Using feeler gauges on revolver

[forrest r]

Any time I get a new or new to me revolver I use a set of feeler gauges to check the cylinder gap, end shake & fit. It takes less than 5 minutes to do and puts my mind at ease knowing that the firearm is safe/within specs.

I typically measure the cylinder gap from both sides. Doing this tells me if the cylinder canted/ uneven to the bbl. I'll write the #'s down along with the end shake and every +/- 5,000 rounds I'll re-check that firearm to see if anything has changed.

If you find that the cylinder is canted DON'T USE THAT REVOLVER.
If you find the cylinder gap is over 7/1000th's DON'T USE THAT REVOLVER

They say that for every 1/1000th of cylinder gap you loose +/- 10fps of a load. It's also said that you'll loose 10fps by using 38spl's in a 357 cylinder. Some use this info, others don't but to me it's a good thing to know & keep in mind when testing loads.

Myself I don't use any revolver that has 6/1000th's or higher cylinder gaps. Same goes for 1/1000th end shake. My carry pieces are 6/1000th max and target revolvers are 4/1000th's.

Some people never measure things like this while dw owners measure (I own 2 dw's) cylinder gap (from both sides) every time I do a bbl swap or give them a good cleaning.

 

[Big Bore TX]

I measure all mine as well. And I've had far greater loss in speed per 1000th of an inch. My standard Smith 460 XVR with 8 3/8" barrel has a gap of .004. I had a BFR 460 7.5" barrel for a brief time and its gap was .002. Identical loads were over 200 fps faster out of the BFR.

 

[murf]

suggest you clean the two faces before you measure. people need to purge their "valve clearance" mentality on this subject. knowing and tracking this spec is easy and important, imo.

murf

 

[stonebuster]

I measure every used or new revolver with feeler gauges before I accept it and don't know why anyone would give you "flack" for doing so. It's just part of a checklist you should go through before buying a revolver. The general gunsmith specs for a DA/SA revolver I got from a respected gunsmith are: B/C gap .004-.008 (.006 optimal) and end shake .001-.005. I was also told for each .001 B/C gap(revolver) velocity loss is 1.5% vs unvented barrel(semi auto) so .006 gap =9-10% loss. I've got a DW also and set B/C gap at .005 on the tightest chamber.

 

[sequins]

My revolvers were made by Ruger so I don't like to check them.... it's easier to ignore a loose gap and a canted cylinder if you close your eyes and ignore it!

(My SP101 is canted badly and my GP100 has a very loose fitted cylinder lol, it makes a muzzle flash from the gap when fired. Ruger said both are in spec sadly... Function is good at least)

 

[JohnKSa]

If you find the cylinder gap is over 7/1000th's DON'T USE THAT REVOLVER

Some years back, I called S&W about a used revolver I purchased. At that time S&W was quoting 0.01" (10/1000ths) as the maximum acceptable cylinder gap.

 

[film495]

I have a couple used revolver checklists, gaps, timing, lock up, trigger, a whole list of function tests to go through. I recheck everything every year or so when cleaning. It does take an extra 20 or 30 minutes for me to go through all the tests and think about what I'm doing and make sure each of the functions is done correctly. I probably do each test and measurement 2-5 times before I feel like I'm sure I did it correctly and didn't miss anything.

 

[LaneP]

Some of the new guns I've seen including my own .45 Vaquero are on the generous side of gap tolerance when new. Mine is right at .007". Short of whipping out feeler gauges at the LGS and asking to go through their display case I'm not sure how you would guarantee getting the best sample of their inventory. But in the case of this Vaquero it times up perfectly, the end shake is not bad and accuracy is excellent. I think when they're getting assembled the workers are trying to get them in the box as quickly as possible. The bushing on my cylinder was shortened about .002" more than I would have if I were fitting it.

 

[TTv2]

Any new production DA revolver that's under $900 is going to have a generous gap because the goal is make things fit with the least amount of effort or work to increase profits. I'm pretty sure every revolver I have is over .005" gap and I care less about that than I do chamber alignment and timing.

If I want utmost accuracy and/or velocity, I'll buy a single shot Thompson Center.

 

[Pat Riot]

Thanks for posting this, forrest r.
It’s a nice reminder to check my existing revolvers.

 

[fxvr5]

Any new production DA revolver that's under $900 is going to have a generous gap because the goal is make things fit with the least amount of effort or work to increase profits.

How many new production DA revolvers under $900 have you measured? What are those gap measurements?

How many new production DA revolvers over $900 have you measured? What are those gap measurements?

How much of a gap is considered 'generous' to you?

 

[ontarget]

@forrest r I can see the performance side of of the B/C gap being too large but you said "Don't use that revolver".
What is the safety concern of a larger, say .010 B/C gap if the cylinder is properly aligned?

 

[Riomouse911]

@forrest r I can see the performance side of of the B/C gap being too large but you said "Don't use that revolver".
What is the safety concern of a larger, say .010 B/C gap if the cylinder is properly aligned?

Other than side-spitting a generous amount of burning and unburnt powder and (maybe) tiny bits of lead in all directions, possibly flame cutting the topstrap faster and losing a good bit of velocity from the wider gap... it'll still shoot.

But I'd send it in to get it tightened up if it was that extreme.

Stay safe.

 

[JohnKSa]

What is the safety concern of a larger, say .010 B/C gap if the cylinder is properly aligned?

There is no safety concern as long as there is no other problem with the revolver. There will be a loss in velocity; this website can provide some general insight into how much velocity loss is probable, but it's less than people usually assume. http://www.ballisticsbytheinch.com/gaptests.html

But I'd send it in to get it tightened up if it was that extreme.

