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Posted: 11/3/2009 3:47:19 AM EST
[Last Edit: 11/3/2009 3:52:58 AM EST by Grouchy-Hermit]

I have ordered a Magpul CTR MIL-SPEC stock which will be installed on an old, pre-ban Oly lower. I am unsure if the current extension is MIL-SPEC or commercial. I have nothing to measure with so I'll have to check the fit when the stock arrives. If necessary, I will obtain a MIL-SPEC tube. Will all of the other related parts fit into/onto a MIL-SPEC tube?

ETA: Will a MIL-SPEC tube even fit into the receiver?

Link Posted: 11/3/2009 4:31:08 AM EST
The two diameters are interchangeable in the receiver-their threads are close enough to identical that they both fit fine. The difference is the part of the tube that the stock goes over, and they're different enough there that a MIL stock won't fit on a commercial tube, while a commercial stock will rattle A LOT on a mil tube.

Lacking a caliper, you will have to just wait and see whether the mil stock you ordered fits. But odds are very strong that your Oly has a commercial tube on it. To replace it you'll need the mil tube, a castle nut, and a receiver back plate. The nut and plate come with some tubes, not with others, so ask before you order.
Link Posted: 11/3/2009 5:05:38 AM EST
I have a Noveske QD end plate coming too, so I'll make sure to get a castle with the tube.

Thank you very much for your assistance.
Link Posted: 11/3/2009 12:46:51 PM EST
Link Posted: 11/3/2009 12:57:02 PM EST
[Last Edit: 11/3/2009 12:57:32 PM EST by warpig8654]
Oly uses & to my knowledge has always used commerical tubes. Your existing castle nut should work with any tube. I say should but there are always exceptions & you'll find out soon enough if you buy a new tube like you suggested.
Link Posted: 11/3/2009 1:38:07 PM EST
I went ahead and ordered a new Daniel Defense Mil-spec 6 position tube. For about 20 bucks, I'll have the correct part at low ready.

Thanks for the feedback.
Link Posted: 11/3/2009 2:27:08 PM EST
You may need to file the inside of the receiver plate a little to get it to slide over the threads of the tube. I just did this today and I had to file it. Now is a good time to replace that plate with a sling mounting plate if you don't have one already.

Link Posted: 11/3/2009 3:04:21 PM EST
I have a Noveske QD end plate on the way and I'll be more than a little ticked if it requires a file.
Link Posted: 11/3/2009 4:18:01 PM EST
It's probably milspec so you should be fine.

fwiw, I just barely had to file the inside edge, it's not visible and nothing significant. My plate was NOT milspec.
Link Posted: 11/3/2009 4:58:50 PM EST
[Last Edit: 11/3/2009 4:59:01 PM EST by Wormydog1724]
its my understanding the Commercial tubes are angled on the end and milspecs are not. I could be wrong and their probably are exceptions. Also My end plate must not have been milspec because I had to force my milspec tube through it. I didn't fck up the threads or anything but it was kinda nerving doing it.
Link Posted: 11/3/2009 5:54:23 PM EST
Yeah, I've read that about the angled ends (I think that info came from Magpul). The story of my life suggests that even though the Oly tube end is 90 degrees, I'll still be required to replace it.
Link Posted: 11/3/2009 6:01:55 PM EST
Not all commercial tubes are angled. Not all milspec tubes are flat. Receiver end plates aren't fitted for one or the other.
My experience with milspec size tubes is many stocks hanging up on the threads, since they're larger diameter than the tube body is. Never run into that with a commercial tube.
Commercial tubes are generally half the price of milspec.
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