Measuring cylinder/barrel gap?


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ClemBert
April 17, 2011, 01:16 PM
What's the consensus here for the procedure to measure cylinder-to-barrel gap on BP revolvers? Do you measure with the hammer down then push back on the cylinder with all your might while using the feeler gauge? Or, do you measure with the hammer cocked?

Also, what is the ideal cylinder-to-barrel gap for efficient shooting with minimal binding due to fouling?

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junkman_01
April 17, 2011, 01:28 PM
Cock the hammer and hold the cylinder back against the recoil shield. I've always considered .005-.010 inches as perfect in a C&B revolver.

ClemBert
April 17, 2011, 02:52 PM
I measured a few of mine...too lazy to measure the boxed ones. This is what I got using that method:

(I got crap...so I deleted it and am going to start over....)

Is it typical that the revolvers with tops straps are a bit tighter?

junkman_01
April 17, 2011, 04:35 PM
Are you sure you are getting the decimal point in the right place? All your listed gaps are very tight, except the last one.

ClemBert
April 17, 2011, 04:51 PM
Deleted due to breathing too many sulpher fumes. :)

SleazyRider
April 17, 2011, 04:52 PM
Your post sent me out to the garage for a feeler gauge, and my relatively new 1858 Pieta Remington measures .011" with the hammer fully cocked and cylinder pushed to the rear. My cylinder gets tight after about a dozen rounds of FFF black powder, but I wipe it down with a wet rag and I'm good to go again. What puzzles me is how dirty the cylinder pin (axle?) gets---how does all that powder residue get in there?

ClemBert
April 17, 2011, 05:03 PM
Wait a minute! LMAO....my feeler gauges have been out in the garage in the heat and humidy and they are stuck all together. Lemme unstick them and get back to you....LOL!!!!

p.s. I'm gonna erase the previous numbers in a lame attempt to cover up my stupidity.....:o

ClemBert
April 17, 2011, 05:29 PM
Okay, here are the "real" numbers. :banghead:

0.0040 Ruger Old Army
0.0065 Pietta 1851
0.0035 Uberti 1858
0.0050 Pietta 1858
0.0080 Uberti Walker w/ cap-n-ball cylinder
0.0120 Uberti Walker w/ Kirst cylinder

junkman_01
April 17, 2011, 06:01 PM
That's more like it. The Ruger is a bushed cylinder, so it is in a different category than the others. All the others seem good, but the Uberti 1858 is a bit on the tight side. ;)

SAA
April 17, 2011, 11:59 PM
Side pressure from the bolt can affect measurements, so I prefer to measure at half cock.

TheRodDoc
April 18, 2011, 05:50 AM
I would say the .008 and .012 for the walkers is to big of gaps. You are losing a lot of pressure through those gaps.
I set mine at .003" for my walker and it works fine.
I probably would choose .004" for your Kirst version due to the fact it might get hotter then the other.
It seems everyone here thinks the gap can foul shut and cause binding. That Can't happen no matter what the gap is. The chamber pressure will always blow through the gap keeping it open. The fouling will always be thinner then the gap.

What causes the binding is the hand spring.
All the repo guns seem to have way to stiff of hand springs which push the cylinder ahead against the fouling that does stick to the cyl. face. That fouling makes a very good brake lining and that spring is putting the brakes on. Enough that you have trouble cocking the gun. You need to thin the original spring or make a new one. It should only be strong enough to move the weight of the hand itself to the cyl. and not push the cylinder ahead.

Even the ruger spring some are putting in is to stiff.

You can prove this to yourself by shooting your gun till you think the cyl. face bound it up. then put the hammer at half cock. hold the cyl. back with one hand then hold the gun up toward the sunlight and site through the gap. You will see that no matter where you turn the cyl. the gap will still be there.

A chart I made to show the area of some different gaps and a equal circle or hole with the same area to give you an idea of the pressure that you might be loosing at 6 to 12 thousandths gaps.
http://www.theroddoctor1.com/1851colt/cylgaps.jpg

SleazyRider
April 18, 2011, 08:09 AM
How does one adjust the gap on, say, an 1858 Remington?

madcratebuilder
April 18, 2011, 08:56 AM
The old Colt specs called for .006-.008 for the cap and ball revolvers. You can run a closer gap but risk binding if you have any powder residue build up. Colt had this problem with the Walker and changed the forcing cone shape with the Dragoon model for less surface area contact.

