GP100 leading need help

[zomby woof]

My GP100 shoots great but leads up terribly after several shots. Here's what I've done so far.
The throat measure .3575 grooves measure .358
I'm using the LEE TL 358 swc. I've shot them sized to .359, .358 and .3575. I've used hard and soft alloy. I've polished the forcing cone. I've used both 38spl and 357 cases. I'm using 45/45/10 lube. The forcing cone leads up and starts traveling down the grooves.

Here's my next steps:
Ream the throat to .358 (buy throat reamer from Brownells)
Change boolit (Thinking LEE 358 158 RF)

What am I missing? Thanks.

[runfiverun]

you have a handle on it.
3575 up to 358 don't work, never has never will.

[Lefty SRH]

Doesn't really matter what sized oversized boolit you use when your throats size whatever you shoot down to .3575". Bottom line your boolits are too small because of your throats. Ream them to .358" and try that first. You may have to ream the throats .359' later but try the .358 first.
My GP100 did the same thing and REALLY bad. I measured my throats and they are .358 so I sized my boolits to match that, problem solved. I don't even know what the barrel measures.
Good luck.

[MtGun44]

I think if you try some good SWC designs with conventional lube you will succeed pretty
well within your current (suboptimal) dimensions. With TL, I think you are done.

CHOICES:

1: stick to jacketed (probably shoots well),

2: switch to conventional lube designs at .358 (Lyman 358477 or RCBS 38-150 SWC, near clones
of each other, are highly recommended) with a known good lube like NRA 50-50 or LBT soft blue,

3: Get the throats reamed to .3585 to .359 and try with .359 boolits in the TL design. Even after
reaming, you may well fail with the TL designs, which have marginal lube capability. You will
then be in the position of probably having degraded your Jbullet accy (looser throats) and not
gained the capability to use TL designs, a double bad.

If I were you, I'd try to buy or beg a dozen or more of a known good conventional design (Lee 358 -
158 RF conventional lube design is also superb) lubed with a known good lube and sized
to .358 and shoot them in your gun after cleaning it well. If you succeed, abandon the
lame TL system and move ahead with one of the good to great designs out there that work
well in .357s with conventional lube.

IMO, reaming a gun should be a LAST resort after trying all the available solutions that are
possible.

Best of luck.

Bill

[geargnasher]

My buddy's stainless GP-100 did the same thing, throats were .357-ish and five-groove bore measured .3575" with vee-blocks. I reamed the throats to .358", then discovered it had some awful thread choke. Took care of that with laps and a forcing cone reamer, now it shoots straight. He bought it cheap from a gun shop because it appeared to have a bulge in the barrel just ahead of the forcing cone that ended up being just lead/copper/lead/copper accumulation from all the choke points.

Gear

[williamwaco]

I have a different idea.

Take it to a gun show and put a sign on your back and sell it.

Then get another one. The next one is not likely to do that.

I have bought two of them this year and they both shoot like a "house afire"

.357 and .327 Mags.


.

[zomby woof]

This was a gift from my Father so I have to keep it. I've just received some commercial 158swc to try. That's the next step. I'll post the results.

[zomby woof]

I shot some commercial 158 swc. They do not lead as much as the TL boolits. I'm still getting leading in the forcing cone area, after 50 rounds It was not traveling down the grooves. It didn't seem to effect accuracy after the 50 rounds. I may ream the cylinder.

[Charlie Two Tracks]

Awhile ago, I gave KYCaster a reaming set up for .357 for this forum. You might want to PM him and see if he still has it around.

[GP100man]

The throats on most are a little ruff for my taste & on mine I flapped em smooth & a 358 will push thru with minimal help.

I have a little build up on the cone itself but the bores are shiney.

If my boolits are under 358 any little bit I`ll get lead in the throats & `bout 1/2" into the bore.

Then again I have a 4" SS GP that`ll digest anything above 357 without a hitch .