Necked Cases for Reliability

[Master Blaster]

Quo

I have read about necked cases having higher feed reliability than straight wall cases. As a mechanical engineer, I understand lead-in chamfers and I can see the parallel. As a owner of a .45 ACP Kimber with a 3" barrel, I have experienced feeding issues. However, I have not studied the kinematics of cartridge feeding and I may be seriously mistaken with my thinking that a necked cartridge will lead to increased feeding reliability.
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I understand that the 357 SIG is mostly manufactured by those who manufacture highly reliable pistols, and I have read about feeding reliability issues with the .40 Super.
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Is there any serious data that supports or refutes the hypothesis that necked cases lead to increased feed reliability for EDC pistol designs?

Use different ammo, try different magazines, or send it in to Kimber.
.45 ACP is a proven reliable round and so is the 1911 if it is correctly fitted.

 

[Justin9999]

I’m just about to reach the 800 round break in on the Kimber, and things are better... just not good enough. So as of now, Kimber is not willing to look at my gun.
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My extractor pin was too long, preventing the case from sitting flush against the bolt face. (Also has a few stove pipes with Federal rounds.) I hand ground it shorter and things improved. The improvement shows up by allowing the slide to reach full battery whenever I have five or fewer rounds in the mag.
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I can see nose dive with the 6th & 7th round in the mag. I’m thinking that the nose dive results in higher friction on the feed ramp, so I polished the ramp last night. To add to my friction hypothesis - I measured the case mouth diameter and found my excellent feeding Federal rounds were about 0.001” below the spec in my Lyman’s manual, but my less than perfect rounds that were about 0.001” over the manual spec. So, for my reload cases, I undersize the taper crimp and feeding is great.
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Now the 3” barrel is for concealed carry. If I need to defend myself, I expect that the gun will be able to eat any ammo I have available. Worrying about a tolerance range of 0.002” is unacceptable, except in a precision target shooter with a long barrel. I suspect Kimber prioritized accuracy over reliability, making a tight chamber.
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A new magazine is next, but first I’m going to see what I achieved with the polished ramp... assuming I didn’t goof it up
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Maybe I should sell the Kimber and buy a Sig in .45ACP.

 

[Texas10mm]

Mags are inexpensive. Kimber mags are OK, I wouldn't give them more than that.

My concealed carry is a 4.25" barreled LW Commander. Barrel length is easy to conceal. It's the grip that causes problems.

Personally I'd never own a Kimber. I had a chance for over 10 years to buy one a year at half of MSRP. I never bought one.

 

[Justin9999]

Mine was a gift. I won’t buy one either.

 

[mjsdwash]

I can't speak to a study, but its well known that bottleneck rounds made machine guns work. 1911's have some issues with where the bullet makes contact with the barrel, and a bottleneck could actually reduce reliability in similar designs. I would assume this is where the .40 super issue comes from. When the bullet hits, it needs to push against the barrel forward, and up, and hitting inside the chamber may just push up. This was demonstrated to me by loading a dummy, pushing the barrel up against a solid object, and dropping the slide. You feel zero resistance because the barrel does not cam up until the slide is at the end of its travel. I don't know if that makes sense, but it was interesting to try.

Your problem, though I hate to say it, is probably the Kimber factor. They are difficult guns to tune, and can be finicky. I recently tried to get one to work, but so many of the parts were proprietary/better (out of spec for us non-Kimber fans), and not compatable with aftermarket parts, I just gave up on it.
I did get it to go from 1 jam per mag to 1 jam per box of ammo with tuning, my Springfield with the same tune just doesn't jam at all. Ever.
On top of all that, the smaller they get, the more problematic. The big driver for 1911 reliability is its controlled feed. Obviously you negate that with Kimber mags, which by design are not controlled. You also harm the controlled feed by speeding things up, and slide mass is what slows things down. Lighter than a government profile, and you letting things run fast, and that often leads to double feeds, or Out of batter, extractor behind rim jams.
Best remedy for that is a flat bottom firing pin stop, heavy recoil springs, with frequent replacement. Alternatively, lighter bullets may help too.
One major factor that differentiates the 1911 from other JMB designs is the chain cam. This was pretty much eliminated by a track cam that does not require tuning, fitting, or most importantly bullet geometry to time correctly. This is why glocks/sigs/CZ and many other don't have the feed issues of the 1911. The snap over extractor plays a major part too.
If you can get a picture of the actual malfunction and post it, someone may be able to give some advice.

