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Old 06-12-2014, 12:07 PM
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What is the minimum and maximum tolerance for barrel cylinder gap?
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Old 06-12-2014, 12:30 PM
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Back in '85 when I went to armorers school it was .004 to .006. But I understand that now .004 to .010 is considered to be acceptable. That's my understanding but I think a phone call to S&W would bring the actual info straight from the horses mouth.

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Old 06-12-2014, 01:30 PM
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Yes I did and I edited it, thanks
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Old 06-12-2014, 02:06 PM
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Yep, in my revolver class a few years ago they told us that .004"-.010" is now considered acceptable.
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Old 06-12-2014, 07:33 PM
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They're people sending guns in to S&W with gaps of 0.012" and having them come back as "in spec".
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Old 06-12-2014, 10:29 PM
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That doesn't surprise me. Might depend if it's a snug/tight fit of the .012" gauge versus an easy fit, too. Not everyone "measures" BC gap the same way, either. (FWIW, S&W revolver armorers are told to put the gauge in from the left side of the frame, at the top of the frame window, for a consistent check.)

Kind of like how the new style (non-recessed cylinder) S&W revolvers have their rear headspace gap checked with Go/No-Go gauges of .060" & .068". While the .068" is the No-Go end of the gauge, we were told that if it goes in behind the cylinder that it's "generous", but still okay.

My second M&P 340 (no-lock version) came with such a "generous end" of the headspace gap, and the primer hits are all normal. If that ever changes after a few thousand rounds, I'll send it back and they can handle it under warranty (easier to let them deal with the aluminum yoke). I've got less than a thousand rounds though it, as I shoot my first M&P 340 (lock model) much more.

I had a good friend bring by his new Ruger LCR a while ago. He said he'd bought it for his wife, who had quickly decided after 5 rounds that she didn't want it. He'd only had time to fire 15 rounds through it by the time he stopped by to show it to me.

Just being curious, not having handled LCR yet, I gave it a quick once-over, which including checking the BC gap. Now, I'm not a Ruger revolver armorer, and have no idea what they think the normal spec is for their new revolvers, but his LCR had "easy" gauge fits running .008 - .009". I imagine that as he starts to get time to shoot that snub (he shoots a LOT on his own range on his property) the normal flame cutting & wear process will open up those numbers.
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Old 06-13-2014, 05:58 AM
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I like a BC gap to be between .003 and .006. Less than .003 is too tight for my liking (possible lead jamming) and over .006 will result in excess velocity loss and possible flame & lead spitting.

Smith and Wesson will CURRENTLY accept up to a .012 B/C gap which in my book is a way too much - but they get to say "that's normal" instead of fixing the larger ones.
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Old 06-21-2014, 09:56 AM
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Saw a test some years ago using a Dan Wesson revolver. He used various B/C gaps to check for velocity loss. I was surprised at how little difference it made with the 357 Magnum. Might be different with other cartridges.
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