I've shoot these with as much as .018 gap and see little or no difference with the same model at .008.

To close the gap you have to set the barrel back, fairly easy on a open top, requires machining on a top strap model.

SleazyRider
April 18, 2011, 09:25 AM
Thank you, Madcratebuilder.

ClemBert
April 18, 2011, 11:49 AM
To close the gap you have to set the barrel back, fairly easy on a open top, requires machining on a top strap model.

On an open top what is the process to set the barrel back? Likewise, what is the process to increase the gap?

I suppose one way is the screw the barrel in or out? But, for the open tops I suppose you'd remove the barrel pins then take a little off the mating portion of the frame?

arcticap
April 18, 2011, 01:45 PM
There's another way to close the gap without permanently
altering the frame as recently described by Smokin'Joe in
Post #99 on page 4 of the following thread:

http://www.thehighroad.org/showthread.php?t=575472&page=4&highlight=cutting

Will this method work with the conversion unit? :rolleyes:


I have made several shims for my Colt clone cylinder.
I made them in .003, .004 & .005” thicknesses. The
cylinder to barrel gap can be adjusted as tight as I
want. As fouling builds I can move to a thinner shim
or no shim at all and keep on shooting. If the idea of
a shim on your cylinder is distasteful it at least can
be used to determine the gap you want before
machining the components.


http://i1215.photobucket.com/albums/cc510/SmmokingJoe/IMG_0060.jpg?t=1299257813

ClemBert
April 18, 2011, 02:59 PM
A round cylinder shim is an interesting idea and not a bad one at that.

ClemBert
April 18, 2011, 03:44 PM
But, for the open tops I suppose you'd remove the barrel pins then take a little off the mating portion of the frame?

If this is the process then I'd have more questions:

1. How hard is it to remove the barrel pins and do they get ruined when you remove them?
2. Wouldn't you need a wider wedge as the distance between the barrel slot and the arbor slot contact points would increase?

Y'all have really peaked my interest now as to your gunsmithing skills and how you increase or decrease the barrel/cylinder gap.

junkman_01
April 18, 2011, 04:54 PM
I did this once to my ASM 1860. I took some metal off the barrel lug to close the barrel/ cylinder gap a little and then added a set screw in the end of the arbor to adjust the wedge slot. You can not use a wider wedge because a wider wedge will not fit into the barrel window.;)

ClemBert
April 18, 2011, 05:08 PM
All tips on all the wedges on mine are narrower than the barrel slots. Assuming a wider wedge still has a tip narrower than the barrel and arbor slot then it should pop right in.

I unboxed a new unfired Pietta 1860 I have and measured the gap to be 0.0125". Kind of wide for an unfired steel open top. Maybe it'll be my first experiment on shrinking the gap.

junkman_01
April 18, 2011, 05:37 PM
It will go in but.....the slot is now longer to the front and the wedge will have nothing to bear against to draw the barrel tight to the frame. The arbor slot has to be adjusted to the rear.

junkman_01
April 18, 2011, 05:41 PM
I unboxed a new unfired Pietta 1860 I have and measured the gap to be 0.0125". Kind of wide for an unfired steel open top. Maybe it'll be my first experiment on shrinking the gap.

Fire it a few times first.

ClemBert
April 18, 2011, 05:50 PM
It will go in but.....the slot is now longer to the front and the wedge will have nothing to bear against to draw the barrel tight to the frame. The arbor slot has to be adjusted to the rear.

That doesn't seem to be the case for my revolvers. On my revolvers the front facing end of the arbor slot is not even with the front facing end of the barrel slot. The front facing end of the arbor slot sits rearward from the front facing end of the barrel slot. From mine it appears to be around 0.055 - 0.065 from a couple of revolvers I looked at. This means that as long as you don't adjust the barrel rearward by more than 0.055 - 0.065 you will still have the front part of the arbor slot to bear against.

