Actual Difference in .308 VS 7.62 X 51 Chamber Dimensions

shootist87122 · November 27, 2003, 22:50

Does anyone know the actual difference(s)? I’m advising two serious 3 Gun shooters on getting set up with FALs for Major Power Rifle events. Both are interested in the new FN made chrome lined barrels that DSA is coming out with, (one for a build and the other for a new DSA rifle).

Match accuracy is nice, but reliability always comes first. Far as I know DSA sets up their rifles for .308 and the reputation is they are a little on the tight side. I want to know if this is only a matter of headspace (1.630 VS 1.632 – easily corrected) or if the ID of the chamber is significantly tighter for .308.

Any help or links to a site that shows the difference would be appreciated. I’m more interested in the FN spec for 7.62 (if there is more than one military cut) as I know that FAL Milsurp barrels run well. Mine are all pretty much 100% will half-way decent Milsurp ammo.

BTW, we all shoot Aussie and have no plans to switch to any version of .308.

**EMDII** · November 28, 2003, 03:33

Here's some INFO from Cruffler:
http://www.cruffler.com/trivia-April01-assembly.html

Look for the section on setting headspace

The significant differences are
- what's allowable NATO versus SAAMI
- the thickness of the web in military ammunition that accomodates 'looser' military chambers. The thicker web allows for more expansion w/o failure of the web IF the headspace is a bit excessive.

BTW-
The FN spec is right smack in the middle of that Cruffler page on assembly of the FAL.

shootist87122 · November 28, 2003, 09:02

Thanks Ted.

I understand the headspace procedure, but that's just one dimension. I found the M14 chamber diagram from the Cruffler site (although it's too small to read) and also note that Cuffer indicates there is no such thing for FN spec reamers (only SAAMI).

I wonder if Ed Vandenberg, GP, or someone that actually cuts chambers in barrel blanks have any thoughts for setting up a simi-auto rifle (for 1. reliability, and 2. accuracy) with NATO spec ammo VS .308. For instance, did FN have a slightly increased front to back taper in the chamber or did they allow an extra .001" or so slop in the ID measurement at the web....

I posted a related question in the DSA Forum several days ago, but this seems to be a sore subject with them.

Right Side Up @ 1000 MPH · November 28, 2003, 17:16

Shootist, there are match reamers out there specifically designed for autoloaders. I know of two. One is called an "Obermeyer" reamer. My AR10 has this chamber and functions flawlessly. It was designed for M-14's in Service Rifle competition.

The other is a "Bisley" reamer. My Vandenburg FAL is chambered with this one. They are both more generous in the body area than a .308 Match reamer for a bolt gun. But they share the tight throat and less freebore of the Match reamer.

shootist87122 · November 28, 2003, 18:56

RSU,

Thanks - that's exactly the kind of information I was looking for. Now if we can get DSA to share this type of information, we will be better armed to make an intelligent decision on what to use for our brand of competition.

In a worst case scenario, can these type of reamers be used to open up a chromed lined chamber or would that be too much of a risk and/or more expensive than it's worth?

Right Side Up @ 1000 MPH · November 28, 2003, 19:11

Quote:

Originally posted by shootist87122
RSU,

In a worst case scenario, can these type of reamers be used to open up a chromed lined chamber or would that be too much of a risk and/or more expensive than it's worth?

No. If the chamber's chromed, don't plan on reaming it successfully.

I have no idea what chamber is used on the FN barrel, but I suspect it's going to be on the loose side, especially in the throat, where it needs to be tight. You'll have to get your hands on one and check it out. It would be a good idea to try and contact someone at FN about the reamer used to cut these barrels if DSA is not forthcoming with that info.

**W.E.G.** · November 28, 2003, 22:00

I know of at least one DSA "heavy" barrel that was definitely too tight (diameter - not headspace) in the chamber. It would NOT feed reliably. We polished it with the WECSOG chamber polishing tool and all was good.

See http://www.falfiles.com/forums/showt...threadid=56113

I've had a couple other brand-new barrels from DSA (one milsurp, one US) which were absolutely fine in chamber dimension.

shootist87122 · November 28, 2003, 22:06

10-4. Untill I hear otherwise, I'll Just have to assume that FN knows more about this stuff than I do!

I hope that when these hit the market we get a lot of reviews.

