GP100 357 mag question on using hard cast lead bullets occasionally

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oldcrab

Bearcat
Joined
Nov 23, 2022
Messages
28
Location
Mukilteo, WA
Happy holiday-weekend, folks!

I have a stainless 6" barrel GP100 357 magnum that is a 2013 vintage.
I would like to occasionally shoot some hard cast bullets in very moderate quantities in the gun, but don't want to hurt it.
Here's what I know about my revolver:
- After finding a couple jacketed bullets that have an exact diameter of .357, I've verified that they will slide through all six chamber throats without putting any "helping pressure" on them. (just barely, so I'm estimating the cylinder throats are somewhere between .375 and .3755)
- I have a couple hard cast lead bullets that are .358 (using a micrometer), and they will NOT slide through the chamber throats... so they are somewhere between .0005 and .001 oversize to the throats.
- I don't know the forcing cone angle, but have seen that many think it is "probably" 5-degrees.
- The gun shoots jacketed bullets very accurately, with no fouling whatsoever.

Do you think I could load up some hard cast at moderate speeds and give it a whirl and see what the leading looks like?
Or, should I forget about testing it with hard cast without reaming the throats to .358?
Or ?????

Thanks much for your thoughts.
 

dannyd

Blackhawk
Joined
Aug 10, 2016
Messages
777
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Jacksonville, Florida
My GP100's can do this all the time with cast bullets and I have one that's north of 30,000 rounds. So use cast don't know about the Hard Cast mine run 12 and 14 bn, but I have run them up 24 bn. I definitely would not over think it.

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Joined
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Oregon City, Oregon
For years I shot mostly hard cast bullets in my .357 and .44 revolvers. They shot well, with no adverse effects on my barrels.

Ya just gotta watch for signs... Check to see if you're leading. Within safe limits, ya might have to step up the charge a little bit to ensure obturation.

And as with many other things, not every gun is the same. A hard cast bullet may work well in one gun, but not in another.








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joecrab

Bearcat
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Mar 25, 2022
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mi.
Shooting cast bullets will not hurt the gun at all. Actually it is easier on the gun than jacketed bullets are. When shooting cast bullets, it is important that the bullets be sized larger than the throats in the cylinder. With .357 bullets plus .001" over throat diameter will give good results unless the groove diameter is too large. So, what it comes down to is this; Slug the bore to determine groove diameter. If necessary ream the throats so that they are .001-.0015 larger than groove diameter, then size your bullets .0005" to .001" over throat diameter and you should have no leading problems.
 

contender

Ruger Guru
Joined
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Lake Lure NC USA
"GP100 357 mag question on using hard cast lead bullets occasionally"

Only occasionally? Heck why not always?

Seriously,,, lead bullets will not hurt your gun at all. As for leading,, there are several potential reasons a lead bullet MIGHT lead up a barrel.
(1) Too soft a bullet.
(2) Bullet too hard.
(3) Wrong size bullets.
(4) Velocity not matching the alloy.
(5) Rough barrel.
(6) Bevel bases vs. flat bases.

Now,, trying to compare a jacketed bullet & a cast bullet is like comparing apples & oranges. NOT the correct comparison.

Using lead bullets is older than using jacketed bullets by a few centuries. You can do it WITHOUT hurting the gun or anything.

In general,, it sounds like you chambers & throats are just fine,, and you should be able to load & shoot those bullets w/o issues. If using a hard cast bullet I'd look for a velocity range of 1000-1100 fps to start with.

That's the short answer to your questions.
Now,, using cast bullets is a venture into a different realm of shooting. Decades ago,, I tried casting, then lubing & shooting bullets. I had issues.
I didn't properly size my bullets to match my bore.
I didn't slug my barrel.
I didn't throat check my gun.
I didn't use the proper alloy with the velocity I tried.
I didn't have a mentor.
I didn't have the internet.
I didn't know what I was doing because I was too young & dumb to study things properly.

Nowadays,, I shoot a LOT more cast bullets than jacketed by far. I also know how to mix alloy's. I know how to slug my bore. I have pin gauges to check throats. I cast, powder coat & size properly my bullets. And I get excellent results. I have a .45 Colt SA revolver,, a kinda rare El Dorado from Chimney Rock that goes bear hunting with me. It's loaded with my cast, PCed, and excellent Miha designed bullets weighing 280 grns. I also carry it for deer using the same bullet, in a Penta hollowpoint weighing about 265 grns.
My point to all this is you can easily shoot cast in your gun. But if you get leading,, you'll need to find out WHY you got leading. It can be eliminated.

So, try it & let us know how it does in your gun!
 

noahmercy

Single-Sixer
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Jun 13, 2015
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Location
Sheridan, WY
I have a 6" GP with probably close to 50,000 rounds through it, and only a couple hundred of those have been jacketed. Seriously. Weekly PPC matches plus practice for several years really racks up the round count!

In all honesty, the only time it has leaded was using commercial hard cast bevel-base bullets with "crayon" lube. My hand cast RNFPs are fairly soft, have a flat base, and wear soft lube. I've run them a little undersized or oversized, and they don't lead even at magnum velocities. My rule of thumb is that I should be able to easily groove the bullet with a fingernail, and I have found some commercial bullets that claim to be "hard" but meet my standards. The only issue is that if they are bevel-based, they still tend to leave some deposits that I don't get with flat base designs.

Caveat: I shoot 160-180 grain bullets, and I can't vouch for lighter slugs.

Desperado Bullets and Rimrock bullets both offer softer alloy bullets for those who don't cast their own, and have a great reputation for quality.
 

contender

Ruger Guru
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I'll add a bit more.

BTW; "Welcome to the Forum!"

