Including both guns in the title because they use the same barrel part numbers and very similar FCUs, so I reason the lockup has to be the same.
I just picked up a P250 Compact in 9mm as I've been threatening to do for years. My daily search results from GB included one that was offered at a fixed price from a local FFL, and I went over and picked it up brick and mortar after work. It appears to have been fired at the factory, but not after. The white grease applied to the FCU with a brush prior to assembly is still undisturbed, and there were only three grains of unburned powder in the frame. A few more in the barrel. Zero wear on the mag follower. Zero smilies. So a brand new gun, at a competitive used-gun price, and was able to avoid shipping and transfer fees.
The problem: It hangs up and doesn't go into battery every time because the locking lug on the barrel hangs too low. I noticed it was a little sticky in the store, and figured it was just "new gun"-ness and would break in. But further examination at home reveals it takes a significant amount of force to drive it into lockup. It's not dry, there's plenty of factory oil still on everything inside it. Unless it has the full inertia of being dropped from all the way back, and sometimes even then, it stops hard at the point where the locking lug meets the cross bar.
This is the second Sig I've gotten with a significant negative-clearance lockup. The first was a used P220 that appeared to have a brand new frame under a nicely broken in (but not too much) slide. It wouldn't go into battery. Most of the problem was a machining defect in the slide that prevented the barrel hood from rising all the way up into position. I reasoned that the negative-clearance lockup would put massively excessive normal force on the rails and tear up the frame in short order, hence the new frame on a slightly used slide. Whoever had put that slide and barrel on the new frame had failed to identify that obvious and serious problem. I fixed the slide defect, but the lug still needed a little burnish after the slide was fixed. I fit it so the lockup was a snug slip fit, and it's pretty sweet.
Based on those observations, I have proposed the hypothesis that variability in the lockup fitting from the factory is a significant contributing factor, if not the "red X," in the observed variation in frame rail wear among classic Sigs. Some barely polish the anodizing in several thousand rounds, some initially wear noticeably and then stop, and others eat themselves in a ridiculously small number of rounds. Of course, when things go badly in a hurry, Sig blames the customer and the internets blame whatever lubing protocol was used.
On my new P250, the surface of the locking lug that bears against the crossbar in the FCU has a different finish from the rest of the barrel. The rest of the barrel is smooth, but the lug has obvious machining tool marks on it, indicating it was machined separately from the rest of the barrel, possibly some time later. This tells me there is at least some special attention paid to the dimension of this feature, if not fitting for each particular gun. But this one was not machined enough. Yet another example of an out-of-the-box unserviceable gun, and why "out of the box to the range" doesn't exist in my world. A person could take this to the range and struggle with it not functioning well while it tore itself up, damaging other features and components in ways that would permanently impair the performance and/or service life of the gun, or they could fix it before taking it to the range and receive long service from a great-performing gun. (It occurs to me that this is ironically appropriate for a gun that is, in a sense, 2.50 K frames.)
The fit of the barrel in the slide is perfect with zero play, so this gun has excellent potential. I look at this as an opportunity to get it just right, rather than relying on Sig's service center to distract themselves from reworking P320s and f it up again. My other P250s are a .22LR and a .380, and neither of them have any issue with this. I guess I could just compare it to them and make everybody matchy-matchy.
Figured I'd put up my hand and see if any of our folks with experience with a large number of P320s or who have been to P320 armorer school know what the spec is on this. (Remember barrels are the same part numbers for P250 and P320.) This gun is obviously too tight, but does Sig want it a little bit tight? Is slight negative clearance a means of compensating for the inherent flexibility of the FCU? Do they wear in and loosen up as the rail "fingers" on the FCU and slide get worn in, or if they are "right on" to start with, will they stay that way and not loosen up?
ETA: I did my deep dive on P250 generations a long time ago. This is a later Gen 2 version, with the contoured rather than flat take down lever. Nothing to do with the Gen 1 suckage here.
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Originally Posted by Kirk
