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  #1  
Old 11-07-2019, 01:39 AM
TRX302 TRX302 is offline
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blown case, .40 caliber

I put together a .40 top end for my 1911. I used one of the Sarco "Roto" .40 S&W barrels. This one required considerable filing around the breechface area before it would lock into the slide, and the bottom of the chamber overhung the ramp. I filed that flush with the ramp, then back a bit at a time, chasing some feed problems. Right now the case has about .030" unsupported from the slight radius at the mouth to the extractor groove.

By .45 standards I thought I was still in the safe zone, but the .40 S&W runs at 35K vs. 21K for the .45 ACP. When the case (new, 165gr Winchester truncated cone) blew I got fire out the ejection port, a bruised hand, and half of the right grip fell to the bench when I shifted my grip.

Oops.

Have I gone too far? If so, what should the maximum overhang for the .40 be? I was using threads like this one https://forums.1911forum.com/showthread.php?t=336859 as a guide.

note: the dent in the case was made during disassembly; chunks of brass were preventing linkdown, which made things... interesting.
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cart1.jpg   cart2.jpg   cart3.jpg   throat1.jpg   throat2.jpg   blown1.jpg  

blown2.jpg  
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  #2  
Old 11-07-2019, 02:26 AM
megafiddle megafiddle is offline
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Yikes! Glad it wasn't more serious.

A .40 barrel will typically overhang the frame ramp on a .45 frame. The top edges of the frame ramps on .40 frames normally sit a bit further back.

Where exactly did you remove metal from the barrel?
Did you move the top edge of the barrel ramp forward?
Did you check headspace?

-
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  #3  
Old 11-07-2019, 06:01 AM
Jolly Rogers Jolly Rogers is offline
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The second bulge half way up the blown case concerns me some. I wonder if the chamber is miss cut or improperly reamed somehow. That is if this damage wasn’t caused during teardown and it is what you called out as a dent.
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Last edited by Jolly Rogers; 11-07-2019 at 06:03 AM.
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  #4  
Old 11-07-2019, 08:13 AM
JeffC JeffC is offline
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I had a case blow out in .40 s&w in a Beretta 96. It wasn't the guns fault in my incident but the ammo. .40 s&w really should have thicker case walls IMHO.
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  #5  
Old 11-07-2019, 10:15 AM
TRX302 TRX302 is offline
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Quote:
Originally Posted by megafiddle View Post
A .40 barrel will typically overhang the frame ramp on a .45 frame. The top edges of the frame ramps on .40 frames normally sit a bit further back.
Hm. It originally hung well over the ramp.

Quote:
Where exactly did you remove metal from the barrel?
From the sides and hood, until I was able to get the barrel to go into battery. Then from the bottom, until it didn't overhang the ramp any more, and then once I had it 1/32-ish ahead of the ramp, I laid the entry back slightly and broke the edge of the chamber. Not a big radius, just enough that it wouldn't shave brass when chambering a round.


Quote:
Did you move the top edge of the barrel ramp forward?
Yes. By the time I was able to get the barrel to go into battery, the original shape of the mouth was completely gone. I've had to adjust the fit of barrels before, but this "drop in" barrel was so far out that I should have started with the angle grinder... any more filing and I would have had to cut the chamber deeper.


Quote:
Did you check headspace?
Formally with proper gages, no. But I used several new-from-box rounds as impromptu gages. The barrel headspaces on the hood, and sighting across a square, I have .001-.003" of clearance from the hood to the case head.

Wiggling a new round in the chamber, I seem to have about as much radial clearance as any of my .45s


Quote:
The second bulge half way up the blown case concerns me some.
After forcing the gun open slightly, I removed the firing pin stop, firing pin, and spring. Then I used a punch and mallet to bend the case down slightly, and another punch to "clock" the extractor enough to get it unhooked from the case so I could remove the extractor. Then I removed the barrel bushing and with careful prying and hammering, managed to work the slide back and forth until the chunks of brass between the barrel and its bed worked their way out, the barrel finally linked down, and I was able to take the gun apart normally. For a while there I thought I was going to have to use a cut-off wheel and sacrifice the slide stop to get it apart.

Last edited by TRX302; 11-07-2019 at 11:30 AM.
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  #6  
Old 11-07-2019, 11:48 AM
BBBBill BBBBill is offline
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As noted, the frame feed ramp is most likely for a 45 and too far forward for a 40. So everything you did made the case exposure problem worse. Weld up the frame or have and insert installed. And make us all happy by staying away from those Roto barrels. I've just seen too many issues with them over the years that they've been floating around.
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  #7  
Old 11-07-2019, 05:17 PM
TRX302 TRX302 is offline
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I was rooting around in the parts box and found a Clark/Para ramped Commander barrel in .40. I think it's an RIA.

