MBC 250 RNFP Leading in USFA SAA

[Maj Dad]

I loaded up some MBC Cowboy 12 BH 250 RNFPs for my new, unfired USFA SAA 45 LC, 40 with 8.5 gr Unique, 10 with 9.0. Published velocities were ~825-875 fps in a Ruger BH. Shot great, powder burned completely, and I rediscovered the one joint in my hands that has symptomatic arthritis: middle finger, right hand, directly behind the trigger guard Anyway, got home, started cleaning & lead was streaked & smeared in the cylinders and bbl, with heavy deposits in the first inch or two. Took a Lewis Lead Remover to get the majority out but some smearing remains, and I am very disappointed. Now, my question: is the bullet too soft or is the gun suspect? I really can't imagine the gun contributing much at all as the cylinders & bore were like mirrors before shooting. I shoot a lot of lead bullets and this is the first time I've had the amount this gun accumulated - usually cast ww w/some Lino, water quenched, and almost no accumulations at all. I may be rambling & repeating myself but I am really aggravated... $ on the gun now this

 

[Walkalong]

Interesting. I would think 12 BHN would be fine for that pressure and velocity.

The bullets are obviously not bumping up and sealing the throats, since you say the leading started there and continued in the first part of the barrel. Either that or the throats are undersized, which on a USFA I would think not. You need to check it anyway.

The throats should be a hair over groove diameter. If groove diameter is .452, then the throats should be .453, or even a hair more. Then the bullets should be sized to fit the throats.

What diameter were the bullets? They should be a snug slip fit to the throats.

Throat diameter to groove diameter relationship is paramount, then bullet fit to the throats, then hardness/strength.

 

[Maj Dad]

The throats are all 452 with my dial caliper; haven't slugged the bbl yet. I'll have to get a soft lead slug this week & see. I felt sure 12 BHN would be fine for the velocities generated, and the bbl & cylinders are so highly polished I never imagined this would happen. Makes me want to use jacketed bullets, but dang it, it's a 45 colt & lead bullets are part & parcel of the round... Like I suggested, :banghead:

 

[Walkalong]

Sounds like it is set up for jacketed.

The good news is if the groove diameter is .452, or even .453, you can have the throats reamed to match, and by match I mean .001 or .0015 over groove diameter.

Hard to measure throats with dial calipers. Inner diameters period. Slug the throats and the barrel.

 

[dickttx]

Try pushing your lead bullets thru the chambers from the front of the cylinder. If they won't push through by hand, with just a little encouragement, they may need reaming. May be only one or two chambers is giving you the leading.

 

[Hammerdown77]

You may have gotten a batch that is undersized. Measure the bullet diameter with a micrometer, NOT a caliper. If it's not at least .452 on all the bullets (or however many you are going to load up and shoot next time), call Brad at MBC and tell him. He will make it right.

Another quick and easy thing to try is to get some Lee Liquid Alox, and lube 100 bullets with it (yes, over the wax lube that's already on the bullet). Shoot those through a clean barrel/cylinders and see what happens.

 

[Hammerdown77]

Also, have you tried any other lead bullets in this new USFA? Have you shot the MBC bullets you have currently in another revolver without leading?

If this is the only bullet you've tried in the USFA, you might try another brand/caster. Stick with the softer 12 BHN or less bullets no matter who you choose. If it leads with those too, you may just have yourself a gun that is prone to leading. I have a couple like that, no matter what I do they lead up a little. Your USFA might have a constriction in the barrel at the frame, or at the rollmarks, that swages down the bullet and then lets hot gasses rush past the sides of the bullet once it gets past the restriction. This is quite common in production revolvers. It would require fire lapping to address.

 

[Super.45]

I would try different powders first. Unique tends to be a hot powder. Try some Trail Boss as that runs a lot cleaner.

 

[Notoast]

Since it is a brand new barrel, you may have some fine machining marks in the barrel. Try polishing with some JB bore cleaner or perhaps fire a box of jacketed rounds followed by a thorough cleaning to remove any copper fouling. Also, if you are using the Lee factory crimp die, don't.

 

[Walkalong]

Unique isn't the problem.

 

[Quoheleth]

You're an experienced reloader, but are you by any chance taper crimping so as to squeeze the bullets and deform them?

I just got done running 100 rounds of that same bullet through my Uberti this morning and no problems from leading. Not saying it can't happen - just didn't happen for me.

Q

 

[Maj Dad]

Up to my eyeballs in work & other un-fun stuff, but this weekend I will do some sleuthing & see what happens. I have some 18 BHN 225 LRNs from MBC for my 45 acps that are 452 & ought to give a comparison. I want to clean the cylinders & bore very well, slug it, shoot it & see what happens. The worst case scenario, bar none is having to shoot jacketed bullets exclusively. Truthfully, I can live with that, but as a boolit caster from wayback I'd like to sling hot lead...

This pistol is extremely well made - almost a work of art - and the bore & cylinders look my Karts & other match grade tubes. If there are any machining marks at all they are microscopic. I did recheck the bullets & they all miked 452 on my micrometer, and the throats are indeed 452. I use a new RCBS carbide set, and the crimp is the appropriate roll into the crimping groove, nothing more (I watch this carefully; lesson learned long ago). It will be a journey of a thousand miles, ... no, wait - wrong metaphor I'll wring it out & repost as I get farther into it.

Thanks to all of you for your input - greatly appreciated!
Cheers, V/R
George J.

 

[Hammerdown77]

Maj Dad, do you have pin gauges to see if there is a barrel constriction at the frame? I'd look there next if none of the other ideas bear fruit.

 

[243winxb]

MBC Cowboy 12 BH 250 RNFPs usually cast ww w/some Lino, water quenched,

Big difference in hardness.

 

[Certaindeaf]

^
For true. Air cooled ww's are about 12. Add lino and water drop, they're not 12 any more by a long shot. Elmer used what, 6-8?