Now,, noahmercy has given some added info to expound upon what I was talking about. Many commercial bullets are often too hard, have that "crayon" lube,, (it's hard lube, and doesn't do the job properly for many,) and has the bevel bases.

I wanted to add a little more info. I failed to mention you can learn a LOT,, and I mean a LOT of excellent information on casting bullets,, how to slug, size & all over on the "cast boolits" forum. There you can find answers to almost any question you might have.
 

the_leper_colony

Single-Sixer
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Mar 5, 2015
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474
Location
the Great State of Wide-open (WY)
...Do you think I could load up some hard cast at moderate speeds and give it a whirl and see what the leading looks like?...

BECAUSE you can get barrel leading for any number of reasons (lead too hard or soft, velocity too high or low, etc., etc.), AND because nobody starts out as an expert, it's probably important to remember that you CAN clean up a leaded barrel.

A while back, I loaded up some .40 S&W target/plinking ammo, using some low cost lead bullets of unknown origin (found on GunBroker). I tried them in four different handguns (Beretta, Kel-Tec, Ruger, Taurus): the reloads functioned great in all four, and were accurate enough for my uses - but I had varying degrees of barrel leading. Kind of funny: I had figured the least expensive barrel might have some leading, but thought the chrome-lined Beretta barrel would be just fine. In fact, it was just the opposite: the Kel-Tec .40 barrel was as clean as a whistle, the Ruger & Taurus barrels showed just a touch of leading, and the Beretta barrel was the worst, although still not bad. (Guess that shows how unpredictable it can be, if you have any unknowns!)

I had read about using pure copper (NOT copper-plated steel) Chore Boy scrubby pad material wrapped around a brush for removing barrel lead, and tried that approach. I couldn't find any locally, so the missus ordered a couple of boxes from Amazon. I checked with a magnet to verify the pads weren't copper-plated steel, cut off a piece and wrapped it around an old 35 caliber brush, and scrubbed the barrels. Worked like a charm (the Beretta barrel looks like a mirror)!

I've also read that you can remove lead from a barrel using a mix of vinegar and hydrogen peroxide, but that is reportedly ONLY SAFE WITH STAINLESS STEEL BARRELS, because the vinegar is acidic and will attack traditional barrel steels.

As always, IMHO, FWIW, YMMV, etc., etc.
:)
 

Johnnu2

Buckeye
Joined
Jun 26, 2003
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NYS
I hate to say this, but I shoot almost anything that I can get cheaply enough.... don't pay any attention to hardness and very little attention to size (as long as they are within reason i.e. no 45's in a 357). Been many years and I haven't blown myself up. YUP get lots of leading sometimes and I scrub the crap outta the barrel(s) without much concern about accuracy. I figure, if my single actions can still hit a paint can at 50 yards, that is more than good enough for me. If you are an accuracy nut, please IGNORE THIS POST.
I do realized that this is just the opinion of someone who has tried not to exceed mediocrity his whole life. Pls. forgive me, I don't mean to sound 'flippant'.

J.
 

dannyd

Blackhawk
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Messages
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Jacksonville, Florida
If you purchase your bullets try these from Missouri bullets. You will need to chamfer the inside of the case neck because of the Hi-Tek coating but they load and shoot great.

 

Durango Dave

Bearcat
Joined
Jul 11, 2017
Messages
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When shooting cast bullets, it is important that the bullets be sized larger than the throats in the cylinder.
Is this a typo? I thought the bullets should fit through the cylinder with no more than finger pressure.
EDIT: I now see what you are saying. The bullets are .0005" over throat diameter
 
Last edited:

Bad Barlow

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Apr 3, 2022
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391
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Norcal
Shooting cast bullets will not hurt the gun at all. Actually it is easier on the gun than jacketed bullets are. When shooting cast bullets, it is important that the bullets be sized larger than the throats in the cylinder. With .357 bullets plus .001" over throat diameter will give good results unless the groove diameter is too large. So, what it comes down to is this; Slug the bore to determine groove diameter. If necessary ream the throats so that they are .001-.0015 larger than groove diameter, then size your bullets .0005" to .001" over throat diameter and you should have no leading problems.

If you purchase your bullets try these from Missouri bullets. You will need to chamfer the inside of the case neck because of the Hi-Tek coating but they load and shoot great.

Several outfits are selling excellent Hi-Tek coated bullets,and they are all I use nowadays. I've been reloading and shooting for 50+ years,and I'm slow to accept "new fangled" things, but Hi Tek has made me a believer.
It won't compensate for the common mistakes, but given correct procedures, they can virtually eliminate leading that would occur with traditional lubes.
 

xtratoy

Buckeye
Joined
Jun 15, 2006
Messages
1,372
Location
Vancouver WA USA
Happy holiday-weekend,
- After finding a couple jacketed bullets that have an exact diameter of .357, I've verified that they will slide through all six chamber throats without putting any "helping pressure" on them. (just barely, so I'm estimating the cylinder throats are somewhere between .375 and .3755)
- I have a couple hard cast lead bullets that are .358 (using a micrometer), and they will NOT slide through the chamber throats... so they are somewhere between .0005 and .001 oversize to the throats.
-

Thanks much for your thoughts.
You may want to rethink your estimates or maybe you just typed them in your post wrong.
 

NikA

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Joined
Nov 2, 2014
Messages
1,542
Location
Yrisarri, NM- high in the Manzanos
I've also read that you can remove lead from a barrel using a mix of vinegar and hydrogen peroxide, but that is reportedly ONLY SAFE WITH STAINLESS STEEL BARRELS, because the vinegar is acidic and will attack traditional barrel steels.
This method of cleaning creates lead acetate in solution, which is toxic and very bioactive. I would strongly advise against it if you do not have a plan to safely handle and dispose of the byproducts.
 

Bad Barlow

Single-Sixer
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