The eyeball-O-meter says the amount of unsupported case is about the same.

I have a couple of different brands of .40 ammo, I'm tempted to just put the gun back together and see if it blows chunks out of some Remingtons or Federals.
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  #8  
Old 11-07-2019, 06:19 PM
log man log man is offline
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I would suggest that you carefully cut through this case, I would cut so the blown area is split so each half will show the thickness of the case at the blown, and opposite side. Also split a fired case and compare.

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  #9  
Old 11-07-2019, 06:23 PM
emptymag emptymag is offline
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How much case is exposed with the barrel (and case/round) installed in the slide?

Also, I would be wondering what the chamber, leade/throat, and actual bore dimensions and measurements are(?).

This is a 5" gun?
What frame and slide?
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  #10  
Old 11-07-2019, 08:31 PM
TRX302 TRX302 is offline
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Quote:
Originally Posted by log man View Post
I would suggest that you carefully cut through this case,
Any suggestions for getting a grip on the case while cutting?

I guess I could sand a dowel down or something.
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  #11  
Old 11-08-2019, 05:50 AM
Jolly Rogers Jolly Rogers is offline
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Quote:
Originally Posted by TRX302 View Post
Any suggestions for getting a grip on the case while cutting?

I guess I could sand a dowel down or something.
What resources do you have? Depending on the cutting implement there are several ways to secure the case. Let us know what tooling you have for the job.
And on second look after your response I do see the “bulge” is actually a dent.
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  #12  
Old 11-08-2019, 07:02 AM
TRX302 TRX302 is offline
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The most appropriate tools would probably be the hacksaw or the milling machine.

It's getting a grip on the case without crushing it that I have doubts about.

Last edited by TRX302; 11-08-2019 at 10:27 AM.
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  #13  
Old 11-08-2019, 08:02 AM
subscriber subscriber is offline
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Case looks brittle around fracture site. Not much of a bulge adjacent to it.

Wonder if a lab could analyze the brass in the head area for correct metallurgy.
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  #14  
Old 11-08-2019, 06:42 PM
megafiddle megafiddle is offline
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Quote:
Originally Posted by TRX302 View Post
I was rooting around in the parts box and found a Clark/Para ramped Commander barrel in .40. I think it's an RIA.

The eyeball-O-meter says the amount of unsupported case is about the same.

I have a couple of different brands of .40 ammo, I'm tempted to just put the gun back together and see if it blows chunks out of some Remingtons or Federals.
Remember that the case will not be sitting fully forward in the chamber upon firing. The barrel will be sitting as far forward as possible against the slide lug recess faces, and the case will be sitting as far back as possible against the breechface. It is in these positions that the case support should be measured.

You need to accurately scribe the case at the point where the case support ends at the top of the barrel ramp. This can be difficult with everything assembled as above.

Alternately, you can place a round in the unassembled barrel and scribe the case. Assemble the barrel, bushing, and round in the slide, and locked in battery. Position the barrel and round both as far forward as possible, and measure the gap between the case head and breechface. Add this gap measurement to the unsupported length indicated by the scribe mark. This total will be the actual unsupported length, as the case will back out of the chamber by the additional amount of the gap upon firing.

edited to add:

In the second alternate method, make sure that the case is not being stopped from moving fully forward into the chamber by the extractor hook. If in doubt, remove the extractor.

-

Last edited by megafiddle; 11-09-2019 at 05:05 PM.
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  #15  
Old 11-08-2019, 07:28 PM
TGR TGR is offline
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Megafiddle, good post. Do you have a safe number for .40 s and w from rear of cartridge to support? How about 9 or 10. 45 has been reported to be .260 or less.
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  #16  
Old 11-08-2019, 08:40 PM
TRX302 TRX302 is offline
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Quote:
Originally Posted by megafiddle View Post
Remember that the case will not be sitting fully forward in the chamber upon firing. The barrel will be sitting as far forward as possible against the slide lug recess faces, and the case will be sitting as far back as possible against the breechface. It is in these positions that the case support should be measured.
The barrel is "hard fit" to the slide; the only clearance is what it needs to unlock. Various fresh cartridges are flush with the end of the hood to .003 below.
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  #17  
Old 11-08-2019, 09:15 PM
megafiddle megafiddle is offline
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Quote:
Originally Posted by TGR View Post
Megafiddle, good post. Do you have a safe number for .40 s and w from rear of cartridge to support? How about 9 or 10. 45 has been reported to be .260 or less.
I am looking for 9mm data on that myself.

The ANSI/SAAMI standards for pressure don't seem to cover it. I wonder if there actually is any official standard. The .260" value for .45 may just be a "de facto" standard.

I'll report here if I find anything.

