New S&W B/C gap Spec.

[shocker]

My 69 is 004 and my 66-8 is 007. Ballistics by the Inch has data on velocity vs. gap for 38/357. My conclusion is that for the barrel lengths most popular these days, 6" or less 001 and 010 wouldn't be noticeably different.
BBTI - Ballistics by the Inch :: Cylinder Gap

 

[Protocall_Design]

My 69 is 004 and my 66-8 is 007. Ballistics by the Inch has data on velocity vs. gap for 38/357. My conclusion is that for the barrel lengths most popular these days, 6" or less 001 and 010 wouldn't be noticeably different.
BBTI - Ballistics by the Inch :: Cylinder Gap

Bullet velocity may not be much different, but the blast out the sides of the cylinder gap is.

 

[Nick B]

Today I looked at a new M69 that the LGS just got in. The b/c gap was .003. That’s the tightest gap on a production S&W that I’ve ever come across.

 

[series guy]

I don’t think that 12 shots in a row is neglecting to clean a gun. I have had quite a few bind up when shooting lead projectiles double action. Between my personal guns and the guns of fellow club members my experience with these guns would be in the hundreds. Definitely not anywhere near the numbers of a revolver smith but maybe more than the average shooter.

 

[Protocall_Design]

If your lead bullets are too soft or have the wrong lube, or both, they will lock up a gun pretty quickly.

Also, sometimes the face of the cylinder is out of square to the rotational axis, so the gap is constantly growing wider, narrower, wider, narrower, etc. as the cylinder turns. Lead can build up during the wider phase and jam the cylinder during the narrow phase.

 

[series guy]

I don’t cast so all my lead is from name brand suppliers. Mastercast, Penn Bullets etc.

 

[muzzlestuffer2012]

You have to have perfect cylinder to bore alignment to avoid leading issues that's why freedom arms can keep a 2-3 though gap they line bore their revolvers I also had a lengthy conversion with Ron power he said .005-.006 Is optimal gap or the lead will accumulate around the forcing cone. My 617 has a .005 gap "snug" but consistent around the whole cylinder but am going to true the crown face to clean it and do my 11 degree chamfer I did the action and replaced the cylinder stop with a power custom and lock up is as tight as my freedom arms prior to that had about .005 cylinder slop but 0 endshake.

Sent from my SM-T813 using Tapatalk

 

[chief38]

I don’t think that 12 shots in a row is neglecting to clean a gun. I have had quite a few bind up when shooting lead projectiles double action. Between my personal guns and the guns of fellow club members my experience with these guns would be in the hundreds. Definitely not anywhere near the numbers of a revolver smith but maybe more than the average shooter.

You may have issues other than a B/C gap being out pf spec. Cylinder may not be rotating on correct axis, something bent, too much end shake, some other problems might exist as well - can't say without seeing the Revolver.

 

[BillBro]

Bullet velocity may not be much different, but the blast out the sides of the cylinder gap is.

As is accelerated erosion. I just bought the proper tools to correct this myself rather than shipping it back to the place that didnt do it right to start with. Now I can make certain its right and done to my liking, set where I prefer it. Sure, proper tools are a small investment of money but its enjoyable, educating and worth the investment.

 

[muzzlestuffer2012]

called s&w today and asked about gap and wether they can set the barrel back he said yes but they are not accepting work right now due to a back log he said max gap spec is .010 clearance i just bought a 629 classic and it's about .011 so i will send it back even if i have to pay will set to .006 gap and fit a oversized cylinder stop even though this one isn't too bad. the guy i bought it from doesn't take care of his guns very well and thankfully it cleaned up after a complete disassembly and scrubbing"proper" the trigger is pretty nice single action wise double not so much i will do a action job soon. there is no endshake

 

[muzzlestuffer2012]

As is accelerated erosion. I just bought the proper tools to correct this myself rather than shipping it back to the place that didnt do it right to start with. Now I can make certain its right and done to my liking, set where I prefer it. Sure, proper tools are a small investment of money but its enjoyable, educating and worth the investment.

what tools did you buy and what's the process ??
thanks !!

 

[.455_Hunter]

It's a sad state of affairs when a Webley MKVI, made in the dire days of 1916, has a tighter cylinder gap than a new S&W.

 

[chief38]

When I first started out and went to a bunch of shows, I'd always carry a .006 piece of feeler gauge stock in my wallet. That would normally be the first item I would check when seriously checking out a Revolver that I was considering purchasing. I was only asked one time not to check the B/C gap on a Revolver in a LGS - while visually it looked OK since I could not check it, I politely handed him back the gun and moved on. I will not buy a Revolver (new or used) that is starting out with problems (with RARE exceptions) before I shoot it.

 

[muzzlestuffer2012]

When I first started out and went to a bunch of shows, I'd always carry a .006 piece of feeler gauge stock in my wallet. That would normally be the first item I would check when seriously checking out a Revolver that I was considering purchasing. I was only asked one time not to check the B/C gap on a Revolver in a LGS - while visually it looked OK since I could not check it, I politely handed him back the gun and moved on. I will not buy a Revolver (new or used) that is starting out with problems (with RARE exceptions) before I shoot it.

Good idea !

Sent from my SM-G950U using Tapatalk

 

[Zipdog]

When I first started out and went to a bunch of shows, I'd always carry a .006 piece of feeler gauge stock in my wallet. That would normally be the first item I would check when seriously checking out a Revolver that I was considering purchasing. I was only asked one time not to check the B/C gap on a Revolver in a LGS - while visually it looked OK since I could not check it, I politely handed him back the gun and moved on. I will not buy a Revolver (new or used) that is starting out with problems (with RARE exceptions) before I shoot it.

So do you check the piston ring end gap before you buy a vehicle? Seems like you should.

 

[6string]

A tight Barrel/cylinder gap, in my opinion, is important as it is one of many check points indicative of high quality fitting.
If S&W is now OK with a .012" B/C gap what else are they letting slide? Of course, if they can't even get barrels fitted straight with the frame, maybe they need a .012" B/C gap! (So much for the "perfection" of CNC machining, at least when it's used as a substitute for quality control!)

There should be no binding issues resulting from a tight B/C gap even with soft lead or cast bullets. If so, then there may be other problems involving chamber to bore alignment, forcing cone taper, timing, crane alignment, etc.

Here's a simple quick check.
Look at your fired cartridges: are the firing pin indentations in the primers centered, or are they slightly off to the left or right?
Not the most precise way to measure cylinder alignment, but if you have a problem with off-center primer strikes you should have your revolver checked.

 

[chief38]

So do you check the piston ring end gap before you buy a vehicle? Seems like you should.

Checking a revolver's B/C gap takes seconds, no disassembly is required and most sellers or gun stores won't object. It is a harmless and quite easy check to make prior to purchasing. I would not have it any other way and you won't read about me here buying a revolver with an out of speck or over 0.006"B/C Gap that needs to get fixed. S&W has changed their spec's to 0.012" (double) which to me and many here is just wrong! IMHO they only did that because their repair dept. was inundated with people sending back out of spec revolvers with B/C Gaps well over 0.006".

As far as cars go, I do not buy used and checking what you mentioned above on new vehicle is not a viable procedure. IMHO, the QC control of todays vehicles has a pretty descent track record.

 

[steelslaver]

I just cast an eyeball at the gap holding the gun up to a good light. I am not concerned about a gap under .010 myself. Plus, fixing it isn't that haed for me.