Help needed with a leading issue

[Lone_Star]

Gents,
I have an issue with leading that I am working to resolve, but need some direction on what to try next.
What I have is a Hi-wall 45-70, 16 twist Green Mountain barrel. My load is 60g of 3F with a .060 veg wad, Starline brass that is annealed each firing, full length sized, and a 540g Creedmoor BACO bullet - 459545C1. I have been using this bullet with DGL lube. I get good accuracy, but I get leading the first 6-8 inches of the barrel. The leading is kinda smeared along the groove and lands, and a long string in the bottom corner of the groove.

I use this load for silhouette, and can shoot the match without any apparent loss of accuracy with only running a couple of damp patches between relays.
I normally blow-tube for fouling control, but have tried more breaths, pushing a damp patch, and bore wipers with no change. I have tried 3 different lubes - DGL, SPG, and homemade. I always get a good lube star on the end of the barrel. I have also tried using different alloys - 16/1, 20/1, 25/1, and 30/1 with no change.

I suspect that I need to go to a larger diameter bullet. What I have drops at .4585 which I lube in a .459 die in a lube-sizer. The barrel measures at .451/.459. The reason that I full length size is that I can take a fired case and slide a .461, sometimes a .462 gauge ping into the mouth. I suspect that I am getting some blow-by, or gas cutting, and need a bullet that slip fits the as-fired case to seal the barrel and prevent the leading.

Thoughts, theories, or experiences?
Bryan

[steveu834]

Have you looked at it with a bore scope? I have a 40 cal GM that does the same thing. There are some tooling marks in the barrel and I am now going to start cleaning it with some JB paste to polish that area.

[bobw]

Shoot paper patch bullets, leading is a greaser thing. Bobw

[ian45662]

I have a c sharps highwall with the same barrel and twist. It shoots really really well but like yours it leads. This rifle is what drove me to paper patch and that worked very well for me but I have pretty much abandoned all that. Since going back to greasers I have had to find a way to mitigate the leading in my highwall(it’s the only one I have with this problem). The chamber is rather large in mine also. I use fire formed cases and I use a LDPE wad. It is a little loose in the fired brass but they will upset like a bullet does. One thing that really seemed to help is spg TROPIC. It leads with regular spg but the tropic really seemed to cut down on it a bunch. I have only shot the highwall in a few matches this year but in the ones I have it has shot very well. I am also shooting the same bullet and about the same powder charge. I load them so that the action pushes the front driving band into the lands about .030. I am also wiping between shots with Preston RV antifreeze. The kind they don’t make anymore. There is some European auto antifreeze that is supposed to work very well also.

[ian45662]

I forgot to mention that I size to .459 also.

[Lone_Star]

Thanks for the replies!
I do have a borescope and use it to inspect it closely. I have some LDPE wads that I will try next time out to the range.

[bpcr shooter]

what is your fired case size? what wad do you use?

matt

[desert deuce]

Green Mountain Barrel leading or any barrel for that matter. Considering the possibility that the problem is at the breech end with the characteristics of the load.

Without going into boring details may I suggest a few things?

#1 Substitute a .060" HDPE Poly wad, NOT LDPE. (May have to add a .462" or .463" veg wad in the wad column also. Think gas seal.)

#2 Keep the HDPE Wad and try either or both 1 1/2 Swiss & 2F Swiss

#3 Suspecting the above will solve the problem I should mention stop sizing the cases and incorporate a taper crimper instead.

Question: Could this be associated with base detonation, blow by or other such bullet base gremlins?

[MikeT]

Load a larger diameter bullet.

Keep on hav'n fun!
MikeT

[Lone_Star]

"what is your fired case size? what wad do you use? " - The outside diameter of a fired case is .480 and I use a .060 veg Walter's Wad.

DD - I will have to check the plastic wads that I tried, they are Walter's Wads also in .060 thickness. I prefer to not have to size the cases, I would rather use as-fired and not have to anneal and not full length size. I measured both the poly and veg wads that I have and both come out to .460. I will add trying Swiss 1 1/2 to a load test.

Mike - I do not have any larger diameter bullet molds, but considering having one made. What diameter would you suggest?

[kwilliams]

I had a .45 1-16" Green Mountain Covid build barrel that leaded so bad with GG, I re barreled my rifle. The grooves and lands had terrible tooling marks as revealed by the bore camera. I was using turpentine between every relay to remove the lead, and that got old fast. New Barrel is Paper patch only.
kw

[Lumpy Grits]

Try sizing in a .45-90 FL die.
Did you slug the bbl for those specs?

[Lone_Star]

I no longer own a 45-90 die, but know where I can borrow one. Yes, I did do a lead slug to determine the chamber mouth, throat, bore and groove diameter. I do not know if this is a Covid build barrel, but inspection with a bore scope shows only shallow tooling marks, but nothing that looks like it would be the reason for leading.

[JonnyV]

I'm an amatuer, but here's what I would try...

1. load powder and compress with a .060 fiber wad
2. add a .060 ldpe wad on top of the fiber wad after the load is compressed
3. go to a .459 mold
4. if all else fails, you could try lapping compound in the bore, but this may present unintended consequences. Even shallow bumps in the road could end up being huge when you're running over them at supersonic speeds.
5. switch over to SPG tropic lube

[Don McDowell]

You’re problem is likely coming from the throat being to big for your bullet. Either need to set the bullet out further or get a 460 diameter bullet