Dialing-In a Fixed Sight Ruger DA: The Repatriated Ruger GP-100

 Ruger GP-100 .357 Magnum, 3” barrel.

My introduction to Ruger’s double-action revolvers came about 1974, in the form of a 4” stainless steel Security Six, in .357 Magnum. My uses for a handgun were purely recreational back then, and that little .357 accompanied me on many a long hike back to a secluded lake that had some of the finest bass fishing in the free world. Too bad “eighteen” doesn’t last forever.

It wasn’t long before I was packing a pistol for more serious purposes, and trying to make ends meet on a patrolman’s wages. Soon another Ruger .357 found its way into my holster; this time it was a blue 4″ Speed-Six. Skeeter Skelton had once postulated that a pair of these revolvers with 4″ heavy barrels would make a prudent man about as well armed as any pistolero could hope to be. Mr. Skelton wore a badge a long time and he was one of the most credible men who ever penned a line on the subject of handguns. His gift of practical wisdom was not wasted on me.

I couldn’t get away with wearing twin Speed-Sixes with my uniform, I could sure pack one of them. I had been lucky with my new Ruger, and its fixed sights were dead on the button as it left the factory. It would splatter a gallon jug out to about 75 paces with Federal 125 grain hollow-point magnums, but still printed 148-grain wad-cutters close enough to pot a squirrel at 20. I shot this gun a lot, and eventually traded it for something that I needed less- but thought I wanted more. At the time, I thought you would always be able to order a new, blue Ruger Speed Six. But changes were coming.

Ruger’s decision to discontinue the Speed/Service/Security Six line in the mid-80’s caught me “flat-footed”- a condition not entirely unknown to policemen in any event. I viewed the new replacement (blandly named “GP-100″) with a jaundiced eye. It was heavier than my old Speed-Six, for no good reason I could think of, and in my eyes it was downright homely. The first one I handled shot OK, but felt like it had a garage-door spring powering the mechanism.

A relative soon acquired another GP-100 and his specimen proved very accurate; it’s action was also notably better than the first one I had handled. While not a thing of beauty, that rubber grip was the most comfortable I had ever used with full-snort .357 Magnum loads. It still seemed unnecessarily heavy to me, but I had to admit that it looked capable of wearing out most shooters, well before the opposite event occurred. I began thinking that one of these with a slender barrel and fixed sights would be about the ideal hard-use .357 wheel-gun. Meanwhile, time was coldly marching on- and decent 4″ Speed-Sixes were getting harder and harder to find.

I held off buying a GP-100 for a long time. Law enforcement had switched to the auto-pistol in droves, not long after it was introduced. My own duty holsters were generally occupied by a good 1911, or a 4″ S&W .44 when I could get away with it.

I stumbled onto a used GP-100 .357 with fixed sights, a 3″ barrel and the short ejector shroud. The left side of the frame bore an importer’s marks from Century Arms International; this gun had evidently seen foreign service, and had found its way back stateside. The electric-penciled “C.A.I.” mark and a dinged front sight provided proper points for haggling the price, and after negotiations the GP-100 was mine for less than half of what a new one would have cost me.

 

I ran the little GP out that evening for a quick function-check. It was a little hard to tell at first because while the sights were pretty close for windage, the front was obviously too short, causing the gun to shoot about 7″ high at 25 yards. Moving in for some fast D/A work revealed that the sight regulation was close enough for government work out to 15 yards or so. But that fast D/A work also revealed another problem- occasional misfires. This would have to be corrected.

Looking into the ‘misfire’ problem revealed a few things, and provided some time and incentive to correct the little revolver’s shortcomings. The first thing I did was get on Ruger’s website, and check the serial number against the dates of manufacture. This excellent resource may be found on the Internet at www.ruger-firearms.com/Firearms/SE-CalSerialHistory.html and it indicated that my GP-100 was made in 1989. This would make the mainspring at least 14 years old, assuming that it wasn’t made when the model was first introduced in 1986. A new mainspring would doubtless improve reliability in fast D/A fire. The second thing I did was to call Ruger, and request their factory specs on front sight height and firing pin protrusion. They were quite helpful in establishing that the front sight for the 3″ model should stand .343″ above the rib; a full .1″ higher than the battered old sight on my gun. A couple of spare sights and pins were ordered for less than $12.00 shipped. Ruger was a little less candid about the factory specs for firing pin protrusion, and after some research on that subject I am beginning to understand why. I discovered that insufficient firing pin protrusion is a common problem with their Redhawk series- although this is the first Ruger D/A I had ever owned, that suffered from it. I also learned that custom gunsmith Hamilton Bowen manufactures an “extra-length” Ruger D/A firing pin, and now installs it as a standard component of all the Redhawk conversions that leave his workbench. This is particularly noteworthy considering that Bowen specializes in building big-bore Rugers which are likely to be employed as defensive implements in ‘bear country.’ This would definitely not be the place to be having a misfire.

