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    I have 4 buffers, 5.4, 6.5, 6.7 and a custom 8.4 ounces. All of them reform similarly in my semi PCC and FA lower with a Foxtrot arms Glock 9mm upper with the fancy forward charging handle. Rate of fire was about the same. Thanks for the tip about heat treating, I will try that out when I get it smoothed out!

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    Buy a bolt professionally already ramped. Then get out and shoot off some of the 9mm ammo you bought by the case load this spring before Covid 19.
    Class 3 shooters blow thier loads faster and with only 1 pull of the trigger

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    Quote Originally Posted by y2k87k2000 View Post
    I have 4 buffers, 5.4, 6.5, 6.7 and a custom 8.4 ounces. All of them reform similarly in my semi PCC and FA lower with a Foxtrot arms Glock 9mm upper with the fancy forward charging handle. Rate of fire was about the same. Thanks for the tip about heat treating, I will try that out when I get it smoothed out!
    If you're interested in slowing the ROF, I would look into the Kynshot 9mm hydraulic buffer and a Tubbs 300 BLK OUT spring in a Vltor B5 length receiver extension. The best way I had found 15 years ago was the Enidine hydraulic buffer and the AAC reduced power recoil spring in a carbine length receiver extension. The stronger the recoil spring, the higher the ROF, as a stronger spring increases the speed of the return of the bolt. A heavier buffer does slow the speed of the bolt group, but part of the problem with the blowback system is the recoil pulse is all at once.

    Think of the direct impingement of of 5.56X45. The gun power is ignited. The bolt is locked into the barrel extension so that initial recoil pulse is contained inside the receiver. The bullet passes the gas port and some of the gas is directed into the bolt/carrier piston. The piston pushes the carrier back which cams the bolt to unlock and pushes the carrier back. The amount of gas should be just enough to operate the bolt group to cycle. The bolt group cycles, ejects the empty shell then strips and chambers a new round.

    With the blowback system all of the recoil energy of the pistol round goes into the bolt group all at once. The greater the dwell time (the time that the bullet is in the barrel so there is pressure on the bolt) the more energy is transferred to the bolt. 9X19 Luger has about the same energy at the muzzle as 45 ACP, yet the blow back bolt group for .45 must have a heavier buffer. Why, because the heavier .45 bullet has a long dwell time. So more energy is transferred into the bolt group.

    I think that if the transfer of energy is spread out over time, that softens the recoil pulse, like the DI system. Granted the DI system impulse in a rifle caliber system has more total energy to deal with, but I think that the DI rifle caliber system shoots softer than the pistol caliber blowback system in an AR. The softer shooting PCCs are those that that transfers some of the recoil pulse into the receiver. The MP5 has been the gold standard of 9mm carbines. Why, because the roller delayed blowback system transfers some of the recoil pulse into the receiver. So the bolt group can be lighter. The lower the mass moving around in the gun, the less movement the gun will tend to have. The new CMMG radial delayed blowback system has less felt recoil. Why, because the angled bolt lugs transfer some of the recoil pulse into the receiver of the firearm. CMMG has had problems with the ejector spring system. This has shown to be a more of a problem for higher volume/full auto applications.

    If you want to lower your ROF in the blowback system, I would look into a lighter spring and a buffer that slows the rate of loading mass to the bolt group like a hydraulic or mechanical buffer like the MGI. I don't know as case hardening would help your existing bolt very much. Case hardening only effects a couple of thousands deep. I would think that the bolt would need to be made from tougher/harder steel. As posted earlier, all of the 9mm blowback bolts I had ramped needed no additional heat treating because the material that they were made from was so strong. Good luck with your bolt project.

    Scott

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    how about adding a tungsten weight to the rear of the bolt. my fm bolt now is 1lb and 1.6oz

    greg
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    Why, because the heavier .45 bullet has a long dwell time. So more energy is transferred into the bolt group.
    no, it's because a 45 ACP bore has 60% more area. The same gas pressure exerts 60% more force. The dwell time is negligible compared to this.

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    Quote Originally Posted by Fishman View Post
    no, it's because a 45 ACP bore has 60% more area. The same gas pressure exerts 60% more force. The dwell time is negligible compared to this.
    Thank you your perspective. Do you have any science to back that up? What you stated sounds possible accept, the pressure is not the same. Can we agree that both 9mm Luger and .45 ACP stantard ball ammo has around 350 ft./lbs at the muzzle? To have the same amount of energy at the muzzle the lighter 9mm bullet would need to travel faster.

    Force = mass X acceleration

    It is my understanding that ft./lbs is a unit of force. So the pressure of 9mm Luger according to Wikipedia is something over 34,000 psi and .45 ACP is 21,000 psi. So equal and opposite reaction, if the bullets coming out of about the same barrel lengths, then the energy at the bolt face should be about the same, right?

    Being somewhat familiar with the M10 RR open bolt submachinegun, the bolt and the recoil springs are about the same. In fact the same lower receiver can be used with a magwell adapter for both .45 and 9mm. The only difference in the bolts and recoil springs is the bolt face is bigger. So if the muzzle energy is the same and the mass of the bolts and the strength of the recoil spring is the same then the cyclic rate should be the same. But they are not. The .45 has a higher cyclic rate.

    Power = Energy ÷Time

    If both rounds have about the same energy, then the difference in power affecting the bolt is the amount of time that energy is applied. So it would seem to me that the dwell time (the time that the recoil energy of the bullet going down the barrel and is held by the bolt) seems to be the difference.

    After doing some searching I could not find any documentation that the increase in surface of .45 caused more felt recoil. I am not a mechanical engineer. I couldn't find much to explain the recoil difference between .45 and 9mm. The one thing that I do have is 9mm roller delayed system. A MP5K-PDW has a 5.5" barrel. When a suppressor is added, it acts like the barrel length is increased. Barrel length increases dwell time. If a suppressor is added then a lower angled locking peice must be used to divert more of the recoil energy into the receiver. The standard K locking peice is 110 degrees. The locking peice with a can is 80 degrees. The only difference is dwell time. YMMV.

    Scott

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