scooter123
Member
Now, one important note. I have been using Speer Lawman TMJ ammunition for ALL of my reliability testing with my centerfire revolvers. All reliability testing has been done in Double Action without staging the trigger. Speer has a reputation for a somewhat "hard" primer and I want to insure that my revolvers will work properly with whatever ammunition I can find. Quite simply, my setups are NOT Federal Primer only guns, they'll run Speer, Remington, Winchester, or Federal or I'll increase the mainspring tension until they do. I don't know about Wolf ammo, I've seen so many reports about how dirty it is that I have no interest in using it. Due to the cost, and difficult availability of the Speer Lawman 38 spl., all of my accuracy testing has been done using Federal American Eagle for the 620 and 40 caliber Federal Champion in the 610. Accuracy and reliability testing for the 617 has been done using Winchester Xpert HV or Federal Bulk. BTW, the Winchester groups 35-40% better in the 617 than the Federal.
Trigger weights have been measured using a Lyman Digital trigger gage and are the average for a full turn of the cylinder, witch means 7 pulls for the 620 and 6 for the 610 and 617. I did not chart the variation, at some point I may do that. However, I didn't note any variation of more than 3 ounces.
As for reducing the power of the mainspring using the strain screw, my method to adjust the tension is to use a hand made shim that fits under the head of the strain screw. The mainsprings used are the factory mainsprings that originally came with each gun. BTW, the dimensions for these shims are a 0.147 ID and a 0.218 OD. They also have to be placed into the counterbore for the screw before inserting the screw because the diameter of the screw is slightly reduced at the head so it can get a touch off center. If you try and put the shim on the screw first it can get trapped between the frame and the head of the screw. By using shims I can fully tighten the strain screw while being able to experiment with different shims and find the point where reliable ignition becomes an issue, then it's a simple matter of removing some shim thickness.
I'll also note that a recent experiment has confirmed that there is more to ignition that the round just going off. When I reduced the DA pull on my 620 from 9 lbs. to 8 lbs. it proved reliable for ignition with the factory firing pin but the group size at 100 feet doubled. The problem was due to inconsistent ignition that caused an increase in the variation of the velocity. Installing the C&S extended travel firing pin brought the group size back to where it was with the factory firing pin at 9 lbs. DA pull.
I'll also note that the mainspring tension has almost ZERO effect on the SA trigger pull in the weight ranges I've been working in. I've taken the 620 from a 10.5 lbs. DA pull to 8 lbs. and there hasn't been more than a 1/2 ounce change in the SA trigger weight. What has had a very noticable effect on the SA trigger weight is the spring for the rebound slide. In the 620 going from the factory 16 lbs. rebound spring to a 13 lbs. spring dropped the SA weight from 4.5 lbs to just a tick over 3 lbs.
I've also found that different guns need different spring setups if you're trying to hit a specific trigger weight for the SA and DA trigger pulls. Basically, I would consider a good trigger pull gage a MUST for any serious tuning, at 60 dollars the Lyman digital is not too expensive to obtain.
With my 620, a 13 lbs. rebound spring and 0.020 shim under the strain screw has produced a 3 lbs. 2 ounce SA weight and an 8 lbs. even DA weight. With my 610, a 14 lbs. rebound spring and 0.020 shim under the head of the strain screw has produced a 3 lbs. SA weight and a 9 lbs. 1 ounce SA weight. Currently both the 620 and 610 have the extended travel firing pin installed and neither gun shows any indication of darkened primers with the trigger at these weights. However, in the 610 installation of the extended travel firing pin produced a 30 percent darkened primer rate with the factory mainspring tension. I would urge some caution when first using this firing pin, it may pierce a primer if there is too much mainspring tension.
I also suspect that the target hammer on the 610 may prevent me from taking the DA pull down to 8 lbs. I've done a bit of reading and primer ignition is a product of Kinetic Energy transfer. Which means a heavier hammer needs more power in the mainspring than a lighter hammer because Ke is a product of Mass times the Velocity SQUARED. Basically, speed matters and it's easier to get high speed with a lighter hammer. However, I am hopeful that I can get the 610 down to 8.5 lbs. but it'll take some time to insure that.
