I notice this difference in sizes and hesistated while ordering 45 bullets. Will it make much of a difference? I use a light to medium crimp.

It will depend on the bore diameter of the firearm you're planning on using, and if you're shooting jacketed or cast bullets.

It is recommended cast bullets be slightly over bore size to obturate properly and seal the propellent gases. If using jacketed, the tighter bore fit will cause a slight increase in pressures and more jacket fouling left in the bore.

If possible, you'd be well served to slug the bore and chambers (if revolver) to determine the exact sizes. Then, order accordingly.

Wow, glad I asked. I am shooting jacketed bullets thru a Taurus pt1911. What do you mean by slugging the bore and chambers to determine the exact sizes? :confused:

Undersize jacketed bullets are OK, most of the time. Undersize lead bullets will lead up the bore as the powder gases melt the bullet as they go past it. Normally we shoot .451" jacketed bullets and .452" lead bullets in a .45 ACP. The problem comes when we have an oversized bore and the standard .452" lead bullet doesn't seal it. Revolvers have 6 extra trouble spots in the cylinder, as a loose chamber throat doesn't work either.

If you aren't having a bad leading problem, just use the sizes above and don't worry about it. If you have a problem, it could be an undersized bullet, or a dimension problem with the barrel. If your revolver chamber throats are smaller than the barrel, you've got a problem.

Slugging the barrel means forcing a soft lead slug through the barrel and measuring it with a micrometer. Fishing sinkers and muzzleloader round balls work well if they're soft lead.

A slightly undersized bullet can be bumped up with a near max charge of fast powder. A gunsmith can ream out undersized cylinder throats.

Bye
Jack

My Springfield 1911A1 has a 0.452" groove dia. Jacketed bullets smaller than 0.452", as in the 0.4515" and 0.451", tend to foul the bore slightly but more importantly is the loss of accuracy. While the fouling is fairly light until you get past 100 rounds or so, there is definitely loss of accuracy beyond 20yds with the undersize bullets.

On cast bullets, I use strait WW alloy as-cast avg. dia. 0.454" pushed with a max charge of Bullseye. I lapped my sizer die so it only takes the cases down 0.001" and the bullets have only a slight resistence entering the case and I apply a very mild taper crimp, just enough to keep the bullet from moving on recoil/cycling. Never had any fouling with cast bullets.

. . . Normally we shoot .451" jacketed bullets and .452" lead bullets in a .45 ACP. . . .Jack
This should be a good general rule to follow especially since the firearm under discussion is neither old nor worn.

This should be a good general rule to follow especially since the firearm under discussion is neither old nor worn.


What does "neither old nor worn" have to do with selecting the bullet size that will perform best in the particular gun?

What does "neither old nor worn" have to do with selecting the bullet size that will perform best in the particular gun?
You may recall I was referring to the selection of bullet sizes "as a general rule". Also as a general rule, barrels today are much more dimensionally uniform as they come off the line. Tolerances are tighter than say something produced in the 1800's. Since the firearm being discussed has not been shot with blackpowder for the last 100 years, IMHO, the "neither old nor worn" general rule would apply. You may not agree. If you are slugging the bore of every firearm that you possess in order to "select the bullet size that will perform best in the particular gun", then so be it but we are discussing a defensive handgun, not a benchrest rifle.

I carry my .45 for SD and used to shoot match with it. The lack of accuracy using 0.451" or even 0.4515" as compared to the full size 0.452" jacketed is enough to cause 50% + misses at ranges beyond 30 yards. In addition to the accuracy issues, blow-by costs you velocity on a round that's not a velocity queen to begin with.

I'm not trying to be rude here, I just don't understand the reasoning of why it would be considered a "rule" to give up accuracy and velocity by deliberately using a bullet that is undersized? I mean that's like saying, "well, I'm only shooting deer at 50 yards so I should use a 0.307" bullet in my 0.308" diameter .30-06 barrel and just live with the 8" group and forget about the 0.5" group the gun is capable of producing."

Yes, I do slug every barrel I buy, measure the chamber, throat, headspace, free-bore and so on. Doesn't matter what type of gun or caliber it is. Sorry, but I'm just not following the reasoning here. Everytime the SKS or AK topic comes up, the first gripe everyone has is "they're not accurate" yet the bulk of the accuracy issues arise from the use .0.308"-0.310" bullets in bores that more often than not have a groove diameter of 0.311"-0.312" Simply using the correct size bullet for the bore often cuts the groups size considerably. You wouldn't run 0.355" or 0.356" bullets in a 357 Sig, what makes the .45acp any different? Like I said, I'm not trying to be rude or argumentive, I'm just not understanding the reasoning.

