Slugged my GP100

[c1skout]

I used some egg sinkers and slugged the cylinders and barrel on my GP100 last night. I've got 4 cylinders at .358 and 2 at .357 (measured with a dial caliper). The barrel was tough to get a reading on since the lands are an odd number but it looks like .356 for the barrel. It seems to have a pretty good pinch at the frame. Would firelapping be my best course of action to open up the barrel constriction?

[9-toes]

Stop - go get a micrometer. Calipers are not good enough.

[c1skout]

Okay, I'll be out shopping today, I'll see if anyone local has a mic. in stock.

[williamwaco]

"Measure twice . . . cut once."

[Ben]

Yes, very good advice.

A nice mic is needed here.

[c1skout]

Okay, so I bought a micrometer tonight. My bore now measures .357 if I catch the edge of opposing lands (I hit all the edges the whole way around the slug) and the 2 throats that measured .357 before show as .3575 with the mic. My bullets drop at .358-.359

[Ben]

I'd be tempted to try some .358 " cast bullets in that revolver !

[geargnasher]

yup, just go shoot it. If it leads badly after the front edge of the frame, but not right where it passes through, you might ought to lap it somehow. My buddy's GP100 had a terrible thread choke and .356" cylinder throats. Had to ream the throats to .3585", hand and firelap the dickens out of the barrel (had numerous restrictions including front sight area and roll-lettering area) and finally recut the ragged-arsed forcing cone to get it to shoot, but it shoots great now with cast boolits and doesn't lead a bit.

Gear

[c1skout]

Thanks guys, I've been shooting my cast through it. I don't size them (yet) and it leads pretty badly,i think. 50rds and I've got streaks 3/4 of the way out the barrel. I've only used straight ww and LLA for lube, both light 38 and warm 357 loadings leave streaks that have me pushing a copper scouring pad through. Guess I'll try a .358 lube and size kit and go from there.

[robertbank]

My GP100 had very tight throats. Three of the cylinders were so tight a .356 boolit would not pass through them and three a .357 boolit would not pass through the others. I had them reamed out to .358 and I have not problems shooting .358 cast now. Seems like a common problem with the GP100's ie very tight throats.

Take Care

Bob

[9-toes]

Thanks guys, I've been shooting my cast through it. I don't size them (yet) and it leads pretty badly,i think. 50rds and I've got streaks 3/4 of the way out the barrel. I've only used straight ww and LLA for lube, both light 38 and warm 357 loadings leave streaks that have me pushing a copper scouring pad through. Guess I'll try a .358 lube and size kit and go from there.


I have not had the greatest luck with LLA. I run the LEE 358-125-RF with ACWW with about 2% tin and then sized to .358 . I then finish them off by lubing with Harlowe's Pan Lube. I'd get a .358 LEE sizer and inspect the bullet after sizing. I look at the areas where the bullet got sized checking for complete bands. I do this with new moulds especially because it may read smaller than .358 on the seam of the bullet. Inspection of the bands shows these undersized areas easily.

[MtGun44]

Good luck on the LLA beyond mild loads. :bigsmyl2:

Congratulations on the mic - necessary move.

I strongly recommend 358-158 RF conventional lube design and air cooled
wwts with NRA 50-50 or LBT soft blue or other KNOWN GOOD lube (IMO LLA
does not qualify) sized to .358 and you will likely be very pleased with accy
and no leading.

Bill

[c1skout]

Thanks for the input, fellas. I'll hafta wait to build my gun-fund up before I order any more supplies, but I do have a few bricks of beeswax here to try and mix up a different (known good) lube, and my 125rf bullets have a regular lube groove so I'll mabye try to pan lube them next.