Finding a good load for my gp-100

[Gunner4h1r3]

hey all, i need some wisdom.

I own a GP-100 .357 with a 4" barrel and like most people, I handload.

I've made two different .38 loads for the gun but after about 20 rounds from either load, the gun locks up to where I can't fire. The first load left unburnt powder in the cylinder, but the second load doesn't

first load: 125 grain FMJ with 7 grains of Blue Dot
second load: 125 grain GMJ with 3.8 grains of HP-38

with factory ammo, the gun is fine but when the handloads come along, it doesn't like em. my s&w 638 gobbles both loads up and asks for more.

or could it be the gun?

 

[Marlin 45 carbine]

useing magnum primers?

 

[Gunner4h1r3]

no i am using Winchester small pistol primers as that is what the load book says.

 

[Bush Pilot]

I suggest you send me the gun, you appear to be a nice guy and shouldn't have to put up with a gun like that.

 

[GP100man]

if anything such as carbon or lead not buildin up on cyl. face i`d say up the powder , not enuff pressure to push case back on primer .
what are the end shake numbers on your gp ?????all mine shoot 4grs clays to plink with under a soft 158gr home cast boolit, on the upper side 14-15 grs of h110 as alloy allows& first one up this time of yr. is a homemade shot shell for Mr. noleegggs!!!



GP100man

 

[joneb]

first load: 125 grain FMJ with 7 grains of Blue Dot
second load: 125 grain GMJ with 3.8 grains of HP-38

LOAD UP !

 

[easyrider604]

Thank you Sunray for catching my error.

I wouldn't use Blue Dot for .38 special, never tried HP38 myself.

Seems you have unburned powder residue jammed between the barrel and cylinder. My GP100 has tight Barrel-Cylinder gap, .002, and if yours is the same, then you will have jammed cylinders due to unburned powder residue just like me.
I even have a little residue jamming problem with 12.5 grains Blue Dot under 125 grain Rainer plated Hollow Point, in .357 brass.

If you want low velocity target loads, use fast pistol powders like Winchester 231, Titegroup, Bullseye or 700X, and always refer to reloading manuals or use powder manufacturer's data. I also prefer 158 grain LSWC for .38 spl target loads.

 

[Sunray]

"...loads are too low for the powders..." 7.3 of Blue Dot is max for a 125 gr .38 Special jacketed bullet.
Your HP-38 load is definitely too low. Hodgdon gives 4.3 as the starting load for a 125 grain jacketed bullet. 3.8 is the starting load for a cast bullet.
(3.8 to 4.8 of HP-38 for a 125 gr cast bullet. 4.3 to 4.9 for a 125 gr jacketed bullet. The data for cast and jacketed bullets is not interchangeable.)
"...the gun locks up..." How? Can't pull the trigger or the cylinder won't move? Two different things. Can you open the cylinder? You using .38 Special cases? Mind you, I doubt that's an issue. It will leave gunk in the cylinders though.
"...could it be the gun?..." Not when it works ok with factory ammo.
"...158 grain LSWC for .38 spl target loads..." 148 gr cast WC's or swaged WC's with 2.5 to 2.8 grains of Bullseye. Loaded flush in .357 cases.

 

[Gunner4h1r3]

Ok guys sorry for the delay (the navy can have some long days)

The gun is in the serial number range of 175-104XX.

When I say the gun locks up I mean that I can pull the trigger about half way back and that's about it. The hammer and cylinder are halfway in cycle, but I can open the cylinder and take out the shells.

The load data I have for HP-38 and 125 grain FMJ is from Lee's 2nd Edition although I should start thinking about upping the load a bit.

 

[GP100man]

grip screw

color grip screw with marker
reinsert screw
shoot till problem arises
remove screw
witness marks???????
main spring rubbin screw?????
titen grip panel screw .
i recontoured my spring struts to avoid this .
also pushin forward on rear bottom of grip will free up space between screw & spring then you can da the trigger.

GP100man

 

[Sunray]

"...I can pull the trigger about half way back and that's about it..." And only with your handloads and on the first shot, right? Aharrrr!!! Have a look at the primers. Sounds like they're not seated deep enough. They may be sticking out enough to stop the cylinder from turning. That'd stop the trigger too.
Mind you, if you've been shooting .38 Specials then try to load .357 brass without cleaning the cylinders, there will be a ring of gunk that needs to be cleaned out first. Having the gunk ring won't allow .357 brass to seat fully and that'll cause the cylinder to stop too.
Loading .357 brass to .38 velocities makes the ring of gunk go away and stay away. There are no issues using .357 brass loaded to .38 velocities either. Same .38 data and bullets. Shot bullseye with a 4" GP for years doing just this. You do have to use .357 dies or a .38/.357 die set.

 

[Kosh75287]

BlueDot seems to me to be on the verge of too slow burning to work well in .38 Special. You say that 7.3/BlueDot/125FMJ is max for .38 Special, and you're shooting 7.0/BlueDot/125FMJ. You may find that increasing the charge weight by 0.1 or 0.2 grains. At 7.0grains, you might be just under the pressure level that achieves complete combustion. If increasing the charge weight is not an option, the incomplete burning might be improved by employing an slightly heavier crimp, or a magnum primer, or both. I'd try the heavier crimp, first. If you're shooting loads that develop .38 special pressures in a .357 Mag revolver, you might not need to reduce the powder charge should you decide to switch from standard pistol primers to magnum, IF YOU STAY AT 7.0/BlueDot.

 

[Walkalong]

Blue Dot is no good for .38 Special even a +P levels. Too erratic. Very position sensitive.