Howdy all,
I have a full-size Series 80 9mm that I picked up for a good price some time ago. It was re-barrelled at some point with a Kart easy-fit (although I also received the original barrel). It shoots to POA, and groups extremely well for me given the tiny sights. I have noticed a couple of things that I have a question regarding. First, there appears to be a slight amount of corner drag/flanging on the LHS of the top barrel lugs. Second, I am seeing low primer strikes (off by about 1/2 the width of the firing pin dimple at the 5 o'clock position). From what little information I have found (Kuhnhausen and on-line forum posts), I get the impression that having too long a link could cause these things to happen. The fix would be to install a shorter link; however, doing so would have repercussions that would include altering the point of contact between the lower lug feet and the link (good contact there now), changing the point of impact on the rear of the bottom lugs (good contact here also), and reducing the surface area for top lug engagement (my smith tells me that I currently have .030” engagement now). This is a range gun only and I purchased it so I could get a little more practice for my buck whilst still using the same FCS. That said, is there any reason I should be concerned about the flanging/low primer strikes? I've never had a mis-fire due to the primer strikes, and keep a shok-buff in it. I figure I'll have it corrected when I am less pecuniarily challenged, but should I be concerned about firing it now?

Many thanks for any assistance you can provide.

kryten asked:

That said, is there any reason I should be concerned about the flanging/low primer strikes?
__________________

Yes. The flanging means that the barrel isn't getting down in time for the slide to get past it. The barrel is still barely
locked to the slide when the slide recoils. Continued use will damage the slide lugs, and could possibly shear the barrel lugs off.

When the slide is .250 inch out of battery, there should be a minimum of .010 inch clearance between the top of the barrel and the underside of the slide. I like to see at least .015 inch, but .010 will do if all is well. The barrel must fall...Don't push on it to get the clearance.

A shorter link MIGHT fix it, but it's not likely. Your timing problem is probably due to the lower lug being set too far rearward or the impact surface in the frame being too far forward. The barrel is stopping too early in the linkdown.

A long link MAY be causing the problem by stopping the barrel before it links down completely. Check to see if the barrel is riding the link around the forward radius of the bottom lug. If it is, you can elongate the slidestop pin hole at the top about .005 inch to see if it will go to bed.
If it's not riding the link, you may need a shorter link. Just
be sure that it doesn't cause the pin to get into a bind with the forward radius of the lower lug as it goes around the corner.

Lay the barrel in the frame and slip the slidestop pin through the link. Will the barrel lay in the curved part of the frame? If not...remove the slidestop pin and check again. If it goes to bed, it's the link. If it doesn't, the lower lug feet may be too long. If the feet aren't holding the barrel off the bed, the issue is with the frame's impact surface or the lower lug location. Go back to Kuhnhausen's manual and study it a little more to see what to do.

The off-center primer strikes suggest that the barrel isn't
centered up with the breechface when it's vertically locked.
It's sitting either too low or too high. If it's sitting too high,
you probably removed a little too much from the fitting pads on the Kart barrel. Time to weld'em up and start over. If it's too low, you didn't remove enough.

Have you marked the ammo at the top to see where the pin is hitting the primer? If you're sure it's at the 5 O'Clock position, the barrel is too high, and the hood isn't centering the barrel laterally with the breechface. Is the barrel hood a tight fit...or does it have a little clearance on either side when it's in-battery? If it's tight, remove a small amount of metal from the right side of the hood.
Easy! If you need to remove more than about .005 inch,
something else is wrong.

Standin' by...

Tuner

Tuner,

You are hired, as our gunsmith expert here. I can hardly afford the paper required to print all your elaborate answers on gunsmithing questions.

Start preparing articles on "How to..." for the Technical Issues section, or else your 0 US$ salary will be reduced by 50%.

LoL

__________________
John Caradimas SV1CEC
The M1911 Pistols Organization
http://www.m1911.org

Okay...But I want the Lear jet and stock options...

Tuner,
Don't forget to ask about time off, holidays, and insurance packages

All that I agree, stock options can be considered, but Lear jet? Wouldn't a propeller plane do??

LoL

__________________
John Caradimas SV1CEC
The M1911 Pistols Organization
http://www.m1911.org

John- Tuner only travels first class!

__________________
NRA Endowment member
"I used to do nothing; now I'm retired." from the movie "Trouble Bound"

Tuner,

Many thanks for the pointers...I guess this sort of information sharing is what Al Gore intended when he invented the internet all those years ago .

