Lets talk 1911 vertical lockup

[BSWilson]

Hello all,

So I've got this fullsize 5" 1911 and an engineer I work with mentioned that it might need looking at as the vertical lockup is a bit shallow.

The slide stop pin shows a great bit of wear in the link area for 700 rounds, the barrel's bottom lugs show almost no wear, it seems like the foremost top lug doesn't engage at all, and the barrel hood only seats about half as high as it could in the slide.

So whatcha think, is anything out of line with this or is it par for the course?

 

[Drail]

The lower lugs on that barrel are very poorly cut and finished and it looks like it's only bearing on one lug. I would consider an oversized match barrel and bushing and fit it to your gun. If you have skill with a file and stones it's not that hard. Look at Bar Sto, Storm Lake Machining, Wilson, Kart, EGW. The difference will be startling. A great reference book is Jerry Kuhnhausen's 1911 Shop Manual Vol 1.

 

[Jim K]

What make of gun is it? Drail's advice is good, but that doesn't sound like a quality gun and a gun that is a POS will still be a POS no matter what kind of barrel you put in it or how much you spend on it.

Jim

 

[BSWilson]

As I would prefer this to be an entirely academic discussion, I'd rather not mention the manufacturer. Let it suffice that they are a reputable company with a reputation for excellent customer service.

My primary questions are 1) is this even an issue, and 2) what do you suppose the cause is.

For example, if the slide rails are off, I don't think that even a hard fit replacement barrel would correct its issues. Right?

 

[Phreakish]

Said engineer speaking.

I've been doing quite a bit of research on the 1911 platform for the better part of 3 years, and have come to understand quite a bit about them; with that said:

In watching the weapon cycle in and out of battery, the barrel could be observed to climb up into lockup, and then descend slightly upon final seating. I believe this is because the link is a bit long (or rather, the lugs are over-cut, and do not contact the slide stop). As a result, the link is able to pull the barrel down slightly in the final .030 or so of slide travel.

We measured from the top of the slide, to the top of the barrel, and then measured the 'thickness' of the slide in the same area. With a bit of math, we found only about .015" worth of engagement! scary!

We set out taking comparison measurements between another (known good) pistol of similar manufacture. I measure approximately .025" difference from the lower slide rails to the apex of the radius of the inside of the slide. If this .025 discrepancy wasnt there, his gun would have ~.040" worth of lockup. Still insufficient IMO, but far better than .015!!

He has elected not to shoot this weapon, although the previous owner obviously has.

Aside from the barrel, most of the weapon looks decent. Its definitely not a turd by any means.

We've mulled over a new barrel, as well as other options, but are of the opinion that the slide is likely the culprit, and as a result, a new barrel probably wouldn't help. Although, it would be nice to have some validation of our findings to help refute whatever they may throw our way.

If anyone (old fuff? 1911tuner? others?) has any reference dimension they could throw our way, it would be much appreciated! as our sample size is rather small for dimension sampling.

 

[VinnAY]

Watching with interest.

 

[1911Tuner]

Well...Since you asked.

First...There is no vertical lockup. The barrel engages vertically, but locks horizontally with the lugs in opposition via recoil when the gun is fired.

Good vertical lug engagement is a must if the upper lugs are to live long and prosper, and equal engagement...where all three lugs are in play...is also a good idea.

To determine vertical engagement, allow the slide to ride forward with a spacer between the hood and breechface thick enough that will stop the slide solidly out of battery...but thin enough to let it almost get there. This thickness will vary according to how much clearance there is between hood and breechface. With a closely fitted hood, it can be as little as .010 inch. For an ordnance fit, it can be as much as .025 inch...but .015 will usually suffice for most guns.

With the shim in place...use a dial caliper to measure the distance from the top of the slide to the top of the barrel. Take several measurements to be sure you're getting consistent readings.

Then remove the shim and let the slide snap to battery from about halfway...and measure. Take several to be sure you're consistent...and subtract. The remainder is the amount of engagement on the first lug. A dial indicator is best for this exercise, if one is available.

Some say that .040 inch is good, and in some cases, it may be good...but there's a little more to it. Measure the depth of the first barrel lug wall and determine how much of the lug is being used. If the lug is .050 inch high, and you've got .040 inch vertical...you've got 80% engagement. That's generally considered to be okay for an ordnance spec gun...but just okay. .045 with a .050 lug is better, and I consider it a minumum for a gun that'll be put to hard use.

