Neck clearance

[Keith Glasscock]

Okay, I'm thinking it is time to order the reamer for my next F/TR (308) barrel. I've learned a lot with the first one, and want to optimize my reamer for the brass and game.

Here is the big question: how much neck clearance do I need? I've been running a loaded neck diameter of .332 and would like to tighten up the neck to the point where I'm not clobbering the brass every shot. Can I safely run .001"? I'm thinking that might be too tight for shooting in the dirt and rain with a barrel that might see 100 rounds between cleanings.

What would everyone suggest? I'm not entirely sold on the idea that a tight neck clearance is required to get good accuracy (at least at the levels needed for F-class). Right now, I'm shooting .332 neck ammo through a .344 neck chamber and getting surprisingly good results. What does sound good is not having to reduce the neck dia .013" every time I size it.

I have been playing with the idea of a .334 neck (.002 on my Win brass) and I could neck turn Lapua down to fit (reduce the neck wall from .0135 to .0120)

Thanks,
Keith

 

[varminthunter1]

Hi Keith.
If you have a .332" neck diameter on a loaded round, that would mean your neck thickness is .012". That is pretty thin for factory unturned brass. Yes, it is being overworked, if that is the case.
A 308 Palma Match reamer is going to be about .341-.342" neck, depending on who`s reamer you choose. I would recommend you start with quality brass (Lapua) and measure neck thickness on all pieces with a quality tubing micrometer. It should be about .014" or so. I would run about .005" clearance on a loaded round. You might be able to run without any neck turning. If you have any Lapua brass check neck thickness.
I`ll check when I get home.
Jeff

 

[spclark]

.001" neck clearance might work for some folks but I'd hazard a suggestion that it's well on the side of being unsafe. 0.003" I trust as an absolute minimum in anything other than a true BR rifle, 0.005" in a gas gun.

I'll measure some of my left-over Palma loads from last season when I get home, maybe an old chamber cast from the rifle those loads were prep'd for & get back to this thread.

 

[jscandale]

Keith,

2 or 3 thou per side would certainly never hurt you. I have made the mistake of ordering a reamer with too little clearance and it never shot any better than on with larger clearance.

JS

 

[Keith Glasscock]

Just for grins, I recently took some brand new Win brass and tried turning it at .012" It cleaned up about 80% at that thickness. .0115 cleans 100%. I suspect that .0117 would also clean 100%, but never tried. Measuring friends' no-turn Lapua brass gives me .338" average (Berger 155.5 Fullbore bullets). That calcs out to .0146 wall thickness.

Lapua has its advantages, Win has others. For now, I'm sticking with the domestic brass, and until it lets me down in the accuracy department, I think I'll stay with it.

Since I'm buying my own reamer, I figured I'd just fit it to what I have...

spclark, thanks, .003 min would have me at a .335 neck reamer - I think my smith has that one...

Now I have another question - if I use a reamer that has too short of a freebore for the bullet I want to use (for example the one my smith already has), is a throating reamer accuate and repeatable enough to be a realistic option, or should I still buy my own reamer with the throating I want?

 

[jscandale]

Its alway nice to have your own reamer, but a throating reamer will do just as good a job lengthening the throat by a competent mechanic. All it does is push the lead angle out as far as you want it and is performed in a lathe having the bore indicated just as you would set up any other chamber reamer. You can accurately increase the throat .001" or .101" or anything in between just as the chamber reamer would do.

JS

 

[Steve Blair]

FWIW, my .308 F-T/R reamer is a .337 neck for a loaded round diameter of .333, using turned Lapua brass. My reamer has a .280 freebore that is optimal for 230 Hybrids. From a 30" barrel and Lapua Palma (SR primer) brass, I am getting 2500 fps at reasonable pressure. I have gone as high as 2580 but got best accuracy at 2500. Take a look at the ballistics for that load. Pointed 230 Hybrids have a G7 B.C. >.390.

 

[dreever]

My loaded round neck diameter for no turn neck with Lapua brass and Berger 175 OTM and 185 LRBT is right on .338 so if it were me I'd just opt right now for the superior Lapua brass and buy a .340 neck reamer. Your Winchester necks are a lot thinner. Yes you could turn down the Lapua that far, but I wouldn't do it. I'd just switch to Lapua now and be done with it. My neck turner is set for .014 go, .015 no go. So I'm just giving the Lapua a very slight clean up at about .0145 per side which gives me a .337 loaded round.

Quite frankly I cannot see a difference between the no turn and the slightly turned on the target, it just gives me a bit more peace of mind.