ClemBert
April 18, 2011, 05:54 PM
I'm going to borrow makos_goods' awesome CAD illustration to show that delta. It's the measurement from the front of the wedge to the front of the barrel slot in his illustration.

http://i627.photobucket.com/albums/tt358/Mako_CAS/1860/Hand22.jpg

junkman_01
April 18, 2011, 07:23 PM
That may be the case on your revolver, but it sure wasn't the case on my ASM !

Hellgate
April 19, 2011, 01:24 AM
Most copy paper is .0035" thick so for a cheap & available "feeler gauge" after cleaning my Cols I merely fold a piece of paper over once on itself and place that between the barrel and cylinder as I tap in the wedge and as soon as the gap starts to "bite" the paper I'm set at .007". I've been told several times that is not the way to set a gap but it has worked for me on all my Colt Italian repros (Walkers, Armies & Navies from ASM, Uberti & Pietta).

makos_goods
April 19, 2011, 02:32 AM
I would say the .008 and .012 for the walkers is to big of gaps. You are losing a lot of pressure through those gaps.
I set mine at .003" for my walker and it works fine.
I probably would choose .004" for your Kirst version due to the fact it might get hotter then the other.
It seems everyone here thinks the gap can foul shut and cause binding. That Can't happen no matter what the gap is. The chamber pressure will always blow through the gap keeping it open. The fouling will always be thinner then the gap.

What causes the binding is the hand spring.
All the repo guns seem to have way to stiff of hand springs which push the cylinder ahead against the fouling that does stick to the cyl. face. That fouling makes a very good brake lining and that spring is putting the brakes on. Enough that you have trouble cocking the gun. You need to thin the original spring or make a new one. It should only be strong enough to move the weight of the hand itself to the cyl. and not push the cylinder ahead.

Even the ruger spring some are putting in is to stiff.

You can prove this to yourself by shooting your gun till you think the cyl. face bound it up. then put the hammer at half cock. hold the cyl. back with one hand then hold the gun up toward the sunlight and site through the gap. You will see that no matter where you turn the cyl. the gap will still be there.

A chart I made to show the area of some different gaps and a equal circle or hole with the same area to give you an idea of the pressure that you might be loosing at 6 to 12 thousandths gaps.
http://www.theroddoctor1.com/1851colt/cylgaps.jpg
roddoc,

I see you are still on your too close of cylinder gap hobby horse...

An ideal cylinder gap with the cylinder to the rear is .008-010". The hand spring does not cause binding, it simply re-engages the hand as it moves from ratchet tooth to ratchet tooth.

I say ideal because many thousands of shooters for the last 175 years who actually understand revolvers disagree with you. This isn't a double throw down diesel sumthin' or other, you're on the wrong forum if you want to toss that out. I think you will find you will always be in the minority with your theory, because it isn't proven out by experience.

The reason you get a gap when you cock the hammer is simple roddoc. The hammer pushes the cylinder forward on percussion revolvers without a gas ring until the cylinder engages the rear of the barrel. There is no mystery there.

And I'm not sure where you came up with this theory that only reproduction pistols have "heavy" hand springs. I have three original Colt's percussion pistols and the two that are in the best shape have hands springs thicker and stronger than the Uberti, Pietta and ASM revolvers I own.

The concept of holding a fouled cylinder up to the light and cocking it is flawed as I said. Fouled, clean, fresh or old it will always show some gap when you pull the cylinder back at half cock like you describe. What happens is that the hand will always push the cylinder forward as Clembert has described because of the engagement angle. I know you claim otherwise, but on the planet I live on the laws of physics and contact angles still apply. It's not the hand spring roddoc it's the hand in motion. No motion no force vector, move it and it moves it forward at the contact angle shown in the illustration Clembert has shown. To deny it show a misunderstanding of vector mechanics.

This should be interesting... You threw that chart up there to "give us an idea of the pressure that we might be loosing at 6 to 12 thousandths gaps." Looks "ominous," so pray tell roddoc how much pressure are we losing at each gap? Let's just jump straight to the .012" gap, that gives you an area of .017 in² which is roughly 10.5% of the area of a Ø.454 hole. Looks bad so far...So tell us what is the pressure loss?

~Mako

BHP FAN
April 19, 2011, 04:08 AM
the whole argument is ridiculous. Look at original Civil War revolvers. some have a gap a sixteenth of an inch wide, and those guns killed folks.we're not talking Nagant revolvers here.

