04-23-2020, 07:07 PM
I took the new barrel and used some stainless steel to make a shim around the extension. (I'd measured the upper and the barrel extension on 4 axes with a caliper: they differed by 1/2 to a full one thousandth.)
I ordered three sizes of shim material (lead time): .004, .002, and .001. Here's a pic of one of them: [ATTACH=CONFIG]16002[/ATTACH]
Since the upper and barrel extension were so close, I ended up using the .001 material for my shim. I cut a section, ensuring the M4 cutouts weren't obstructed, and made a "V" around the barrel alignment pin: [ATTACH=CONFIG]16003[/ATTACH]
With the .001 shim, the extension would not fit in the upper. Perrrrrfect.
Next, I put the barrel (with shim rubber banded around it) in a plastic bag and tossed in my freezer, set to -6F. Yes, minus 6. Then, a day or two later, I took the upper and tossed it in the oven. [ATTACH=CONFIG]16004[/ATTACH]
I pulled it out a bit later. (30-45 minutes? 300 plus degrees?). Then, I tossed the upper on a wood cutting board, grabbed the barrel out of the freezer, and here you go: [ATTACH=CONFIG]16005[/ATTACH]
It slid in like butter. No slop, just slid right in. A few moments later, it was NOT going to come out.
I ordered three sizes of shim material (lead time): .004, .002, and .001. Here's a pic of one of them: [ATTACH=CONFIG]16002[/ATTACH]
Since the upper and barrel extension were so close, I ended up using the .001 material for my shim. I cut a section, ensuring the M4 cutouts weren't obstructed, and made a "V" around the barrel alignment pin: [ATTACH=CONFIG]16003[/ATTACH]
With the .001 shim, the extension would not fit in the upper. Perrrrrfect.
Next, I put the barrel (with shim rubber banded around it) in a plastic bag and tossed in my freezer, set to -6F. Yes, minus 6. Then, a day or two later, I took the upper and tossed it in the oven. [ATTACH=CONFIG]16004[/ATTACH]
I pulled it out a bit later. (30-45 minutes? 300 plus degrees?). Then, I tossed the upper on a wood cutting board, grabbed the barrel out of the freezer, and here you go: [ATTACH=CONFIG]16005[/ATTACH]
It slid in like butter. No slop, just slid right in. A few moments later, it was NOT going to come out.