1911 .45 bore diameter

Slugged my ATI 1911 at .448. Seems odd to be undersized versus oversized. Used calipers with multiple careful measurements. Going to have my machinist Neighbor verify with his better micrometer.

Gunna run .450 sizer after PC. Doubt I can run as dropped in this gun it seems (yet to buy mold).

What is the biggest over bore size you have run?

Secondary note. These rifling grooves seem real shallow compared to 9mm. https://uploads.tapatalk-cdn.com/201...3a2f566bd3.jpg


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Please remember that you are supposed to measure the largest diameter when slugging the barrel to determine the groove diameter. Then make sure that you are measuring a barrel with an even number of grooves. An odd number will not be exactly what you think it is. The next step is to know that the throat measurement is also to be considered. If accurately measured, the groove diameter will tell you the absolute smallest diameter it needs to fill the grooves. Most times an added one or two thousandths will help, and a large chamber will allow an even larger diameter cast bullet to be used and still pass the plunk test.

Is that the widest measurement around the boolit? Don't worry about the smallest diameter measured, look for the widest.

Did you use a pure lead slug?

That was the widest diameter. It was AC Range scrap. Is what I had access to. Cast in a spent 45 case.


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Please tell us what the as cast measurement of the range scrap slug was before you drove it through the barrel. Perhaps it was undersized because the spent case has an internal taper. It must produce a clear complete impression of the inside of the barrel as it is driven through. Some will use a hammer to upset (smash it a little shorter which also makes it a wider slug) the slug for a good measurement.

In my thinking, .450" is too small, as even my jacketed bullets run .451" and lead bullets are usually larger (my cast bullets are sized to a "generous" .452", possibly ,4525"). Perhaps a more accurate measurement at the largest diameter? BTW all the slugs I run through a barrel are at least .010" larger than suspected groove diameter...

The widest diameter is not bore diameter. It is groove diameter. The narrowest measured diameter on a slug is bore diameter.

Using terms correctly avoids confusing your responders and helps answer your question correctly. Know the difference between what bore diameter means and what groove diameter means. For some reason it is popular to be trendily incorrect on this board and elsewhere on the internet.

35rem. Thanks. My measurement was groove diameter. The slug was certainly over barrel diameter. I drove through end of barrel and shaved a ring all the way around the slug before it drove completely into barrel. I would say it was probably at least .040 over my final measurement when I started. It left a complete ring to be removed. I think I will melt some fishing weight or SOWW today and see if i get a different result.

I drive through from end of barrel so I can drop it through easier once the slug reaches the chamber side.


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Get some commercial cast bullets, load them with a target-level charge of suitable powder, and shoot them. If they are 0.451" (as most are), and your groove diameter is actually 0.448", the 0.003" oversized condition will not make a wit of difference. If they shoot well, which they probably will, then don't worry about measuring slugs.

You will make much greater gains in accuracy by practicing than you will by measuring slugs.

SAAMI Specs for the 45 acp barrel is .450" groove diameter, and a .442" bore diameter. USGI specs are .450" + .002" and .442" + .002".
SAAMI Specs for the bullet are .452" - .0030" for jacketed and .453" - .003" for lead.

As a comparison. My Ed Brown barrel slugs at a .451" groove diameter.
My no name, el cheapo, Palmetto State Armory barrel slugs at very slightly less than .450".
My 30 year old Springfield Armory Mil Spec barrel slugs at .454". It was replaced by the "el cheapo" PSA barrel with a vast increase in accuracy.

Quote:

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Originally Posted by Tatume

Get some commercial cast bullets, load them with a target-level charge of suitable powder, and shoot them. If they are 0.451" (as most are), and your groove diameter is actually 0.448", the 0.003" oversized condition will not make a wit of difference. If they shoot well, which they probably will, then don't worry about measuring slugs.

You will make much greater gains in accuracy by practicing than you will by measuring slugs.

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I like this plan. I was just hoping to avoid the unnecessary leading (and save buying 3 different sizers). I appreciate all of the responses

Have the barrel throated to .4525" and size to .452" don't worry about what the groove diameter is, it will swage and seal in the bore quite nicely.

Really need pure dead soft lead to slug with, and a good micrometer that reads in .0001" tenths for measuring. I use the egg sinkers in the fishing section at walmart to slug barrels with they work great, are dirt cheap, and can get them anywhere.