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Discussion Starter #1 (Edited)
I noticed when cleaning my 9mm conversion that the area in the yellow rectangles on the rear of the the bolt and on the extractor angle .......



...are striking the corresponding areas in the yellow rectangles here....



The softer aluminium has yeilded to the steel and I have since relieved the areas on the receiver block so there is no contact. Has anyone else noticed this on or in any caliber?? (9mm-.45-.40)
 

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Only the extractor angle on mine. Mine is a 45 sbr running a USC bolt if it matters.
 

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Hmm. Here's some pics of mine after 35 rounds.



 

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Discussion Starter #5
So the next question is: Is the 9mm bolt somehow different dimensions in the rear and is this going to be a problem because it is impacting here instead of just on the buffer. If left unchecked something will fail.
 

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I doubt it will cause any issues.
 

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So with the aluminum out of it's way are you noticing any further wear marks on the stock block?
Because if all it's doing is taking a small piece of the aluminum off and then impacting as usual on the
buffer, there shouldn't be any further problems.

Which bolt are you guys who are noticing this using?
 

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I don't remember my .45 USC bolt carrier looking like that..? I'll take pics when I get home. My main area of concern with my conversion has been the recoil rod nestling against the stock block B metal to metal. It's causing some damage to the stock block's softer aluminum similar to the problem you're having with those metal tabs. Anybody got a solution? I'll take pics when I get home.
 

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So with the aluminum out of it's way are you noticing any further wear marks on the stock block?
Because if all it's doing is taking a small piece of the aluminum off and then impacting as usual on the
buffer, there shouldn't be any further problems.

Which bolt are you guys who are noticing this using?
The photo suggests he's using the Hkparts michaels machines version. I have a factory bolt group in 9mm and 45 but I won't be able to check if I get wear until my conversion comes back from Chop. I imagine it'll stop wearing the stock block down if material is removed by dremel or shooting. The bigger worry would be what kabob suggests but isn't the original lower backplate in factory UMPs made of polymer with the buffer attached? Does that part wear out where the recoil spring sits?
 

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Discussion Starter #10 (Edited)
The photo suggests he's using the Hkparts michaels machines version. I have a factory bolt group in 9mm and 45 but I won't be able to check if I get wear until my conversion comes back from Chop. I imagine it'll stop wearing the stock block down if material is removed by dremel or shooting. The bigger worry would be what kabob suggests but isn't the original lower backplate in factory UMPs made of polymer with the buffer attached? Does that part wear out where the recoil spring sits?
It is a MM bolt and I have not shot it since I relieved the areas. I have re-blackened the relieved areas and will re-examine when I shoot it again. It appears compression of the buffer when impacted during recoil is enough that it allows contact in these spots. I also have 2 .45's and have not had a chance to examine those. They are USC bolts and hope it is not doing like. The 9mm has had around 800 rounds through it. I have not seen any wallowing or wearing to the female divot that accepts the recoil rod cone in any of the 3 guns.
 

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I have the same problem with my 9mm USC Conversion (MM Bolt).

After 200rds of Selliot&Bellot 124gr:





With the original "HK" USC45 Bolt, I hadn't this problem !!!
 

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Fordemti: 35 rounds?? How could you have only put 35 rounds through it? You are fired!

Oreaopla: I haven't heard a single complaint about a single HDPS block wearing at all in that spot. It might be that you got a block that was just a hair off right there? Keep an eye on it, if it gets bad talk to Ed? He might be able to cut it back a little bit there and put a buffer that will absorb the shock a little better than the aluminum?

Anyone: Having any problems with this and their factory USC .45 bolts or the SEF 9mm conversion bolt?
 

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Discussion Starter #13 (Edited)
I haven't heard a single complaint about a single HDPS block wearing at all in that spot.
There are 3 in this thread.
It might be that you got a block that was just a hair off right there?
There are 3 in this thread
It has to do with the bolt tolerances or the recoil cycle that is different than the .45 bolt.
Adel's block is exactly what mine looked like, could have been mine it is so close.
.
 

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Well, lohe, I decided to sell my AK to fund the full conversion as I'll be quite honest, the purist in me is screaming. So I'm trying to keep this block in great shape as I plan to sell it shortly. So hah!! I'll be picking up the receiver stub shortly.
 

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My usc also shows one mark on the stock block.
It the above pics, I have the lower of the two marks closest to the buffer.
I do not have a 9mm conversion and have maybe 200 rounds through the conversion.
 

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So yeah, I went ahead and inspected my USC and the .45 bolt carrier doesn't have those metal tabs hence no wear spots in those two places on the stock block. But the finish/coating on the stock block is wearing away in the cradle that the recoil rod sits. Even found some metal shavings around the face of the stock block. Argh. I've managed to lessen some of the friction by applying CLP in the cradle, though.
 

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My usc also shows one mark on the stock block.
It the above pics, I have the lower of the two marks closest to the buffer.
I do not have a 9mm conversion and have maybe 200 rounds through the conversion.
This right here is enough to put a halt to my $2000 conversion/SBR plans. Thanks for the tip.
 

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There are lots of people with these conversions. Kinda crazy people are just now noticing this stuff.
 
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