B/C gap on Ruger Six Series and old GP100s

I measured the B/C gap on my "new" lightly used 1989 GP100 3" tonight and was surprised it measured only .004. My two 2015-16 GPs both measure .007 or a whisker less. I suspected the previous owner may have added a shim because of cylinder end shake which would've pushed the cylinder forward a bit. I then measured my 1987 Police Service Six and it too measured .004. I measured my 1980 Speed Six and sure enough it also measured .004. None of these older revolvers have seen many rounds. It seems the older models were built to tighter tolerances. Anyone else notice this?

 

“Tighter tolerances” or not, a tighter B/C gap is not the end all, be all for defensive revolver positive attributes.

In fact, too tight a gap can lead to cylinder drag and other issues, and too tight of an endshake, especially on the GP100 series, can lead to issues if any fouling finds its way under the ejector star or even in the B/C gap itself.

Ideal endshake for a GP100 is approx. .002”-.004” with a B/C gap of anywhere from approx. .003” to .008”. These are production grade service-style revolvers, and just because one doesn’t lock up bank-vault tight, does NOT mean there is an issue, and sometimes just the contrary.

 

Never said it was "the be all and end all" just making an observation my four 1980's Rugers .have 004 b/c gaps & my two newer GPs both .007. By tighter I meant smaller not implying better or worse. Your numbers are what Ruger considers within acceptable tolerances not necessarily ideal. A b/c gap of .008 isn't ideal, just within tolerances. BTW, they all (old & new) shoot very well.

 

It’s a sample size of just a few. They are all mass produced production revolvers that are well within specs. Stop overthinking things.

 

I've not only noticed it, but have seen its effects on the performance of ammunition through the chronograph. My 6-inch Security Six sports a .005" b/c gap.

My S&W 686 was sent in to the PC to be rebarreled in Dec 2020 from 4-inch to 7-inch and they returned it to me with a .009" b/c gap (in all fairness, no doubt well within their tolerance range, but disappointing nonetheless).

What that does with velocity, along with any other contributing factors such as bore diameter, cylinder throat dimensions, etc, is to cause my 6-inch Security Six to have higher velocities despite having 1-inch less bbl length to work with. Here are a couple recorded examples:

Lee C358-200-RF
10 gr 2400 in Starline brass, CCI 500
Ruger Security Six, 6-inch = 1123 fps
S&W 686, 7-inch = 1083 fps

Remington 125 gr JHP
20.5 gr H110 in R-P case, CCI 550
Ruger Security Six, 6-inch = 1658 fps
S&W 686, 7-inch = 1622 fps

I was hoping putting a 7-inch tube on the 686 would make it the velocity champ of my safe, but 'twas not to be the case.

 

I have a GP 100 that gets great velocity somehow but gives me two muzzle flashes, the one at the gap is even brighter than the bore on film.