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Discussion Starter #1 (Edited)
I was looking at the new flat from ORF, and compared it to a couple SW flats and noticed something fairly significant.
In the below photo, left to right, are SW MP5 flat, SW G3 flat, and the new ORF G3 flat. Notice how the channel pressed into the metal for the bolt carrier is rounded, comparing this to a real HK, they should be more of a squared cross section. My conclusion from this is that completing these (at least correctly) is not as simple as simply rolling them and welding them. There has got to be another stamping or pressing process in doing these, perhaps after they are rolled, pressing them into the rails into a mandrel or jig to square them. I don't think this is significant as far as function, because it looks like the bearing area to the bolt carrier is the same, but it would cause problems with the receiver cap going on, and definitely a problem if using a sliding stock.



HK cross section, notice circled area is a lot more square:

 

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Discussion Starter #4
I wasn't aware SW ever sold any of their receivers as flats.
They are supposedly imported flats, but they have one on Gunbroker now.


Another issue, reading the ATF letter very carefully, if somebody is going to fold these themselves, they better weld the shelf on BEFORE folding.
 

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They are imported, from MKE of Turkey.

I am curious if anyone can take a look at the back of their HK94 to see if the channels are rounded or flat.
 

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I woud imagine that a two peices could be made to square the bottom of the hole... kind of a slot and a trapaziodal die that fits inside the slot... with a 1/16" or so of slop... does look like it could work as is...

Seems like the shelf would have to be put on after folding... looks like it fits over the whole works...

But there is no push pin hole so maybe that makes it safe to fold it and put it over where the hole might go? I guess only the ATF knows?

LO
 

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Discussion Starter #8
With regard to the shelf thing, read page 2 below very carefully. I think one would be much better off welding on a two piece shelf (one on either side) before folding.

 

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Do those flats have the pushpin holes, as delivered from ORF?

The way that letter reads one would think they come from ORF WITH the holes.
 

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I wonder if we could get Jayson from IGF to chime in, he has forming dies for rolling the MP5 flats. I'm sure he knows more about this than most of us.
 

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With regard to the shelf thing, read page 2 below very carefully. I think one would be much better off welding on a two piece shelf (one on either side) before folding.

A few things about that letter - first, it doesn't take any "specialized" equipment, unless you call a vise, a piece of round stock, and a tig welder "specialized" equipment.

Secondly - the receiver doesn't have a hole in it, so even by their definition in the letter, it is not a machinegun receiver.

But lastly - unless your workshop is in the BATFE offices, and you're not selling folded and welded receivers with or without a hole, you will be fine as long as you weld the shelf onto it before you finish it.

When that letter was typed, perhaps the receivers had the front pushpin hole in the flat. Just guessing, but since he did first write them, it would be foolish to start selling them in the configuration they had just told you were machine gun flats.
 

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I am looking at the MP5 buttstock I have, and I notice that the tabs that slide into the receiver rails have the same curvature as the pictures of the MKE flats. Is this significant?
 

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...some of the foreign HK liscened guns have channels that are rounded - ie some of the MKE guns which are made in Turkey.
What makes you believe so? Do you have ANY evidence of this?

"Project 64" has photos clearly illustrating the flat channel rails of a MKE made Turkish MP5. In addition, it also illustrates the mag well dimple which the supposedly Turkish MP5 flats lack.

"Heckler & Koch" has photos of 7 licensed G3 manufacturer's G3's, including MKE of Turkey, and ALL of them have flat channel rails.

The ONLY rounded channel rails that are supposedly HK or HK licensed that I've seen are ORF's G3 flats and the supposedly Turkish MP5 flats. Great post ptoguy. Anyone have any other info?
 

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The reciever of my PTR is flat in the area in question as is the corresponding point in the buttstock. This gun was made on FMP dies, right? The cross section of my receiver is identical to the folded HK receiver in the OP, fwiw.
 

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I said some of the MKE guns, didn't I?? As to where I got that info from, dont worry about it. It is either true or it isnt. Believe it if you want and if you dont - I could not care less. There are probably a small handful of people here who read this site and know I am right and exactly where I got my info from, but I doubt they are going to chime in either. So I guess you are just stuck either believing it or not believing it. How bout that.
Ok then, I guess that answers that. Ridiculous.
 

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Perhaps the flattening of the receiver rails is part of the rolling process? Aside from the squaring of the channels, I can't see any difference, stamping wise, between those two stages of a G3 receiver.
 

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flats

stronger squared off? will rectractable stocks slide into rounded area without damage to receiver. is it legal to bend these ourselves? bob
 

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Good observation. All of my german guns have the flat channels. Perhaps a step has been skipped along the way. Certainly there are reciever flats that came from Turkey without the final channel stamping. Also, it is true, that they can be and have been folded and used just fine without the channel being flattened. So, I am not sure what benefit having the channel stamped flat ends up providing. Any ideas?
I don't really think it's been skipped, I think they were designed that way. The reason I think so is that the distance between the tangent points on the curved channels is the same as that between the curved channels. At least it is to the accuracy of my calipers, measuring one of these flats.

It shouldn't affect normal operation, but there's one thing I can think of that could be a potential disadvantage - the rollers will be pushing against a smaller area when the bolt carrier reverses direction after firing, so they might be more likely to develop the receiver rail dimples.

Other than that it shouldn't make any difference.
 
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