December 23, 2019, 06:13 PM | #151 |
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Here is a pic of a chamber casting showing the "bad chamber" issue that was found in a batch of KAK barrels. It was caused by running the roughing reamer too far in.
This was first noted in a 5/3/19 post at: https://www.ar15.com/forums/AR-15/35...ds/121-739384/ |
December 23, 2019, 06:36 PM | #152 | |
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Winchester 150 0.355" Winchester 180 0.355" Federal 180 .... 0.356" |
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December 23, 2019, 06:46 PM | #153 |
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I found my chamber cast--it does not have the "Mississippi two step."
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December 23, 2019, 07:04 PM | #154 | |
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An engineer at a large ammo manufacturer explained it to me this way: While you may have a range of bullet specs that might work for the bore specs, what it comes down to is what is most likely to work with the widest range of barrel bore cuts. So, when winchester rolled out the legend and submitted it for SAAMI specs, it was based on everything being tested to a standard of bullet diameter of .355. This includes ammo specs, pressures etc. What I was told was simply sure, I could easily go outside of the specs with different bullet diameters--but who has published data for loads for those bullets? I was reminded that even between lots of same dimension components they were seeing fairly wide variations in pressures (which is why I called them, I wanted a baseline pressure I could calibrate pressure trace to).
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December 23, 2019, 07:12 PM | #155 | |
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. Last edited by mehavey; December 23, 2019 at 07:40 PM. |
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December 23, 2019, 08:32 PM | #156 | |
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December 23, 2019, 08:40 PM | #157 | |
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(I can deal w/ that. Life wouldbe so boring otherwise) |
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December 23, 2019, 10:48 PM | #158 |
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With a good chamber, you are doing pretty good at eliminating possible causes.
This really does not line up with just a larger than bore bullet. Maybe there was something going on with the larger bullet and the new brass. You did have problems pulling a bullet from a loaded round. I have one other that sounds unlikely. If the round was near max with some space above the powder, it is possible for the bullet to have a glancing blow on a edge on the way in and get pushed deeper into the case. This will push pressure up, but probably not as much as the case indicated. Also, this seems real unlikely based on the hard to pull other round. Where are we now on "not eliminated" causes. I can only swag 2, are there any others still worth talking about?
Last edited by P Flados; December 23, 2019 at 10:57 PM. |
December 24, 2019, 12:58 AM | #159 | |||
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December 24, 2019, 01:03 AM | #160 | |
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December 24, 2019, 07:41 AM | #161 |
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When I did my test loads yesterday, little did I realize they would be the very last of LD's 125 gr extreme defense bullets that I would use, I can't find them anywhere and when I went on Lehigh Defense's website they appear to be out of production. Too bad, I got a group at 106 yds that was hovering near MOA (except for that one darn flier) at a velocity of 2700 fps.
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December 24, 2019, 08:00 AM | #162 | |
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For the time being, in any new loads I do I will simply work them up to the point I see extensive gas leakage and stop there. In the loads I did yesterday that point was achieved at under 50,000 psi as projected. The excessive gas leakage started at around 45,000 psi projected. The only actual test data I know of that has actual pressure data associated with it are on Hodgdon's web page--and that's using a 24" test barrel. Who produces one of those?? PS--I had to raise my start pressures in QL to around 6000 psi in order to get my charge weights/velocities close to what I was seeing in my recorded data.
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December 24, 2019, 09:57 AM | #163 | |
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As to slamming the case back hard enough to cause brass extrusion, that would also be the case w/ over-sized (overly-shorten) high-pressure bottleneck cases like the 300WinMag/NormaMag which operate at 63,000. Doesn't happen. Concentrate on timing. postscript: You know the commercial stuff is loaded to the gills. Are you getting the same leakage/pressure/extrusion signs? |
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December 24, 2019, 10:48 AM | #164 | |
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December 24, 2019, 10:51 AM | #165 |
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Stag,
In the early days of the 357AR, it was found that carbine length was needed for cycling. The early batches were all 16" barrels. The 5.56 is a bottle neck that retains plenty of pressure after the bullet goes past a rifle length gas port. This pressure and the length of barrel past the port combine to operate the DI gas system. The 357AR and 350L are straight wall rounds that use faster burning powders. They do not retain near as much pressure after the bullet goes past a rifle length gas port. Have you looked at how your cases eject? With a longer barrel and hot loads, you might get to "overgassed". This pressure and the length of barrel past the port combine to operate the DI gas system. |
December 24, 2019, 11:49 AM | #166 | |
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The weather is lousy today--very cold and very windy--but I have a new load to test, and I moved up to a heavier buffer. I'm using an adjustable gas block and it's turned pretty far out from full gas pressure to help reduce "slamming" on recoil.
