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Leading in a GP100

This is a discussion on Leading in a GP100 within the Reloading forums, part of the Firearm Forum category; After I shot about 30 reloads (From a lee reloading manual, 4.9gr of w231 under a 158gr sns rnfp bullet) I get leading the first ...


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Old February 2nd, 2017, 06:25 PM   #1
 
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Leading in a GP100

After I shot about 30 reloads (From a lee reloading manual, 4.9gr of w231 under a 158gr sns rnfp bullet) I get leading the first inch and a half after the forcing cone. I reread Iowegan's lead bullet library post just to make sure that load would match a 16BNH bullet. Also I shot this same load out of my sp101 357 3in barrel and got no leading. I'm wondering if this could be a load/bullet issue or something with my gun(357 GP100 6in)?




Last edited by tstring; February 2nd, 2017 at 06:29 PM. Reason: added bullet and gun information
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Old February 2nd, 2017, 06:43 PM   #2
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tstring, You're a little light on information. Was it a 357 Mag case or a 38 Special? What's the bullet weight? Either way your load is way short of producing the necessary pressure for a BHN 16 bullet. It should have about 16x1400=22,400 psi to match hardness to pressure. This is too high for a 38 Special where 17,000 psi is max. Your load would produce about 17.5k psi in a 357 Mag case using a 158gr bullet .... less with a lighter bullet. 5.6gr of W-231 in a 357 Mag case would be a near perfect match for your BHN 16 bullets provided they are 158gr.

A BHN 12 158gr bullet would be a great match in a 38 Special case with 4.6gr of W-231.
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Old February 2nd, 2017, 06:48 PM   #3
 
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Quote:
Originally Posted by Iowegan View Post
tstring, You're a little light on information. Was it a 357 Mag case or a 38 Special? What's the bullet weight? Either way your load is way short of producing the necessary pressure for a BHN 16 bullet. It should have about 16x1400=22,400 psi to match hardness to pressure. This is too high for a 38 Special where 17,000 psi is max. Your load would produce about 17.5k psi in a 357 Mag case using a 158gr bullet .... less with a lighter bullet. 5.6gr of W-231 in a 357 Mag case would be a near perfect match for your BHN 16 bullets provided they are 158gr.

A BHN 12 158gr bullet would be a great match in a 38 Special case with 4.6gr of W-231.
Thanks Iowegan! I must have done my math wrong somewhere. I am using a 357 case with a 158gr bullet.
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Old February 2nd, 2017, 07:23 PM   #4
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tstring, Try 5.6gr of W231. It will work much better. If you still get some lead fouling, it might be because of tight cylinder throats. They should measure .358" or you can test them with a known good .358" bullet and see if they can be pushed in the throats from the front (nose first) with just finger pressure. If not, you will need to get the throats reamed to .358". Forcing cones can also cause leading. I like to chamfer all revolvers that shoot lead bullets with a 11deg reamer. It usually improves accuracy and reduces lead fouling.
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Old February 2nd, 2017, 07:38 PM   #5
 
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Iowegan,

Already put the 5.6gr in my noted for next time. I did try one of my bullets both ways in all of my cylinders and they would not go. Looks like she'll be off to a smith soon then to get the proper alterations. I just measured the throats and they are at .357 on my digital calipers so that would make sense.

Thanks again for your help, I wouldn't be half as far along as I am with out you and this forum!
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Old February 5th, 2017, 01:19 PM   #6
 
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My GP100 also had tight throats and I tended to have leading just past the forcing cone. I reamed the throats and it is much better now. I changed from lubed to polymer coated bullets, but I expect that a tight throat will scrape off the coating and lead the barrel anyways.
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Old February 7th, 2017, 06:35 PM   #7
 
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This just my experience with my GP100 with 6" barrel. I was loading Missouri 158 grain LSWC. I tried several loads with Unique powder. Every thing from light loads of 6 grains to MAX listed loads in three reloading manuals. I always had lead in the barrel. I switched to Blue Dot powder and had the same experience, maybe with a little less lead. I had fired somewhere north of 150 rounds through it and always had some serious lead in the bore. I switched to Accurate Arms #9 at 11.2 grains and had almost no lead. After 50 or so rounds I had no lead. Three or five brushes with a brass bore brush and Kano Kroil then a couple of patches and no lead in the barrel. Since that time most of the 1000 Missouris are shot and I often up the charge to the MAX listed by AA, which is 12.4 grains for the 158 grain LSWC.
Now I mostly shoot Hi-Tec coated SWC.
I can not help but wonder if the bore had some roughness that had to be worked out. No dogmatic statement here. Just my experience.
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Old February 7th, 2017, 08:14 PM   #8
 
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I don't know if this is relevant, as I have a Blackhawk, but I also use Accurate #9. My Lee powder measure thingy drops 11.1 grains most of the time. I shoot 158 grain lead bullets, and they work just fine. No problem with leading. Velocity is about 1,100 fps, at least with my 5.5 inch barrel.
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