Timing and accuracy question

[mike h. buness]

I've been following Tuners timing & clinic threads and a component seams to be missing... the position of the bullet at the time of unlock. Due to the fact that the bullet must still be in the barrel at unlock and the larger radius of the barrel will at some point move out of the bushing, what effect does this have on accuracy? A barrel that is left "hanging" past the bushing can't be expected to be very accurate even with lower lug and shroud in perfect order. I'm stumped! Help! Mike.

[1911Tuner]

I've been following Tuners timing & clinic threads and a component seams to be missing... the position of the bullet at the time of unlock. Due to the fact that the bullet must still be in the barrel at unlock and the larger radius of the barrel will at some point move out of the bushing, what effect does this have on accuracy? A barrel that is left "hanging" past the bushing can't be expected to be very accurate even with lower lug and shroud in perfect order. I'm stumped! Help! Mike.

Nope. Go back and read it again. The bullet has to be gone before unlocking starts. If the bullet is still in the barrel when it begins, the pressure is still too high to safely open the breech. Unlocking nominally begins at .100 inch,
but this can vary from .090 to about .110 inch and still work as intended.
If pressure is still high, it's not only dangerous for the breech to partially open,
it's not likely that the lugs will disengage because they lock under pressure. The barrel does, however move rearward for a short distance with the bullet in the rifling.

[mike h. buness]

OK,I trust what your saying, but I still remember the guy from JPL with the high speed photos. As I recall, the bullet was just visable outside the muzzle with the accompanning gas plume and the slide appeared to be about 1/2" back. You could'nt see the muzzle directly because of the angle. I undrstand the rearward movement of the barrel about.10 before unlock......ARRRRGH!!! Now I get it. Thanks, Tuner I'll be an expert after about another 100 of your replys. Mike.

[1911Tuner]

Hey Mike,

If you consider how fast the bullet accelerates through the barrel as opposed to the slide, by the time the bullet is a tenth inch out, the slide probably would be that far back, or even more. A close approximation would be to think of the slide being about 30 times heavier than the bullet as well as being under the recoil spring's
resistance. Since they both start to move at roughly the same instant...and the spring slows the slide a little as well... the bullet is accelerating more than 30 times faster than the slide.

To better understand all this, consider how the 1911 locks. It's not a true locked breech design in the sense that a bolt-action or falling block rifle is.
It doesn't actually lock until it fires. The bullet passing through the barrel holds the barrel firmly forward while the slide is being slammed in the opposite direction. The front faces of the barrel lugs hit the rear faces of the mating slide lugs...and there's a ballistic tug-of-war at some 20,000 psi. If the barrel moved back far enough to initiate unlock, the poor link would be under some pretty serious tensile stress, and would stretch and break within a few shots. Even if it COULD break that lock, the corners of the locking lugs would be worn away in less than a hundred rounds due to the high frictional forces.

Clear as mud? ;)

[mike h. buness]

One more question O Great Tuner. Can accuracy, reliability and stopping power co-exist with all the movement of the various components of the 1911 without very close tolerances? All that's left on my current 1911 project is to tighten the slide/frame fit. Is It worth the trouble. Mike

[1911Tuner]

Howdy Mike,

Depends on how tight you intend to go. Yes...It can be done, but the tighter the fit, the more dead on everything has to be. .003 inch of play in both the vertical and horizontal slide/frame fit will give you a much tighter gun than about anything you can buy for less than 2,000 bucks and still be
loose enough to allow for dirt and fouling. My rebuilt '43 Colt has about .004
total sideplay and .005 vertical, and if you oil the rails a bit you can barely feel it by pulling hard...and you can't feel much if it's dry. The gun is dead reliable under harsh conditions and will shoot into an inch at 25 yards from a rest with good ammo. If it was only half as accurate, it would still be more
accurate than it needs to be for its intended purpose.

Unless the slide fit is super-loose, the difference in potential accuracy is very little...maybe 5% of the total...assuming that everything else is right. Barrel fit is much more important for accuracy. Contrary to a widely-held
and mistaken belief, the 1911 can be too loose for reliability. Beyond a certain point, it can and does get compromised...but by the time it gets that far gone, you could nearly field-strip it by shaking it vigorously.

[mike h. buness]

Thanks for the slide/frame fit specs Tuner. After the rebuild with the new Wilkson barrel/bushing and the new sear/hammer it was printing 2"-3" groups at 25 yds. after about 500 rds with no malfuctions I've opened up to 5"-6". My front slide to frame fit is .010, rear is .007. This is the only area that is not real tight. after your advice I dont think my problem is the slide fit but I dont know where to go from here. Any thoughts? Mike.

[stans]

You don't have fouling build up in the barrel, do you?

[mike h. buness]

No, No fouling. I clean it after every session of 100 rds. I use 4.6 gr of Tightgroup behind 230 gr copper plated round nose and it's a little sooty. All the groups I mention are off the same custom rest at the same yardage. This load leaves no copper or lead in the barrel. Just to be shure it isnt my reloads I ran 100 rds of Winchester 230 fmj last Saturday with the same 5"-6" 5 shot groups. This is bugging the hell out of me! Maybe my eyesight?
Mike.

[1911Tuner]

A couple of questions:

Are you using the same ammo? Same headstamps from the same lot with reloads? Have you sandbagged the gun to eliminate as much human error as possible? Was the barrel hard-fit or drop-in?

The only real variable with a good barrel fit is the headspace. Case lengths
sometimes vary a lot. You can control that with reloaded ammo by measuring every case and using the ones that fall closer to your static headspace...whatever that is. If you don't know and don't have the
equipment to measure it, shoot for a case length of .892-.895 inch.

The other issue is that...The barrel lugs seated during the initial 500 rounds and didn't seat/equalize squarely with the bore axis, and when the gun is fired, the barrel shifts. This one is a fairly rare, but has hapened.

Load some brass with consistent lengths and sandbag the gun to see if the groups fall into line.

[mike h. buness]

Thanks, Tuner for getting back to me on this frustrating challange. My static headspace is .897. chamber diameter is .476. My first thought was my reloads were not consistant so I bought the new 230 gr fmj to compare groups. Same 5"-6" pattern [off my custom rest]. Measuring the new and my reloads showed a .08 AOL differance [mine are shorter.] Factory rounds were.470 diameter, reloads are .468. As for the barrel, I hand fitted a Wilson combat match grade barrel/bushing. These,as you probably know, are over sized in top & bottom lugs. It took a lot of time to mate everything but I believe I have a good fit. #1 & #2 lugs have full engagement at lockup by my die method. .002 clearance at hood & breach face, same at hood sides. Lower lug sits on slide stop pin with no feelable movement at lock-up. It functions flawlessly.You mentioned that after about 500 rds the barrel may have opened up the clearances enough to reposition the barrel every shot. I'll have to re-check my lug clearances. I will Check my brass for length from now on though. I use mostly range brass of all types. Thanks Tuner, Mike