That said, when I pull the slide back the requisite amount, the barrel does fall unaided. The resulting gap between the top of the barrel and the slide is on the order of .020". I suspect that it is probably a bit more, but I think the flanging on the top lugs is causing it to appear less.

I took the top end off and put the barrel back in the frame using the link only. It seems to go down into the frame bed OK. I do not see any gap and it does not seem to move when I press on the rear of the barrel. That said, I do see an unexpected wear pattern on the frame bed and also on the rear lugs. I took some pics (hopefully the'll be visible): colt 9mm

The wear on the frame is greater on the right than on the left and it feels like it is higher. As for the bottom lugs, it looks like all contact is happening in the small space just below the barrel.

I am fairly certain that the primer strikes are at 5 o'clock. I marked a few cases after I noticed it and also looked at their location wrt the marks left by the extractor. Looking at the barrel hood, there appears to be clearance on both sides, with the right being at about .020" and the left closer to .010" (or less).

Although I am more concerned about the corner drag, I am nonetheless curious as to the ramifications of fixing the low primer strikes. Doing so would typically necessitate lowering the barrel when in battery. In that case, it would also have the effect of reducing top lug engagement with the slide. If it is currently at .030", how much lower (if any) can it safely be reduced?

Again, many thanks for your assistance. I find your technical posts to be quite interesting and educational.

kryten

Howdy kryten,

Since everything checks out, it's likely a slight vertical dimension issue in
the frame/slide/barel tolerance stack...and it's gonna be tough to call this one
without the gun on the bench. Since I'm not an FFL holder any more, I can't
receive it.

It sounds like your barrel could stand to begin linkdown a little earlier in the
slide travel. Pull the slide rearward and watch the barrel closely...It may take 3 or 4 tries to determine at exactly what point the barrel starts to move downward. It should BEGIN to link down at .090 to .110 inch of slide travel.
.125 is the absolute limit...and that only in precisely fitted pistols. .100 inch
is about right. When I say it should begin to link down...I mean the slightest
perceptible downward movement. You'll have to watch closely.

.030 inch of lug engagement is about half of the total, and you really can't afford to lose much, if any. If the barrel is standing on the link...even a tiny amount, you can try a slightly shorter link to start the linkdown a little earlier
in the cycle. About .003 inch is the limit.. Even if the barrel ISN'T standing on the link, you may be able to go .003 shorter...IF...the shorter link will allow the slidestop pin to gt around the forward radius of the lower lug and
vertically lock without getting into a bind. A very light bind between link, lug, and slidestop pin can be reduced by dressing the surfaces lightly...but
very little.

You can try dressing the front corners of the barrel lugs LIGHTLY at a 45 degree angle to create a camming surface and to give the barrel a little more time to get out of the way of the slide. This works in about 30% of the pistols with this problem if you make other minor adjustments. In your case, I'd scrape the corners with the tip of a pocket knife instead of using a file.
Go all the way around the radius of the lug evenly. Remove very little...only
enough to see the scraped line.

At this point, I don't advise dressing the rear of the barrel lug. Chamfering
the leading edge of the frame's impact surface lightly may be an option later...(the area that the rear of the lug makes contact.) That will likely
be better determined by a smith who can examine the gun.


When dressing for clearance, it's best to take a little from several areas than all from one. Lightly dress the lower lug's radius. Enlarge the hole in the link
a thousandth or two with a chain saw sharpening stone bit for your Dremel.
They come in 3 sizes...Use the 3/16ths bit, and a "swinging" motion to enlarge the hole enough to fit the slidestop pin. Be careful to keep it square in the hole. Use very light pressure and recheck the fit carefully. You will
be mainly polishing away the high spots, and honing the hole to fit...about
.002 inch maximum. Chamfer the hole on both sides with a scrape when you're through. The clean end of a triangular file will work for this

Determine the length of your link by measuring centerline spacing across the correct size pins, and subtracting half the diameter of both pins. If you use a
dial caliper for this, figure on an accuracy tolerance of +/- .001 inch. A
micrometer is better, if you can arrange it. Any machine shop can do the measurement for you in about 30 seconds, if you don't have the equipment.
Round the measurement up or down to the nearest full thousandth.

That's about all I can tell ya here...Wish I could nail it closer to the mark.
Best of luck with the project.

Tuner

Tuner,

Many thanks for the advice. At this point, I am thinking that it is time to visit my friendly neighborhood 'smith. I've made arrangements to have it looked at. this weekend and I'll post the results as soon as I hear something (for those who are interested)...


k