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  #18  
Old 11-08-2019, 10:25 PM
megafiddle megafiddle is offline
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Quote:
Originally Posted by TRX302 View Post
The barrel is "hard fit" to the slide; the only clearance is what it needs to unlock. Various fresh cartridges are flush with the end of the hood to .003 below.
In that case, you could use one of the flush fitting cartridges in the barrel alone and make an accurate scribe line at the top of the barrel ramp.

I would not use the .45 value of .250" to .260" for the .40 though. There are too many differences.

Might be best to get a measured value from a known good design.

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  #19  
Old 11-09-2019, 07:54 AM
Sailormilan2 Sailormilan2 is offline
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The unsupported area doesn't look that large to me. I've got 9mm, 38 Super, and 10mm barrels that look similar, if not a bit larger. I believe that my 9mm barrel has an unsupported area that is larger than what is shown in your photo.
So the next question is this. Did you finish ream the chamber? Most 1911 aftermarket barrels need to be finish reamed. May one, an only, 9mm case blowout was in a barrel that I have not yet finish reamed.

Last edited by Sailormilan2; 11-09-2019 at 08:14 AM.
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  #20  
Old 11-09-2019, 06:46 PM
megafiddle megafiddle is offline
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Quote:
Originally Posted by TGR View Post
...
Do you have a safe number for .40 s and w from rear of cartridge to support?
...
I have some information about .45 and .40, but nothing "official".

The maximum value of .250" to .260" appears to be derived from Jerry Kuhnhausen's recommendation that the unsupported case length not exceed .090" from the case extractor bevel *.

Measuring from base to extractor bevel for .45 cases from two different manufactures, I am seeing .164" for Hornady, and .170" for Remington. Adding .090", this provides overall unsupported lengths of .254" and .260". So this is very likely the source of the .250" to .260" value.

For the .40, I measured the overall unsupported length in the slide/barrel of a Glock 23. In this example I am seeing about .215". I believe this to be accurate within a few thousandths. The base to extractor bevel of the Winchester case I used measures .142". This leaves an unsupported length from the extractor bevel of .073".

I have seen some mention that the early Glock .40's suffered from case blowouts, but not with later models. This was a 3rd generation 23 that I used. I would assume that the unsupported length I measured could be considered adequate. It's only one example of something that apparently works.

* Kuhnhausen's "The Colt .45 Automatic Volume 1"

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Last edited by megafiddle; 11-09-2019 at 06:56 PM.
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  #21  
Old 11-09-2019, 06:53 PM
subscriber subscriber is offline
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Would images like this help?





.38 Super? Second image from here: http://castboolits.gunloads.com/show...dd-45-ACP-case
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Last edited by subscriber; 11-09-2019 at 06:59 PM.
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  #22  
Old 11-13-2019, 08:55 PM
TRX302 TRX302 is offline
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So, while waiting for the next chance to get to the range, I expanded my web searching from 1911-specific to .40 s&w in general.

Typing "glock 40 unsupported chamber" into Google and clicking on "images"... great googly moogly! I have way more support than most of those, and more than a lot of other production .40 pistols. So, no, I don't think I have over-throated the chamber.

https://www.google.com/search?lr=&as...OseXD2Ox6zskQM

Searching ".40 kaboom" I wound a few pages - mostly written by .40 detractors - claiming the .40 is very sensitive to bullet setback, and a bad feed or a re-chamber could set the bullet back enough to send pressure way up and blow the back of the case. I don't know how true that is, and I don't remember if I had problems chambering that round... but the whole purpose of that range trip was to check for feed problems, so who knows...

So, before any other changes, I'm going to try the gun again, with a few of each of the several brands of .40 I have on hand.
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  #23  
Old 11-13-2019, 09:11 PM
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TRX302,

I get the same impression. That your case blew for a reason other than lack of support. My money was on a brittle or flawed case head, but bullet setback seems more likely.
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Old 11-13-2019, 10:16 PM
Sailormilan2 Sailormilan2 is offline
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Quote:
Originally Posted by subscriber View Post
TRX302,

I get the same impression. That your case blew for a reason other than lack of support. My money was on a brittle or flawed case head, but bullet setback seems more likely.
I will agree with this.
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  #25  
Old 11-14-2019, 12:02 AM
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TRX302,

How about a clear image, showing the inside of the chamber? Specifically, how steep the rifling lands start in the throat. Why? Because Sailormilan2 makes a lot of sense, below. A lack of finish reaming will push up the peak pressure, because the throat is shorter and steeper than it is meant to be.

You may have ignored that question before, because it is a factory barrel. Factory barrels often end up in factory assembled pistols, without being finish reamed.

Quote:
Originally Posted by Sailormilan2 View Post
Did you finish ream the chamber? Most 1911 aftermarket barrels need to be finish reamed. May one, an only, 9mm case blowout was in a barrel that I have not yet finish reamed.
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