Ravensmith
April 20, 2011, 04:10 PM
Rod Doc,
"I probably would choose .004" for your Kirst version due to the fact it might get hotter then the other."
Although .012 is a little excessive, .004 is way too tight. Recommended setting is .008 - .010 Conversion (Kirst) revolvers need that gap to function correctly. .006 would be OK if you are going to shoot smokeless only

Ravensmith AKA Jay Strite
Kirst Konverter LLC

makos_goods
April 20, 2011, 05:10 PM
Hey Raven,
Good to see you here, welcome to the forum. I was wondering why you didn’t post over here.

You're going to find that roddoc has some very odd ideas about cylinder gaps.


He bases most of this on a 2nd generation '51 that he says he personally picked up (with the help of a "serious" collector who had a run of the factory) at the factory in 1971 (made entirely in the factory in Hartford instead of from parts imported from Uberti) that now has a cylinder gap of only .002" and shoots itself clean. He recently had to remove .02” of an inch off of the back of his cones to allow it to work with “modern” CCI caps. But it never binds, doesn’t foul, cures warts and halitosis.

I’ve been telling him for some time now that the ideal cylinder gap for reliability and function is .008-.010”, so he will probably dismiss your recommendation as well. It’s really too bad you don’t have any gunsmithing experience, or other bona fides to base your recommendation on. I mean if you had any manufacturing experience with BP revolvers or had maybe been doing it most of your life he might listen… Yep, it’s too bad.

Some day when you need a smile, ask him about the preferred "super light" hand spring pressure and their relationship to the mystical .002" cylinder gap.

Anyway, good to see you Jay.

Regards,
Mako

72coupe
April 20, 2011, 06:13 PM
I once had a Dan Wesson 44V pistol with 3 different barrels. It came with a feeler gauge to set the cylinder gap. It measured 0.004 inch.

I experimented quite a bit with larger and smaller gaps but 0.004 worked best. Of course this was all with smokeless powder.

junkman_01
April 20, 2011, 07:05 PM
....And a modern revolver, which is a different animal than a cap & ball revolver!

72coupe
April 20, 2011, 07:43 PM
Junkman01 the Dan Wesson is as very modern revolver but I don't see it as all that much different from the Colt's and Remingtons.

Respectfully I would like to know what you think makes them different.

robhof
April 20, 2011, 08:49 PM
The powder residue is the difference, real B/p is the worst followed closely by most of the subs, except 777. Compared to that all modern powders are clean. My DW 357max has a .002 gauge and none of my b/p revolvers would make many rounds with that gap, heck even dirty modern powders and cast bullets stop my DW after 20 or so rounds.

makos_goods
April 20, 2011, 09:15 PM
roddoc,
I have to disagree with you on this. You need a refresher in Fluid Dynamics, specifically on gas flow. Go crack the books and get back to us.

A loss of 100fps/.001" is totally erroneous, where did you pull that from?

I need to look through my old files, but about 40 years ago (probably in the late 60's or early '70s) there was a good article in the American Rifleman about the effects of cylinder gap and velocity loss. This was a subject of interest at the time because of the introduction of the .22 Jet in the S&W 53. "Everyone" was convinced it was a losing velocity because of the revolver's cylinder gap. A chambered test barrel was constructed and they found there was NOT a significant loss as they expected. The author of the article set out to find just how much of a loss there was for each .001" of cylinder gap. He started with the cylinder literally butted up against the barrel face using shims and a yoke he sacrificed for the project. Then he moved it back in .001” increments until he reached .010”. He found the first .001” experienced a 3% loss in velocity. Then contrary to what anyone besides someone who understands gas flow, each additional .001” only experienced an incremental (not overall) additional 1% loss.

So if you started at 1,800 fps with zero gap you would be at 1,579 with .010” That’s a loss of 220 fps. No one in their right mind would run a revolver at “zero” so let’s extrapolate a bit and assume a “super tight” gap of .002” That means it would start at 1,728 (which is actually about right for a .22 Jet) and then end at 1,579 for a .01” gap that a loss of only 149fps or 8.6%. I have an interest in that info because I have built some improved short .22 K-Hornets on Smith revolvers, not the Kay-Chuk I had to be difficult and do it the hard way with a personal wildcat ( I was younger and more hard headed then…).

