Hard Fit Barrel vs. Bomar Accuracy Tuner vs. Kart Xact Fit Pistols

I’ve wanted to share this information for quite some time to educate anyone interested in knowing what we’re talking about in regard to a hard fit full engagement barrel (Kart & KKM, etc) lock up, a Bo-mar Accuracy Tuner Rib lock up and a Kart Xact Fit barrel lock up.

Full barrel engagement into the slide locking lugs is crucial to proper barrel fit. Why? In my opinion it slows the slide recoil velocity and will shoot better from hand than a barrel that is not fully engaged into the slide locking lugs. I’ve seen tons of old school pistols over the years as a pistolsmith that had Bo-mar Accuracy Tuners, shimmed upper barrel lugs, and welded tabs on slides to hold the barrel centered on the firing pin. These pistols all typically exhibit wear in the slide locking lugs from minimal barrel upper locking lug engagement. In other words, because the barrels are sitting lower in the slide locking lugs there is noticeable wear on the locking surfaces. The barrels unlock faster and the slides are travelling faster due to this. The result is a stripped unlock that the corners of the barrel lugs and the corners of the slide lugs are stripping violently past each other. Over time they wear. I’ve seen several old GI US Property pistols that were built into BE pistols and because they are softer (not hardened very good) they barely keep the pistols locked up because of the excess wear. 

So I’ve drawn up what a fully 100% engaged barrel fit looks like, a Bo-mar Tuner Built Barrel and Kart Xact Fit Barrel. I measured some pistols I have on hand to get these dimensions. The Tuner barrel and Kart Xact Fit are nearly identical so to keep it simple I am calling them equal for this example.

A barrel which is hard fit 100% to conform to the slide lugs provides 100% engagement of vertical lockup. The Bo-mar Tuner Colt barrel and Kart Xact Fit barrels both in this case provide 48.84% of the vertical lock up of the hard fit barrel. Less than 50% of the locking surface! 

Pistols built with all three methods of barrel type/fit can shoot well from a machine rest; they all do! But shooting from hand is another story. The hard fit barrels are much more forgiving from hand. It is easier to shoot consistently better with one. I routinely shoot older pistols when I receive them side by side with a newly barreled pistol. I do this to remind myself that I’m on the right path in my barrel fitting techniques. The old pistols beat me up! The fresh barrel fit with full engagement is pleasant to shoot. There is that dramatic of a difference. I’ve had many shooters tell me my pistols feel like they recoil less than their other pistols. Yeah I know what the physics say; F=ma^2. I’m not questioning that. Our pistols have frictional forces and barrel unlocking/camming that is difficult to measure the contributions to slide speed during recoil. But I believe barrel fit can work to our advantage.

There is no excuse to not getting a barrel properly hard fit. I’m seeing $$$$ pistols with Kart NM Xact fit barrels installed. For that kind of money it should be criminal.

Anyhow, take a look at the attached pdf…..I hope its legible and understandable.

 

My 2 cents!

 

Jon

Nicely done and an excellent description of what a properly fitted barrel looks like and does. The benefits are obvious and make me for one appreciate even more the skills, time and effort involved in building a true match grade 1911! Thank you Jon!

I've saved this in my notes and plan to compare my RRA 1911 BE and a SA RO 1911 that my local gunsmith and fellow bullseye shooter built for me with a Kart barrel.

Will a hardfit barrel still have a noticeably different feel and slower recoil speeds with factory ammo (Atlanta, zero, etc)? Or is that just with lower power reloads.

dapduh2 wrote:Will a hardfit barrel still have a noticeably different feel and slower recoil speeds with factory ammo (Atlanta, zero, etc)? Or is that just with lower power reloads.

Everything. More noticeable with lighter loads but still feel the difference with factory 185’s
Jon

Very interesting write-up I barely understand how these pistols work and would love to talk to my pistol smith about this with your drawing at my side.  

thanks for show us.

Jon, as a new properly fit barrel in a gun gets broken in and it doesn't take more muscle to rack it, does that mean it's not engaging the lugs just as deep as when newly fitted? I imagine that has a lot to do with the link and the shape of the lower lug and slide stop pin wear. Another question what wears more the link hole or the pin?
 Stan

chopper wrote:Jon, as a new properly fit barrel in a gun gets broken in and it doesn't take more muscle to rack it, does that mean it's not engaging the lugs just as deep as when newly fitted? I imagine that has a lot to do with the link and the shape of the lower lug and slide stop pin wear. Another question what wears more the link hole or the pin?
 Stan

Stan,
In my opinion its a combination of barrel upper lug and barrel bottom lug being slightly forced into shape. The link and link pin shouldn't wear much if properly fit. The link is only to unlock the barrel and allow the barrel to ride on it just before barrel lugs pick up the slide stop pin. Slide stop pins get abused when barrel links are too short. To a small degree the slide will wear at the upper lugs.

There's too tight and just right tight. That's the goal any ways...
Jon

Jon Eulette wrote:...The old pistols beat me up! The fresh barrel fit with full engagement is pleasant to shoot. There is that dramatic of a difference. I’ve had many shooters tell me my pistols feel like they recoil less than their other pistols. Yeah I know what the physics say; F=ma^2. I’m not questioning that.

Felt recoil is more of an "impulse" thing - force over time. The same force, over a longer interval, feels like less force.

It makes a lot of sense that if the barrel stays locked for longer while the slide starts to move back, then unlocks and proceeds to eject, is better than both happening basically at once. For accuracy too!

