Measuring mainspring strength

[Navy Six]

I intend to conduct a series of tests on Colt style percussion pistols in regards to mainspring strength and its affect on percussion cap performance. I would like to accurately measure and compare a variety of mainsprings. I do have a trigger pull gauge and considered measuring that as I swapped out different mainsprings on the same gun. Is there a better way of doing this? I don't want my results to be based on "well, this spring feels heavier than that one". Any thoughts would be appreciated.

[Coffinmaker]

Navy Six 

Well Ok, a couple of thoughts.  First thought, Trigger pull only measures trigger pull.  A poorly fit trigger can have a heavier "pull" than a well fit trigger, regardless of Main Spring.

One would have to build a jig to hold ALL subject Main Springs in a like position, then connect them to a gauge that measures the amount of "pull" required to move the action end a measured amount of deflection.  Then one would have to measure the effect of "stacking" (increased pull) over the full deflection of the spring.  Once documented, one would have to insure there was absolutely NO drag in the moving parts of the subject test action.

The results, as applied to the reaction of Percussion Caps, would then be skewed by the differentiation of material used by the manufacturers of differing cap brands.  Also skewed by the differing types/amounts of explosive material and thickness of sealant, also skewed by specific lot numbers of the various manufacturers.

The same variations would also be observed in various Main Springs, by manufacturer, based on lot numbers (unknown) and varying dates of manufacture.

Considering ALL the variables and complications, I think the objective "Gee, That one feels different" is as definitive as it's going to get.  along with measuring the specific Brisbane of the various caps.  Also, the test subjects would all have to be tested on exactly the same set of nipples.  Yule also need to arrange for a High Speed High Frame Rate camera and a skilled operator with a concurrent trigger mechanism.

Have Fun!!

[Navy Six]

Thanks Coffinmaker. I received a response from Mike Brackett about how he does it(uses trigger pull gauge after hammer is brought to half cock. Hook gauge behind hammer face. When hammer moves record numbers).
My testing is to satisfy me as to why, some of my Colt style percussion guns will still occasionally suck caps despite:
arbor length correction
Slix Shot nipples
polished hammer face and safety notch
polished internals
One or two of my problem guns have responded to a heavier mainspring which cut down the problem significantly. I have no intention of installing a "cap rake". I feel the real problem is the darn caps. The thin construction material of caps combined with hotter caps along with generally lighter factory mainsprings has created this "perfect storm" of cap sucking, at least in my opinion. Having the opportunity to examine several original Colts, both SAA and percussion, I've noted a much heavier mainspring in all of them. Even though I am actively involved in SASS and enjoy a smooth, light action as much as the next person, if I have to go to a somewhat heavier mainspring in my percussion pistols in order to avoid problems, so be it. Besides, all this testing gives me an excuse to shoot more!

[45 Dragoon]

 

[45 Dragoon]

 

[Professor Marvel]

Well.
Darn.

Here I was about to devote little grey cells to inventing a most ingenious and complicated contraption...

[Navy Six]

You still can, Professor. I'm sure it will be a "Marvel" of ingenuity.

[Navy Six]

Well, just to satisfy myself that I wouldn't be wasting my time, this morning I did a brief preliminary test. A pair of Uberti mainsprings that came out of Cattleman(circa 1998 & 2000 and are definitely heavier than current production) were installed in my Uberti 51 Navy squarebacks. These two cap suck at the rate of 2/3 every 30 rounds or so despite everything done to them. After 60 total rounds I didn't have a single issue. No changes from usual other than the mainsprings. So I will hunt down more mainsprings of a similar weight as I intend to continue testing these two guns as well as a pair of 61 Navies and 60 Armies. I want to know about what weight mainspring is required to make these things work.

[Malamute]

 I found this thread some time back when looking for info about Uberti soft mainsprings and how to correct that. I had considered approaching someone on the Colt forum that said they swapped heavier factory mainsprings for softer ones.