Then there are several articles that have been done using Dan Wesson revolvers because you can set the barrel gap. They have been done with the .44 mags, .357 and at least one with the .22LR. I had a “kit” model 15-V and I played around with it in the ‘80s. That’s what taught me the practical application of cylinder gap.

Here is an article from Shooting Times, June 1983 about a well done test with a Dan Wesson 22-VH. You will see the results were once again different than what the wives’ tales recount and even what the author expected.

http://i627.photobucket.com/albums/tt358/Mako_CAS/Odds%20and%20Ends/ShootingTimesJune1983_CylinderGap_Page_1.jpghttp://i627.photobucket.com/albums/tt358/Mako_CAS/Odds%20and%20Ends/ShootingTimesJune1983_CylinderGap_Page_2.jpghttp://i627.photobucket.com/albums/tt358/Mako_CAS/Odds%20and%20Ends/ShootingTimesJune1983_CylinderGap_Page_3.jpg

ADDED 4/20

I couldn't find my older American Rifleman magazines but this report was originally published on THR a couple of years ago.

Notice how little it changes per .001". The .38 spl low pressure loads are what we should be looking at for BP, it is right in the velocities and corresponding pressures we discuss on this forum. The high pressure table is there to provide another set of data points. Notice how this correlates well with what I remembered from the American Rifleman article and correlates with the Dan Wesson test above.
http://i627.photobucket.com/albums/tt358/Mako_CAS/Odds%20and%20Ends/Velocityloss.png




So, Clembert I wouldn’t worry too much about your cylinder gap. The problem is the amount of BP and the barrel length to burn it in. You’ve run up against the wall of diminishing returns even with the fastest granulation that would be safe in that revolver. I will recommend that you compress the “tar” out of your loads and apply a very heavy crimp. Fill your case vibrate it down and add more if necessary, a drop tube might be called for. Then make sure you get at least 1/8” compression (more if you can get it).

BP is a very inefficient propellant, you get 60% uncombusted materials even with an optimized barrel length for the charge. So, only 40% of the charge is potentially converted into propelling gases and that once again assumes you have a tube long enough to take advantage of it. At some point you’re just spewing burning and unburned particles out the muzzle. It makes for “purty” night shooting and some hair singing results…

Try and compress it more and see if you can squeeze a bit more velocity out of it. Crimp it hard to help the pressure build a bit.

You seem like a bright guy, what is your training in? I have several friends who are engineers out of Clemson.

Regards,
Mako

Hey all,
I am pasting this over here as well.

Junkman, it's really not any different. Look a the Gun Digest Treasury table above. The .38 spl loads could be considered an analog for our BP loads considering pressure, bullet weigh and velocity. It was done on a 19th century designed SAA, not a "modern" Dan Wesson.

72coupe, what do you mean by "worked best?" Better accuracy, more consistent velocity? What? I have had a 44VH and a 15 and I used to close mine down smaller than the .006" Dan Wesson spacing gage because it "seemed better." Like I said though I actually conducted a test with the 15 and I found very little difference between .003-.006". On the .44 mag I closed it down a bit to reduce the side blast because I used it for metallic silhouette, but other than that it had no practical advantage.

robhof, you are correct about the gap with BP, which is what this thread is all about. The point is and remains that you can and should run a gap of .008-.010" with a percussion revolver and about .006-.008" with a cartridge pistol if it has a gas ring (if the percussion pistol has a gas ring you could run it at the tighter dimension).

The whole point that we should all be seeing is that CYLINDER GAP is NOT the boogie man that wives' tales and what we have assumed actually is.

So when someone tells you that if you run your cylinder gap where it should be for reliability that you will lose all of your velocity, just shake your head and know the truth of the matter. This ain't rocket surgery, but it's close...

Regards,
Mako

junkman_01
April 20, 2011, 09:37 PM
Mako,

I beg to differ, but modern revolvers (and even open top Colt cartridge guns) have bushings/gas shields that prevent the cylinder from moving forward and closing the gap and dragging when fouled.

makos_goods
April 20, 2011, 10:10 PM
Junkman,
I have addressed that. Read above.

