Ruger GP-100 and Leading

[robertbank]

OK I need some collective thought. I own a Ruger GP-100 4.2" Stainless revolver. I have had all the cylinders reamed out to .358. The cylinder throats were all very tight from the factory. Using WW alloy air cooled boolits sized .358 I am getting leading in the first 1/4" of rifling. The forcing cone remains as it came out from the factory 5 degrees. I am told a 11 degree cut would improve the guns performance using lead. I use 38spl brass.


I use the gun in IDPA shooting RCBS RN boolits weighing in at 160gr. The bevel base has been removed from the mold. I practice a lot with the gun and cleaning out the lead is a PITA to say the least.

My question is would going to a harder alloy help. I could for instance water drop the bullets to harden them up. Thoughts?

Take Care

Bob

[btroj]

Try a .359 bullet. Harder may make it worse. The bullet isn't sealing well and stuff is getting blown ahead of the bullet. I find a softer bullet, depending on load, helps. Give the bullet a chance to bump up and seal the bore.

My GP doesn't lead with soft .359 bullets and mild 38 loads. Same powder charge and a hard bullet or one undersized and I get lead I could mine.

Balance the alloy, size, and pressure/burn rate. Harder for higher pressure, softer for less.

[Wayne Smith]

You forgot to measure the bore. Let us know what the barrel measures and our answers can be more meaningful.

[robertbank]

I have never heard a Ruger being out of spec on the barrel size by .003 but will see if it is an oversize bore. The leading only occufrs in the first 1/8th" of rifling so I am guessing the barrel is near the .357 if should be. I'll post the results here later.

Bob

[cbrick]

You didn't say what the load is but when leading is in the first part of the rifling "only", just past the forcing cone it's usually because the boolit is not taking the rifling and stripping. A bit further down the bore and it has taken the rifling and all is well. A case where a bit harder alloy may help or better yet reduce the load.

With the variability in WW alloy it's possible that you have a batch low on Sb and thus a bit softer than normal WW, water quenching could, might, maybe help BUT on the other hand it could also make them too hard. It's one of those things where "try it and see" if it's better, the same or worse.

The first thing I would try were it me is reduce the load. Could also try a slower powder (your using a fast powder right?) to give it a more gentle push to get it going.

Rick

[robertbank]

Thanks Rick for the reply. I am using 2.8gr pf Clays. Load is very soft shooting making about 110PF for IDPA SSR Division. It certainly is not a heavy load. I'll try some water quenched boolits and see if hardening them up a bit helps. I'll get back to this after Christmas when I have more time to do some casting. We have both boys and our daughter in law home for Christmas this year so I'll be fairly busy.

Take Care

Bob

[cbrick]

How did I know you were using a fast powder? Clays is a very fast powder. What happens with fast powders is it's like slamming it in the hieny with a sledge hammer giving it all of it's velocity right now as opposed to slower powders that start to push and then continue to push on down the bore. You can go too slow of course and end with big muzzle blast or even so slow that the desired velocity cannot be reached. The point is that a mild load can be used with slower powders and still have the accuracy, possibly even improved.

Merry Christmas to you and yours. Enjoy the family.

[GBertolet]

If you have leading in the cylinder throats, forcing cone and the first inch or so of the barrel, the cause is your bullet is not sealing the cylinder throat. Hot gas containing vaporized lead from the bullet's base, is getting past the bullet, flame cutting the sides of the bullet along the way. The gas condenses and is ironed in by the passing bullet. There are several ways to approach this problem. First, for lower pressure loads, use a softer alloy, which will slug up easier during firing, sealing the cylinder throats. Secondly, upping the load pressure will upset harder alloys, giving the same results. My vote would to be go softer on the bullet alloy for your purpose. As long as your bullet diameter matches your cylinder throat size you are off to a good start. I had a similar problem in a 38 revolver. I was getting leading with WC bullets cast of Lyman #2 alloy. Casting 50% WW and 50% lead, fixed the problem instantly. One other thought I just had, it is possible your bullets are being sized down a few thousandths, during taper crimping, or when seating the bullets, if your expander plug is undersize. Try pulling the bullet from a loaded round and measure it.

[cbrick]

Hot gas containing vaporized lead from the bullet's base,

GBertolet,

Bob didn't say he had leading in the cylinder.
Bob didn't say he had leading in the throats.
Bob didn't say he had leading on the forcing cone.

Bob did say he had leading in the first part of the rifling . . . Thus the bullet is stripping at the beginning of the rifling.

Next, I can assure you that it is not possible to VAPORIZE LEAD in the cartridge case, the throat or the bore or any combination of. Not only can you not vaporize the lead you couldn't even melt any of it. Lead absorbs heat very slowly and the millisecond it's exposed to the heat of the burning gas cannot possibly melt it. If it could explain this to me, plastic has a much lower melting point than lead, why doesn't plastic shot-gun wads melt? Why don't cardboard shot-gun wads burn?

