Sizing dia.

[Ole_270]

Double checking some basics on the 45 acp in the 230 TC thread. drove a .490 Hornady round ball through the barrel and mic'd it at .4510-.4511. Guessing there might be a slight amount of springback since it was a solid ball, not a hole through like a sinker. Ran a few unsized PC'd 230 TC bullets through the NOE sizer, used .451 and .452 marked bushings. The bullets were fairly soft, roughly 1Sn, 2 Sb. Mic'd the results at .4512-.4514 and .4525-.4527. Curious which the group here would prefer to run in this pistol.
By the way, when I patched out the barrel following slugging it I got more sparkles than I was expecting. Thinking the small step from the throat diameter to the start of the taper on the lands might be the culprit. I have been fighting some leading with these bullets whether PC'd or lubed and a coat of BLL.

 

[Rick]

.4525" or .4527"? I don't know of a way to tell the difference. Your only talking 2 tenths of one thousands. I can't imagine the gun or the targets could tell the difference, I know I couldn't by shooting them. If they chamber ok shoot'em up.

 

[Ole_270]

No, no, the .451 bushing results in bullets .4512-.4514 dia. The .452 bushing sizes to .4525-.4527. The bushing itself is a bit larger than marked.

 

[Brad]

Sizers are a bit tricky to mark exactly. The size of the hole may not be the same as what it sizes to.
A pure lead bullet will end up smaller than a high Sb alloy bullet when run they the same sizer.
Spring back is a real thing.

 

[Ian]

I think the alloy is perfect, the bullet is perfect, and would choose the smaller size.

How big is the throat entrance again?

 

[fiver]

yeah,,, i think I'd look at the throat closer.

 

[Ian]

Might even "look" at it with a steel lap and try to get the last bit of raggedy out of it.

 

[Ole_270]

Throat measures .4515 with telescope gage and by slugging

 

[fiver]

it's not the measurement your looking at.
it's the shape and condition.

 

[Ole_270]

I used a cheap borescope on it. Throat has very minute remnants of the original lands, with a shallow angle taper into the full land height with a slight radius between the cylindrical portion and the taper. By eyeball it looks like a step where that transition is but the scope shows a smooth transition. The surface condition is fine. No roughness or erosion

 

[fiver]

something is causing the sparkles and the sparkles are causing the leading.
if your getting it with P/C your cutting through the coat somewhere.
gas alone generally won't do it so it is generally a mechanical problem or the coat has a flaw that's being exploited.

 

[Brad]

Is this the barrel that has a bit of a step on one land at the end of the throat?

Is this a barrel that MIGHT benefit from a little firelapping? Just a question, not a suggestion. I was thinking some .451 bullets with a 400 grit compound. Just smooth things up.

 

[Ole_270]

I thought there was a step but once I got access to the scope it doesn’t show one

 

[Ole_270]

something is causing the sparkles and the sparkles are causing the leading.
if your getting it with P/C your cutting through the coat somewhere.
gas alone generally won't do it so it is generally a mechanical problem or the coat has a flaw that's being exploited.

This is what I’ve thought all along. Just haven’t spotted the culprit yet

 

[Brad]

Not easy to do but can you get a photo of the throat from the chamber end? Maybe with some light from the muzzle by have the muzzle end about a piece of white paper?

 

[Brad]

This is what I’ve thought all along. Just haven’t spotted the culprit yet

What size have you been using? I have gone to a slightly smaller diameter in my 1911 since I went to PC in it.

 

[Ole_270]

.4512 or so.

 

[Brad]

Ok,

Somewhere the coating is either failing or being shaved off.

What happens if you push a coated and sized bullet then the barrel?

 

[CZ93X62]

More pedestrian stuff from my quarter......to be expected from a social science major, I suppose. Bias alert--I don't PC my castings, and I have Chore Boy pads and played out bore brushes if things really go south.

.452" sizing has worked wonderfully for me in 45 ACP since I started casting in 1981. The only times I have leaded 45 ACP systems were through the use of soft, swaged Speer or Hornady bullets and undersized expander spuds meant for jacketed applications or when a long-departed Model 25-2 with .456"-.457" throats x .451" grooves was fired with .452-sized castings. THAT was a mess.

45 ACP throats and grooves have been pretty reliably .451"-.4515" IME. The makers tend to get the dimensions right, just as they do with 38 Special and 357 Magnum. And 40 S&W/10mm, come to think of it. Why these calibers have such close, reliable specs while 9mm, 44 Special/Magnum, and 45 Colt are so reliably ALL OVER THE MAP is a real poser. It is what it is, to use a becoming-trite saying.

 

[Ole_270]

Pushed a .4513 sized recently PC’d bullet through, marked for index. A little tough to see since all I had on hand was silver/grey pc. A small spot where the top land first contacted was scraped. Spot was 2/3 the width of the land and maybe .03 long. Possibly a result of tipping while starting into the constricted portion of the barrel but that is the land that usually shows the worst fouling close to the muzzle whether pc or lubed. I should say the top two lands foul the worst, the start of each are offset from top center.
A closer look with the borescope doesn’t reveal anything suspicious