View Full Version : !.5" vs. 2.25" 20 yd. groups. Identical Gp100's.

October 17, 2006, 04:56 PM
Working up +P 38 spcl loads for two identical SS, 4", GP100's to take to Thunder Ranch. Settled on a 125 gr, JFP, Bullseye load and made up lots of practice loads. I was pleased as punch with my Ruger's 5 shot, 2.5" groups when my daughter asked me to check hers after she set up the rear sight. Same load, same day, consistent 1.5", five shot groups! Needless to say I tried to mix up the guns but it didn't work. She smirked, walked away with that shooter, and checked S/N's after every shooting session. I've tried to check cylinder-barrel alignment under strong light, cylinder and chamber mouth dimensions for an explanation. The alignment thing is too dependent on eyeball position and the biggest dimensional variance is .0005". Any tips on what I can measure and what I can do to improve my Ruger's accuracy ( or precision for the ballistic nit pickers out there )?

October 17, 2006, 07:00 PM
It's probably simply manufacturer's normal variations between guns.

This is common. You'll have two identical revolvers, on which everything gages to specification.

One shoots better than the other, and you can find no reason for it.
Your next step is to start trying different brands/types of ammo to find one the "bad" Ruger "likes".

This too is normal. You'll have two identical revolvers one of which shoots astounding groups with a specific ammo, and one just won't shoot.
Play around with ammo, and the "bad" gun out-shoots the "good" gun.

October 19, 2006, 02:49 PM
Yeah DafarisWheel, that's what we were doing for a couple of months, trying lots of bullet/powder combinations. That's how we got to the load we were using, it was the hands down best in my gun. I've since tried more combinations with no improvement. I wouldn't give it a second thought if I didn't know it could be better. After about 20,000 rounds the barrel is polished bright, .002" cylinder gap. No discernible cylinder play. Straining my eyeballs on both guns it seems to me that maybe one has a bit less barrel-cylinder misalignment. The good (excellent is more like it) GP100 looks very close to my pride and joy, tack driving K-38. Does anyone know: (1) Does Ruger simultaneously bore GP100 barrels and cylinders? (2) How to measure cylinder-barrel alignment, maybe a tool from Brownells? Don't know what the heck I could do about it anyway short of a new cylinder bored with the barrel. Way more than I want to get into. ( 2) The dead on correct cylinder dimensions for a .357, GP100? Are they dependant on bore dimensions? (3) Brownells has lot of cylinder reamers. Any real 'Smith out there want to comment on cylinder ( and maybe forcing cone ) dimensions vs accuracy? How about a recommendation on a really good gunsmithing book that talks to some of this stuff.
I know, I should just try to buy my daughter's GP100 (for a profit I'm sure) and stop wasting time on this, but I'm an engineer and everyone knows we are all obsessive/compulsive.
Bye the bye, wouldn't it be a hoot to spend a few days at a Wilson, Kimber, Bowen, Reeder, Hamilton, Baer, C&S, Daly, Freedom, shop watching them do their work?

Jim Watson
October 19, 2006, 03:47 PM
I am not a gunsmith or manufacturer but it is my perception that...

1. Ruger (or any other production line revolver maker) does not "line bore" cylinders through the barrel or the barrel opening in the frame. Pay Freedom Arms or a big name custom shop for that.

2. Brownells sells "range rods" to gauge barrel-cylinder alignment. I think they have "duty" and "target" grades. But what will you do with the information? If all chambers are off by the same amount, it might could be corrected in the timing. If one or a few are off, you are out of luck, and would require a new cylinder... or a new gun.

2nd 2. I have an old NRA manual with chamber drawings. Dependent on bore dimensions? Not really.

3. Revolver pros write that the most important dimension in a revolver is the cylinder throat. It should be at or near bullet diameter and at or just over barrel groove diameter.

Let your daughter feel like she is a step ahead of old Dad.

October 20, 2006, 02:59 AM
Jim, your a good man. I'm sure she would be tickled if I could catch up but not by going after her prize shooter. To tell you the truth, one of the highlights of the trip was to hear a compliment or two on her shooting from three talented San Jose LEO's, especially one young fellow that consistently centered his Beretta 92F rounds into about a 3"" circle on a lateral start-stop fast mover. Mild 9mm vs our +P 38 spcl, that's still awfully good shooting. Ultimately though his Beretta ended up a basket case on a picnic bench, reinforcing my firm resolve to never, never trust my life to a semi-auto. Every firing line failure amongst the twenty student in our Thunder Ranch class during our five days was a semi-auto. Not one was amongst the three wheelguns, all GP100's.

