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Fitting Aftermarket Barrels


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#1 reconbob

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Posted 31 December 2008 - 08:41 PM

This has come up before, and I just did another batch of these and
figured I'd pass along. The aftermarket barrels are notorious - and always
have been - for oversize threads and diameter making it difficult, sometimes
impossible to even get started on a receiver. If you return them, the
barrel you get back could be as bad or worse than the one you sent.
(NOTE: The barrels I am refering to are the barrels sold by the big
parts houses. Doug Richardson and PK make excellent barrels with
the correct threading and are a perfect fit.)
The aftermarket barrels can be fixed and fitted without too much trouble.
The first thing is to remachine/reform the thread which takes only a few minutes
in a lathe. When this is done you can see by the way the tool cuts that
the form of the thread is not a true square (which it should be) due to
inaccurate machining, improperly formed cuttting tool, or both. After
recutting the thread you can file the outside (major) diameter of the thread
on a trial-and-error basis until you get a good fit.
Pictured below is an aftermarket barrel which would not screw on
to a recever at all. The first photo shows the new barrel chucked up ready
to remachine the thread. The second photo shows the result of recutting the
thread with the correct tool (0.05" wide) and you can see how the thread
has been corrected by the machining away of the bluing.





After remachining the thread the barrel screwed almost all the way on, but
got stuck. By light filing of the thread major I was able to get the barrel to
esily screw all the way on for a perfect fit. I have done this so many times now
I consider this to be a reliable "standard routine".

Also, for reference purposes, here is a photo of the chamber end of an
aftermarket barrel on the left, and an original barrel on the right. Note that
the aftermarket barrel (left) has a short chamfered (angled) breaking of the mouth
of the chamber. The original barrel (right) has a deeper fileted (rounded) mouth
which is much more reliable for feeding. There is no reason the new barrels
can't be chambered this way, but for whatever reason the makers choose not
to do so.



Bob

Edited by reconbob, 31 December 2008 - 08:55 PM.

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#2 deerslayer

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Posted 31 December 2008 - 09:35 PM

Bob, I was thinking about posting the same story....I just used two barrels from Numrich. First wouldn't thread on, and when I did finally touch it up so it would thread on, I found the headspace was cut too deep (or long) wouldn't even fire as the firing pin would just push the cartridge forward (using it on a semi auto SBR). So, sent it back. 2nd barrel same headspace problem but I decided to fix it as I needed a barrel right now. Interestingly enough, it did thread right on.
Dan
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#3 reconbob

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Posted 01 January 2009 - 09:51 AM

So the chamber was so deep the firing pin would not hit the primer? Thats bad. My opinion
is that the Gun Parts/Sarco/Kahr barrels all come from the same source, although one of the
barrels I just did was a smooth barrel and had been roughed up on the outside to remove the
distinctive CNC turned finish to appear more authentic.
With todays CNC technology these barrels should all be perfect. There is no excuse for
bad chambers, headspace, and threads. It would not take any longer to do it right. I sometimes
wonder if the barrels are made dirt cheap by the truckload in Taiwan, China, or India, imported
en masse and distributed to the parts houses who sell them as spares, or as in the case with Kahr,
assemble them on guns. It doesn't have to be that way of course. look at the low-priced but
very high quality "Crosby" drums...

Bob
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#4 dalbert

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Posted 01 January 2009 - 10:37 AM

reconbob,

Another excellent post! I added a link to it in the "Technical Interest" section of the Thompson Reference Thread pinned post. (I'm still working out some technical difficulties I've experienced with that thread)

David Albert
dalbert@sturmgewehr.com
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#5 fortyfivecal

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Posted 01 January 2009 - 11:28 AM

QUOTE (reconbob @ Jan 1 2009, 10:51 AM) <{POST_SNAPBACK}>
It would not take any longer to do it right. I sometimes
wonder if the barrels are made dirt cheap by the truckload in Taiwan, China, or India, imported
en masse and distributed to the parts houses who sell them as spares, or as in the case with Kahr,
assemble them on guns. It doesn't have to be that way of course. look at the low-priced but
very high quality "Crosby" drums...

Bob


Thanks for your post Bob, your pictures speak a thousand words. Your statement quoted above is well founded, it is directly related to both what is wrong with some contemporary corporate thinking, quality coming in a poor second to profit margin, and to what draws us to the thompson legend, quality first.
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#6 giantpanda4

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Posted 01 January 2009 - 12:24 PM

Bob,

I wonder if the reason they won't fit is intentional. I just put two garand barrels I got from the CMP store on a couple guns. They are Krieger Criterion barrels, from a known excellent manufacturer.