I run a .008-.010" gap without gas shields and .006-.008 with gas shields using BP. When I used to build PPC revolvers I ran .004-.006".

The gap pressure loss doesn't care if there is a gas ring or not, but it does come into play when indexing the cylinder. I think you and I are in agreement on this. I don't agree with roddoc about the magic force keeping a cylinder from moving forward when engaged by the hand.
~Mako

72coupe
April 20, 2011, 10:55 PM
Makos it has been years since I owned that revolver. I was using it for Hunters Class sihlouette so I am sure my testing was accuracy related as I didn't have a chronograph at that time.

makos_goods
April 21, 2011, 03:27 PM
I once had a Dan Wesson 44V pistol with 3 different barrels. It came with a feeler gauge to set the cylinder gap. It measured 0.004 inch.

I experimented quite a bit with larger and smaller gaps but 0.004 worked best. Of course this was all with smokeless powder.
72coupe,
Are you sure it had a .004" feeler gauge? I have owned two Dan Wesson revolvers and they both had .006" setting standards. In fact I still have the one for the .44 and it is .006".

This is from the Dan Wesson Instruction manual:
http://i627.photobucket.com/albums/tt358/Mako_CAS/Odds%20and%20Ends/danwesson_large-frame.png

The only reason I bring it up is that a lot of people think it was tighter than .006". You may have used a different gauge, but the .006" was factory. Like you I used a Dan Wesson .44 mag. for Silhouette and I shot it in the standing as well as the freestyle class where I used the reclining "creedmore" position. I used a leg shield but I wanted to attenuate the cylinder gap blast a bit so I cranked it down to .003". I tried .002" but it got "sticky" halfway through a match.

The only reason they had the .002" gap on the .357 Maximum was because of the trouble Ruger had with top strap cutting. I know people who backed the maximum back out because it got sticky. Dan Wesson did it just to cover themselves from liability. Ruger killed the Maximum, not top strap erosion. They cut and ran. (pun intended...)

Anyway, back to the cylinder gap issue. Like I said when I first got my first Dan Wesson, a .357 mag. model 15 kit I applied the "common wisdom" of closer cylinder gaps and thought I really had something. Then one day an older shooter asked how much I gained with the tight gap I was running. He had noticed I had to clean the cylinder face and barrel face sometimes while shooting. I then decided to find out and ran some tests across my Oehler 33 and lo and behold I was gaining less than 10-12 fps between .003 and .006" with 125gr bullets cranked up to just below maximum recommended loads.

I have learned over many decades of shooting that a lot of what we "think we know" is actually just wives' tales, voodoo and tradition instead of tested and confirmed data. Just look at Dick Metcalf's article above, he didn't expect those results. Reality is sometimes counter intuitive, well not really...it is actually counter to what we have been reading scribbled on bathroom walls, in magazine articles, the movies, TV and on forums such as this.

TV and Movies have almost destroyed realistic expectations of how firearms function and their affects on targets.

~Mako

72coupe
April 21, 2011, 09:03 PM
Mako you could be right about the factory guage being .006 but I am pretty sure I was setting mine with a .004. What experimenting I did cuased me to use the .004 for accuracy. I didn't make notes on my testing but that is what I remember.

robhof
April 22, 2011, 12:55 AM
.004 for the 357 mag DW was common with competition shooters and many of my friends experimented with gaps on their 44 and 22 DW's. The factory only provided .006 though.

makos_goods
April 22, 2011, 02:37 AM
.004 for the 357 mag DW was common with competition shooters and many of my friends experimented with gaps on their 44 and 22 DW's. The factory only provided .006 though.
Yep, I did it myself as I wrote. But I can tell you it didn't make a discernible difference. You give a guy a "knob" to turn and he's gonna twist it. You could "tweak" your pistol and make it "better." You know... harder, higher, faster, bigger, better... and all because you could set your gap not at .004" but at .0039", which course "has to be better."

There are other articles out there about Dan Wessons and testing the cylinder gaps. I have posted the one and referred to two others. One is posted on the THR forum and you won't find one telling you that tighter is demonstrably better.

Have y'all figured out the relationship between cylinder gap and pressure yet? I don't mean velocity, I mean pressure.

~Mako

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