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Posted: 8/28/2010 9:01:08 AM EDT
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I recently had an upper built using a D.D. unit. It uses the .315" pin diameter. My wife's Lightweight Sporter uses the smaller pin and there is more beef around the the hole there.
The fit between the upper and my Colt lower is excellent. Almost zero play between the two pieces. Is there any reason for concern about the thinner boss that uses the larger pin? Is that possibly why a smaller .285" pin is used? |
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The .315 was originally used on Colt civilian models, mainly SP1's. It had more to do it not allowing the mating of M-16 lowers than anything else. I've never seen or heard of the area being a problem. You can find an offset pin to mate the big hole upper to the small hole lower. And, I think the small pin is .250.
There was a little modification to the front pin bosses between the switch from A1 to A2 lowers. If you compare the two side by side you will see the A1 has a straight edge under the boss where the A2 has angled edge with more material. Not sure why, but it's different. There is no reason for concern mating the combinations or with the big hole upper. That has not been a failure point if that is your question. |
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