They are deliberately short chambered. I got a Manson reamer (worth its weight in gold!) and headspaced them. I was told it is liability as well as forcing each user to fit for proper headspace. If you let someone else machine your barrel after you, you claim no liability. I know not fitting into a receiver is not the same as short chambered, but maybe the same "logic"?

JMHO.


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#7 reconbob

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Posted 01 January 2009 - 12:51 PM

I guess anything is possible. I do know that it is normal for military
high-powered rifle barrels to be made with short chambers. Back in the
good old days when you could get an original mint-in-the-grease barrel
for a Springfield or Garand, (even BAR) you had to cut the headspace to
match the bolt. It wasn't much - the chambers were probably no more than
0.02-0.03" short - but still you had to ream to match the bolt. Which
was good of course since you could start off with "perfect" headspace.
Different story with Thompson barrels of course. The main concern
is correct chamber depth. A short chamber would still fire a round, a long
chamber would result in Deerslayers problem of not firing at all. You'd
think that after so many years of people returning and complaining about
barrels they'd do something about it,but apparently not.

Bob

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#8 mike in pa

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Posted 01 February 2009 - 08:15 PM

Soon I will be building a SBR out of a Kahr M1, what are the current barrels of choice for building a shorty? How are the front rings sights held on the barrel, pinned, press on or silver solder?

Kahr/Tommy Gunner...
Numrich/Gun Parts...
PK... (any idea on current price?)
Other...


Thanks!

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#9 deerslayer

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Posted 01 February 2009 - 10:04 PM

Best bet would be to get a GI barrel. 2nd, see if PK has one in stock, 3rd, Numrich and be prepaired to alter threads/chamber. Tommygunner can arrange service if desired. Front sights for a M1 should be snug as slid into place, then pin holds it tight. No glue or silver solder. Last ring sight I took off a new Kahr was on VERY tight and took considerable effort to remove.
Dan
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#10 reconbob

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Posted 02 February 2009 - 11:18 AM

Adding more to the aftermarket barrel saga I just had one in here
where the front of the barrel that holds the sight was so undersized
the sight just slid past it down the barrel. I never would have thought
to check that....

Bob
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#11 ron_brock

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Posted 02 February 2009 - 06:58 PM

QUOTE (reconbob @ Jan 1 2009, 12:51 PM) <{POST_SNAPBACK}>
You'd think that after so many years of people returning and complaining about
barrels they'd do something about it,but apparently not.

Bob


Probably still cheaper to send another barrel than to retool them some place where there are no issues reading a print properly, or where quality standards are a bit higher. Besides, this way they can send your returned barrel for someone else to try out for fun.. banghead.gif

Bob,
Do you order a special cutter for the square threads, or just use a standard cutoff bit that has the correct width and radii on the ends? (if it's a secret I understand)

- Ron

(edited for bad spelling)

Edited by ron_brock, 02 February 2009 - 07:02 PM.

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#12 reconbob

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Posted 02 February 2009 - 08:01 PM

You can use a cutoff type tool with a width of face of 0.05".
You will probably have to grind a clearance on the back so it does
not rub against the thread. Or, if you don't feel like grinding a tool
you can use a 0.05" O-ring tool, but you still need to grind the back
of the tool so it doesn't drag. Here is the tool I use:





It is an O-ring groove tool with the clearance ground as shown. I only use
this for barrel threads now, but back in the day I used it to thread receivers
on a lathe. Thinbit is the name of the company that sells the toolbits and
the tool holders.

Bob
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#13 ron_brock

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Posted 03 February 2009 - 09:10 PM

Thanks Bob,

Thanks for the info. I always wondered what bit to use. I found one I thought was correct for"square threads" but never thought of using a cutoff bit. I have an old Clausing lathe, but am having some issues with the phase converter I built getting the lathe to start. I am hoping to get the bugs worked out when it gets a bit warmer out.