So, those green and red areas in your pdf are in the slide, a very tricky place to cut. Is your magic mostly applied to the slide, or the lugs? Ok, I know you'll say "both"

-TT- wrote:

Jon Eulette wrote:...The old pistols beat me up! The fresh barrel fit with full engagement is pleasant to shoot. There is that dramatic of a difference. I’ve had many shooters tell me my pistols feel like they recoil less than their other pistols. Yeah I know what the physics say; F=ma^2. I’m not questioning that.

Felt recoil is more of an "impulse" thing - force over time. The same force, over a longer interval, feels like less force.

It makes a lot of sense that if the barrel stays locked for longer while the slide starts to move back, then unlocks and proceeds to eject, is better than both happening basically at once. For accuracy too!

So, those green and red areas in your pdf are in the slide, a very tricky place to cut. Is your magic mostly applied to the slide, or the lugs? Ok, I know you'll say "both"

99% barrel fit. Very little is done to the slide.
Jon

Very interesting information, thanks jon!!

Yeah, this is great. Thanks.

I've been sorting thru the Keefer pic's JB archived, and there are a couple showing the barrel set up to deepen the lugs. Is/was he cutting clearance between the barrel and slide, or attempting to make full contact of both top and bottom of lugs? Seems you'd want some clearance in there somewhere for dirt. And that's the only reasonable place to create it.

This also prompted me to look at my SA-A1. I fit an angled bore bushing and a .203 pin. Barrel is untouched other than lapping the muzzle round. Eyeball measure with the depth rod of a caliper suggests I've got 3 thou at most of clearance when it's locked up. There's really no noticeable play up-down. But the hood is sloppy all around ...

No clearance WesG, slide lugs pushing hard against barrel lugs, then transferred down into slide stop pin. You want zero play, thus hard fit. Over time it will slightly loosen, that’s why you want to start out tight.
Jon

Here's one of the pic's. Several others, including setting up to grind the rear most on one.



Grinding it suggests he was looking for a precision surface to fit, but there are plenty of other pictures that suggest maybe he was just being a perfectionist ;-)

So are all these points, top and bottom of the lugs hard fit? Or just to tops of the barrel lugs in the slide 'grooves'?

At the least, it's obvious this needs to be corrected:




And there are pic's showing he lapped the slide bore to true it up all the way back, so he'd have a good surface to fit the grooves to.

The nicely ground shiny section of the barrel is fit to the slide and making contact; typically only the rear shiny lug. The red portions do not make contact.
Jon

Wasn’t there also the use off single lug barrels by Keefer?

Jon Eulette wrote:The nicely ground shiny section of the barrel is fit to the slide and making contact; typically only the rear shiny lug. The red portions do not make contact.
Jon

Thank You !!!!!!

And the low engagement you've pointed out can lead to burring of the lugs in the slide and is the reason for dressing it up as 'step 1' of fitting a barrel?


James,

Seems to me the single lug barrels were on 38's? Or I'm mixing this up with the M-52?

There's a massive amount of stuff in the picture archive. Some of it is fairly straight forward, some of it requires some educated guessing, and some of it is just Greek to me. Mainly, what kind of gun is this? M-52 extractor ... or a .22 of some kind, maybe a Hammerli? I've been 'working' on it for hours, sorting by gun type, tooling, etc. Eventually by component, or whatever. Renaming the files might take the rest of my life ;-) Certainly searching his posts and associating the pictures with broken links would require the efforts of someone younger than me. Or someone who knows how to really use a computer ...

james r chapman wrote:Wasn’t there also the use off single lug barrels by Keefer?

Hello James,

Yes, Jerry Keefer and Chuck Warner both worked on what you call "single lug barrels" for M1911s.  I'm not quite sure that is the correct name for them as they were derivatives of the typical Sig lockup, i. e. a locking block in the injection port.  Nonetheless, they each took that concept and ran with it.  Chuck, in my mind, got a lot further with the concept; completing several pistols and thoroughly testing them.

Jim

99% of the time the forward barrel lug NEVER makes locking contact. I sometimes run into fitting issues on Baer pistols because his slides are machined slightly different. It could be removed from all BE pistols and not be a detriment. Colt 38 spl kit guns from the 60’s were all single lug. I believe my 38 AMU is also single lug. Clark 38 long slide conversions were almost always single lug. So it’s been around long before I started gunsmithing lol.
Jon

Here’s underside of 38 AMU slide. The slide has two upper locking lugs and the slide is lightened both at the rear on each side of the disconnector rail and forward of the locking lugs. Barrel is 0.500” diameter with single lug; it’s not sleeved, they were made like this. Has the JE Clark stamp dated 9.61..
Jon
 

Hi Jon.
How can I verify the fit of my barrel ?
What tools are needed?
And the big question, can the average laymen do It?

Great job on the original post.  
The rationale makes sense to from the standpoint of subjective perception of recoil.

All factors considered, is it possible that the complications involved make a strong case for the SIG style locked breech approach employed by Pardini in their GT45?

I would be very interested in hearing from Pardini owners, many of whom extoll the virtues of the shooting characteristics of this unique 45 caliber pistol. 

Again, my thanks and admiration to Mr. Eulette whose expertise he so freely shares here on the forum.

larryx asked;
"Hi Jon.
How can I verify the fit of my barrel ?
What tools are needed?
And the big question, can the average laymen do It?"
There didn't seem to be a reply and I am interested in what the answers would be. I would like to check my old Clark built BE gun to see if it may need to be reworked or is it just fine and I need to concentrate on a better ammo load?

I forgot to mention that it does have a Kart barrel in it and I would like to see if it was done correctly.

Just a thought

https://www.indianagunowners.com/threads/the-method-i-use-to-fit-1911-barrel.481247/

Or
http://how-i-did-it.org/1911-project/the_kart_of_barrel_fitting.html