308 neck clearance recomendations

[Peterla]

Hi Everyone.

I am currently building a 308 fclass rifle. The reamer I am going to use is .339 neck size.
I am going to using Lapua cases and neck turning them down to give a specific neck clearance
The neck thickness on the cases range from 0.014 to 0.0145 so what is a good neck clearance for a 308
I would guess .003 to .004 would be ok but am looking for someone who has done this and any recommendations.

Thanks

Peter

 

[Keith Glasscock]

I use .003 with my F/TR rifle. .335 neck with .332 loaded round.

Works good, shoots HM scores at 600 despite the driver.

 

[fdshuster]

Peter: My dimensions also: a .339" chamber neck diameter with my PTG spec'd reamer, loaded round neck diameter of .336" using Lapua that has been outside neck turned to .014", just enough to remove the occassional high spots.

Life is good.

 

[stgw77]

Have custom reamer with .340" neck for F-TR rifle. Factory Lapua loaded round is .338", so I neck turn brass to loaded .336" round, thats .004" total clearance. Works very very well for me, case life is very good, no excessive pressure.

 

[broncman]

I use a .340 and no turn Lapua with very good results. Consistent headspace I feel is VERY important as well.

 

[Peterla]

Thanks for all the comments.
Looks like I will split the difference and head for somewhere around the 3.5" inch neck clearance.

Peter

 

[jsthntn247]

I have a .339 reamer and turn to .01375 per side for a loaded neck of .3355. I turned once when the brass was new and again after the first firing. I left the turner at the same setting and it took a good amount off on the second turning also(especailly near the shoulder) because of brass flow.

 

[Peterla]

Thanks for that update
Did you have to trim the case for the second turn so they were the same length.
I would like to do the same but have only ever neck turned once from new cases

Peter

 

[TimP]

Thanks for that update
Did you have to trim the case for the second turn so they were the same length.
I would like to do the same but have only ever neck turned once from new cases

Peter

If you are going to turn them again after you fire form check to see how much variance you have in case length. The .308 Win case will grow and I would not be surprised to see them vary a couple of thousands with some as much a .005 after the first firing. The case length will determine how far your cutter cuts into the shoulder and it is best to keep that as consistent as possible.
I have a .339 neck as well and I turned my necks so my loaded dimension is just shy of .336. My cases to date have been fired eight times and when I mic a loaded round I am still getting a loaded dimension of ~.336.
I have read some pros and cons on turning a second time. The biggest concern is the cut at the shoulder neck junction getting to thin and having the necks separate from the case. I am sure if done right this isn't an issue but if your loaded dimension doesn't change not sure if its necessary.

 

[jsthntn247]

Thanks for that update
Did you have to trim the case for the second turn so they were the same length.
I would like to do the same but have only ever neck turned once from new cases

Peter

I should have added this. Trim before turning the second time and set your turner where it turns to the shoulder and not into it. It will be easy to see the line where you need to stop. My brass grew about. .006 after the first firing and resizing to bump shoulders minimally.

 

[Peterla]

Thanks all for the comments.
Steering me in the right direction is greatly appreciated.

 

[artbosco]

I am currently building a 308 fclass rifle. The reamer I am going to use is .339 neck size.
I am going to using Lapua cases and neck turning them down to give a specific neck clearance
The neck thickness on the cases range from 0.014 to 0.0145 so what is a good neck clearance for a 308
I would guess .003 to .004 would be OK but am looking for someone who has done this and any recommendations.

I reload my son's 308s to give .003" of total neck clearance. .0015" on each side. With your .339" reamer that would give you an OD of .336" with a bullet seated.

 

[6fatrat]

Be advised FTR rules call for an un modified .308, you might want to confirm the min. SAMMI neck dimension.