Leading in my GP100

[Bazoo]

I am getting a bit of leading with the gun. It starts in the forcing cone and seems to build if I fire a couple boxes. But it also has a trace of lead in the rifling down the bore. It brushes out with a reasonable amount of effort.

Both of my loads I've tried are 5 grains unique and either the RCBS 38-150-SWC or the Lee358-140-SWC. Both in special brass and with BAC lube. I've tried both ww alloy and a softer alloy, 50/50 ww/Pb I'd guess. Sizing them .358

I slugged the bore which is 5 grooves. Using a soda can shim the best I can figure it's .354. I've re-measured it and really tried to get a good feel and a light measurement. I can feel some change in the resistance when going through the area of the barrel where it threads into the frame. It's not a huge change though.

So I run as tight a fitted patch on a brass jag(didn't have a plastic one) as I could get started down the bore and it didn't get tighter at the threads. Now if I'm not mistaken Doug was suggesting this method with a plastic jag to feel for tightness. Will it not work with a brass jag or is the danger just getting the jag stuck?

I slugged just the muzzle by inserting a brass rod in the bore to tap the slug back out and it was .354 too. Seems small for a 357 bore, don't ya think? Is this common for Rugers? Looking back, I'm going to remeasure this.

I slugged the cylinders they all measure .3575. Yes all this with calipers as I don't have a micrometer.

So my query, Will sizing the bullets over throat diameter cause leading in of itself? Where should I go from here? Straight to having the throats opened up?

Should I buy a selection of pin gages? And if so, which sizes. Minus Z gages right?

Megasupermagnum has suggested I pull a bullet make sure it isn't being swaged down by the case which I will do.

Thanks for your help.

Bazoo

[Neverhome]

I have nothing to offer except to commiserate with you about measuring a slugged 5 groove barrel. Absolute pain. I used the soda can shim too and never felt 100% positive about any measurements I got.
Good luck figuring out your leading!

[Bazoo]

Thanks. It's not horrible leading but it's there. I'm not confident with my shimmed measurements either.

[Cosmic_Charlie]

About the best you can do is size your boolits to fit through the cylinder throats with slight resistance. If the throats or forcing cone is tighter than the bore it will need work.

[BigAlofPa.]

I had that issue with my SW 25-5 5 45 colt. Lubed and coated cast. Jacketed and plated no issues. I was shooting BHN 18 in it. I ordered some BHN 12 coated cast then. They work fine. I have not tried 38 special in my GP 100 yet. That i can run the BHN 18 loaded to 357 mag. Leading is very agravating. I know how you feel.

[Petrol & Powder]

That groove diameter sounds small even with all of the efforts to measure it correctly. I wouldn't put much faith it that number.
I'm with Cosmic Charlie, size your bullets to fit the throats (because that's what size they will be anyway after passing through the throat) and go from there.

I would almost bet you have some thread choke based on your description. I fire lapped a GP-100 once and that steel is HARD. So if you go that route be forewarned that it takes more than a couple of rounds.

I will offer this - I was using BAC lube for most of my handgun bullets and getting some leading with the tame loads. I switched to NRA 50/50 and that made a huge improvement. So, before you start removing metal, I would try a softer lube and bullets sized to the throats.

[Piedmont]

Bazoo, I have nothing to comment on your leading but wanted to suggest something on measuring that barrel. Several years back I was really into milsurp rifles and slugged a pile of them. Some of them were 5 groove and I am confident I was accurate to .001 whereas with even numbers I'm confident to half a thousandth. Take the soft slug that you pounded down the barrel and roll it in your micrometer. Let the jaws kind of float open when the slug catches and doesn't want to go around as you roll it. It seemed pretty simple when I got the hang of it and lacking a "v" block to compare my results to I'm still confident I was getting very close to reality. This only gives you a groove measurement.

[Bazoo]

I appreciate the replies.

Well BAC lube for whatever reason hasn't impressed me. I can't quite put a finger on it. The lee bullet leads more. Maybe it has something to do with the amount of lube that cavernous RCBS lube groove carries.

