625 loads Keyholing

[BillD]

200 gr RNFP cast, 5.8 gr 231, fed 150 primers, 860 fps.

They keyhole badly, probably 75%.

I was going to switch to a 230 gr cast RN.

Think that will help?

Thanks for your help.

 

[BillD]

200 gr RNFP cast, 5.8 gr 231, fed 150 primers, 860 fps.

They keyhole badly, probably 75%.

I was going to switch to a 230 gr cast RN.

Think that will help?

Thanks for your help.

 

[Amici]

231 and 200 gr. RNFP bullets are a perfectly viable combination. Have you checked the O.D. of the bullets?

Also, is that an actual chrono reading, or just what some manual says you should be getting?

 

[BillD]

Actual chrono reading. But I am telling from memory, which mine sucks. I will double check when I get home.
I haven't measured the bullets, I will when i get home.

What causes keyholing?

Thanks again

 

[crgaston]

Keyholing is caused by instability, or lack of enough spin to stabilize it. If your bullets are too small, they might not be gripping the rifling well enough to spin correctly. The rifling in my 625's is pretty shallow, so I assume yours is too. Are you getting a lot of leading, too?

 

[BillD]

I am getting a fair amount of leading. The rifling is very shallow.

I'll measure the bullets when I get home.
Thanks, really.

I'm going to a mastercast 230 gr bullet.

 

[Beans]

I am shooting the 200g gr RNFP and the 185 gr RNFP in both of my 625's (MG & 1989) I am using 5 grains of Unique.

This combo is giving me excellance accuracy.

As I am casting my own bullets I am sizing to .454.

 

[S/W - Lifer]

This could possibly be due to projectiles that are too soft. Try a harder bullet for comparison.

 

[Amici]

Try a poly-coated bullet, such as Precision's. Less smoke and FAR less leading at any reasonable velocity.

 

[Steve C]

This could possibly be due to projectiles that are too soft.

I would guess its the opposite, The bullets are most likely too hard to obturate to seal in the bore at the low pressure and velocity you are loading at. The bullet could be undersized or the cylinder throats could be undersized in comparison to the bore. Either case could lead to key holing with a bullet not filling the bore and engaging the rifling. The leading is most likely coming from gas blow by melting the bullet material to the bore.

 

[BillD]

I was wrong on my velocity, it's 785 fps. And I have loaded all of these so I can't check the diameter. These bullets are from Missouri Bullet Co. and are supposed to be hard cast to a Brinell of 18, if I remember correctly.

I think I will just switch to mastercast bullets.

Thanks for all of the info.

 

[arkypete]

Does the keyholing occur at the begining of your shooting session or after a few cyclinders full? If it's after 12 or 18 shots it's the leading in the barrel and chamber mouths and such.
I had the same thing, keyholing, after several cyclinders full in a Ruger Blackhawk. I used the recommended sizing diameter of .452, with 8.5 grains of Unique, with an alloy of WW/Linotype.
The problem went away with sizing diameter of .454.

Jim

 

[gwalchmai]

Slug your bore.

 

[BillD]

It's a 625 -8. Were there several different bore sizes in this model? I would think the barrels were the same. NO?

 

[gwalchmai]

Originally posted by BillD:
It's a 625 -10. Were there several different bore sizes in this model? I would think the barrels were the same. NO?

No, barrel sizes can vary, even among two diff guns off the same assy line. Sounds like your boolits may be a thousandth or two small.

 

[44wheelman]

After you slug your bore, also check your chamber diameters. My 29 chambers usually run a couple thousandths on the large size (.432-.433). I once had a C**t that had a nominal barrel diameter, but the chambers were all .002-.003" smaller.