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December 24, 2019, 03:06 PM | #167 |
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I went out again today--and tested some more of LD bullets--this time I was using a heavy spring and 5.75 ounce PCC buffer. The carrier was still slamming back pretty hard even with the gas block letting off a lot of the gas at the port.
Long story short--I have no idea what's going on. My quest is now to get a "real-world" pressure rating on factory ammo (not somebody's "way back when 26 inch barrel using ammo that isn't even made to that spec now") and then see what I get with pressure trace. Even though I got no notable signs of pressure or gas leakage, I feel like I'm operating in the dark.
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December 24, 2019, 06:37 PM | #168 |
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The Federal 180s have got to be your boundary-value test for both pressure
& residual/over gas conditions when combined with soft(er) brass. Got access to any? |
December 24, 2019, 07:15 PM | #169 | |
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December 25, 2019, 07:45 AM | #170 |
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I decided to use Hodgdon's data and reproduce exactly one of their loads. It's interesting to see all but one of their loads is under SAAMI specs for cartridge min length; and their case trim is the absolute minimum, resulting in a full .01 headspace "slack."
The more I work with this cartridge, the more I'm convinced I'm working in "whacky-town."
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December 25, 2019, 09:17 AM | #171 |
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I'l be honest Stag: I don't understand your concern (focus) on the specified headspace tolerance. As discussed prior, it's exactly what all straightwall auto's use, and insures highest probability of bolt closure when dealing with a hard stop.
SAAMI OAL is that of the magazine. Actual OAL with actual bullets is a tailored/unique function of where the actual shape/ogive bumps up against the chamber dimension/short freebore leade. Stubby shapes/long straight-shank bullets are limited to short OALs as a result, while longer/skinnier nose shapes get to poke out further. One of the reasons I semi-standardized on the Speer 180 FP, the SAECO 252-245, and the LEE 358-200 is that they have a nose shape that perfectly fits max magazine OAL and leade shape. Are you seeing something else going on against that backdrop? I'll admit I can not explain what you're seeing with increasing/apparent gas leakage at higher (QL-predicted) pressures. Last edited by mehavey; December 25, 2019 at 09:27 AM. |
December 25, 2019, 01:51 PM | #172 |
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Sorry my friend--let's just say you have your opinion, and I have mine. I do not agree with your assessment on the excessive headspace as being largely inconsequential. Perhaps in a barrel where the dynamics of a gas system they are less influential, but at least in my barrel I'm not confident it's working in a reliable or predictable manner. Most of all, I have no idea what pressures I'm actually generating as an end-user--and I'm not aware of anyone else who really does either.
I just got back intending to do a ladder test of 170 interlocs of Hodgdon's published data for their powders for the 350L--I replicated it exactly with the one exception I did not use winchester primers and instead used CCI BR-4 primers. My very first charge--Hodgdon's lowest charge of H110 @ 24 grs--showed signs of gas leakage a wee bit of compression at the rim, once again in the area where the extractor would be contacting the groove. I was getting velocities over 100 fps faster out of my 20" barrel than Hodgdon achieved in their 24" test barrel. Bottom line, I personally don't have confidence the system is working in a predictable manner for me. I'm pulling the barrel for now, maybe somebody will come out with a "type 2" AR 350L bolt with a shallower depth bolt face and I'll put it back together then. For a change of pace, I'm starting a Glock build. : )
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December 25, 2019, 02:52 PM | #173 |
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Don't get me ... somethin' ain't right.
My problem that with the exception of Flados' idea of entrapment, nothing else makes sense either. Last edited by mehavey; December 25, 2019 at 03:10 PM. |
December 26, 2019, 03:07 AM | #174 |
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I just double-checked for the possibility of a "case mouth crimp" by the chamber step-down with a dummy round. The chamber cast I did conforms with SAAMI specs. The dummy round after dropping the carrier on it had an OD of .376 both going in and coming out. A fired case had an OD of .381 at the case mouth. All of this indicates to me dimensions are performing as they should. The step down diameter in front of the case mouth prior to entry to throat proper in the chamber measures .359 (which includes the .002 delta for diameters as per SAAMI spec).
The consistent indicator of an anomaly I see in almost all of my fired brass that show signs of extensive gas leakage is the slight asymmetric compression of the rim. That compression is more pronounced in the failed brass.
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December 26, 2019, 09:17 AM | #175 |
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Three questions haunt me:
1. What can then be producing the Velocity <--> Pressure* combination being seen? 2. What produces one-side compression (other side stretch?) of the rim/extractor groove? 3. What can cause gas leakage(?) at that groove-stretch w/o repeated/immediate catastrophic failure? * V=at=Ft/m |
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