I do have some 50/50 that someone made which I got out of the swap box. I will see about switching lubes and see what improvement I get.

[C.F.Plinker]

Try taking one of the boolits you slugged the barrel with and pass it through each of the cylinder throats. Since it is now groove diameter it should pass through the throats easily. If it doesn't then that throat could be sizing it down to less than the groove diameter.

Sometimes you can measure the diameter of a 5 groove boolit by catching the edge of one land with one of the anvils of the micrometer and the edge of a different land with the other anvil. It helps if you pad the frame of the micrometer with a piece of leather and use a vise to hold the micrometer so you can use both hands to manipulate the boolit and adjust the micrometer thimble.

[Petrol & Powder]

I appreciate the replies.

Well BAC lube for whatever reason hasn't impressed me. I can't quite put a finger on it. The lee bullet leads more. Maybe it has something to do with the amount of lube that cavernous RCBS lube groove carries.

I do have some 50/50 that someone made which I got out of the swap box. I will see about switching lubes and see what improvement I get.

As much as I like BAC for some magnum loads (and it makes the bullets easier to handle before seating) it is just a little too hard for standard velocity. I tried to have "one lube for all handgun cartridges" and BAC was almost it. I really resisted going back to NRA 50/50 for standard loads but when I did, it was the right call.

BAC has its place and I still keep a little on hand for the few occasions I need it. For the vast majority of my loading, 50/50 has proven to be better.

[dannyd]

I use Carnauba Red,Blue and Commercial 160 in five GP100's with no problems. Mid range target loads. 125 and 158 grain bullets.

[nannyhammer]

I use Carnauba Red and size to .359 in my GP100, no issues to date.

[Petrol & Powder]

.359" seems a bit larger than Ruger GP throats tend to run. Can you even push a .359" bullet through the throats?

[megasupermagnum]

.359" seems a bit larger than Ruger GP throats tend to run. Can you even push a .359" bullet through the throats?

It appears he is sizing to .358", which is normal to me. I would actually be sizing to .357" myself, but being slightly oversize should not cause any problems except possibly not chambering fully on a bullet with more front nose.

[dannyd]

It appears he is sizing to .358", which is normal to me. I would actually be sizing to .357" myself, but being slightly oversize should not cause any problems except possibly not chambering fully on a bullet with more front nose.

I was using.358 for about 25 years and then switched to .359 groups got better.

[ABJ]

My Ruger double actions have been problems as well. sp-101 and gp-100 both stainless. Gas check bullets helped but I finally found a gunsmith that would clean up the rough forcing cones which was the major source of the leading in mine.
That steel is beyond hard, most pistol smiths charge extra if they will do it at all. Take a good look at the forcing cone first.
Tony

[Petrol & Powder]

I use Carnauba Red and size to .359 in my GP100, no issues to date.


This is the post I was referring to and he's using .359"

[megasupermagnum]

I was using.358 for about 25 years and then switched to .359 groups got better.

I've found that many, if not most 38 caliber revolvers will take a .359" bullet. My own GP100 takes a .358", although my other loads (some don't fit) with a .359" shoot just as well. Being as Bazoo says his throats are .3575", a bullet sized .357" would be ideal, although no problem with .358" if they chamber.

[Bazoo]

I appreciate the help folks. My .358 bullets do chamber okay in both 38 and 357 brass. The bullet will not pass through my throats however. The bullet I slug drops through the throats with room to spare.

I am going to first try changing lube. And I have a line on a .357 sizer.

[243winxb]

Add linotype for a better buller.

[gwpercle]

My Ruger Blackhawk 38/357 prefers cast to be sized .357" . a 150 grain boolit, 50/50 COWW - soft lead, with soft Lithium-beeswax lube over 5.2 grains Unique ( 38+P load) shows no leading.
Give the .357 size a try and make sure your lube is a good one . I believe soft lubes work better than hard lubes in these applications .
Gary

[nannyhammer]

This is the post I was referring to and he's using .359"

Have tried both .358 and .359 and the 359's shot best. I also run 50/50 alloy so maybe it being a little softer is why I have no issues with the size.

