223 rem chamber freebore/throat lengths

[Gondels]

Hey, seems to be that freebores of 223 rem bolt guns are not available information from gun manufacturers. Apparently freebore/throat length affects pressure of cartridge and I'm aiming to be able to use 5.56x45 Nato cartridges and do custom loads where longer throat adds flexibility.

I'm currently intetested in:

Tikka T3X CTR 223 rem 24" 1:8 twist
CZ 600 Alpha 223 rem 24" 1:7 twist

If you happen to have idea about freebore/throat length of weapons mentioned or can measure them I would be very happy. Also experiences with CZ one are very appreciated as there's not too much information.

 

[GuitarmanNick]

Unless the barrel is marked 5.56 NATO, do not load over .223 pressures or use 5.56x45mm rounds.
Remington .223 loads can be quite accurate.
Freebore in a 5.56 chamber is about twice that of Remington .223.
I have 4 builds using 5.56 NATO 1:8/1:7 twist barrels that I load for. To achieve the best accuracy, all of my loads are below the maximum charge recommended for .223 Remington with bullets ranging from 55 to 69 grains. They are all also below the maximum recommended COAL.
Each is more than capable of firing 5.56x45mm NATO ammunition, they just aren't very accurate when using it. The rifles are all 1 MOA or better with my hand loads. The 10.5" pistol is about 2 MOA when I am having a good day.

 

[Laurie]

Ypu might find this article interesting:

https://www.luckygunner.com/labs/5-56-vs-223/

There is a table of chamber reamer dimensions there if you scroll down ........ but the piece overall is useful / interesting.

The key dimension for you in the reamer table is 'N' (Freebore length)

Buying a factory rifle, you should (in theory) get the standard SAAMI 223 Rem 0.025 freebore, but as the 'Luckygunner' author points out, your chances of meeting such a chamber outside of a ballistics lab and its pressure barrels are low to nil, as most manufacturers put a longer freebore in to handle 5.56 / avoid litigation over people blowing their guns up / injuring themselves with unsuitable ammunition and / or dangerous handloads. So you have to hope a Tikka or CZ owner can help. Short of somebody measuring / divulging this (and I've yet to see anybody doing this for a factory 223, so I reckon your chances are poor here - but stand / hope to be proved wrong in this instance), you literally don't know what you're getting until you have the rifle in your hand and can try suitable bullets in it with a Hornady OAL gauge + modified 223 case or similar.

Unless you want to use very heavy bullets at optimal COALs (well above magazine lengths), the NATO or 223 Wylde chambers are the usual custom choice (similar freebore lengths, but smaller clearances and more shallow throat angle on the Wylde for better accuracy). Rather than a new factory rifle, you might want to look at a shot-out Tikka or similar and have a properly chambered match barrel put on with a Wylde chamber.

As @GuitarmanNick says, most 5.56 ammo isn't very accurate though.

 

[Ggmac]

Hey, seems to be that freebores of 223 rem bolt guns are not available information from gun manufacturers. Apparently freebore/throat length affects pressure of cartridge and I'm aiming to be able to use 5.56x45 Nato cartridges and do custom loads where longer throat adds flexibility.

I'm currently intetested in:

Tikka T3X CTR 223 rem 24" 1:8 twist
CZ 600 Alpha 223 rem 24" 1:7 twist

If you happen to have idea about freebore/throat length of weapons mentioned or can measure them I would be very happy. Also experiences with CZ one are very appreciated as there's not too much information.

You can measure it yourself. Remove bullet , primer and powder , lightly size a case , invert a flat base bullet , point down . Push in just enough to hold the bullet . Load and close bolt , open bolt and if all has gone well theleade will bush the flat base bullet in the case . Measure the amount . If too much neck tension , slice the neck partially . Repeat

 

[searcher]

Hey, seems to be that freebores of 223 rem bolt guns are not available information from gun manufacturers. Apparently freebore/throat length affects pressure of cartridge and I'm aiming to be able to use 5.56x45 Nato cartridges and do custom loads where longer throat adds flexibility.

I'm currently intetested in:

Tikka T3X CTR 223 rem 24" 1:8 twist
CZ 600 Alpha 223 rem 24" 1:7 twist

If you happen to have idea about freebore/throat length of weapons mentioned or can measure them I would be very happy. Also experiences with CZ one are very appreciated as there's not too much information.

This doesn't answer your question - but if deciding between the two rifles you mention - the safe bet would be the 1-7 barrel, which would presumably chambered for heavier (longer) bullets. Would be nice to get more tech info from gun manufacturers - but they don't want to advocate putting reloads in their rifles.

 

[William Vogel]

Don’t know what bullets you intend to use but the freebore and leade angle I believe is what helps the 5.56 NATO and .223 Wylde tolerate higher pressure than the .223 Remington chamber design. I have a Remington 700 that was probably a SAAMI chamber spec and I rented the PTG precision throater reamer kit from 4D Reamer rental to modify the freebore and leade angle in my rifle. It changes the leade angle from the 3 degree 10 minute angle to 1 degree 30 minutes and has a floating pilot and adjustable stop sleeve that allows precise control of the cutting depth. I increased the freebore of my rifle to the point that my cartridge length is 2.550 with hornady 80ELD bullets. I’m running them -.020 from hard jam and it took the rifle from being maybe 3/4 MOA to 1/4 MOA accuracy. Doing this also allows greater case capacity and higher velocity without excessive pressure. I had to modify the internal magazine box which was simply removing the stop bracket that Remington welded into the back of the box. The rifle will now accept up to 2.800 COL cartridges. I used the 80 ELD example because it’s what I had available to measure. I typically shoot 73 ELD from this rifle because it’s a 1:9 twist but I believe the 2.550 dimension is still pretty accurate. I also shoot Berger 70VLD and they measure 2.400 COL. Of course they won’t fit in a magazine for an AR15 but I think you’re talking about a bolt action. Here’s a picture of the difference between a mag length 77 grain load for AR and my 80ELD load for my bench gun.