November 27, 2003, 22:50	#1
shootist87122 Registered FALaholic #: 7202 Join Date: Aug 2002 Location: NM Posts: 5,126	Actual Difference in .308 VS 7.62 X 51 Chamber Dimensions Does anyone know the actual difference(s)? I’m advising two serious 3 Gun shooters on getting set up with FALs for Major Power Rifle events. Both are interested in the new FN made chrome lined barrels that DSA is coming out with, (one for a build and the other for a new DSA rifle). Match accuracy is nice, but reliability always comes first. Far as I know DSA sets up their rifles for .308 and the reputation is they are a little on the tight side. I want to know if this is only a matter of headspace (1.630 VS 1.632 – easily corrected) or if the ID of the chamber is significantly tighter for .308. Any help or links to a site that shows the difference would be appreciated. I’m more interested in the FN spec for 7.62 (if there is more than one military cut) as I know that FAL Milsurp barrels run well. Mine are all pretty much 100% will half-way decent Milsurp ammo. BTW, we all shoot Aussie and have no plans to switch to any version of .308. __________________ "So in the Libyan Fable it is told, That once an eagle, stricken with a dart, said, when he saw the fashion of the shaft, it is by our own feathers, not others hands, are we now smitten." -Aeschylus

November 28, 2003, 03:33	#2
EMDII Evil Moderator Silver Contributor FALaholic #: 6 Join Date: Jul 2000 Location: Kennesaw, GA Posts: 13,971	Here's some INFO from Cruffler: http://www.cruffler.com/trivia-April01-assembly.html Look for the section on setting headspace The significant differences are - what's allowable NATO versus SAAMI - the thickness of the web in military ammunition that accomodates 'looser' military chambers. The thicker web allows for more expansion w/o failure of the web IF the headspace is a bit excessive. BTW- The FN spec is right smack in the middle of that Cruffler page on assembly of the FAL. __________________ "The Spartans do not enquire how many enemy there are. The SPartans merely enquire WHERE they are." E.M. (Ted) Dannemiller II 1*

November 28, 2003, 09:02	#3
shootist87122 Registered FALaholic #: 7202 Join Date: Aug 2002 Location: NM Posts: 5,126	Thanks Ted. I understand the headspace procedure, but that's just one dimension. I found the M14 chamber diagram from the Cruffler site (although it's too small to read) and also note that Cuffer indicates there is no such thing for FN spec reamers (only SAAMI). I wonder if Ed Vandenberg, GP, or someone that actually cuts chambers in barrel blanks have any thoughts for setting up a simi-auto rifle (for 1. reliability, and 2. accuracy) with NATO spec ammo VS .308. For instance, did FN have a slightly increased front to back taper in the chamber or did they allow an extra .001" or so slop in the ID measurement at the web.... I posted a related question in the DSA Forum several days ago, but this seems to be a sore subject with them. __________________ "So in the Libyan Fable it is told, That once an eagle, stricken with a dart, said, when he saw the fashion of the shaft, it is by our own feathers, not others hands, are we now smitten." -Aeschylus

November 28, 2003, 17:16	#4
Right Side Up @ 1000 MPH Registered FALaholic #: 9286 Join Date: Feb 2003 Posts: 1,754	Shootist, there are match reamers out there specifically designed for autoloaders. I know of two. One is called an "Obermeyer" reamer. My AR10 has this chamber and functions flawlessly. It was designed for M-14's in Service Rifle competition. The other is a "Bisley" reamer. My Vandenburg FAL is chambered with this one. They are both more generous in the body area than a .308 Match reamer for a bolt gun. But they share the tight throat and less freebore of the Match reamer. __________________ " I think that this would be the true way to go to paradise; learn the way to Hell in order to flee it". *~Machiavelli~*

November 28, 2003, 18:56	#5
shootist87122 Registered FALaholic #: 7202 Join Date: Aug 2002 Location: NM Posts: 5,126	RSU, Thanks - that's exactly the kind of information I was looking for. Now if we can get DSA to share this type of information, we will be better armed to make an intelligent decision on what to use for our brand of competition. In a worst case scenario, can these type of reamers be used to open up a chromed lined chamber or would that be too much of a risk and/or more expensive than it's worth? __________________ "So in the Libyan Fable it is told, That once an eagle, stricken with a dart, said, when he saw the fashion of the shaft, it is by our own feathers, not others hands, are we now smitten." -Aeschylus

November 28, 2003, 22:00	#7
W.E.G. Administrator Silver Contributor FALaholic #: 1211 Join Date: Oct 2000 Location: Virginia Posts: 31,052	I know of at least one DSA "heavy" barrel that was definitely too tight (diameter - not headspace) in the chamber. It would NOT feed reliably. We polished it with the WECSOG chamber polishing tool and all was good. See http://www.falfiles.com/forums/showt...threadid=56113 I've had a couple other brand-new barrels from DSA (one milsurp, one US) which were absolutely fine in chamber dimension. __________________ . . . Ask me about the Mason-Dixon FAL Collectors Association.

November 28, 2003, 22:06	#8
shootist87122 Registered FALaholic #: 7202 Join Date: Aug 2002 Location: NM Posts: 5,126	10-4. Untill I hear otherwise, I'll Just have to assume that FN knows more about this stuff than I do! I hope that when these hit the market we get a lot of reviews. __________________ "So in the Libyan Fable it is told, That once an eagle, stricken with a dart, said, when he saw the fashion of the shaft, it is by our own feathers, not others hands, are we now smitten." -Aeschylus

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