Please help me understand chamber dimensions...

[DoSqH]

Not all of them...but in particular the neck and freebore.

The rifle I just picked up was chambered with a 223 Remington Match chamber reamer. I was told that the neck dimension is .253" and that is has 0 freebore.

Typically when loading for my Service Rifle I've always used LC brass, unturned necks, and a Redding S die with a .245 bushing. All of the barrels were White Oaks and chambered with a 223 Wylde reamer.

So in this new Remington Match chamber it's my understanding that the throat is right there at the end of the case mouth...and the lands right there too. So seating to touching the lands will have to be measure for each of my bullets vs. previous loads. From a neck tension standpoint would I benefit from turning my necks and finding a new bushing size to better suit this chamber?

I feel like I'm missing something here and looking for a little guidance on where to learn from.

Thanks!

Jake

 

[spife7980]

The .253” is the diameter. Measure the neck diameter of a loaded round. You want .003” difference in then minimum for a field rifle.

.253-.224=.029” of neck thickness possible for an exact fit. -.003 for clearance gives you .026 of total brass thickness possible.
.026 divided in half for the thickness of each side gives you a neck thickness of of .013”

My loaded 223 with lapua brass measures .249 (.013 neck thickness) so it would be a pretty exact match fit for your chamber without measuring.
If I were to use brass such as lake city which should have a neck thicker than the .013 that my lapua does then I would want to turn to have enough clearance.



For freebore, yes. You will always want to measure each different bullet you would be loading to find the proper seating depth. With zero freebore shooting long heavy bullets you will severely be robbing case capacity by shoving the bullet so deep into the case. For shooting light 30-50 gr bullets I doubt you will have too much issue.

What’s the twist rate of the rifle? Given the freebore I’m betting it’s a 12-24 twist so shooting heavy bullets would be out if the question right off the bat.

 

[DoSqH]

Thanks, @spife7980. This is what I'm looking to learn more about. I appreciate your reply.

Barrel is a 20" Bartlein cut 5R 1:8

I'm very interested in optimizing a 75/77/80 load of either Hornady or Sierra bullets I can buy in bulk. If they prove to be challenging I'll move to something more boutique like Bergers.

Very excited to document and share in order to have some more learning input sent my way.

 

[spife7980]

I would get a box of 100 first just to make sure they will fit with your zero freebore. You’re going to want to measure everything.



The 8 twist should handle up to 80s fine stability wise. Seems strange they would do a fast twist barrel with zero freebore... definitely measure to your lands.

 

[Huskydriver]

The .253” is the diameter. Measure the neck diameter of a loaded round. You want .003” difference in then minimum for a field rifle.

.253-.224=.029” of neck thickness possible for an exact fit. -.003 for clearance gives you .026 of total brass thickness possible.
.026 divided in half for the thickness of each side gives you a neck thickness of of .013”

My loaded 223 with lapua brass measures .249 (.013 neck thickness) so it would be a pretty exact match fit for your chamber without measuring.
If I were to use brass such as lake city which should have a neck thicker than the .013 that my lapua does then I would want to turn to have enough clearance.



For freebore, yes. You will always want to measure each different bullet you would be loading to find the proper seating depth. With zero freebore shooting long heavy bullets you will severely be robbing case capacity by shoving the bullet so deep into the case. For shooting light 30-50 gr bullets I doubt you will have too much issue.

What’s the twist rate of the rifle? Given the freebore I’m betting it’s a 12-24 twist so shooting heavy bullets would be out if the question right off the bat.

^^^Nailed it... You may have issues running heavies optimally as he said with no freebore just depends on how the lead into the rifling was cut.

 

[918v]

Zero freebore chambers need to be throat reamed for the bullet you’re going to use. Zero freebore won’t work with the heavies. Make a dummy round and you’ll see.

 

[bax]

Zero freebore chambers need to be throat reamed for the bullet you’re going to use. Zero freebore won’t work with the heavies. Make a dummy round and you’ll see.

Mr. 918v, seems to me that you may be jumping to a conclusion. As a guideline, I agree zero-freebore should not be ideal. I shoot 77 SMKs seated deep to fit in a magazine and they shoot pretty well. People do all kinds of odd things but it strikes me as peculiar that someone would chamber a 1:8 barrel for light bullets. Maybe the chamber is not quite as reported. I would give it a shot.

 

[918v]

I jumped to my conclusion based on the 6.5” twist rate which is not designed for mag fed 77’s. It’s for 80+ grain bullets who need a freebore.

 

[bax]

I jumped to my conclusion based on the 6.5” twist rate which is not designed for mag fed 77’s. It’s for 80+ grain bullets who need a freebore.

Jakeb posted this: "Barrel is a 20" Bartlein cut 5R 1:8 " at Thursday at 12:56 am. I cannot find "6.5" anywhere in this thread.

 

[918v]

That’s because I was thinking of the other thread when I replied to this one. I’m suffering from thread confusion. Too many threads.

 

[Lynn Jr]

The 0.253 is the chamber dimension so if your loaded rounds are 0.249 you have 0.004 clearance or 0.002 per side.
All you need to do is seat a bullet in a dummy round and then measure the neck on that round and see how much clearance you have.
The zero freebore gets used for two reasons
One is for lightweight bullets and two is so your bullet will fit within a magazine limitation.
The 223 WSSM and the 243 WSSM both have to fit in the same length magazine. The 243 runs 100+ grain bullets so Winchester just seated them very deeply.
It looks funny but it does work.

 

[DoSqH]

Thanks @Lynn Jr, this helps also!

 

[Lynn Jr]

Jake
Should you wish to just shoot heavy bullets and the magazine length isn't an issue you can have the throat lengthened by a gunsmith or you can do it yourself using a Pacific Tool unithroater at home.
It's easy to do.