Harry Bonar
October 22, 2006, 10:29 AM
Dear Sir:
Bbl. cylinder gap, bbl. crown, cylinder hole exit diameter - a whole plethora of things could cause this variation. It's like gun bbls for rifles - cut off of the same steel bar no two bbls. are identical - no two guns are identical.
As to semi-autos: A properly tuned and built one is probably the most suitable gun for combat extant! A revolver can be tied up by short cycling the trigger in D.A. mode in a gunfight. Some revolvers will jam when going up-stairs due to the gun alignment - a semi-auto PROPERLY TUNED (not out of the box new) is as reliable as any revolver although I have revolvers and am very fond of them.
Harry B.

October 24, 2006, 12:09 AM
Sorry Harry but it just ain't so. I own some of the best semi-autos money can buy, Sigs, HK, Para Ord, a new XD, Kimber, and even an old, old, .32 Pocket Pistol. All but the old Colt have been tuned ( ramps, chamber mouths, breech faces polished, fitted barrel bushings, extractors tuned, the whole nine yards ) by such as Cylinder and Slide, Kings, etc., and the best mags money can buy. I love shooting them and I do that a lot. Every one of them has at one time or another failed to feed with factory ball ammo, the bullet shape of choice for semi-autos. I have never had or seen a wheel gun malfunction, break down, fail to fire in training, informal range sessions, desert plinking sessions, but at almost every session at the outdoor ranges I use (the San Gabriel range is going to close soon, a real sorry thing ) I see folks trying to clear their semi-autos ( almost exclusively 1911's).
Getting a machine to consistently strip rounds held in a magazine below the barrel axis, with spring tension changing drastically from first round to last, change the bullet direction, bounce it off a ramp, slide it up between a breech face and extractor, and enter an off an off axis ( from the plane of the mag) chamber, go into battery, and have the extractor ( If I read one more gun rag article about 45's chambering on the case mouth I'm going to puke) hold the round securely enough for the firing pin to whack the primer hard enough to go bang. I'm amazed that that Browning, et al, made these things work as well as they do. Short cycling a revolver is not a hardware problem, it's an operator problem. I've never done it and don't know anyone that has even under stressful, life threatening situations. I have no idea what your talking about with uphill or upstairs problems. Revolvers don't give a rat's ---- about bullet shape, if they are upside down or sideways, or limp wristed. They just go bang every time you pull the trigger, Rugers, S&W's, Colts, doesn't matter, even when you don't clean them for 7200 rounds ( Not cool but I did it). Finally, if I thought there was any chance I would need more than six rounds, I would be carrying my P-14 or my XD and taking my chances.

T. O'Heir
October 24, 2006, 01:08 AM
Misfire, it's perfectly normal for two firearms to shoot the same ammo differently. It's just as normal for one not to get any better even with massive load development. Mass produced machines are like that. And you know it's not the larger group your's shoots that bothers you. It's the smirk. You still got to go shooting with your daughter.
By the way, failures with semi's is about maintenance, the mags and the ammo. I love my GP, but I wouldn't want to fight with it.

October 25, 2006, 11:34 PM
You are absolutely right T.O. We did a lot of shooting together until she moved to Nevada. That brings up an interesting point. Having taken a fair amount of handgun training, I feel I can provide at least a modicum of help to new shooters. My observation is that a great deal of the time, women seem to progress faster and ultimately shoot better than men. My daughter is one of those. Smaller groups, faster reloads, faster and more controlled lateral and backward movement, better situational awareness, than me and the half dozen or so folks I could see on the firing line at Thunder Ranch. ( All except for one young San Jose LEO. He was either a natural born pistoleer or he practiced an awful lot.) This was only about six months after she fired a handgun for the first time. I was busting my shirt buttons when Clint Smith and Dennis Tueller paid notice to her shooting.

October 29, 2006, 12:29 PM
Suggest different ammo in the 'crappy' one, or send gun to someone here along with enormous wads of money:


Me? I just keep trying to make a better load....

October 31, 2006, 12:19 AM
Alas Weshoot2, I think mayhaps I have done the the durn thing in. The old girl has about 80,000 rounds now, most of them full house .357's, with jacketed bullets. Hard to tell but I don't think cylinder play or timing has suffered, but groups are starting to spread. Time for a checkup, maybe with Ruger?