[megasupermagnum]

I never did like BAC either, although it seemed plenty soft to me. I didn't like it because it didn't seem up to the task for high pressure handguns and rifles. 50/50 lube is such a crumbly mess, I'd hate to resort to that. Being as it is essentially a 38 special +P load, I can't imagine there is a huge demand on the lube, but who knows. It is easy to try others. If you have some Alox lube, you can try tumbling the bullets you already have lubed.

[megasupermagnum]

Have tried both .358 and .359 and the 359's shot best. I also run 50/50 alloy so maybe it being a little softer is why I have no issues with the size.

It depends on your throat diameter, and bullet design. If your front band is long enough to extend into the throat, and your throats are .358", then your .359" bullets wouldn't fully seat without force. Chances are your throats are that big.

[Bazoo]

I bet that being swaged down going through the throats puts a demand on the lube that we don't understand. Or at least I cannot understand at present. Lube does funny things.

The fact that I have less leading with the RCBS bullet vs the lee I'm inclined to think it's a lube issue. My guess is the RCBS uses twice the lube judging by the use of my Lyman 450s handle. So my first step will be changing lubes.

That 50/50 is mighty soft. But I have taken to storing my lubed bullets in foam cartridge trays to prevent lube from getting on the noses.

[megasupermagnum]

The oversized bullets aren't hurting anything. You're talking about .0005". It's likely you can push those bullets through your throats with only minor effort. Did you ever pull a loaded bullet and measure it? Someone had mentioned thread constriction again. If you did have a constriction, the first 1" of the barrel would be spotless.

[Bazoo]

I disassembled a loaded round. The bullet was mystery alloy but softer than ww substantially. It still .358. Same batch of winchester brass was used through all.

It will not push through a cylinder throat with all the thumb pressure I can give though it barely will start.

Slightly off subject, I've had ongoing leading issues with my super blackhawk. After a trip to Ruger it's experiencing similar leading as the GP100. BAC lube there too. Be an interesting test if a change in lube cures both.

[Petrol & Powder]

The throat is nothing more than the last sizing die the bullet will pass through before it reaches the barrel.

If the throat is .357" and the bullet is at least that diameter, the bullet will be .357" after it leaves the cylinder, even if it started as .359"

Just because a cartridge with a .359" diameter bullet will chamber, doesn't necessarily mean that bullet will still be .359" when it exits the cylinder.

[Bazoo]

I know those things petrol, But I'm wondering if the bullet being swaged down in the throats will contribute to my leading issue. Maybe it's squishing some (too much) lube out of the grooves? I do have some lube in the end of the chambers.

When the bullet is swaged, the grooves are narrowed and the bullet elongated as the driving bands are compressed. Lube, like liquid won't compress, so where does it go? I'm thinking that it might be making enough of a difference.

[Sig]

I used this method for measuring my GP100 slug

[Petrol & Powder]

Sig, I agree, If you have a V-block, that's your best bet.

[Wheelguns 1961]

Are you getting a lube star on your muzzle?

[reddog81]

I've tried .358 and .359 bullets in my GP100 and others. My GP100 has .357 throats and I have never been able to tell any difference between .358 or .359 diameter bullets. Either way the bullet leaves the throat .357. I don't think it makes any difference if it's the throat or the sizing dies is sizing the bullet down that final .001/.002. The charge hole tapers from the brass diameter to .357 and I've never had a problem using .359 bullets.

If there's a bore constriction at .354 or .355ish I don't think any small variation of sizing will make any difference. Taking care of the bore restriction will be what fixes the leading problem.

[megasupermagnum]

No, the sizing down in the throats does not cause any problems. Lube pumping is what you describe, and is one method the lube gets around the bullet when fired, which is a good thing. The rifling displaces much more lead and lube than the .0005" or so your throat is.