Well all my 45 ACP's are .451 bore so they will shoot .451 JHP or .452 cast bullets. They even state that in the manual to use only .451 jacketed bullet's. I don't know of any Maunfactor that makes a 452. jackets bullet for the 45 ACP? For 45LC/454 Casul yes but not for 45 ACP!

The lack of accuracy using 0.451" or even 0.4515" as compared to the full size 0.452" jacketed is enough to cause 50% + misses at ranges beyond 30 yards.

Are you saying half of your shooting beyond 30 yards misses the the last scoring ring on a target? To me, a miss is when the bullet does not impact any of the scoring rings.

I'm not trying to be rude here, I just don't understand the reasoning of why it would be considered a "rule" to give up accuracy and velocity by deliberately using a bullet that is undersized? I mean that's like saying, "well, I'm only shooting deer at 50 yards so I should use a 0.307" bullet in my 0.308" diameter .30-06 barrel and just live with the 8" group and forget about the 0.5" group the gun is capable of producing."

That is not what I'm advocating at all. If you are discussing rifle, I would expect better accuracy especially at greater distances hence slugging barrels would be beneficial. Since I thought we were discussing what size bullet to use in a handgun that is "neither old or worn", the general rule would provide adequate accuracy for most of us. What size group would you expect from an open sight handgun shooting at distances under 50 yards? Most would be very satisfied with about 3" groups (smaller than the 10 ring on a pistol target) and .451" jacketed or .452" cast will do that in a quality handgun. Sure, you could probably better that if you wanted to, however, is it really necessary?

Simply using the correct size bullet for the bore often cuts the groups size considerably.

Yes, that is very true.

Like I said, I'm not trying to be rude or argumentive, I'm just not understanding the reasoning.
If you are shooting at a target, regardless of size, you simply want a bullet that is accurate enough to hit it. For the .45 ACP, as a general rule, .451/.452" bullets are accurate enough for most of us. If you are searching for greater accuracy, then go for it and no one will fault you for this. The accuracy needed by a world class shooter is not the same accuracy needed by a weekend plinker. I'm also not trying to be rude or talk down to you. I'm just saying we all have our own standards of accuracy so let's live and let live. Hope I'm getting my point across to you.

Marshal, no offense intended nor taken, I just wasn't picking up what you were putting down. My Springfield's & RIA's came with 0.452" groove dia's and there was definitely a noticable degredation of accuracy at 20yrds using the 0.451" vs 0.452" bullets. When I shot match, steel plate sets were at 16, 27 & 44 yards (15, 25 & 40 meters), on the combat side the last man-size target was engaged at 40-60 yards depending on how fast you took out all the prior targets. Back then it was an absolute must to squeeze every last drop of accuracy and function from every gun used in the match...I haven't changed my ways since then, doesn't matter what the gun or caliber, I still squeeze all I can get from everything. An obsession I suppose?

. . . Back then it was an absolute must to squeeze every last drop of accuracy and function from every gun used in the match...I haven't changed my ways since then, doesn't matter what the gun or caliber, I still squeeze all I can get from everything. An obsession I suppose?
An obsession possibly, but a worthwhile one. Understand now why you are slugging all barrels including handgun.

When shooting NRA 2700 Matches (Bullseye) the slow fire course is fired at 50 yards. Most match winners could shoot in the mid to high 90s using an accurized 1911 with factory 185 grain jacketed match ammo sized .451". Plinkers (like myself) would use cast bullets of the same weight or more (200 grain) sized .452" and shoot in the low to mid 90's. Never knew if a better fitting bullet would gather me more points as I would do well enough at 25 yard timed and rapid fire to usually medal at the end of the match. If I had a better bullet, say one that will shoot a half inch group from a test barrel, I doubt that I could do any better as the shooter is also a variable. Believe the .451/.452" bullet is good enough for most of us but would never fault anyone for trying to do better. Good enough means enough to accomplish the job, not anything less. Good discussion.

Big difference between the combat matches and others. You tote your rifle, pistol, all mags and a full pack through the whole course. The pistol didn't even come into play until the last stage ... thus, every little bit of accuracy edge you squeeze out was welcomed.