Now, one final note. In addition to tuning the 610 and 620 I've also done some tuning on my 617. I purchased the 617 used and a previous owner had the SA sear tweaked for a lighter weight, an approach that I don't really approve of. The problem with adjusting the sear angle on the trigger for a lighter SA pull is that you are creating an "assist angle" on the sear and I believe that long term this assist angle will increase the wear on the SA sear notch on the hammer. At some point I plan on correcting that. However, currently it has a 14 lbs rebound spring that produced a 2 lbs. 2 ounces SA trigger weight. It also has a 0.010 thick shime under the strain screw and a DA weight of 9 lbs. 3 ounces. Since extended travel firing pins are not to be found for the rimfires, it has the factory firing pin installed. With Winchester Xpert HV it will group 2 inches at 100 feet and that hasn't been effected by reducing the DA weight.
At this point I consider the 620 to be "just right". Finshed the range session last weekend with a 2 inch, 14 round group at 30 feet in DA fire with a .7 second split. Also shot a 1.75 inch group with it at 100 feet from a bench rest.
The 610 I want to do a bit more experimenting to see just how light I can take the trigger with the extended travel firing pin before losing accuracy or reliability. Unfortunatly, that means I'll have to ditch the Pachmayr Decelerator it's wearing currently, the grips screw is right at the point where it'll bind the mainspring if I take it any lighter. I really like the 500 magnum grip on the 620 so I'll order another for the 610, however last time I tried this particular grip on the 610 it showed a gap at the top of the backstrap, so I'll have to hope for a slightly different mold result that fits well or reshape the grip frame on the 610 so it fits properly.
The 617 is almost done, however I do want to adjust the sear angle on the trigger to take the SA weight to 3 lbs. with a 14 lbs. rebound spring. Target hammers have become very difficult to find so I don't want to wear this one out. In addition a 2 lbs. trigger is much too light for a newby and it's light enough to make me quite cautious with it.
As for the point of this post, it's proof that with a bit of work you can get reliable ignition and good accuracy with the factory mainspring and it doesn't have to come at the price of limiting yourself to using only Federal primered ammunition. I'm also quite curious as to how light I can take the target hammer on the 610 before accuracy falls off or ignition becomes unreliable. It also shows that the rimfires do have some tolerance for a lightened mainspring, however at 9 lbs. 3 ounces I'm calling it good.
Trigger weights have been measured using a Lyman Digital trigger gage and are the average for a full turn of the cylinder, witch means 7 pulls for the 620 and 6 for the 610 and 617. I did not chart the variation, at some point I may do that. However, I didn't note any variation of more than 3 ounces.
As for reducing the power of the mainspring using the strain screw, my method to adjust the tension is to use a hand made shim that fits under the head of the strain screw. The mainsprings used are the factory mainsprings that originally came with each gun. BTW, the dimensions for these shims are a 0.147 ID and a 0.218 OD. They also have to be placed into the counterbore for the screw before inserting the screw because the diameter of the screw is slightly reduced at the head so it can get a touch off center. If you try and put the shim on the screw first it can get trapped between the frame and the head of the screw. By using shims I can fully tighten the strain screw while being able to experiment with different shims and find the point where reliable ignition becomes an issue, then it's a simple matter of removing some shim thickness.
I'll also note that a recent experiment has confirmed that there is more to ignition that the round just going off. When I reduced the DA pull on my 620 from 9 lbs. to 8 lbs. it proved reliable for ignition with the factory firing pin but the group size at 100 feet doubled. The problem was due to inconsistent ignition that caused an increase in the variation of the velocity. Installing the C&S extended travel firing pin brought the group size back to where it was with the factory firing pin at 9 lbs. DA pull.
