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I see you are a relative new poster on the forum, so not sure of your level of build experience. Are you aware that barrel to trunnion journal interfacec is an interference fit? As 6526 previously posted how much larger is the barrel than the trunnion?
 

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nasifg, use a caliper to measure the outside diameter of the barrel journal and the inside diameter of the front trunnion down to the thousandth of an inch. Also, what is the origin of both parts?
 

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That's 0.004" of press fit. That seems high. From what I've read, 0.001" to 0.002" is ideal. Did you measure the inside of the front trunnion in multiple places? They're often not perfectly round.
 
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Discussion Starter · #10 ·
nasifg, use a caliper to measure the outside diameter of the barrel journal and the inside diameter of the front trunnion down to the thousandth of an inch. Also, what is the origin of both parts?
I bought the barrel from Atlantic Arms I believe and the Trunnion I am not sure.
 

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If the barrel and trunnion were both original to the same kit, then I was going to tell you that you're good to go. In this case, that assumption can't be made.
 

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if you cannot feel comfortable with your measuring go to a machine shop and ask them to do it.
 

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I use dial/digital calipers for the majority of my machining if the accuracy required is within a couple thousands. For an interference fit the micrometer and hole gauges come out. You can get a import standard 1"/.0001" micrometer around $20 that will do. The .0001" will look just like a .001" micrometer with the addition of a vernier usually above the main number line which gets you the 4th place. A ratcheting style is nice if you're not used to useing them to keep you from over/under tightening them. The cheaper ones usually don't come with a standard to calibrate them, but for limited use you should be fine. A set of telescoping hole gauges are about the same, but there are also different style inside micrometers from $35 on up to as much money as you want to throw at it. I've seen guys using a dial/digital caliper to take an inside measurement and lock it, then use the micrometer to measure the ID jaws on it with the micrometer to get their reading. That works, but it is much easier to use a hole gauge and you're less likely to get a inaccurate reading.
 

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Just for reference, original AKM spec is the following:

Chamber OD: 23.12mm/23.05mm (.910-.907in.)
Trunnion ID: 23.00mm/22.97mm (.905-.904in.)

Your measurements: Trunnion is 22.93MM and the barrel is 23.03MM

Based on that, I'd recommend reaming the Trunnion a bit.
 

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To add to what Moleman said about telescoping gauges, if you want to get a "good" one, the Mitutoyo part number to look for is 155-123. That's the gauge for .75"-1.25" holes, so it's the proper range for the trunnion bore.

If you also want a gauge for the rear sight, gas block, and front sight, it's Mitutoyo part number 155-128. It's labeled as a "metric" gauge for 12.7mm-19mm bores.

Both gauges were around $23 each when I got them in 2018. Most places I looked wanted to sell them in sets for $100 or more, but once I figured out the part numbers, Google got me the vendors that sold them individually. Looking through my old emails, I got the smaller gauge from MSI-Viking and the bigger gauge from MeasurementSupply.com. Googling those part numbers will probably work too.

The cheap 0-1" mics from Harbor Fright, Northern Tool work ok, probably better than a caliper. I splurged and got a nice Mitutoyo mic but it was like $125. It's smoooooth as butter, though.
 
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