- Ron
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#14 thompson

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Posted 24 November 2009 - 11:47 AM

QUOTE (deerslayer @ Dec 31 2008, 10:35 PM) <{POST_SNAPBACK}>
Bob, I was thinking about posting the same story....I just used two barrels from Numrich. First wouldn't thread on, and when I did finally touch it up so it would thread on, I found the headspace was cut too deep (or long) wouldn't even fire as the firing pin would just push the cartridge forward (using it on a semi auto SBR). So, sent it back. 2nd barrel same headspace problem but I decided to fix it as I needed a barrel right now. Interestingly enough, it did thread right on.
Dan


Dan,
I have a barrel from Numrich and from Unique canes. Both wouldn't screw on my display Phil Ord receiver. Have you ever experienced any problems with their receivers??
thanks
Thompson
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#15 darrylta

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Posted 24 November 2009 - 12:36 PM

QUOTE (thompson @ Nov 24 2009, 11:47 AM) <{POST_SNAPBACK}>
QUOTE (deerslayer @ Dec 31 2008, 10:35 PM) <{POST_SNAPBACK}>
Bob, I was thinking about posting the same story....I just used two barrels from Numrich. First wouldn't thread on, and when I did finally touch it up so it would thread on, I found the headspace was cut too deep (or long) wouldn't even fire as the firing pin would just push the cartridge forward (using it on a semi auto SBR). So, sent it back. 2nd barrel same headspace problem but I decided to fix it as I needed a barrel right now. Interestingly enough, it did thread right on.
Dan


Dan,
I have a barrel from Numrich and from Unique canes. Both wouldn't screw on my display Phil Ord receiver. Have you ever experienced any problems with their receivers??
thanks
Thompson


I recently built a display gun with a Philly receiver. I used a W. Hurley barrel and it screwed right on. You should direct this question to Recon Bob, the Philly Receiver expert.
-Darryl
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#16 zebcoboy

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Posted 24 November 2009 - 01:12 PM

QUOTE (deerslayer @ Dec 31 2008, 10:35 PM) <{POST_SNAPBACK}>
Bob, I was thinking about posting the same story....I just used two barrels from Numrich. First wouldn't thread on, and when I did finally touch it up so it would thread on, I found the headspace was cut too deep (or long) wouldn't even fire as the firing pin would just push the cartridge forward (using it on a semi auto SBR). So, sent it back. 2nd barrel same headspace problem but I decided to fix it as I needed a barrel right now. Interestingly enough, it did thread right on.
Dan

As a retired machinist myself many possibilities come to mind that would explain the threads that don't fit. First of all gun barrels should be installed by a gunsmith who understands all the issues like, major diameter, minor diameter, thread pitch, thread width, thread shape( square, 60degree or acme threads ) and of course chamber head space. Is it possible that the threads were left unfinished so that variables in receiver threads could be compensated for? It would seem to me ( not a gunsmith ) that I would machine the thread for fit first then machine the shoulder and end of the barrel to provide for the proper headspace. When we cut threads for aerospace we had go and no-go gages. It could be said that with proper measuring the headspace could be cut before instalation but with so many issues and so many receivers an unfinished thread would be the way to go. That's my thoughts.

Edited by zebcoboy, 24 November 2009 - 01:16 PM.

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#17 reconbob

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Posted 24 November 2009 - 01:25 PM

If you got a barrel from Numrich that would be the standard "wrong thread" barrel.
Numrich supplies barrels to many other suppliers.
If Unique Canes got their barrels from Numrich, it would also have the wrong thread.
If you want you can send the receiver and the barrel to Phila Ord and I will be glad
to fix/fit the barrel and/or receiver as needed.

Bob/Phila Ord
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#18 deerslayer

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Posted 28 November 2009 - 08:58 AM


Dan,
I have a barrel from Numrich and from Unique canes. Both wouldn't screw on my display Phil Ord receiver. Have you ever experienced any problems with their receivers??
thanks
Thompson
[/quote]


See Bob's first post on this. His receivers are good, I've used quite a few and I've screwed vintage thompson barrels right on with no problems though almost invariably have a problem with non vintage barrels. You'll have to touch up the barrel. Take Bob's offer up. Or if you really want it done right now you can basically replicate what you see in his pictures with a small file and careful work. If you are making a dummy gun, it won't really matter if you screw if up really bad and its loose and sloppy, the barrel just needs to sit on there to look at. I have had my paws on a recent Kahr barrel or two and they seem to have got their act together with a generous chamber and a better rounding of the chamber mouth.
Dan


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#19 casper

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Posted 12 December 2009 - 04:52 PM

just replaced 2 barrels with 10.5 inch new ones from Kahr
I'm happy to report that both had good threads, function of the guns was flawless, this was on smg's not semi's woot.gif


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#20 JimFromFL

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Posted 12 December 2009 - 06:47 PM

I recall one "aftermarket" barrel had a chamber a tad bit too small. ("tad" is an official unit of measurement tongue.gif )

You really couldn't tell except when shooting. The round would fire no problem but the extra tightness during the extraction slowed the bolt down where it cause a runaway as the bolt would never move far enough back to get locked by the sear.
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