I'll also note that the mainspring tension has almost ZERO effect on the SA trigger pull in the weight ranges I've been working in. I've taken the 620 from a 10.5 lbs. DA pull to 8 lbs. and there hasn't been more than a 1/2 ounce change in the SA trigger weight. What has had a very noticable effect on the SA trigger weight is the spring for the rebound slide. In the 620 going from the factory 16 lbs. rebound spring to a 13 lbs. spring dropped the SA weight from 4.5 lbs to just a tick over 3 lbs.
I've also found that different guns need different spring setups if you're trying to hit a specific trigger weight for the SA and DA trigger pulls. Basically, I would consider a good trigger pull gage a MUST for any serious tuning, at 60 dollars the Lyman digital is not too expensive to obtain.
With my 620, a 13 lbs. rebound spring and 0.020 shim under the strain screw has produced a 3 lbs. 2 ounce SA weight and an 8 lbs. even DA weight. With my 610, a 14 lbs. rebound spring and 0.020 shim under the head of the strain screw has produced a 3 lbs. SA weight and a 9 lbs. 1 ounce SA weight. Currently both the 620 and 610 have the extended travel firing pin installed and neither gun shows any indication of darkened primers with the trigger at these weights. However, in the 610 installation of the extended travel firing pin produced a 30 percent darkened primer rate with the factory mainspring tension. I would urge some caution when first using this firing pin, it may pierce a primer if there is too much mainspring tension.
I also suspect that the target hammer on the 610 may prevent me from taking the DA pull down to 8 lbs. I've done a bit of reading and primer ignition is a product of Kinetic Energy transfer. Which means a heavier hammer needs more power in the mainspring than a lighter hammer because Ke is a product of Mass times the Velocity SQUARED. Basically, speed matters and it's easier to get high speed with a lighter hammer. However, I am hopeful that I can get the 610 down to 8.5 lbs. but it'll take some time to insure that.
Now, one final note. In addition to tuning the 610 and 620 I've also done some tuning on my 617. I purchased the 617 used and a previous owner had the SA sear tweaked for a lighter weight, an approach that I don't really approve of. The problem with adjusting the sear angle on the trigger for a lighter SA pull is that you are creating an "assist angle" on the sear and I believe that long term this assist angle will increase the wear on the SA sear notch on the hammer. At some point I plan on correcting that. However, currently it has a 14 lbs rebound spring that produced a 2 lbs. 2 ounces SA trigger weight. It also has a 0.010 thick shime under the strain screw and a DA weight of 9 lbs. 3 ounces. Since extended travel firing pins are not to be found for the rimfires, it has the factory firing pin installed. With Winchester Xpert HV it will group 2 inches at 100 feet and that hasn't been effected by reducing the DA weight.
At this point I consider the 620 to be "just right". Finshed the range session last weekend with a 2 inch, 14 round group at 30 feet in DA fire with a .7 second split. Also shot a 1.75 inch group with it at 100 feet from a bench rest.
The 610 I want to do a bit more experimenting to see just how light I can take the trigger with the extended travel firing pin before losing accuracy or reliability. Unfortunatly, that means I'll have to ditch the Pachmayr Decelerator it's wearing currently, the grips screw is right at the point where it'll bind the mainspring if I take it any lighter. I really like the 500 magnum grip on the 620 so I'll order another for the 610, however last time I tried this particular grip on the 610 it showed a gap at the top of the backstrap, so I'll have to hope for a slightly different mold result that fits well or reshape the grip frame on the 610 so it fits properly.
The 617 is almost done, however I do want to adjust the sear angle on the trigger to take the SA weight to 3 lbs. with a 14 lbs. rebound spring. Target hammers have become very difficult to find so I don't want to wear this one out. In addition a 2 lbs. trigger is much too light for a newby and it's light enough to make me quite cautious with it.
As for the point of this post, it's proof that with a bit of work you can get reliable ignition and good accuracy with the factory mainspring and it doesn't have to come at the price of limiting yourself to using only Federal primered ammunition. I'm also quite curious as to how light I can take the target hammer on the 610 before accuracy falls off or ignition becomes unreliable. It also shows that the rimfires do have some tolerance for a lightened mainspring, however at 9 lbs. 3 ounces I'm calling it good.
