Optimal freebore for 75 grainers out of 223 rem Match chamber
- Thread starter Mike112288
- Start date
I have always preferred to throat so that a bullet with was touching the lands would be seated so that the base of the bullet (the forward corner of the boattail if the bullet has that feature) is just ahead of the neck/shoulder juncture. This was semi-critical if necks were turned and one wanted to avoid the dreaded donut but is probably not all that important otherwise. As for the amount of freebore, there is always some confusion regarding exactly how that is measured. Some will call freebore that portion of the throat to where the rifling commences. Others will assign that term to the distance to where the throat is bore-size. Still others will specify freebore as being the actual distance from the mouth of the case to where a given bullet contacts. Often, a gunsmith will have a couple (or more) reamers with different specs and will use one reamer or the other based on conversation with the customer. Other gunsmiths might cut the throat to fit a specific bullet seated to a specific length.
If you already have a rifle of known freebore, you could create a test round and jam the lands with the actual bullet you want to use to determine the OAL.
Once you have that you can compare that OAL to how you would like the bullet to sit in relation to the neck shoulder, much like Leeper is suggesting above... with the back end of the bearing surface forward of the neck shoulder junction.
Then you are only looking for the dimensional difference between what you have and what you would like to have.
Leave yourself a little room to chase throat erosion.
Often times a guy will load a few dummy rounds with the bullet seated where you want it and send them to the pipe fitter for reference so he can ream the throat to suit.
Just keep in mind the magazine max OAL when doing this... assuming its a repeater. If its a single shot rifle, it doesn't matter.
Oh ya... what action are you using? If you use something like a Rem 700 or clone, then you can feed and eject up to about 2.6" from an AI mag... but if you're using a different action that is shorter, you may not be able to eject a live round if you run as long as possible.
You can get into certain technical problems as you run a long 223 from a mag... one is finding a mag that will feed it, or modifying a mag so it will feed it. I like the Accurate Mag for 223, but you will need to modify it... I can tell you how if you need help.
Then there's the action itself... as the bullet feeds out of the mag there is a feed ramp inside the action and normally the neck will touch this feed ramp and lift the center line of the bullet before the tip of the bullet touches the back of the barrel, so it aligns with the chamber. But... Once you start running close to 2.6" OAL, the tip of the bullet can contact the back face of the barrel before the neck touches the feed ramp and this leaves the center line of the bullet about 0.010" low and it can catch the corner of the chamber and cause and FTF.
To get around that, you need to think like an M14... and add a small chamfer (about 0.030") at 6 oclock to help lift the bullet tip into the chamber.
If you do all that, you can really get the 223 moving and will feed reliably with these long rounds.
Once you have that you can compare that OAL to how you would like the bullet to sit in relation to the neck shoulder, much like Leeper is suggesting above... with the back end of the bearing surface forward of the neck shoulder junction.
Then you are only looking for the dimensional difference between what you have and what you would like to have.
Leave yourself a little room to chase throat erosion.
Often times a guy will load a few dummy rounds with the bullet seated where you want it and send them to the pipe fitter for reference so he can ream the throat to suit.
Just keep in mind the magazine max OAL when doing this... assuming its a repeater. If its a single shot rifle, it doesn't matter.
Oh ya... what action are you using? If you use something like a Rem 700 or clone, then you can feed and eject up to about 2.6" from an AI mag... but if you're using a different action that is shorter, you may not be able to eject a live round if you run as long as possible.
You can get into certain technical problems as you run a long 223 from a mag... one is finding a mag that will feed it, or modifying a mag so it will feed it. I like the Accurate Mag for 223, but you will need to modify it... I can tell you how if you need help.
Then there's the action itself... as the bullet feeds out of the mag there is a feed ramp inside the action and normally the neck will touch this feed ramp and lift the center line of the bullet before the tip of the bullet touches the back of the barrel, so it aligns with the chamber. But... Once you start running close to 2.6" OAL, the tip of the bullet can contact the back face of the barrel before the neck touches the feed ramp and this leaves the center line of the bullet about 0.010" low and it can catch the corner of the chamber and cause and FTF.
To get around that, you need to think like an M14... and add a small chamfer (about 0.030") at 6 oclock to help lift the bullet tip into the chamber.
If you do all that, you can really get the 223 moving and will feed reliably with these long rounds.
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Speaking of the tool, I want to throat my RPR 223 so I can load longer COAL, but don't want to spend $100+ on the tool for one barrel. If anyone has one to lend out for a month please send me a PM.
I have a bighorn tl3 action in my 223 rem build. I also have accurate mags. Best mags in my opinion from what I seen so far. I don’t wanna go too crazy hotroddimg anything but I’m hoping with .070 freebore that I’ll still manage 2900-3000 FPS with 75 eldm’s out of my 24” benchmark barrel without having to tweak the chamber