Danny

 

[Keith Glasscock]

Thanks Steve.

That is exactly where I was headed. I was planning on running a 10 twist for the next barrel to give me the option of running the 230's and 215's. I've had great success with the 200 hybrids in a .120" freebore (measured from a chamber cast).

I have gone from the 175 SMK through a variety of bullets while learning a simple lesson. The traditional way of doing things wins if one has the skill to overcome the competition, and none of them have original ideas.

Personally, I am always looking for any ballistic advantage I can get. I'm running an 11 twist barrel right now and testing 210 JLK long tails. These bullets are easy to get 2500 out of with a 26" barrel and have a pointed BC of ~.360 (G7). I've had some indications of good precision, but I need to have more range time with them to be sure. They outperform the pointed 200 hybrid by .1"/mph at 1000. By comparison, the 230 is yet another .7"/mph better than the JLK @ 1000.

What is the bearing surface length on the 230? Where is the bullet in the neck with that freebore? What powder are you running to get 2500?

 

[Steve Blair]

My barrel is a 10" twist, probably necessary for the 230's. The bearing surface is ~.50" and bullet length is 1.64". It is a big bullet. I load them .020" off the lands for 3.130" OAL. The shank is just forward of the neck-shoulder junction and the boat tail is below the body-shoulder junction. Did I mention that this is a big bullet? I am using Reloder 17 but H4350, H414 or N550 could all likely hit 2500. I use RL17 because of high density and not needing compressed loads. My Savage with a Shilen barrel is grouping .3 MOA and below, from the bench.

The .308/230 combination is really pushing the limit of what the case can do. Capacity is the limiting factor. Even though a .280" freebore seems huge, it could actually use .330" and still have almost .25" in the neck! I have a throating reamer for caliber .30 and may try moving the throat out another .050".

 

[Keith Glasscock]

Sounds like you are in the same spot I am with the 200's. I have an OAL .140 shorter with a bullet that is .140" shorter...

I would like to have a bit more freebore myself, but for different reasons. I just spent last week cutting all of the donuts out of my brass... They do not lend themselves to significant accuracy.

I'm launching the JLK with Varget. It makes pressure without having to crush it into the case. Having done a little testing with RL-17 and LR primed cases, there is nothing there for me. I'd end up at the same velocity (cant make it to the next node safely) and temperature sensitivity.

I'm wanting to try the Palma brass, but it is awful expensive to buy a hundred just to experiment with. Maybe I will with the next barrel. This one has suffered enough messing with.

 

[thefitter]

My loaded round neck diameter for no turn neck with Lapua brass and Berger 175 OTM and 185 LRBT is right on .338 so if it were me I'd just opt right now for the superior Lapua brass and buy a .340 neck reamer. Your Winchester necks are a lot thinner. Yes you could turn down the Lapua that far, but I wouldn't do it. I'd just switch to Lapua now and be done with it. My neck turner is set for .014 go, .015 no go. So I'm just giving the Lapua a very slight clean up at about .0145 per side which gives me a .337 loaded round.

Quite frankly I cannot see a difference between the no turn and the slightly turned on the target, it just gives me a bit more peace of mind.

Danny

My loaded round is also right at .338 neck diameter with Lapua brass and Berger 185 LRBT but I slightly turn my necks just to knock down the high spots. When I was ordering my reamer Keef at Pacific Tool and Gauge suggested a .342 reamer. That way I can shoot any factory rounds I need to also. So far it's working out very well. But I do neck size in 2 steps to reduce run out.

 

[dreever]

The Fitter,

My current neck also is a .342. two thousandths to a side is nothing to worry about and I too just turn enough to take off the high spots. I suggested a .340 reamer for a target rifle, but you're right a .342 is much better for an all around rifle that may use some factory loads especially foreign manufacture. I bump the shoulder .002 every loading just to make chambering more consistant. Hasn't shown any negatives as far as my accuracy goes.

Danny

 

[thefitter]

The Fitter,

My current neck also is a .342. two thousandths to a side is nothing to worry about and I too just turn enough to take off the high spots. I suggested a .340 reamer for a target rifle, but you're right a .342 is much better for an all around rifle that may use some factory loads especially foreign manufacture. I bump the shoulder .002 every loading just to make chambering more consistant. Hasn't shown any negatives as far as my accuracy goes.

Danny

Yeah I bump the shoulder .002 every time also. I do run them through a body die after annealing just to work the brass a bit. I'm still trying to decide on a annealing rhythm to work into the cycle.