1911 guys riddle me this brass issue:

[Drail]

Someone has hacked on that barrel. I wonder what else they did while they had it on the bench. Please don't shoot it until a smith can look at it.

 

[shibumiseeker]

There is something very wrong with the ramp on that barrel. You should never see that much brass exposed when the case is fully chambered, especially on a 10mm. That is much more than a "smiley". The ramp and throating should not go all the way around to the top of the barrel either. I would not fire that until you find out what's happening.

I don't think so, I have now seen three other DE barrels and they all have the same amount of chamber support. I'll be calling Colt today to see what they have to say. As I posted in my followup, I have been unable to replicate the issue.

 

[shibumiseeker]

Someone has hacked on that barrel. I wonder what else they did while they had it on the bench. Please don't shoot it until a smith can look at it.

It is a brand new gun from the factory from a reputable dealer. Which isn't to say that a gun cannot have problems from the factory, but it hasn't been hacked. The problem didn't occur when it was first fired and in the first 40-50 rounds and hasn't recurred since in spite of my best efforts to replicate the problem. The chamber is identical to one other CDE barrel I have had chance to hands-on and looks identical to two others I've seen in pictures with rounds chambered.

The only other variable not accounted for was my field stripping the gun and reassembling it.

 

[shibumiseeker]

Listen, something has got to contain the back end of that case. It cannot fire like the picture on the right and NOT have a smiley on it.

When the barrel is in the gun, does the hood of it come back and hit the slide? If there is any gap there at all, it is put together wrong.

What's interesting is that the first brass fired from the gun has no issues, no bulging, even slight. And later brass has no issues. So somehow I'm strongly leaning towards improper reassembly after field stripping. I wish I had thought to check to see is the barrel hood was properly in battery. I know the slide itself was.

A perplexing problem to say the least.

 

[ghitch75]

1911 gurus, what do you think? If the slide stop hadn't recaptured the barrel link when I reassembled might that have cause it to unlock early? The only other thing I can think of is the springs somehow didn't get seated but every scenario I can think of there makes the spring action stiffer not softer.

the slide stop won't go in if it don't go through the link.....i don't think you put it together wrong....

 

[shibumiseeker]

Problem Solved

I have managed to reliably replicate the problem.

It is a combination of lower chamber support, weaker brass, and bullet setback due to recoil and/or chambering because of some rounds having less crimp due to changes in brass characteristics.

The experiment:

10 rounds of the 8x fired nny brass with the load listed in the OP (my standard plinking load) Federal 150 primers (not noted in the OP). I noted carefully which ones seemed to have less resistance to the bullet seating. All seemed to have the same feel in the Lee FCD.

Set the chrony up.

Measured the OAL, loaded one full magazine. Chambered one round, shot it. #1 was 1029fps, within my normal range for my plinking loads. Looked at the magazine. The next in line (top of the magazine, round number 3) had excessive setback, like only the tip of the bullet showing out of the brass.

Shot #2 at 1051fps. #1 and #2 had normal looking brass.

#3 shot with a little more felt recoil and 1125fps. Looked at the brass and saw the bulge pictured in the OP. The primer showed a little more pressure but certainly not excessive and well within what I consider normal for a medium load.

All the remaining bullets were showing signs of some setback, varying from a few thousandths to maybe 15 thousandths.

#4 shot at 1078fps with no bulge.

I ejected #5 before firing and saw the bullet set very far back like #3. It shot at 1143fps, but had no bulge and the primer looked similar to #3, but again, not excessive flattening.

#6 was 1097fps and had a bulge.

#7 was 1065 no bulge.
#8 was 1057 no bulge.
#9 was 1048 no bulge.

I think I found my culprit.

But because I am a scientist and an engineer, this study would not be complete without further failure mode analysis. So I took 10 more rounds of the 8x loaded nny brass and reloaded it.

I loaded these into my Glock 20 with the stock barrel (the one on the left pictured up there), shot two and inspected the remaining ones. None had more than a couple thousandths setback. Shot the remaining magazine and all 10 were somewhere between 1040 and 1060fps which is what I have measured for many years with this load.

Loaded 10 more and repeated the above with the LWD barrel in the Glock. Identical results.

So now I wanted to see what running it a little hotter would do so I loaded 3 of the 8x fired brass and pushed the bullets back until they contacted the powder which put it at the same OAL as the ones that bulged above in the Colt.

Fired all three through the Glock20 with the LWD barrel. 1139, 1155 and 1136fps. No bulge, primers looked about the same as the ones in the bulged brass in the Colt.

So now we have to compare brass. Took 5 once fired nny brass and deliberately loaded it with the excessive bullet setback. Shot all five through the Colt. Same results as the first round of firing through the Colt, 3 had bulges not all correlated with the highest velocities. Lowest was 1123fps and highest was 1145fps. Primers still fine.

Now the moment of truth: Took 5 new Starline brass and loaded it and pushed the bullets back until it met the powder so it had the excessive bullet setback. Shot all five through the Colt. No bulges at all, primers looked fine. Velocities were 1131 for the lowest and 1150 for the highest.

As an added bit of fun, took 9 rounds of the once fired nny brass, loaded normally then loaded the Colt and shot a couple of rounds. Measured the remaining rounds, maximum setback was .002", most were less than .001". Fired the remaining magazine. For the entire string the range was 1035-1057fps. Loaded one more and chambered it ten times. Setback was .003"

Repeated this with 9 rounds of new Starline brass, no setback greater than .001" was noted after the first two shots and the range for the entire string was 1033-1049fps. Loaded one more and chambered it ten times and setback was .002".

Just for giggles, I loaded two more of the Starline lot and chambered them one each ten times with the stock Glock barrel and the LWD Glock barrel and setback on each was less than .001".

Conclusions:

The nny brass has less web support and less quality control than the Starline. Combine this with less chamber support makes it more likely to bulge as pressure rises. Add to that a tendency for the feed geometry and recoil of the Colt to increase the likelyhood of bullet setback. Multiple times fired brass is less consistent so a crimp that was fine with newer brass led to some bullets setting back.

I now trust my Colt again. I am going to run some of my warmer rounds loaded in new Starline brass (chronying ~1180fps through my Glock) and see how it fares, then increase the powder in .1gr increments until I start seeing brass bulging or other pressure signs. I am NOT going to try any of my nuclear 10mm loads I run through my Glock with the LWD barrel in this Colt.

And just for your fun I found this:

 

[shibumiseeker]

And thanks to everyone who made meaningful suggestions.