While I'm sure it is possible, my own experience with a bore constriction left the first part of the barrel sparking clean, and then abruptly turned to a sewer pipe right after the frame. If you can't feel anything with a tight cleaning patch, and you are getting even fouling from start to end of the barrel, I wouldn't think you have any notable constriction.

A different lube is worth a shot. A lot of people use BAC with no issues, but I was not one of them. I too got leading, which I blamed on it being an improper lube for the very high pressures I was running. If you don't have any other lube, White Label Lubes sells a sample pack of everything they make.

[Bazoo]

Sig, thanks but I can't do math like that.

I am getting a lube star.

I can't feel anything with a tight patch but I do feel a constriction when I push a slug through.

[Bazoo]

I have made and fired 50 rounds with the changes of 50/50 lube and .357 diameter bullets as opposed to BAC lube and .358 diameter. Leading was reduced but still present in the bore. I'd say it was reduced by 50%. Forgot to mention, I had leading in the cylinder throats. I don't understand this.

Also the .357 bullets will push through my cylinder throats, where the .358 would not.

[Cosmic_Charlie]

You may want to try powder coated boolits at this point. Size them to .357 after coating. If your problem is a roughly cut forcing cone this may not work either. Maybe use a dentist mirror to get a good look at it. I had that problem with a 4" SP101 and I sold the gun to a buddy who shoots only jwords.

[Bazoo]

I fire lapped it, 36 rounds 220 grit and 12 320 grit.

I made a box of magnums with W296 powder, RCBS 38-150-SWC WW+Sn sized .357, 50/50 lube. Fired them and no leading in the barrel. Only very minor leading at the forcing cone. Very much improved.

Switched to some specials I had with BAC lube and leading began in the rifling after only 6 shots.

[Cosmic_Charlie]

I fire lapped it, 6 36 rounds 220 grit and 12 320 grit.

I made a box of magnums with W296 powder, RCBS 38-150-SWC WW+Sn sized .357, 50/50 lube. Fired them and no leading in the barrel. Only very minor leading at the forcing cone. Very much improved.

Switched to some specials I had with BAC lube and leading began in the rifling after only 6 shots.

Feels good hugh? Nothing more frustrating than a revolver that leads up.

[Bazoo]

Yessir, real good. I measured some of the groups I shot yesterday, at 20 yards, 1 1/2". I was having a bad day yesterday for my eyes and hands. I was able to cloverleaf some of them but not a whole 5 or 6.

[robertbank]

I purchased my GP-100 .357 several years ago and have used it for IDPA Revolver division using my cast bullets in the main. Mu cylinders were so tight 3 would not let a .356 bullet pass through them and three would not let a .357 bullet through. I just had all six reamed out to .358. I had my forcing cone cut to 11 degrees. Since doing this I have yet to have any leading shooting my RCBS 158 gr RN bullets sized .358 or any other lead bullet iteration sized .358.

In the process of dealing with my new GP-100 10MM. It has leading just past the forcing cone. I intend to shoot lead through it so it will spend time with my gunsmith to have the cylinders checked out and teh forcing cone cut to 11 degrees.

Take Care

I know all guns can be different but if you are looking for best accuracy and no leading I think the quick fix is what I described above. I doubt your cylinders are greater than .358 at the throat.

[Bazoo]

I have a new report. I fire lapped probably 40 rounds (can’t recall without my notes). Upon doing this I could still barely feel a resistance when slugging. Leading was not improved with specials but was somewhat improved with magnums.

I recut the forcing cone to 11 degrees. I fired 6 of the previous 38 specials and leading was not improved. Without cleaning I fired 6 357 magnums and the previous leading was gone. It shoots without leading with full power 357 magnums.

The load was
38-150-SWC WW+Sn alloy sized .357
50/50 lube
W296 16.8 grains
CCI 550

I’m still thinking it through and experimenting slowly. I am going to slug again as it’s been so long I can’t remember. I may firelap more. I think my issue is cured by obturation, so I’m going to try some softer bullets for 38 loads. I probably will try some special level loads in 357 brass just to rule that out.

