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Old December 23, 2011, 07:57 PM   #1
Formyguns
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Can a 5.45x39 upper receiver fit a 5.56 lower receiver?

Can a 5.45x39 upper receiver fit a 5.56 lower receiver? I've been looking at the 5.45x39 AR-15 rifles. I found a really nice upper but i cant seem to find a 5.45x39 lower. So i was wondering if it would fit a 5.56 since they are so close of a caliber.I would also like to know if i could use regular AR-15 mags for the 5.45x39 round.
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Old December 23, 2011, 08:03 PM   #2
357 Python
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Considering that a .50 Beowolf upper will fit the 5.56 lower, My guess would would be yes. This is a guess only so don't hold me to it.
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Old December 23, 2011, 08:24 PM   #3
Formyguns
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Never thought about that but that makes sense
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Old December 23, 2011, 11:10 PM   #4
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5.45x39 upper will fit a milspec lower.
The only real difference between a 5.45 vs 5.56 AR is the barrel and the bolt. Maybe, the hammer spring may need to be stronger for a 5.45 depending on ammo you use.
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My S&W 5.45x39 upper is on a Spike's tactical lower. Prior to the S&W 5.45x39 S&W, I used the lower with a BCM 5.56x45 upper.
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More than 7 rounds of 5.45 in a 20 round 5.56 magpul polymer magazine will produce a jam.
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30 round C-products SS 5.45x39 magazine is good --- came with the S&W upper.
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I like the felt recoil with the 5.45 than 5.56. It is milder and it shoots just as well as any 5.56 at 50 and 100 yards.
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Beware of corrosive ammo. My S&W bolt has pits after 2000 corrosive rounds. Must clean after range trip.
If you plan to shoot a lot of rounds per range session, 5.45 corrosive is good to save on cost. If you shoot a few rounds once or twice a week, stay away from corrosive --- too much cleaning.
Non-corrosive 5.45 steel case ammo is just as expensive as low end steel cased 5.56.
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Last edited by pilpens; December 23, 2011 at 11:20 PM.
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Old December 24, 2011, 07:19 AM   #5
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Old December 24, 2011, 12:07 PM   #6
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well just to reiterate what has already been said, yes. however a word of caution;
it may not be completely hot swappable with your existing 5.56 lower. some of them require heavier hammer springs, some require beefier hammers in addition to. if you have a 2 stage trigger it may cause light strikes. the reason for this is 5.45 primers are harder than 5.56 primers.
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Old December 24, 2011, 12:49 PM   #7
Formyguns
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I was looking at the spikes tactical lower. When i go to the range i like to shoot atleast 100 rounds. Thanks for all the advice, and this helps me a lot!
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Old December 24, 2011, 01:10 PM   #8
Formyguns
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Also is there any attachments, stocks, ris systems, etc that you guys prefer for a 5.45x39 ar rifle?
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Old December 24, 2011, 05:58 PM   #9
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a 5.45 has almost identical recoil to a 5.56 so there is no real need to swap furniture to compensate. if I did have a 5.45 upper to swap out I would probably go with a MOE handguard and red dot to lighten up the front for easier off hand shooting. it depends on if you want a wabbit swayor or a long range coyote thumper. more weight up front stabilizes the gun from a rest position but less weight up front puts less stress on the non firing arm while shooting free hand.
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Old December 24, 2011, 06:55 PM   #10
5.45 Shooter
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Quote:
I was looking at the spikes tactical lower. When i go to the range i like to shoot atleast 100 rounds. Thanks for all the advice, and this helps me a lot!
If you like to shoot 100rds at a time you could try one of these 100rd mags.
http://centerfiresystems.com/drum-ar-100.aspx
I know they are made for the .223/5.56 but they will also work for the 5.45.
Just be alert to what mags have which ammo in them if you are shooting ,223 ARs with the 5.45s. I have found some duct tape on the mag with the cal. on it helps a lot.
Full mag of 5.45.

Full mag of .223/5.56

Make sure you use the dry lube on the follower before you load your ammo.
My S&W 5.45 AR just eats them up.

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