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Old December 23, 2019, 06:13 PM   #151
P Flados
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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/

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Old December 23, 2019, 06:36 PM   #152
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he only reasonable conclusion I can come at this point is that using anything other than the .355 bullets is wildcatting.
Again see actual Comm'l ammunition (Post 129 above):

Winchester 150 0.355"
Winchester 180 0.355"
Federal 180 .... 0.356"
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Old 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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Old December 23, 2019, 07:04 PM   #154
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Again see actual Comm'l ammunition (Post 129 above):

Winchester 150 0.355"
Winchester 180 0.355"
Federal 180 .... 0.356"
Hmm, trying to figure out how to word this that makes any sense..

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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Old December 23, 2019, 07:12 PM   #155
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....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.
How do we explain this, then . . . ?




.

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Old December 23, 2019, 08:32 PM   #156
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How do we explain this, then . . . ?
Well, if you want my honest opinion...I think Winchester pushed this to market way before there was adequate R&D into a range of ammo/components to see what works and what doesn't. I think they developed narrowly for a marketing hype point--just like federal did when they rolled out the 224 valk. Seems the new cartridge model now is roll it out and let the market deal with working out the kinks.
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Old December 23, 2019, 08:40 PM   #157
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...the market deal with working out the kinks.
Market spelled "U&I"








(I can deal w/ that. Life wouldbe so boring otherwise)
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Old 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?
  • Having a film on the ID of a new case combined with a real tight fitting bullet such that the bullet is "glued" in place firmly enough to cause a spike.

  • A very strange primer/powder interaction with a secondary pressure spike (very low probability)

Last edited by P Flados; December 23, 2019 at 10:57 PM.
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Old December 24, 2019, 12:58 AM   #159
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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 agree, I do not think the issue is associated with the larger dimeter bullet and the bore measurements alone. It might be as simple as wimpy brass--I have some winchester and hornady brass coming in and I want to carefully compare all the alternatives.

Quote:
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.
I thought about this too--while out live firing I made a point of double-checking the cartridges--and ejected some without firing after cycling--I saw no notable signs of abrasion or bullet movement.

Quote:
Where are we now on "not eliminated" causes. I can only swag 2, are there any others still worth talking about?
Having a film on the ID of a new case combined with a real tight fitting bullet such that the bullet is "glued" in place firmly enough to cause a spike.

A very strange primer/powder interaction with a secondary pressure spike (very low probability)
Yesterday's test with the .355 bullets were interesting in that many of the cases fired and came through clean--but I reached a point eventually where gas leakage down the side of the case and to the base started happening--I stopped at the top charge weight after I saw the tell-tale gathering of carbon deposit in the area of the extractor claw on the rim. Why? I don't know. I tend to think it's not associated with head spacing properly off of the case-mouth per sae--but there is a lot of room for movement between the case mouth step in the chamber and the bolt breech face. Also, as I've said, the use of carbine gas system producing an unusually long dwell time length in my 20" barrel is definitely something I don't understand--at least from the point of view for timing. I guess I should give Faxon a call and try to get some dope on that.
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Old December 24, 2019, 01:03 AM   #160
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(I can deal w/ that. Life wouldbe so boring otherwise)
I understand, makes life interesting, but it can also be very expensive and somewhat risky being an unofficial and unpaid staff. When the 224 valk came out there were various "flavors" of chamber reamers floating about among the manufacturers initially--what became apparent is that for whatever reason there was a disconnect between SAAMI specs submitted, which ones were the "official" production specs and what was actually being used and tested during initial testing and release. I've heard the criticism that the American market is inconsistent in "abiding" to the SAAMI specs--when, where by whom and who is actually checking "compliance."
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Old 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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Old December 24, 2019, 08:00 AM   #162
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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?
Having a film on the ID of a new case combined with a real tight fitting bullet such that the bullet is "glued" in place firmly enough to cause a spike.

A very strange primer/powder interaction with a secondary pressure spike (very low probability)
OK--I'm still torturing myself over this one, I keep coming back to the very long headspace slack and barrel timing things as the two variables that I generally don't see in any other AR I've had experience with. I don't think the problem is associated with the cartridge dimensions or whether or not the case mouth is wedging to the chamber step--my latest "pet guess" is that there's a timing issue while pressure is still rising in the case to peak pressure--and the case seal to the chamber is overcome and "slams" the cartridge back into the chamber bolt face. That's my latest guess after yesterday's tests in which the first two thirds of the cases showed very little sign of gas leak on the ejected cases--while the higher pressure ones (at approx. 50,000 psi projected) showed extensive signs of gas/carbon leak all the way down the case and accumulating in the extractor groove area.

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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Old December 24, 2019, 09:57 AM   #163
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very long headspace slack
Put that in the Don'tFretAboutIt pile. As mentioned before, 10-thou tolerance is standard for all straight-wall gas guns (look up the 450 Bushmaster as well)

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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Old December 24, 2019, 10:48 AM   #164
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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.
The deformation of the case rim towards the web in the area of the extractor has been quite consistent in the cases that show signs of incipient pressure issues--even while the primer appears perfectly normal.
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Old 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.
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Old December 24, 2019, 11:49 AM   #166
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In the early days of the 357AR, it was found that carbine length was needed for cycling.
I figured something along those lines was the case--the DI carbines I'm aware of that use a locking bolt with the straight wall pistol cartridges also have very short gas systems. I feel it's highly likely there is a timing issue of some sort going on--what's missing is if/how that can be connected to over-pressure.

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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Old 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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Old 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?
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Old December 24, 2019, 07:15 PM   #169
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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?
What I'm interested in knowing is what actually was the baseline for the test to submission to SAAMI--that's generally a pretty expensive procedure--looking at SAAMI specs it says 145 gr @ 2250 fps--I'm assuming that was winchester early 145 gr power point cartridge--but I don't know. In addition to that what I really need is a pressure rating for a known lot number that I can access (I believe most ammo manufacturers have to test each lot, but I'm not positive about that). In other words, if I buy a box of factory ammo I need to know what the pressure rating for the lot of the box that I have so I can use that as a baseline reference to calibrate a pressure guage on my pressure trace. Not necessarily something a manufacturer is willing to give freely to the public for various reasons. A certain amount of "hit or miss" accuracy is not unexpected in a pressure trace--somewhere around 3 to 4K psi depending upon things like the molecular elasticity properties of the barrel material, where the gauge is relative to the chamber (I've never done a straight wall cartridge before) etc.
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Old 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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Old 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.
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Old 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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Old 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.

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Old 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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Old 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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