Checking barrel-to-slide lockup

I read here recently that barrel-to-slide lockup is a key -- perhaps the key -- to accuracy in semi-auto pistols, and I gather that this lockup refers to the proper alignment of the barrel, when in battery, with the sights mounted on the slide.

Makes sense to me, but how do you check or evaluate such a thing?

I'm thinking that in the Performance Center semis that have a Briley barrel bushing out at the end of the slide, the spherical titanium-nitrided bushing helps assure proper mechanical alignment of the barrel and slide. This feature of the custom guns is an advantage over the production guns, where the barrel end is not supported out at the end of the slide -- which, I assume, could allow enough misalignment between barrel and sights to cause accuracy problems.

But in the production guns, including the TSWs, how do you know if you have proper lockup? Is it something you can check when buying a new or used pistol without a barrel bushing?

Since lockup is a feature across all the calibers and models of semis, I hope this thread will be helpful to many of us here. Thanks in advance for any advice here.

Great question. I wish I could help, but I am awaiting answers, too.

To heck with the sights; they can be moved. What is needed is for the barrel to lock to the same position each time. Unless the barrel is crooked, that means checking to see the fit at the back of the barrel facilitates complete and consistent lockup. Who cares how much it wiggles when you push it out of battery as long as it comes right back?
The 1911s with bushings and the M&P types differ in the details.

This really isn't something you need to get all wrapped around the axle about.

I suspect this question arose from a statement I made the other day regarding a given pistol's slide to frame fit being perceived as somewhat loose. I said the slide to frame fit has little to no effect on a weapons accuracy potential. What truly makes for good accuracy is consistent repeatable lockup such that each time the weapon goes into battery the barrel is in exactly (or nearly so) the same relationship to the sights.

Some years back I had a match conditioned hardball gun I was competing with. The slide was flappy loose on that old thing but Lord did that gun shoot. Barrel bushing was rock solid in the slide, very tightly fitted. Press down on the barrel hood and it didn't budge a micron in any direction. Bushing to barrel fit was equally tight. But, if you picked up that pistol and shook it a bit, it sure did rattle. I won the service pistol rapid fire match at the Inter service Matches in '92 with that gun.
As an aside, A little habit I picked up from the guys at Quantico... Never turn the barrel bushing match conditioned 1911. Learned how to take a 1911 apart the same way you would a 4506 and capture the recoil spring. Don't turn a precision fit bushing on the barrel and in fact don't turn it in the slide and remove unless absolutely necessary.



Anyway, back to our scheduled program.
In your typical recoil operated locked breech tilting barrel type pistol you have whats often referred to as a three point lockup. In other words there are three points that hold the barrel fixed in position when the weapon is in battery.

These are:
Barrel fit to the barrel bushing.
Aligns the muzzle end in relation to the sights and is the fulcrum upon which the tilting barrel tilts. There many different bushing arrangements from no bushing at all to cone shapes barrels, rubber o-rings, angle bored bushings, removable or fixed spherical bearings, and so on. Regardless of the design they all share the same purpose which is to position the business end of the barrel in the same place every time. What to look for? excessive slop where the barrel interfaces with the bushing, or, a bushing that's poorly fit or loose in the slide. Making damn sure the weapon is clear, press a finger firmly on the crown and try to wiggle it, You shouldn't be able to discern any movement even though there may be a couple/three thousandths of clearance. It's good.

Barrel hood fit to breechface.
This is the tab on the top rear of your barrel's chamber. It engages a slot machined in the top of the slide's breechface to align the barrel's breech end on the horizontal. Again, look for excessive movement side to side. Try to wiggle it side to side, you shouldn't be able to discern any movement. Examine the hood under magnification looking for excessive gaps where the sides engage the slot. A couple thousandths is fine.

Underlugs or link or cam surface fit to crosspin.
Lots of different designs here too. As the slide runs forward this engages the crosspin to shove the barrel upwards engaging the locking lugs and the hood. In battery, aligns the breech in the vertical. Press down on the hood. On a 3rd gen it may give a little and you may see some slight rearward movement in the slide but, you let go and it pops right back up. Say you do the same on a 1911. Press down on the hood and it drops about a 1/16" inch and stays there. That's bad, lugs cut wrong or wrong size link. Anyway not really something to be concerned with on a 3rd gen. The nature of the design basically has the chamber being shoved upwards under constant pressure from the recoil spring pushing the cam against the crosspin.

In summary look for these things;
Loose barrel bushing in slide or loose barrel fit to bushing
Barrel hood side play
Vertical slop at the chamber end


Ok, now that I've gone way out in the weeds here (sorry about that). Useful tips for gunshow shopping anyway

Here's what you really need to look for. How well does the thing shoot. Look, if you have a few pistols that easily chew the x-ring out of the aiming black but there this other one that spits bullets all over the place, lucky to hit the berm at 15 yards, well that the one that need a serious looking to.

Don't get too wrapped up with super tight dimensions and absolute minimum of slop. Keep in mind there need to be some slop so the thing will keep running. There need to be room to allow for heat expansion sometimes with dissimilar alloys having different expansion rates and there needs to be room allowing for buildup of junk/dirt/debris from firing. It's not necessarily the super tight dimensions that make for good accuracy but like I said up top, It's lockup that's consistent & repeatable.

There may be some slack here and there but so long as the lockup is the same every time... it'll shoot.

Cheers
Bill

BMCM, great write-up.

Thanks.

Thanks, Master Chief. Your comment in the other thread was, in fact, the source of my question. I thought everyone here on the Semi-Autos thread could benefit from a thorough description of this aspect of our pistols, and you sure have provided it for us.

And I'll keep in mind not to get too "wrapped around the axle" about this issue as long as my pistols still keep the holes on the paper and not in the berm!

Our semis are fascinating machines, and learning more about 'em is part of the fun of owning 'em!

I have a few PC semi autos with the Briley Bushing and match grade, fitted barrels. They are nice pistols and are very accurate guns. I would opine that they are probably more inherently accurate than my ability to shoot them that accurately.

That said, I have some standard production 3rd gen pistols that have tight barrel to slide fit, standard factory bushings and EXCELLENT TRIGGERS that are every bit as accurate, in my hands, as their more expensive rare cousins. Again, probably more inherently accurate than my ability to employ that accuracy. Barrel thickness and a smooth crown also being big contributors to a guns inherent accuracy as well.

While I see folks these days concerned about barrel to slide fit and sometimes with slide to frame fit, which is less important in my opinion, don't forget or overlook the importance of a good smooth trigger in the accuracy equation. To me, it is a primary and essential building block to handgun accuracy, every bit as important as barrel to slide lock up.

You can have a tightly fitted match grade barrel and bushing, but if you don't have the smooth excellent trigger with a crisp break, how will you be able to take advantage of the guns inherent accuracy? My 0.02 Regards 18DAI