Brownell’s, on the other hand, didn’t have any problem at all telling me that the industry standard for firing pin protrusion on revolvers was .050-055 inches. It was time to grab a set of micrometers and get to the heart of this matter. Luckily, this revolver’s short barrel length allowed me to use my 6″ micrometer to take a direct measurement from the muzzle, to both the protruding firing pin and the standing face of the breech.

 

Putting the micrometers to good use: checking firing pin protrusion.

The original firing pin protrusion checked at .036 inches. A careful refitting of the transfer bar and hammer nose got it up to .040″, while actual pin reach (pin depressed directly against frame with a flat object) maxed out at .045″. CCI primers in resized brass were then run through the gun D/A, as fast as the action could be cycled- 6 shots in a shade under 2 seconds. Ignition was now 100%, but with some primers still showing light indentations.

Things were obviously better, but I wasn’t about to settle for anything less than 100% reliability- with some room to spare. I looked closely at the channel in the frame where the hammer rests. Casting marks were still clearly visible, and by depressing the pin to its full depth (below ‘flush’) it was apparent that there was another .005-.006 that could be gained by relieving the frame in that location. The part of the pin engaged by the transfer bar was blackened with a fine-point marker, so as to immediately show when the frame had been relieved to the limit of the pin’s rearward extension. The pin was then fully depressed and retained in the forward position by clamping a reloading die lock ring onto its nose. Judicious work with a safe-edge file brought about the desired results, and after a second re-fitting of the hammer nose and transfer bar, firing pin protrusion now stood at a dead .050″. In addition to finally being on US soil again, the little gun was also finally up to industry specifications.

The new front sight had been received and installed while all of this was underway, and I was anxious to see what improvements, if any, my efforts had produced. I took the GP out for a short function-check, using the old, light mainspring that had been in the gun when it had the initial problems.

To make a long story short, bringing the firing pin protrusion up to .050″ fully corrected the light strikes and misfires. Needless to say I didn’t buy this little revolver to shoot silhouette matches with. It was time to find out if this little .357 would shoot.

We will establish from the outset that my expectations are maybe a little higher than some other folks. I learned a long time ago that when somebody else gets to start your fights, they’ll hardly ever ask if you’re ready, sighted in, or how much of their anatomy you’d like to be able to shoot at. You had better be able to shoot up to the hand you are being dealt. A powerful, accurate, and well-regulated handgun is a comforting thing to have- and one less variable to have worry about when the balloon goes up.

The GP snub didn’t embarrass itself. This belligerent-looking little sixgun showed promise right from the outset, grouping almost anything under 3″ at 25 yards. The new front sight corrected the elevation perfectly, but the gun was now shooting about 4″ to the left at the aforementioned distance. This wasn’t real bad- but it was not something to be ignored, either. More on that later…

The first set of reloads tried used Winchester 231 powder. This is perhaps the finest powder extant for the .45 auto, and it gave a fair account of itself in the .357. Best accuracy came with Winchester’s 158 grain SJHP- but the Sierra 125 JHP was not far behind. Vertical dispersion between the 125 and 158 grain loads was just under 3″ at 25 yards. This was close enough for me.

The results of my initial efforts at reloading for the GP-100 are listed below. Be advised that they are all maximum loads, and that you should start lower and work your way up, watching for pressure signs as you go. They may react differently in your gun than they did in mine.

Bullet Charge Published Velocity

(10″ barrel)Group for six shots at 25 yardsWin. 158/SJHP6.9 g. W-2311260 fps1 ½”Sierra 125 JHC8.1 g. W-2311460 fps2 “Win. 158/SJHP9.5 g. HS-61375 fps2 5/8″Sierra 125 JHC10.9 g HS-61629 fps2 5/8″

 

 Decent 25 yard “snub-nose” accuracy-

125 grain Sierra load highlighted in yellow;

158 grain load highlighted in blue.

 

There is a common misconception with fixed-sight handguns, that you are stuck with the factory sight regulation- and that you simply must have adjustable sights if you expect to be able to make precise shots on anything smaller than a refrigerator at 50 feet. Another misconception is that the consumer is limited to either sending the gun back to the factory, or enlisting the services of a gunsmith to correct this malady. I have nothing against gunsmiths and I’ll be the first to proclaim that I am not one. I am however an Armorer-level gun mechanic who can solve his own problems.

