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Thread: Who knows about moderator threads?

  1. #1

    Who knows about moderator threads?

    I recently bough a Sako 75 in .308 that has been screw threaded. I was told simply that it was threaded 1/2" UNF. I have a thread protector from my CZ rimfires in the same thread that fits the Sako thread easily.

    So today I go out and buy a moderator with said thread - it doesn't fit! Starts to bite for a full turn then sort of jams. I've not forced it. I took the moderator off and it easily screws on my other rifles cut 1/2" UNF.

    So as I see it one of two things are going on:
    1. the rifle is cut to a different thread
    2. the rifle thread is somehow damaged

    Anyone got any suggestions of what the thread may be? My searching would suggest these were not factory cut so it could be anything! (I have also contacted the chap I bought it from)

    Thanks in advance!

  2. #2
    There are two threads commonly used for moderators, UNF (fine) and UNEF (extra fine) the UNF has 20 threads per inch know as 20 TIP, while the UNEF has 28 threads per inch. It is possible that one has a UNF thread while the other has UNEF thread, hence why one will not screw on.

    The other possibility is that both threads have not been cut to ISO standards, so one thread might be slightly oversize or undersize.
    If you put the barrels side by side you should be able to see the difference between the UNF and UNEF threads, use a magnifying glass is you eye sight is not up to much. If they both look identical then one might have not been cut to ISO standard, in this case you need to take them to an engineer or a rifle smith that knows his stuff and has a set of thread gauges and a digital calipers/Micrometer to find up who has cocked it up.
    Shame you are not nearer or I would look at it for you.

    ATB

    Tahr

  3. #3
    I had a the same problem just took the rifle down the local engineers shop and he ran the tap + dies over the rifle threads and mod threads took 2 mins prob solved !

  4. #4
    hi mate i switch my s5 mod between 25-06 and 30-06 with no probs,18/1 thread,30 cal hole,25-06 shoots 3/4 inch groups at 200yds with butt supported through 30 cal hole,atb swarovski

  5. #5
    Quote Originally Posted by 375 mag View Post
    I had a the same problem just took the rifle down the local engineers shop and he ran the tap + dies over the rifle threads and mod threads took 2 mins prob solved !
    I've been in contact with the bloke who I bout the gun off. He tells me that the thread was touched up with cold bluing to smarten it up for sale. I suspect that may be causing the problem. I'm going to order a 1/2" UNF die from ebay, since my tap and die set doesn't go that high. I strongly suspect running that over the thread will cure the problem.

    Thanks for the help!

  6. #6
    Have to agree, it does sound like a damaged or oversized thread. It's a little worrying that he "touched it up" prior to sale, what else has he botched?

  7. #7
    One of the disadvantages of custom.......nothing is interchangable.
    I was never a friend of mating two threads as it often means one or both are not to standard.

    edi

  8. #8
    If its been factory threaded by Sako I suspect it will be M14x1 if its a sporter'ish weight barrel? To be honest, I'm supprised that moderator threads haven't become standardised by now. I'm certainly supprised that 1/2'' remains popular especially for .30 cal's. Glyn.

  9. #9
    Quote Originally Posted by Holkham Estate View Post
    If its been factory threaded by Sako I suspect it will be M14x1 if its a sporter'ish weight barrel? To be honest, I'm supprised that moderator threads haven't become standardised by now. I'm certainly supprised that 1/2'' remains popular especially for .30 cal's. Glyn.
    Unless my sums are wrong, 1/2" gives a diameter of 12.7mm so the mod wouldn't even start to bite on the threads if it was 14mm.

    It's a heavy varmint barrel.

  10. #10
    I think one of my 85's with a heavy fluted barrel is M17? No idea what this compares to in Imperial measurements. The fact that the moderator fits on other rifles that you know are 1/2'' UNF and the thread protector from your .22 fits is confusing. Glyn.

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