I much prefer it to be at or near 100%....so that the bottom of the slide lug is bearing low in the corner of the junction of barrel lug and barrel because that's where maximum strength is obtained. The lug is deformed and set back less rapidly with that kind of engagement.

Due to the tilting barrel, depth of engagement on the 2nd and 3rd lugs will be less, so the main strencth of the breech is obtained by the first lug. The 2nd and 3rd are in the supporting role. Rule of thumb, if you have 100% on the first lug, you can expect 90-95% on the second, and 80-85% on the third...assuming horizontal engagement is equalized...which is rarely obtained with an off-the-shelf pistol unless the barrel is carefully fitted for equalized engagement.

If the lugs happend to be very close to equal engagement...say within a thousandth or so...shooting the gun will often seat and equalize them over time and enough use, but as the lugs deform under the pounding of recoil...headspace will increase by the amount of setback. If headspace is on the low end to mid-spec...it's not a problem. If it's near maximum...it can go to excessive...and it increases in such a way as to lead to a condition of non-support in the head area. While a little unsupported area normally isn't a problem with a 1911 in .45 caliber...if the tinkerer also goes at the barrel ramp to effect smoother feed...and it isn't done correctly...it can become a problem...pronto.

With ordnance-spec...or military issue guns...are issued, it's assumed that the unit armorers will run periodic checks to see if the guns still have acceptable headspace.
If not, then the barrel is replaced and the gun retested. If it fails, the next step is to replace the slide. If still unacceptable, the slide is scrapped and the whole top-end is replaced. Military armories have dozens of replacement slides and barrels on hand...so a barrel that needs to be replaced say every 5-6 thousand rounds isn't an issue. For the guy with one gun and no ready resupply of major parts...it gets to be expensive. This is why the government ordered a dozen or extra slides and other replacement/rebuild parts for every finished gun they took delivery of. Everything except the frames were considered to be expendable service parts. As long as the frame was viable, a finished, working gun could be assembled on it. It may not be an optimal gun, but it will be serviceable.

 

[Phreakish]

Thanks Tuner!

What you describe, is about what we did. We have no indicator on hand, so to suffice, we checked carefully with a set of calipers, the distance between the top of the barrel, and top of the slide. Then measured from the inside of the top of the slide, to the outside top of the slide. With some quick math, we found only about .015 of engagement.

We get approximately the same result when we use a shim and measure from the top of the barrel to the top of the slide (within a thou or so).

In order to rule out the barrel/frame, we took some comparison measurements -- then found some legit 1911 prints to verify our findings. The barrel (although arguably rough) conforms, the frame conforms (when it comes to slide stop hole location and size), the slide stop conforms. The slide however...

The slide measures from the bottom of the rails, to the top of the inside of the slide at the chamber engagement surface about .025" DEEPER, which would cause a net loss of .025 worth of engagement. .015" of current engagement, plus the .025 discrepancy found with the slide, would equal about .040" of engagement. Considering the depth of the lug is actually about .052, .040 isn't great, but at least it would live a fruitful life.

Granted, the print dimensions don't call-out the distance we measured, but the .118 dimension on the lower rail thickness (on the slide), plus the dimension from the center of the .699 bore, plus half the .699 dimension, gives us something close to that. Granted, there are 3 tolerance contributions here, but they add up to more like .010", NOT .025"! Nominal values were used to determine this dimension.

 

[Jim K]

Again, I'll play devil's advocate. If the company really is reputable and has good customer service, why ask here what to do? I am sure Tuner, who knows a lot more about the 1911 than I ever will, is happy to answer your questions, but it seems to me that the problem originated at the factory and a real solution should come from the factory that has your money, not from folks (no matter how skilled) on a web site. Call the maker, describe the problem and if their CS is good, they will send you a shipping label to return the pistol.

Jim

 

[BSWilson]

I'm not asking what to do, I was frankly seeking a second opinion (aside from my esteemed friend) from someone like 1911Tuner on what the issue was, if any, and how a shade tree gunsmith could go about fixing it on their own, as well as possibly helping others identify this potential issue in their own pistols.

With that said, I already have a label printed and it's going back tomorrow, on the mfg's dime.