Windage correction is best accomplished by moving the front sight towards the windage error, as seen from the shooter’s perspective. On this particular gun, the barrel screws into the frame with conventional right-hand threads. This would simply mean turning the barrel just a little more tightly into the frame.

 

Barrel screws in to the right, moving the front sight to the left

(as seen from the rear) in the process.

The sixty-four dollar question was just how much to move it, and how to measure the movement as it was accomplished, to avoid going too far.

Close examination the stripped frame revealed that a baseline measurement could be taken from the left side of the frame, to the left underside of the ejector shroud. This provided two relatively square surfaces from which to obtain the measurements, and a means to determine how far the barrel had been turned once that operation was underway. Several readings determined that .090” was the original offset between these surfaces and after careful consideration of the sight radius and the amount of correction required, an end measurement of .095” was set as a goal. This would result in moving the front sight slightly more than that distance to the left, as its rotational axis is slightly further out from the centerline of the bore.

 

Getting a baseline reading on barrel position, using the frame

and ejector shroud as reference points.

No degree in rocket science is needed to grasp the notion that a magnum revolver’s barrel must be screwed in tight when it leaves the factory. Loads generating nearly 40,000 CUP might otherwise loosen it from the frame, perhaps causing embarrassment for the shooter at an inopportune moment. It would obviously require some carefully-applied torque to get the job done.

Anyone who has ever had a flat tire fixed, understands that impact is one of the most effective means of moving tight, threaded fixtures on a rotational axis. Since Ruger thoughtfully provided me with an ejector shroud built like a battleship fitting, there was a suitable point on that axis for applying some impact. I could spend another hundred words explaining the process, but the photo aptly illustrates what was done.  A short section of 2×4 was used to support the frame, and an oak bench block was used to transfer the hammer blow to the ejector shroud.

 

Setting up for the barrel adjustment.

 

The entire process required about eight good licks with a small ball-peen hammer, stopping to take measurements about four times along the way.

 

Impact-turning of the barrel in the frame.

 

When the barrel had been turned in .005” the gun was re-assembled and another trip to the range was made. The results were gratifying.

Results worth the effort; 10 of 12 shots at 25 yards,

 using both loads, print within 1” of the target’s centerline.

It’s not quite as slick as my little Speed Six was, but it shoots plenty well enough for a woods or defense gun- and I can live with it.

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6 Responses to Dialing-In a Fixed Sight Ruger DA: The Repatriated Ruger GP-100

  1. Hobie says:

    An outstanding article plumb full of useful information.

    I have 2 Speed Sixes, Dad’s 4″ blue and a much later 2-3/4″ stainless gun. I have S&W’s 13s, 19s, 65s and 66s as well and I think the Six series is just as much gun and they sure were less expensive. “Were” is the operative term as we sometimes sell Six series guns for as much as the corresponding S&W guns if we can get them.

    I have officially entered into the phase of my life when I am nostalgic, opinionated, and curmudgeonly but the GP100s are excellent revolvers and I’ve never seen one come back for repairs. What works has a lot of value!

    Keep it up with the good articles.

  2. rjf415 says:

    Sarge–my LGS just got in 3 “brand new” Ruger GP-100′s, fixed sighted, 4″ half-lugged barrel in .357mag. Had one back in the day for 5 years, sold it in 1992 to cover grad-school expenses, been looking for a replacement ever since. I couldn’t believe it when I saw it, thought it was used. As memory serves it was the best “woods walking-deer hunting-house” revolver that I ever owned. Will be shooting it this weekend, thank your for the article on the 3″ GP-100… :)

  3. Ken says:

    I have a Ruger Speed Six in .38 caliber. There is no rear sight. Did it become dislodged or does the gun not come with rear sights? The photo of your gun on the website also does not appear to have a rear sight. Can you advise me on this?
    Thanks,
    Ken

  4. Sarge says:

    The fixed rear sight of Ruger (and many other) revolvers is just a square grove milled down the top of the frame, Ken. There is nothing to become dislodged.

  5. Very good post indeed. I feel very comfortable in your blog. I’m looking for how to subscribe to receive new entries via email or my browser but can not find :( Keep writing as well!

    • Sarge says:

      Thank you for your kind comment. I am not aware of any email notification feature in WordPress-based blogs. Check back in every so often, you might find something else you like.

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