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Discussion Starter · #1 ·
I took my barrel off for the first time, Yesterday, and discovered that my barrel bolt requires a 5/16" wrench, which, based on the info in this thread, means it is one of the "correctively machined" uppers. Terra indicated, in her post, that a mistake was made on these uppers, and the barrel bolt holes had to be machined for a larger bolt. This fact, on it's own, does not disturb me so much, but werra indicated that his new upper, which was correctively machined, would not work properly with his 6.8 conversion, even though his old upper worked fine, and his resolution appears to have been the acquisition of a replacement upper. I also noticed that my upper appears to have a thread insert in the barrel bolt hole. I guess all of these things, collectively, make be a bit concerned, so I have a few questions. I apologize, in advance, for my rapid-fire questioning, but I decided to try to address all of my concerns with one post, instead of several. I think many of these can probably only be answered by Terra, but anyone who can shed some light, please do so.

Were the barrel bolt holes the only thing that was abnormal, non-standard and/or correctively machined on that batch of uppers?

Why wouldn't werra's correctively machined upper work with his caliber conversion? Do I need to be concerned about the compatibility of my receiver with any caliber conversions that I might buy in the future? When you addressed werra's problem, you suggested he try his old bolt carrier. Was this just to determine if the new bolt carrier was malformed, or is it routine for a bolt carrier/bolt/barrel combination to have to be matched up to work reliably? Should I ask for a matched bolt carrier along with any future caliber conversions I order?

Does my upper have a thread insert in the barrel bolt hole? If no, then please disregard the remainder of my questions. If yes:

Are thread inserts used in the barrel bolt holes of all XCR uppers? If not, what am I lacking, in the way of relative strength or durability, by having a thread insert? I am worried about this because, if, and when, I acquire a caliber conversion, that bolt could be removed and installed on a routine basis, and needs to be tightened to a relatively high torque every time. If my threads are in any way sub-standard, I could be hastening the demise of my upper!

The insert appears, upon casual inspection, to be a bit more shiny than the upper. Is the insert steel or aluminum? If steel, was it plated or coated to prevent a galvanic reaction with the aluminum upper?
 

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Sinjin

I believe all upper have a Helicoil insert due to the upper being made of aluminum.

The Helicoil is standard practice when you need to have a bolt into an aluminum housing regardless of the need for the correction machining.

The Helicoil is made out of stainless steel that is why the color difference.

The Helicoil is stronger than needed for the application, the ususal reason for using the Helicoil is to prevent the stripping of the threads due to overtighting the bolt.

By using the Helicoil it prevents people from stripping the threads out of the upper and then having to have the Helicoil insert put in once this occurs.

In my mind this is just shows the though that went into the rifle and the rather than cutting cost they would rather insure that the rifle is the best they could produce upon leaving the factory.
 

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the only thing wrong with those uppers was the barrel bolt hole was off center. That is the only thing we changed on them.

all the uppers have helicoils, both in the barrel bolt holes and the brass deflector holes. It's to provide longevity.

I don't know why his conversion didn't work with the upper. Honestly, I didn't have time to look. I just sent him a new upper in my rush. The old one is in a box under my table.

there is nothing wrong with the uppers. Just an issue with the programming on the barrel bolt holes.
 

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Just as a side note.....I'm an engineer on the Apache program.....you NEVER want to thread a steel screw into aluminum without a Helicoil. The aluminum will break out once you torque to spec. There is nothing wrong with having a Helicoil in there....in fact, that's how it should be.

HTH,
Sean
 

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Discussion Starter · #6 ·
Thanks for the insight regarding the threads. As far as the caliber conversion questions, I guess I'll just have to buy one and try it out.
 

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Thanks for the insight regarding the threads. As far as the caliber conversion questions, I guess I'll just have to buy one and try it out.
I'm with ya there.....I'm waiting for RA to make the 6.8 SPC with a 1:11 or 1:12 twist bbl. If they don't announce it soon, that money may be going to a Glock 21SF instead.

Sean
 

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Discussion Starter · #8 ·
.....I'm waiting for RA to make the 6.8 SPC with a 1:11 or 1:12 twist bbl....
I ordered a 6.5G conversion, last year, but I'm beginning to doubt it's going to happen. Here's hoping any impending gun regulations won't prevent me from buying a caliber conversion for the gun I already own.
 

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Ditto. I'm hoping conversions for existing guns will be okay for awhile at least. Problem is: evil features like FHs and threaded bbls may be banned.


Sean
 

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the only thing wrong with those uppers was the barrel bolt hole was off center. That is the only thing we changed on them.

all the uppers have helicoils, both in the barrel bolt holes and the brass deflector holes. It's to provide longevity.

I don't know why his conversion didn't work with the upper. Honestly, I didn't have time to look. I just sent him a new upper in my rush. The old one is in a box under my table.

there is nothing wrong with the uppers. Just an issue with the programming on the barrel bolt holes.


Terra-

You wouldn't be willing to part with one of these blems at a discount, would ya? ;D
 

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But I'd have to keep a different sized wrench around then. Oh I'm just messin' with ya!
 

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[/quote] I ordered a 6.5G conversion, last year, but I'm beginning to doubt it's going to happen. Here's hoping any impending gun regulations won't prevent me from buying a caliber conversion for the gun I already own. [/quote]

Go with the 6.8. I think the 6.5 is proving to be a fussy cartridges and that's not worth it in a AR.

The XCR is not intended to be a super precision rifle, the 6.5 is intended to be just that. You need all three related items to work to get super precision, that being the barrel/chamber, the round itself and the trigger. You can get a new trigger, but the barrel/chamber is not going to be that tack driver you want (or would be buying the 6.5 for).

It can be done, but the cost is high vs the return and they have to make decisions on where to put their efforts to keep the company in business. If they have to drop the 6.5, that's ok, you have a very good option in the 6.8, and can get the 7.62 as well.

I would wait for the 6.8 in the 1-11 twist, but if concerned, get the current 1-10 (I think the administration is not going to mess with this AR field ever, and if you think they are, its way down the road, there's a huge economic mess and a nasty situation in Afghanistan/Pakistan to deal with, Iraq to get out of, and the Israeli/Palestinian mess.
 

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Just as a side note.....I'm an engineer on the Apache program.....you NEVER want to thread a steel screw into aluminum without a Helicoil. The aluminum will break out once you torque to spec. There is nothing wrong with having a Helicoil in there....in fact, that's how it should be.

HTH,
Sean
+1

I have a side saddle for my 870 that is useless because the threads broke and fell out of the aluminum side plate when I was putting the mounting screw in.
 

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Without seeing what broke you should be able to purchase a helicoil set and repair the aluminum part. I had to do that once on an intercooler on a car. Drill and tap the old hole, screw the helicoil in and you are set (with a slightly larger screw).
 

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Discussion Starter · #16 ·
Without seeing what broke you should be able to purchase a helicoil set and repair the aluminum part. I had to do that once on an intercooler on a car. Drill and tap the old hole, screw the helicoil in and you are set (with a slightly larger screw).
As it turns out, there is no real problem. My OP was motivated by my desire to insure that I did not have a flawed rifle. I have tremendous respect for RA and its staff, but, as the saying goes, "trust but verify".

My previous understanding of thread inserts was that they were generally used for repairs, as you indicate. I now understand that this is standard practice when using steel bolts in aluminum. I had a conversation with a machine designer at work who corroborated this. He indicated that they do use cad plated inserts, presumably to inhibit galvanic corrosion.
 
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