gap

[hennuc]

What should the gap be between cylinder and barrel?

I am getting lots of powder burn on the top of my cylinder. I am guessing that the gap is too large and allowing lots of gas to exit.

This is a new S&W 627PC. I sent it back once because the cylinder seemed too loose. Not loose anymore, but I can see a bit of day light around it.

Thank you for any insight.

[Bill Sahlberg]

Factory S&W specs are .0006

[gp100man]

Top of the cylinder? Is the powder burn on the top of that round thing that spins around or on the underside of the strap above the forcing cone? And loose is kind of vague. Do you have excessive end shake? You don't want too much, but like Bill said, you do need to have a gap between the face of the cylinder and the forcing cone.

Steve

[gusshuman]

factory S&W specs are .0006

Shouldn't that be .006"

[Waltermitty]

You should be able to "see some light" at the barrel to cylinder gap and just be able to detect very little endshake.

Powder will definitely build up all around the gap and in the forcing cone.

.006" to .008" is typical. You really want to be able to fit a .006" gage in the gap and you really don't want a .008" to fit. Take measurements with the cylinder pulled back as far as it will go.

You are dependent on the tolerance stack of all the components so you kinda get what you get. So if a .006" gage won't quite fit you may be ok, but at zero the gun won't run.

Edited February 4, 2012 by Waltermitty

[Toolguy]

If you only shoot jacketed and all other specs are perfect you can get by with .002 for a while until endshake develops. Under normal conditions, only shooting jacketed .004 to .005 is ideal.

For a combination of lead and jacketed or only lead, .005 is the minimum. As mentioned above, .006 to .008 is pretty common. You will be able to see light between the barrel and cylinder if there is any gap. The way to check this is with a clean gun and a set of feeler gages. Whatever feeler fits in the gap with a slight amount of drag is the size of the gap. Any endshake will reduce the gap because the centerpin spring pushes the cylinder forward.

Too small a gap with lead bullets means that lead will build up between the barrel and cylinder and get blown out, build up and blow out, etc. in a somewhat random pattern. This makes for some easy trigger pulls, then some hard, then easy. With a wide enough gap, the lead doesn't build up enough to close the gap. The forcing cone, cylinder alignment to the bore, bullet size and alloy, bullet lube, and powder all affect this to some degree too.

[hennuc]

I bought a feeler gauge and measured, its between .006 and .007. So i guess its within spec. Can a gunsmith close some of the gap?

I think i am getting too much power burn directly above the charging holes on the cylinder. Cleaning almost doesnt remove it, needs to be polished off.

[Bubber]

I bought a feeler gauge and measured, its between .006 and .007. So i guess its within spec. Can a gunsmith close some of the gap?

I think i am getting too much power burn directly above the charging holes on the cylinder. Cleaning almost doesnt remove it, needs to be polished off.

hennuc, one can close the cylinder gap at the forcing cone but it will add it at the other end. If it is specs shoot it and don't worry. I will let you know how to clean the area around the forcing cone as soon as I start cleaning mine. Dental pics works wonders but if it is relatively clean between the top of the forcing cone and top strap it should not affect much. Later rdd