 

[barnetmill]

Feeding from a single stack magazine can present some issues. You might find the article below of interest.

https://americanhandgunner.com/gear/nosedive-and-feed-angle-in-the-1911-45-acp/

You know with standard fmj ammo I do not ever recall have a .45 that did not feed. Perhaps it is 'nose dive' the causes hollow points to jam. What I need to understand is why double column/stack mags do not have nose dive.

 

[fxvr5]

You know with standard fmj ammo I do not ever recall have a .45 that did not feed. Perhaps it is 'nose dive' the causes hollow points to jam. What I need to understand is why double column/stack mags do not have nose dive.

Some double stack mags do have nosedive, and I've had nosedive feeding failures in double stack mags.

Also, See post #25.

 

[Justin9999]

Perhaps it is 'nose dive' the causes hollow points to jam. What I need to understand is why double column/stack mags do not have nose dive.

The article shows that the case rim of the upper round nests inside the extractor groove of the lower round, which creates the angle between these two rounds. The cross-sectional view that shows how these two rounds are nested is parallel to the walls of the magazine. With double stacked mags, the cross-sectional view that shows the nesting of two bullets will not be parallel to the walls of the magazine, which means the angle developed by the nesting will be reduced by the side walls of the magazine. So the wider the double stack mag, the lesser the nose dive.
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My aluminum frame shows evidence of the bullet nose impacting the frame just below the feed ramp of the barrel. I imagine that a hollow point bullet (i.e flat face bullet) that nose dives and punches straight into the frame wall will jam, whereas as round nose bullet can roll at this impact and feed better. If this is correct, then smaller tipped hollow points & smaller tipped semi-wadcutters should feed better.
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Perhaps, a chamfered meplat semi-wadcutter would feed well in a 1911. Or, if the flat face of the bullet catches the sharp bottom edge of the feed ramp, then the feed ramp needs to be extended further below the top of the magazine (which could be why a compact 3” barrel has more feeding issues than a full size barrel).

 

[fxvr5]

My aluminum frame shows evidence of the bullet nose impacting the frame just below the feed ramp of the barrel. I imagine that a hollow point bullet (i.e flat face bullet) that nose dives and punches straight into the frame wall will jam, whereas as round nose bullet can roll at this impact and feed better. If this is correct, then smaller tipped hollow points & smaller tipped semi-wadcutters should feed better.

If the bullet tip is too narrow or too short, the round will be at a steeper angle when the bullet tip hits the top of the chamber and it can stop dead (3-point jam) because it can't cam over and slide into the chamber.

Feeding is complex. There is a range of dimensions which will allow reliable feeding, but if the round is outside of that range then things can go wrong and the gun jams.

 

[Justin9999]

Have you tried different mags in your 3"? If not then you really should.

How do you choose a magazine? Do they all just try to minimize nose diving, or is there more to it?

 

[fxvr5]

Do they all just try to minimize nose diving?

No.

 

[zaitcev]

SIG P220 is well known for exceptional reliability when feeding from a single stack magazine. H&K Mark 23 is very reliable too, feeding from a double-stack, single feed magazine. This was proven by testing them. So it can be done.

 

[Texas10mm]

How do you choose a magazine? Do they all just try to minimize nose diving, or is there more to it?

I've been in the 1911 game for over 40 years. I have a huge stock of magazines. I've owned 3 and 3.5" 1911 pistols in the past. If I had problems with the stock mags I'd simply grab a full size magazine to see if the problem was the magazines.

I've sold all the short ones. My smallest 1911 pistols are 4-4.25" models.

The stainless steel Officer's Models I've own are heavier than a LW Commander. The LW New Agent had XS big dot sights which I could not get used to. Also defensive loads in that small little package were unpleasant to shoot.

I also had a Glock 36. Very unpleasant to shoot defensive loads in it.

IMHO if I buy another carry 1911 it will be a CCO style. Officer sized grip and Commander length slide. The grip is what causes printing, not the slide. But I have no printing problems with full sized grips.