Barrel Cylinder Gap is Too Large

[Hondo44]

It keeps gas cutting of the top strap to a minimum, a real problem with the 357 Max.

 

[FergusonTO35]

.007 is a bit wider than I prefer but I doubt its going to cause any problems. Barrel length affects a revolver's performance alot more than b-c gap, in my experience.

 

[The Bolt Man]

Thanks to all for their replys.

My question about correcting the barrel cylinder gap in my Ruger Security Six has been answered. It will cost more than it is worth at this point. Simplier to rebarrel.

A question of interest would be, "Has anyone seen a test or research, testing barrel cylinder gap affect on velocity?" It would be interesting to see the affect using .002" as a starting point and increasing the gap in increments of .001" and up to say .012".

I understand barrel length has a significant affect on velocity. Some fast powders less so than mid range and slower powders.

 

[jlinz]

Not sure if anyone was aware, but bbti has some interesting info on how cylinder gap affects velocity.


http://www.ballisticsbytheinch.com/gaptests.html

 

[gramps]

Not sure if anyone was aware, but bbti has some interesting info on how cylinder gap affects velocity.


http://www.ballisticsbytheinch.com/gaptests.html

It sounds interesting till you see the format. Too small to see on the phone. Graph is unlabeled!
gramps

 

[coach]

The spreadsheet is interesting. I wish they would have averaged the velocity for each load and CG. Pretty easy to do if done in excel.

 

[tjironhorse]

I have similar experience with my FA single actions, and in fact I just had a Ruger Blackhawk set up with minimum clearance and it measures a little under .002 - and it works fine so far.

My problem with the .003" clearance was on a double action Security Six .357 mag. I had problems when shooting rapid fire exercises and the cylinder got hot from firing. Just thermal expansion will cause the gap to close by .002" or so if I recall correctly.

This is the exact issue I'm having on my Security six. Cylinder binding after only 12 rounds. Heat, expansion, bind. I would leave that .007" b/c alone and shoot the heck out of it. MY B/C is also .003

 

[bcgunworks]

I have set guns up with .001 gaps
Everything has to be perfectly true when set up

.005 is the sweet spot for most wheelguns

 

[Rclark]

Wonder if the FA shooters loaded up with black powder for fun .

 

[Varminterror]

I doubt you could get a revolver hot enough to cause enough expansion to bind it up at the B-C gap.

If you get a gun hot, then the frame window expands too. Little fun fact. Reminds me of an experiment we did in one of my first engineering materials courses in college - if you heat a block of steel with a hole drilled in the middle, does the diameter of the hole grow or shrink? It grows.

Comparing a custom FA with a production line Ruger really isn't a fair comparison. Bcgunworks is doing INCREDIBLY tight B/C gaps on GP100's these days, but he has to true the cylinder face, frame, and barrel tennon to make that possible.

Ruger's spec is 0.003" to 0.010" for their single actions and current production double actions. Not sure about the old SS line, but would assume it would be the same.

"They say" in general that you lose 1.5% of muzzle velocity per thousandth of gap, so shrinking a 0.007" gap to a 0.003" gap would increase your MV by 6%. Not sure I believe it's that dramatic, but I AM sure that 75fps on a 357mag load or 50fps on a 45colt load really matters much, and I AM ALSO sure that I don't believe it's worth the price of the smithing job to fix it unless you have some other reason to set back the barrel.

In my eyes, the solution is pretty straight forward - set back the barrel, and readjust the tennon depth to tighten up the gap to where you want it. A lot of work to gain 60fps.