Yes, gas cutting is a reality but melted or vaporized lead has nothing to do with it and gas cutting isn't what Bob described.

Bullet bases melting is an old wives tale to explain why gas checks work. Let's not continue to pass on old wives tales.

Rick

[btroj]

Whatever it takes to get a seal at the forcing come, that is the fix.
Small bullets, alloy issues, wrong powder/burn rate. A small change in something will likely fix the leading.

I would tend to listen to Rick, he has been around the block a few times.

[GBertolet]

cbrick, I never said leading in the cylinder throats or forcing cone was the problem described in the OP. Rather that these symptoms independently, or along with leading alone in the beginning of the rifling, was due to a bullet not sealing the cylinder throats.

[btroj]

Maybe. Maybe not. You can get a good seal in the throats and still not seal the bore initially.

Rock is saying the bullet could be skidding on initial contact with the lands. This allows gas leakage until the entire bullet enters the lands, engraves fully, seals the bore. A harder alloy resists this skidding and allows a seal to form faster.

A slower burning powder can help because it gives a more gentle push into the lands and because of lower acceleration the bullet resists skidding better.

It is all about balancing many, many factors

[cbrick]

Rock is saying the bullet could be skidding on initial contact with the lands. It is all about balancing many, many factors

That's me . . . The Rock!

Rick er, the Rock. Dang, who put the "o" that close to the "I" on these key boards?

[RobS]

Sounds like some good responses so far. Also depending on the seating/crimping of the boolit and the age of the boolit the intended .358 diameter may not be as expected. I would also pull a dummy round and see if the very edge of the base is still at your desired diameter. Reloading dies can create issues for cast boolits and I've also seen many people load a freshly cast boolit and have it swage down and then as it age hardens in the case the lighter loads won't have enough pressure to seal the bore etc. I've loaded light 45 auto loads the day of being cast that I know swaged down in the case and didn't lead because the alloy was still soft enough to upset and seal the bore yet a week later the same handloads leaded light crazy because the alloy had age hardened (WW alloy boolits) therefore the boolits were too small for the bore.

[GP100man]

cbrick

I think Bob is using 38 cases with that 2.8 load , could it be he`s gettin blow by & it all is hitting the edge of the rifling at the same time ??

I run 3.2gr. Clays in mag cases & get O leading ??

That did`nt make sense ??? the boolit is keeping the gas behind in in the throat !

Let`s see ,Hmm , front band damaged by blow by ,then hits the cone& rifling ??

What`s the dia of the front band ???

[btroj]

That Rock totally ricks?

At least this typo wasn't insulting?

This type of leading is what can drive a guy nuts. It takes some playing around to get figured out.

Try a different powder and see what happens.

Try a different alloy and see what happens.

Try a different lube and see what happens.

I have had this and a simple light coat of LLA on the exact same bullets stopped the leading.

Every gun/load combo is a unique situation. This is where the rubber meets the road in shooting cast. Time for some expiremtnation to find a solution.

[robertbank]

OK here is the game plan after Christmas. First I will try water dropped boolts - 50 should be sufficient using the same powder load in 38spl cases. Remember this is an IDPA competition load where soft recoil aids in target recovery. Too, Clays burns about as clean as I have found any powder which contains fouling issues that might arise during a match.

If this fails I will try .357 cases. The shorter .38spl cases are easier to reload than the longer .357 cases but my reload times suck anyway so the net effect on my scores is not going be all that great anyway. A man has to know his limitations...Rob Leatham I am not.

From there, if the problem continues I will work with slower powders starting with my air cooled boolits then transitioning to harder bullets. Looks like I have a nice winter project. I should be done by March. I'll post my results as they come in.

Merry Christmas to all and thanks for the replies.

Take Care

Bob

[Larry Gibson]

Bob

That is a very light load. Also you don't say (or I missed it it) what lube you are using? A quality softer lube in sufficient qualnity is needed with such loads.

I'm going to say the alloy is already too hard. Many, many of us are former, or still do, shooters of target .38 SPL loads out of .38 SPL chambers and .357 chambers. Many bajillion rounds have been shot with cast bullets of 140 - 160 gr over 2.7 - 3.5 gr of Bullseye, 700, 231 and Clays. The alloy used in most of those is very soft; consider that the best of the factory .38 SPL target loads use swaged almost pure lead bullets. Our cast bullet target loads were always hard pressed to equal them in accuracy and in non leading of the barrel. I suggest you add 2% tin to your COWWs and then add 50, 60, 70 or even 80% lead to that alloy to cast very soft bullets with a balance of tin/antimony.

With a softer alloy and a quality lube appropriate for the load you will probably find the leading stops and accuracy increases.

Larry Gibson

[44man]

I did not need to read all the posts. Rick is right, the boolit is skidding from the fast powder.

[bowfishn]

aha it's leaving skid marks!