I also tried bullseye for 38 special loads with the same results as unique; severe leading in the forcing cone and rifling beginning.

Another question that hasn’t been answered, will bullets larger than throat diameter cause leading in of itself.

Thanks for everyone’s suggestions and ideas.

[robertbank]

How about we tale a deep breath. First stop lapping your barrel not sure why you are doing it but stop.

To answer your question about cylinder throats. It has been my experience Ruger cylinder throats are for the GP-100 are spot on at .358 OR more likely less than .358. Measure each one. If they are smaller than .358 have a gunsmith ream them out to .358. If any or all of them are smaller than .358 the bullets will be sized down by the cylinder throats to what ever diameter the individual throat is. You are not going to size your bullets to individual cylinders hence my suggestion to have them all cut to .358.

Size all your bullets.358. I am assuming your barrel is .357 in diameter. You can slug it and measure the slug. Use a sift lead slug. Check to see if your sizing die is sizing your bullets /358/

If the diameter of the barrel measures .357 you then should size your bullets .358. I have had dies that were not what they said they were ir at least not sizing my bullets as indicated on the die/

Your forcing cone you say is now cut to 11 degrees.

Observation: IF you had leading in the grooves of your gun you will not shoot it out by shooting lead .357 bullets. I have never been able to do is with plated or FMJ bullets either.

Backk to your GP-100. I don't water quench my 38 spl lead bullets cast from WW alloy. They shoot well in my gun. I do get occasionally some leading in the first 1/8th inch of the rifling. I credit that to slightly undersized bullets. Ignoring those few occasions I do not incur leading with my GP-100 using ww alloy in 38spl. For .357 I do try to water quench them. Again I do not get any leading in the rifling. If I shoot a lot IU do get lead build up outside the forcing cone. That lead build up can be blown away with some stiff plated/FMJ .357 mag rounds.

Assuming you do not have a barrel that looks like a railway track row of sleepers if your cylinders are .358m your barrel .357 and the forcing cone is cut to 11 degrees you should not and will not get leading in your gun using WW alloy air dried bullets in 38spl or water quenched bullets in your .357Mag.

Personally I think you are over thinking this issue. TRake a deep breath. Start with your cylinders. You have already cut your forcing cone. Just for the hell of it measure your bullets you are using out of the mold. I have a 44mag Lyman mold that casts ww alloy bullets .428 when they should be.431. I could not figure out why my Rossi 44 mag lever gun was shooting all over the park. Undersized bullets, leading and one ticked off caster. ie me.

Different powders will not have any effect on leading, assuming your loads are within reason/

Tale Care

Bob

[RedHawk357Mag]

Just spitballing... maybe change up the dies your using. 357 doesn't lead, 38 Special does. If you don't have a buddies dies to borrow, maybe load up a couple cylinders worth of 38s with just the belling of cartridge removed. A Redding Profile crimp die and I went round and round with a similar issue a few years ago. It somehow stacked the tolerance against me to cause leading no matter how loose a crimp I attempted to utilize. Bought enough second hand dies cheap enough to determine they aren't all the same; minor difference can stack tolerance against you and befuddle you. Good luck finding a solution. Maybe segregate headstamps of 38 brass to reduce variance while pinpointing the cause. Case length of your test brass within .003" till you pinpoint what is causing the issue. Check to see if crude rings forward of the throat are maybe reducing bullet diameter. Maybe use a nonsense alloy certified by Rotometal to see if alloy is gotten out of whack. Have purchased RAW bullets from Missouri Bullets to chase down alloy shenanigans and sized lubed or coated them. Wish primers were more plentiful so you didn't have that aspect to consider while figuring the problem out. Best of luck in chasing it down.

Sent from my SM-G986U using Tapatalk

[Bazoo]

Robert, thanks for the suggestions.

I fire lapped it because I felt a constriction when slugging. I don’t have a way to accurately measure the bullet as it’s 5 grooves. However, a slugged bullet goes through my throats easily.

