So, we've had discussions around here about how to fit a barrel. How do you go about deciding if the barrel you've got--whether it was fit by someone else, came stock that way, or was a supposedly "drop in" replacement--is actually properly fit? And then how do you go about correcting the fit, given that you don't (by definition) have lots of extra material to file off?
I've seen the Schumann timing tests, so that's one thing to check, right after Bigfoot and I have tea and he hands over the test kit he's hiding. But they don't do much for (for instance) horizontal lug engagement, or possible torsional forces from uneven contact with he barrel lug recesses.
My priority is durability. I don't want something that functions well today but is going crack in a couple thousand rounds. Advice?
You can check for barrel hood fit with feeler guages or just looking at it.
You can check for vertical engagement by using a depth micrometer from the toop of the slide to the top of the barrel hood, measuring with the barrel "locked" into the slide and 1/4" out of battery.
You can check to see if the lower lug is resting on the slide stop pin when in battery by marking the lug and seeing if its rubbing off.
Horizonal engagement is a little trickier. One way is with modelling clay. Put a little bit on the lugs and push the barrel up into the slide. When you pull it back out you'll be able to see your engagement.
There's not much you can do about it though, as you'd have to be able to add metal. How much it matters really depends on what you expect the service life of the pistol to be. Most shooters won't ever come close to shooting enough rounds for it to matter. Modern 1911's are made from harder steels than before, so one with .045" vertical engagement on just the first lug will still outlast most shooters. Now, if you're into serious training or competitive shooting it matters. In that case have a new barrel fit properly.
So, on the Schumann timing test--how exactly does one get a feeler gauge under the slide to test fit? I have a pretty small set of gauges--about 1.5" x .25"-- but I can't get more than a corner in there because of the curvature of the barrel. The first lug is plenty clear, should I assume the rest are, too?
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--how exactly does one get a feeler gauge under the slide to test fit?
Use either narrower flat feeler gauges or feeler wires.
In a pinch, a piece of small-gauge annealed copper wire can be flattened until it just fits and then the copper wire can be measured.
I cut some feeler gauges down to be narrow enough to fit. You just have to be careful not to raise an edge on them when they're cut, or dress it down if you do.
The first lug has the most clearance. The barrel is tilted up at the rear when in battery and tilts down toward horizontal as the slide moves rearward. That's the whole reason that you need so much first lug clearance, so that the other two have enough.
For those who are interested, I found a bit of copper wire that measured exactly .010. That passes in easily with a bit of wiggle room. A twist of two of those, which measured just over .020, didn't fit, so my clearance is somewhere in between those two, which should be good enough.
Headspace in .906, engagement is .044 (by "popsicle stick" method), and contact in lug recesses and on the feet seems pretty even. Hood gap is smaller than .010, which is my smallest feeler gauge. The frame ramp gap is very small, which is a little worrisome, but I'll be shooting it for the first time tomorrow (I hope), so we'll see how it goes.
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The frame ramp gap is very small, which is a little worrisome
The frame ramp to barrel gap is not, in itself, a problem unless the barrel overlaps the frame ramp. The gap is just to ensure that the nose of the feeding round doesn't strike the barrel ramp in such a way (low) that would push the barrel upward and forward. The gap just helps ensure this, it doesn't mean that in your particular pistol it will be enough or not.
If your pistol feeds well its probably fine. If you really must know, you can mark the barrel ramp with something (layout fluid, marker, etc.) and see where it rubs off.
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The frame ramp to barrel gap is not, in itself, a problem unless the barrel
overlaps the frame ramp. +1 for this!
IMHO, that 1/32" gap is little more than insurance in the event the bullet gets set back in the case upon striking the frame feed ramp. When this occurs, the bullet will slide up along the frame feed ramp instead of glancing upward off of it. The setback induced sliding increases the liklihood the bullet will contact the barrel feed ramp down low and lead to a stoppage.
If having that 1/32" gap was such a necessity, you'd think after nearly 100 years the blueprints for the 1911 would reflect it. The most recent blueprints will, however, result in an average M1911A1 Gov't Model with a gap of only 0.005 inch.
Well, for anyone who's curious, it shot beautfully today, no hesitation. Only 50 rounds down range through 3 different mags, but no problems at all. Very accurate. The Sharpie on the right side of the hood rubbed off, but everything else seems symmetrical and safe. Several bounce marks on the frame ramp, which I presume are from rounds at different places in the mag. The barrel ramp had big marks at the top and a little one near the bottom, but was smooth. So I judge the overall fit to be just fine.
Something you can try: Remove the recoil spring, guide rod, and plug and reassemble. Hand cycle rounds. You should be able to feed rounds from the magazine with only moderate thumb pressure - just keep the motion consistent - don't start and stop. A well fit pistol will hand cycle with no hesitation.
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You can check for vertical engagement by using a depth micrometer from the
toop of the slide to the top of the barrel hood, measuring with the barrel
"locked" into the slide and 1/4" out of battery.
Taking these measurements at the barrel hood (instead of at the front of the ejection port, as close as possible to the #1 lug) gives a value of lug engagement that is inflated by a factor of about 1.28.
The actual #1 lug engagement is about 78% of the value attained at the hood.