 I have a Cimarron/Uberti old model P in 357 cal made in 22 or 23. The mainspring is definitely soft feeling from the factory. My uses are mainly outdoors, some hunting, some mountain and hills carry, more daily carry use in rural life. Ive shot a handful of CAS shoots long ago, but its not a factor in any of my uses or possible modifications. Reliability in all conditions is the higher goal.

 Something kicked my memory in reading various discussions about springs, I watched a good DA revolver smith tune an S&W DA mainspring by tweeking the spring with a plastic wedge back and forth until he had it where he wanted to slick DA use. I pulled the backstrap and grips off the model P, removed the mainspring, then re-installed it behind the hammer. I snugged a medium crescent wrench on the mainspring and frame just above the screw so tweeking wouldnt be stressing the screw hole in the spring, then used a small crescent to bend the spring rearwards. I ended up about 3/16 to 1/4" clear of the back of the hammer. I re-installed the spring under the hammer, and was satisfied with the heavier hammer action. I have no way to measure it but its very definitely stronger.

 The Miroku Winchester 73 also had a soft mainspring when brand new, it occurred to me the check the tension screw, it was about a half turn out from fully seated. When bottomed out it had noticeably stronger hammer strength. Much better as a field gun.

 Outpost75, aka Ed Harris mentioned on one forum about how there were specs on S&W mainsprings for .fed LE use, and described how they tested them. I was unable to find the quote, but it entailed measuring the force to pull the hammer fully back, possibly with a heavy thread or wire around the hammer. That was in lieu of having the gauge with copper piece to measure firing pin indent depth when fired. The coppers were made to spec for the purpose (I believe from a certified source) and used in a fixture that went in the chamber or frame from what I gathered. There were also specs on end shake before testing indent as well as headspace and barrel cylinder gap. Firing pin protrusion and the amount of off center hit allowed on a primer, were also spec-ed. I believe half the diameter of the firing pin being max allowed off center. I had no idea there were specs and methods to check such things. He gave indent specs on a couple revolver make/models as well as the m4. He commented that he felt few current commercial made (non-LE use) revolvers would pass the specs today.

 An interesting related side point to the above paragraph, several writers/match shooters tested firing pin/striker hit strength/mainspring strength vs velocity, and the higher level strikes had higher and more consistent velocity deviations. Vertical stringing in formerly good shooting rifles was often correctable with a fresh mainspring.

 Another side note, the model P had more end shake than desirable, sloppy BC gap (.012-.15), and the throats were .366". In searching, others had similar results and Cimarron said they were within their spec. I found what ended up being an apparently unfired 2nd gen Colt 357 cylinder and bushing for very reasonable, it dropped in, indexes perfectly, tighter gap, better end shake, and has .357" throats.

[Abilene]

... I found what ended up being an apparently unfired 2nd gen Colt 357 cylinder and bushing for very reasonable, it dropped in, indexes perfectly, tighter gap, better end shake, and has .357" throats.

Very interesting! 

[Coffinmaker]

Uberti Main Springs, traditionally, are not "soft."  Quite the opposite.  They are ground and specifically heat treated to standard specification.  Those specifications are more than heavy enough to set off ANY primer.  Anyone declaring differences in end performance of a cartridge based on primer strike is using "smoke and mirrors." 

I also find it very doubtful you found an actual "Colt" 2nd Cylinder that dropped in and functioned perfectly.  Colt dimensions are quite different from Uberti.  What you acquired is more likely a new Uberti cylinder and bushing that had never been fit to a specific Mod P Uberti.

Optimum Head Space is .004 measured between the cartridge and the recoil shield.  Normally accompanied by .001 end shake.  There are always manufacturing variances in Barrel to Cylinder Gap and most guns show .003 to .005 as more common gaps.  Most Main Springs don't respond well nor permanently to being "bent" to increase impact. So long as the primer is detonating, firing pin impact will have no measurable effect on ignition.  Main Springs can, and sometimes do, "take a set" and will fail.  Replacing those springs is the only good option.  Over all, I do wish you good luck.