 

[1911Tuner]

Sending the gun back is an option, but the problem many times is that they harumph and tell the customer that it falls within "their" specs and will not admit that there's a problem unless there is obvious damage such as shown the the picture.

This is a Norinco barrel that had less than 500 rounds fired through it. The upper lug vertical engagement was .030 inch on this one. The lug deformation is straight line, and the upper part of the worst one showed .018 inch of setback. Viewed from the side, the lugs have a stair-step profile which is partly visible on the first lug...and the static headspace dimension...measured with a NO-GO gauge and added feeler gauges was a whopping .942 inch.

Linkdown/drop timing and clearances checked out fine.

Send it back if you wish. Might get some results, but don't be surprised if they call and tell you that the gun checks within spec.

 

[Phreakish]

I think my good friend here just didn't completely believe me when I said "ooohh... not good" and wanted to see if he could prove me wrong

We were also looking to see if anyone else had ever seen something similar, and knew what may be the root cause, or if it was a common issue associated with certain manufacturers.

 

[BSWilson]

There's no harm in seeking a second opinion.

 

[BSWilson]

Okay, so with a .026" shim (.019" won't cut it), I'm getting an average of .154 (+/-002) between the top of the barrel & slide.

Shimless & in battery, I'm getting .126" at rest, or as much as .136" if I press the barrel down first.

The first lug (part of the chamber) has right at .056" depth.

So am I correct in saying that I'm have somewhere in the neighborhood of .020-.030" engagement, assuming all measurements are correct?


ETA: Would it be reasonable to think that the Norinco barrel shown may have been a bit soft relative do most other barrels? That seems like a great deal of setback for so few rounds...

 

[1911Tuner]

.030 isn't enough...even with .050 lug height. You're at about 50% where you stand.

Yes. Norinco barrels are fairly soft under the chrome...but no softer than early USGI barrels. If the vertical engagement is good, they don't exhibit this level of setback for several thousand rounds.

Having to use a .026 shim demonstrates just how loose some Norinco barrels can be. Norincos are generally very good, aside from their barrel fit...which is universally sloppy, even though I've seen several that are actually pretty good. It's hit and miss. Of the half-dozen Norinco pistols that I own, none have the original barrels.

The early Norincos had issues with the vertical frame/slide dimensions, and made either a hard-fit barrel necessary to address the lug engagement depth, or a fairly radical lowering of the frame rails. Most people opt for the barrel. I've gone both ways, and either one is satisfactory. The later examples were much better in that regard, and any vertical lug engagement issues were due to the lower lug dimensions. Kart Easy-Fit barrels took care of things nicely.

Every Norinco that I've fitted a barrel to...hard or easy fit...the slide's middle lug was mislocated too far forward...making it necessary to remove .003-.005 inch from the mating barrel lug face to equalize horizontal engagement. Not a major problem with the right equipment...but a little tricky and tedious if all you have is a pillar file. Occasionally, the forwardmost slide lug is located too far rearward, but I don't mess with fitting for that one when I find that condition. If I can get the first and second lug to bear the brunt with a good barrel...that will suffice.

 

[1911Tuner]

I think my good friend here just didn't completely believe me when I said "ooohh... not good" and wanted to see if he could prove me wrong

If you can make him understand what happens with the slide/barrel lug interfaces when the gun first, he'll be able to see why .030 inch of vertical engagement isn't a good thing.

Basically, the lugs engage in opposition as the barrel is yanked forward by the bullet, while the recoil forces are driving the slide backward at the same time. The slide grabs the barrel by the lugs and drags it backward while the bullet is fighting to keep it forward.

If the barrel also has a little endplay in the slide, you can add impact to the event. While a couple thousandths isn't much of a running start, it accelerates the lug deformation. Think of two hammers slamming together. If they're perfectly aligned, they'll peen...but if they're offset...they'll peen more with each blow, and they'll peen faster. As the lugs deform, the endplay grows, giving the barrel and slide a progressively longer running start...which accelerates the deformation. It's a vicious cycle.

Fitting for good vertical engagement...equalized horizontal engagement...and a hood to breechface engagement that keeps the barrel lugs forward against the slide's lugs before the gun fires maximizes the strength of the breech and minimizes lug deformation.

The 1911 has relatively small radial lugs that don't provide a lot of surface area. That's why it's important to utilize all that's available.