My throats measured .3575 or thereabouts but measured with my calipers. I’m sizing to .357.

My bullets are .3585/.359 out of the mould and my sizing die is right on .357. My expander plug is long enough and .356 diameter and a pulled bullet isn’t swaged down.

I don’t see how opening up the throats to .358 will do anything given these parameters.

I don’t water drop.

I crimp both 38 special and 357 magnum. RCBS dies. I don’t see how a roll crimp could cause an issue but I’ll think on it.

I use same headstamped brass trimmed for consistency. Winchester brass in this case.

I don’t have commercial bullets, either cast or jacketed, nor desire to use them for 38special/357 magnum.

I will reslug both bore and cylinder. And I’ll try the shim measuring thing on my slug again since I have a mic now. Which btw confirms my calipers and my feel for them are spot on.

[robertbank]

1. With your revolver you can be certain your barrel is .357 in diameter. The proper size for your cast bullets sized is .358[B] not .357. .358 sized bullets will ensure a tight fit in the barrel and prevent gas cutting, the primary cause for leading. lead bullets sized .357 are to small in diameter and will lead your barrel as they will allow gas to blow buy your barrel.

2. Size your bullets .358 with a .358 sizing die. Take those sized bullets and see if they pass through your cylinders. If they do your leading problems should end. At the very least you will eliminate one of the major cause of leading and poor accuracy ie under sized bullets.

3. If your [B]bullets fail to drop/push through your cylinders when sized .358 then have them reamed out to .358. If you don't ream them out you will be shooting bullets sized down to what ever diameter each cylinder throat is. I don't think crimping your bullets is going to have the effect of reducing bullet size as they leave the case. Use your bullets to determine throat size. Use bullets sized .358.

4. I'll assume you have had your cylinder throats all reamed to .358. The reaming will not affect plated or FMJ commercial bullets. Accuracy using those type of bullets will not be affected.

5. I generally do not roll crimp my 38spl cartridges. I say generally. When I do, the crimp is not excessive. I am not one to hotrod .38spl. If I want to build what you would describe as a hunting/slef defense round I water quench my bullets as they fall from the mold and use them in .357 Mag cases. I then use a a more aggressive roll crimp.

6. Lastly, load a cartridge with a measured bullet sized .358 as you normally would then pull the bullet and measure it. The bullet should not have swaged down .001". If they do harden the bullets up a bit. This exercise is just a way of eliminating any question that your bullets are smaller .358 as they enter your barrel. The barrel will size the bullets down to it's diameter but in so doing provide a tight seal to prevent gasses from getting by the bullet and causing gas cutting and the inevitable leading of your barrel. The OAL of your case is important as to wide a difference can affect the quality of your crimp. For what I use my revolvers for eg action shooting sports and bear/cougar protection while in the bush I don't spend a lot of attention in case OAL I just shoot to much to take the time to concern myself about OAL of my cases. They will all shorten over time if they have not cracked before get a chane to shorten where it would be a concern.

I shoot IDPA, steel and some IPSC. Off a bench and over my Chrony I have never noticed a significant difference in accuracy or bullet velocity using mixed brass. I am working with 76 year old eyes now. Fine accuracy beyond 20 yards with a handgun using iron sights is not now happening. I am not a candidate for bullseye shooting anymore. Not that I ever was. LOL The above two posts should cure any leading problems you have.

Take Care

Bob
ps If after all of the above steps have been taken and you still are getting small amounts of leading in your gun in the first 1/16th to 1/i18th of the barrel you might be experiencing barrel constriction. At that point you might choose to live with the slight annoyance or attempt to remove the possible constriction in the barrel. I'll pass you off to some else who has some experience with barrel constriction. I should ask is your GP-100 the regular model or the Match Champion. If the latter your barrel might be a sleeve barrel. If you have a sleeve barrel you won't have any barrel constriction. My 10MM MC has a sleeve barrel, I am not certain the 9MM MC does.