45acp freebore: how much is too much?

[totaldla]

Kimber 5", stock barrel.
I've been thinking of reaming just the throat to increase the freebore (0.4525" dia) - the goal being to be able to use WFN bullets seated reasonably. I was thinking of lengthening the freebore to about 0.150". I'm assuming the reamer will cut some sort of leade, so I'm not concerned about that.
Is 0.150" too much?

 

[Scorch]

If you're going to add freebore you will need a custom reamer. I don't know of anyone who makes a .4525" throat reamer, but they probably do just because it's such a common caliber.

As far as feeding wide meplat bullets, I would try a few first to see if you can get them to feed.

 

[Jim Watson]

All the reamer companies make throating reamers, I just don't know the exact diameter.

Agree with Scorch.
Load some of those bullets at the OAL you want and see if they feed up the ramp and into the chamber. They won't go all the way but they should be well started in.

 

[44 AMP]

Freebore, how much is too much????

Considering the number of revolvers made in .45acp, and the acceptably satisfactory results from many of them, I wouldn't worry about "too much" freebore.

Of course what I find acceptable might be too much, or not enough for you.

 

[Jim Watson]

I shot IPSC with a 9mm Miller Major for a while.
At the time the rules said 9mm P may not be scored Major at an overall length of less than 1.26". (SAAMI maximum is 1.169" which is about the most a regular 9mm magazine will accept.)

Paul Miller had molds cut for 145 and 160 gr bullets with the lube groove way down close to the base so it would be still be covered when seated to 1.27" and loaded in a .38 Super magazine. But that was too long for the standard 9mm chamber so when you bought his bullets he would loan you a reamer to cut a long throat to suit. (Sorry, I don't know the dimensions.)

It all worked very well in my first generation single stack comp gun.
But when I went to shoot some standard 9mm, jacketed bullets were very inaccurate and cast bullets keyholed, that throat was just TOO long for them.

 

[44 AMP]

But when I went to shoot some standard 9mm, jacketed bullets were very inaccurate and cast bullets keyholed, that throat was just TOO long for them.

This has me wondering, if perhaps it wasn't just the length of the throat in your modified barrel, but possibly something else, as well.

It would be an interesting comparison, the length of the freebore in a modified semi auto barrel compared with the "freebore" distance a revolver bullet has to move to reach the rifling.

In a revolver, you have the length of the chamber throat, plus the cylinder gap, and whatever the distance from the rear face of the forcing cone to the rifling leade. So, not only do you have this combined distance but also the potential for the chamber throat and forcing cone to be different sizes. Despite all the possible points for accuracy harming issues, some revolvers shoot quite well.

Not saying bullet distance to the lands has no effect, it most certainly does, what I am saying is that the distance to the lands alone is not always the most important factor in every instance.

 

[tangolima]

Keep shooting, and the free bore will elongate with number of rounds fired.

If you can't wait, you will need to buy / rent a neck/throat reamer. A chamber cast may be needed to determine the existing free bore's diameter. The new free bore should be no smaller than that. Also you may want to make sure the bore hasn't been especially hardened, or it will ruin the reamer.

It may not cost much more if you let a professional to do it for you, as he may already have the cutter.

-TL

Sent from my SM-N960U using Tapatalk

 

[44 AMP]

It may not cost much more if you let a professional to do it for you, as he may already have the cutter.

Additionally, if you hire a professional to do the job, it is implicit in the contract that the work will be done "right". This is one of those things where a tiny bit of error or misalignment can screw up the end result.

If the smith botches the job, its their responsibility to fix their error, and out of their own pocket. That's part of what you are paying for. If they don't do it right, you have legal recourse.

If you do it, hoping to save a few bucks, any and everything is all on you, good, or bad, its your responsibility and all costs come out of your pocket.

 

[FrankenMauser]

Even in rifles, a long free bore can have no real impact on performance.
I wouldn't worry about it.
There have been several videos and articles recently testing such, in fact. The old "best accuracy is found touching/jammed into the lands" idea is losing traction in the precision rifle world. People are finding that there is generally a window of about 0.120" to 0.200" of "jump" that is the same as, or superior to, jamming or long jumping.

You can also step back and think about all of the .357 Magnum chambers that get used in various competitions with .38 Special ammo. Doesn't seem to matter.

Personally, I shoot a lot of .32 S&W Long in .327 Federal chambers.
Long jump.
But it doesn't seem to hurt down range. (.32 S&W does, though. That is a looooong jump to the throat.)

 

[44 AMP]

Interestingly, while the difference in case length between .38 and .357 is 0.135", the difference in max loaded length is only 0.04", so I don't think there is much of a difference in bullet jump, unless you are shooting flush loaded wadcutters.