[Cheyenne Logan]

I have often thought that part of the problem isn't so much cap sucking, as it is the mainsprings are too light......my original cap guns all have hammer springs that are noticeably heavier than current reproductions....even the ones I have from the 70's are heavier....and surprisingly, I've not had a cap jam in them (yet).

Era's Gone did a video on testing some of his bullets in an 1860 replica and he noted that the back blast of the shot was lifting the hammer! This would allow caps and fragments to be blown under the hammer, inducing a cap jam. He had it in slo-mo which showed the hammer having considerable movement.

[45 Dragoon]

All that being said, it all depends on what the owner wants!!
If you want to go "fast", you need a lighter main. That means possible cap fragment problems which can be taken care of with a cap post. The cap post not only blocks fragments but arrests hammer blow back.
 So, if you want to pull back a 10 lb hammer because  "that's the way they were" .  .  .  no problem.  If you want to compete or enjoy a lighter (4-5lb.) draw, it may call for additional "upgrades".
 You can in fact "impart" a slight upward bend in the spring just under the hammer which will  increase  "tension" for an additional speed increase of the hammer right at the end of the throw (ignition insurance!).

Mike

[Coffinmaker]

  Cheyenne

Since we have "drifted" from Suppository Shooters to Cap Guns, there are a couple of salient things I'd like to point out.  First item up for bids, is the Caps themselves.  Cap[s in the percussion era were made from sterner stuff and gripped the cones very tightly.  Even Waterproof.  Todays caps are not so heavily made, and thus do not require an F-150 Main Spring for proper ignition.  The Back Blast thru the Nipple is attributable to fragile Caps.  So, to mitigate fragile caps, some of us Gunplumbers developed mechanical means to keep cap frags out of the Hammer Raceway.

If one just wants to "go Out Back" and roll some cans, and occasionally play with a Cap Gun, those uber heavy OEM Main Springs are suitable, will will cause eventual damage to the end of the Nipples.  On the other hand, as pointed out by The Dragoon, you wish to play in the CAS games, that heavy Main Spring ain't gonna cut it.  Lighter Main Springs will become a necessity as will "other" applicable things to make a Cap Gun as reliable and as Fast as Cartridge Guns.  In CAS circles, the main spring only needs to reliably detonate the Cap - EVERY TIME.  Any more than that is extra work for yer thumb and extra time on the clock.  You pays yer Money - You takes yer Chances.

Oh.  Shucks.  Almost forgot.  About Era's Gone.  You only get enough Back Blast to lift the Hammer when you're running a maximum + powder charge under yer bullets.  And he IS shooting bullets and not swaged or soft cast Ball.

There are also some fairly simple things one can do to mitigate Cap Sucking.  Seek out Mike Belliview's video on just that subject.  Lots of good stuff that doesn't involves paying Gunplumbers for their invaluable services.  Burma Shave

[Cheyenne Logan]

Agreed that the modern cap is made of a material that is a lot thinner than the originals. Duke Frazier has an interesting video on cap jams.....

 

He also quotes Military records as recommending a thicker cap for the Colt revolvers.....and has some measurements per Eras Gone on thickness of modern caps and ACW era ones.  In a perfect world, manufacturers would make a thicker cap, but, getting them to make any caps is enough of a chore.

 

[Cheyenne Logan]

PS-My regular loads are "full" loads as they are either paper cartridges, or Hazard cartridges....

I understand the 'game', SASS # 5279, and a Regulator to boot........the game's emphasis has changed over the years.

[Coffinmaker]

   WHOOPS 

I forgot to include in my verbose dissertation, when looking for Mike Belleview's stuff on You Tube, you need to look for "Dualist1954."  To include prepping a NEW Cap Gun for the range.  Some real good stuff.