You may be able to pay a manufacturer to reduce a cylinder gap that's 0.010", but if you're talking about S&W or Ruger, I doubt they will do it for free as they believe that is not extreme at all, but within the acceptable/normal range for cylinder gaps.

 

[TTv2]

How many new production DA revolvers under $900 have you measured? What are those gap measurements?

How many new production DA revolvers over $900 have you measured? What are those gap measurements?

How much of a gap is considered 'generous' to you?

IMO, anything over .006 is generous and that's almost every new production revolver under $900, at least for double actions.

I don't own a revolver that is over $900, but I just checked all my DA's and all of them a piece of paper that mics out to .005" would fit in the gap. The loosest feeling and thus largest gaps were on the two Ruger's I have that were made in the past 4 years, the tightest was surprisingly the Charter Arms Professional, which cost half what the Ruger's did.

I would use my feeler gage set, but they're in my toolbox at work. Will have to grab them when I go back in January and remeasure.

 

[forrest r]

Too large of a cylinder gap creates premature wear on the forcing cone. That "spitting lead" is actually the bullet hitting the forcing cone and pieces of it shaving off. With low pressure/low velocity cartridges it isn't that big of a deal. Start shooting hot 125gr bullets in a 357 and the forcing cones don't last long.

Myself, I could care less about the velocity loss a cylinder gap causes unless it's a snubnose carry piece. A couple snubnoses that me and the misses carry.


The bottom revolver is a ca undercover. It had a cylinder gap that a 7/1000th's feel gauge would fit & a 8/1000th's feeler gauge would not. I pulled the bbl & trued the face and radiused the edge of the forcing cone and changed out the cylinder. Now the gap is 3/1000th's & I picked up +/- 50fps with the misses sd load. The shiny new cylinder with a minor turn line.


The top revolver (wood grips) is a 2" bbl'd ca bulldog/44sp. It to had a 7/1000th's+ cylinder gap. I hate those high hook sights so I bought a used 2 1/2" bbl off ebay for $20 and set the shoulder back, radiused the forcing cone's edge, trued the face and did a bbl swap. The gap is now 4/1000th's and the low profile front sight is a huge plus.

 

[forrest r]

Interesting that s&w now excepts cylinder gaps up to 10/1000th's. I know in the 80's to 2006 it was 7/1000th's max. Colt was the same 7/1000th max. Both mfg's would tell you not use the firearms due to damaging the firearms (forcing cone) and risk of possible injury.

Colt Pythons were good for 30,000 to 40,000 rounds with a steady diet of target loads with some hot loads mixed in. Just send then back to colt and they would rebuild them along with re-blueing them. Typically the bbl.'s wouldn't need to be set back.
s&w 586's were good for +/- 100,000 rounds of anything from mild to wild put thru them then they'd need rebuilt. S&W would redo the timing, set the bbl back, redo the forcing cone and set the cylinder gap.

Both company's would send a spec sheet along with the work that was done. This was from the 1980 to 2006 the last time I sent a firearm back for a rebuild.

This bbl came off of a s&w 586 that I bought nib back in 1987



Bought that 586 nib and ran +/- 100,000 rounds thru it and sent it in for a rebuild. Sent it back a 2nd time at the +/- 200,000 round count to get rebuilt again. That 586 took a lot of abuse, heck used to buy the ww820 pulldown powder a case at a time at the midina gunshow off of pat's reloading. A case ='s 4 8# jugs or #32 of powder that either aa#9 or h110 equivalent. The bbl pictured above was off that 586 @ the +/-270,000 round count the lands finely gave up the ghost. That's what the forcing cone looked like at the +/- 70,000 round count with a 6/1000th cylinder gap.

I ended up re-barreling that 586 putting a 4" bbl on it along with changing out the cylinder.

Anyway forcing cones and cylinder gaps go hand in hand. Excessive cylinder gap in itself will not hurt anything. But it can and will cause premature wear on the forcing cone & from there bad things happen.

 

[JohnKSa]

Interesting that s&w now excepts cylinder gaps up to 10/1000th's. I know in the 80's to 2006 it was 7/1000th's max.

I went back through some records and I actually called them 3x because some of the things they told me in the first two calls didn't seem to make sense and didn't agree on some of the other issues I was asking about. This was after I purchased a used 629-1 in really nice condition. Cylinder gap was 0.007" which seemed ok to me--I was really calling about the endshake on the gun and about the possibility of getting the gun upgraded to a -2E. Endshake was 0.003" which didn't seem ok at all. Got a different person each time. One of them didn't know the max cylinder gap spec, the other two agreed it was 0.01". I've since found other sources that provided the same information. My guess is that they relaxed the spec at some point to cut down on warranty returns, but also because they found they could do so without taking on unacceptable liability. That's what it often comes down to these days, liability and the bottom line.

If you think that 0.01" is bad, I recently saw one Ruger LCR owner claim Ruger told him that 0.012" was acceptable on that gun.

Another part of it could be that the manufacturers realized only a few owners were shooting the guns enough with hot ammo to get into the issues with forcing cone wear and they decided they could handle the warranty/return work on a few guns with worn forcing cones more economically than dealing with getting the gap tight on all the guns they put out the door.

 

[stonebuster]

Some years back, I called S&W about a used revolver I purchased. At that time S&W was quoting 0.01" (10/1000ths) as the maximum acceptable cylinder gap.

Correct, the S&W manual says .004-.010. Pretty broad range reinforcing why you should check B/C gap with feeler gauges on a new gun as well as used. If the gap measured .010, I'd keep looking until I found one closer to .006.