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#1 brucea4


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Posted 01 April 2019 - 01:26 PM

Are the feed covers interchangeable?  What I mean is can you put for instance an E3 top cover on a standard E1 gun?

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#2 Normal1959


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Posted 01 April 2019 - 03:51 PM

Yes you can. I try to keep them original but you can interchange them. The e-4 Mod1 has the scope rail. You can also close the newer ones with the bolt forward. I keep several spares for mine which I think is a good idea. You never know what the future holds. This is an E-4 and an E-4 mod1 top cover. I would use the E-4 top cover on the pig since it looks the same and has the upgrades. Put the mod1 cover on if you want to use a scope.


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Edited by Normal1959, 02 April 2019 - 06:28 AM.

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#3 MGTedFL


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Posted 01 April 2019 - 04:37 PM

Yes, I've had an E1, E3, E4 Mod1 and an E6 top cover on my RIA.  The more recent top covers with the enhanced internals have significantly more pulling power on the belt, as well as the integral Picatinny rail (MIL-STD-1913). As I understand, a more aggressive angle on the feed cam (for bolt actuator) and some profile changes and hard-chrome on the feed pawls.  Been using the E4 Mod 1 cover mostly, and it has been near-perfect feeding quality.


Here is what I think I know....please step in and add additional info. I'm doing this from memory, not comparing part #'s


E1: Original, can not close top unless bolt to rear.


E3: Cover a bit lighter (metal removed), feed lever and some internals modified to close on closed bolt. Cover has a small bumper. Can be distinguished externally from E1 by "hump" the encloses feed lever bumper.


E4: A bit confusing, as there was E4, E4 Mod 0 & E4 Mod1. I have seen lots of mix & match of features as the E4 evolved, then was transitioned to USO.

Early E4, by SACO, not sure if internals are E3 or upgraded feed lever. There was also a version that had a the old-style E3/E4 top cover that had a Picatinny rail screwed on from the top-cover interior (I have one of these - still available from BPP), I have seen several pictures of this, including a SACO brochure in the SAR Archives, but never seen a template or instructions exactly where to drill the top cover. Not going down that rabbit-hole.


E4  Mod 0: is the E3 style top cover with the improved internals, including a silver (Nickel-plated) feed cam and and USO chromed feed pawl.


E4 Mod 1: is the billet top cover with the integrated Picatinny rail. Pulls a belt up off the floor with no problem while standing.


E6: Very similar to the E4 Mod 1, slightly slimmer billet profile on upper. Same internals as E4 Mod 1. Current USO production. Only mates to E6 buttstock, as the radius where it interfaces with the buttstock is different than the E1,3,4.


As I understand E3, E4 and E6 internals interchangeable, not counting for dimensionally similar improvements. 


Again, I find the period of transition from the end-of-the-line SD E4 through the MK43 - USO E4 Mod 0 and E4 Mod 1 production very interesting. Early on, USO offered "upgrade kits" to E4 Mod 0 and E4 Mod 1. Top covers, hand-guards, barrels, butt-stocks, forward sling holders and bipods among other items were in development. Many pics out there of mix-n-match.


Picked-up a SA DO E4 Mod 1 years ago. Beautiful gun for a semi. Been test-shot & that is it.....the pig can only be done justice in FA. Has all the E4 upgrades including: billet E4 Mod 1 top cover, commando fluted barrel manufactured by USO - with E3 gas system, billet front hand-guard, E4 bipod, E4 buttstock, E4 trigger group modified for striker-fired closed bolt semi.


The pig is like the LEGO of guns. Between the options of the E1,3,4 & 6, it is sometimes tough decide how to dress her up to come out and play.  RIA E1 currently in "franken-gun" set-up with E4 Mod 1 billet top cover with ELCAN mounted, E1 hand-guard, E1 butt stock, E1 barrel cut to commando length or E-3 shorty with handle removed, E3,4,6 spring, drive rod and E3 op-rod. Always goes bang. The full E6 on the RIA is also fantastic; light, reliable with upgrades for ergonomics, just doesn't look like anything like a "classic" Vietnam era M60E1. Makes you want more than one.......

Edited by MGTedFL, 21 June 2019 - 04:46 PM.

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#4 mattnh



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Posted 05 June 2019 - 11:56 AM

Never mind... Delete

Edited by mattnh, 05 June 2019 - 06:21 PM.

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#5 michaelkih


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Posted 06 June 2019 - 01:09 PM


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