308 Win deficiency?

gunrunner8

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Yes, I know 308 Win is proven performer, accurate, efficient etc, etc and it is hard to argue with the success. Me? I have mixed fillings about the chamber design. Well I measured close of doz different 308 Win brass, military brass included and found out that the biggest dia of the neck with loaded bullet is almost .337", usually about .332" to .334". I have 3 x 308Win rifles and chamber necks are .3445 or so. I am thinking about building new target rifle, bought the barrel, action and reamer. Stock on the way. Now the question is; the reamer's neck dia is .344", wouldn't be wise to send the reamer for neck reducing dia (I think it is) if so to what dia? Benchresters are useing .002" clerance so even with slight "cleaning" of high spots on brass, the .338" dia would be plenty big even for the military brass and I would be able to squeeze even more accuracy. I also noticed that 7x57 has the same problem with "oversized" chamber neck . Any advice?
 
Lapua Brass runs around the .014-.015 brass thickness at the neck (Win runs about .013 avg). Lets say you were to turn the necks to .0135 to even them all out.

.0135 + .0135 + .308 = .335 loaded round + .003 (.0015 each side) = .338

If you cleaned up to .014 then your at .339 with .003 clearance.

You can order your reamer to whatever spec you want but if you want a no turn neck chamber then you would have to know what the thickest brass you would be running in it and add .0015-.002 to each side for clearance.
 
I'm running a Kiff reamer in my .308's. I told him I wanted to use unturned Lapua brass and he recommended a .341 neck. My loaded rounds are right around .338, so .0015" clearance each side. FWIW. Seems to be working.
 
20-30 years ago the norm in "Target Rifle" shooting was to use issued military ammo. Pretty much any trick you can think of to improve the performance of the ammo from "poor" to "at least consistently mediocre" was tried. (Fortunately the days of "tune to the rifle to the ammo" are behind us now).

Some rifles were built with tighter necks, based on observations of the ammo actually used. I can't recall if neck diameters of .340" or .341" was used. I don't think these rifles had a note of this tight neck stamped on their barrel but to be honest even if they did it would have made little difference. Some time later these rifles encountered problems, some ammo came along that was an interference fit to these chambers. (note that the ammo was not defective, it was within accepted norms).

Quite honestly I would recommend to not sweat it, and to use a standard neck diameter (e.g. brass fired in my .308 Obermayer measures .343"). I wouldn't absolutely recommend against mpwolf's .341" neck, but really that should only be done if you are pretty sure that you will always own the rifle and therefore know what you can and should not be doing with it.

By the way you will not find any accuracy advantage from a tighter neck clearance.

As for brass life (really the only other possible reason to consider tighter necks) you can reasonably expect at least 20 firings from a neck that is cycled from .335" to .344" on each firing. Even if you are paying a buck a case this still means that your per-shot cost of brass in down in the noise.

With respect to turning necks for fullbore shooting, I have yet to see anyone show any real benefit from it. I know that Palma matches (i.e. long range world championship team matches) are won with unprepped brass.

Personally I just take Winchester or Lapua brass as-is (sometime sorted by weight but usually not), load and shoot.
 
There are literally dozens of magical 308 chambers claimed to be better than anything else. I agree with Matt: A Kiff reamer is just fine. I would be more concerned about the throat length. This determines what bullets you can optimize for your rifle.

Mick McPhee in Kamloops has a few excellent 308 reamers, and he shoots 30 cal exclusively. I would chat with him.
 
A second vote to talk to Mick. Local and knows a thing or two :)

If you can't decide, Clymer M852 reamer. Works really well, clearance in all the right places and tight where needed. Nothing special but it works and I have shot this chamber with super results.

Many gunsmiths will also have this reamer.

Tight necks DO NOT improve accuracy. They just help support case necks especially when they are super thin.

If you are shooting this rig in weather, more clearance better.

Jerry
 
Tight necks DO NOT improve accuracy.
Jerry
I just have to take your word for it. It is hard to belive b/c the benchresters do prep their brass religiously with no more than total of .002" of neck clearance. I think I will compromise and use .440" neck for use as is Lapua brass and I will talk to Mick, he is good friend of mine and I value his opinion greatly. Thank you all for your input.
 
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I agree it is hard to believe but it really is true. BR shooters go with "tight necks" or with "fitted necks" in order to make it easier to work with their brass (only need to shrink the neck by 1 thou to half a thou at each loading) and also by to make the brass last for many, many loadings (as in 50-100 or more).

Most .308 target reamers will use "min spec" dimensions in most locations ( i.e. they conform to the standards but they are right at the minimum allowable dimensions) for reasons of safety and/or convenience and compatibility.

I will try once again to persuade you not to use a .340" neck. It is an accident waiting to happen, especially by a person other that yourself who built the rifle and knows and understands this particular feature of your .308. Lapua brass certainly will fit and will be safe, as will 99%+ of all commercial and military brass you will ever encounter. Which in a way makes it even more of a subtle and lurking danger; some day somebody (you, a friend of yours shooting your rifle, or perhaps someone you have sold the rifle to) could chamber a round of Portugese or Spanish milsurp ammo with a .341" or .342" neck, and be set up for an extra 10,000psi or 15,000psi. This may or may not turn into an accident, but it is a good step down that road.

In a way a real tight neck chamber (like .333") in which basically no commercial ammo will chamber is perhaps safer and less likely to get into an accident.
 
One more safety thought - if you go with a neck anything besides SAAMI, make sure your smith STAMPS the neck chamber diameter on the barrel.

It may go into the chamber but if the neck cannot expand when you pull that trigger, think KABOOM....

If you decide on min clearance, make sure your case prep is meticulous and constant. Brass flows and what is 12 thou today, can be 13 thou after a few firings. Add in a bit of fouling and you may have a very exciting day.

I am just as interested in case life as the next guy. Maybe more so, as I shoot wildcats and forming brass is a bit tedious sometimes. I know things are ok when a bullet can slip into the neck after firing. This proves there was enough clearance even with spring back.

If a bullet CAN'T go into the necks after firing, sure hope that was the intended consequence and the shooter is on top of all loading aspects cause there is no room for error.

It is ironic that we see alot of comment on tight neck chambers and the possibility of better accuracy yet, the parts that do matter - throat and leade - are hardly ever discussed.

Jerry
 
Tight necks serve a variety of purposes in BR. Brass life is one, as mentioned above. Nobody hates brass prep more than BR shooters since we do so much of it, and any excuse to get away from a tight neck would be welcome. Unfortunately once you get beyond about .004" of clearance, accuracy will suffer in the context of BR competition. For F-class I can't imagine tight necking a chamber. You would have have to prep hundreds (500+?) of brass at a time. If you go this route be sure and stamp the neck diameter on the barrel as a reminder.

FWIW it would not be that easy to get oversize brass into a tight neck chamber, otherwise BR shooters would be blowing barrels up any time a mistake was made in turning necks too fat or the donuts impinged on a deep seated bullet.
 
Thanks Rick always nice to hear from a BR shooter, since I only know about BR stuff second-hand!

When you say 4 thou of clearance, do you mean 2 thou on each side, or 4 thou on each side?

Yes a smaller-than-min tight neck should always be stamped on the barrel shank but realistically that does little to prevent accidents. Even moreso when the rifle is chambered in an extremely common commercial/military calibre such as .223 or .308. With such a wide variety of ammo available, Mr. Murphy is sitting there waiting to pull a trick on you (or worse, the poor guy ten years from now who bought your rifle from the guy that you sold it to).

With a purpose-built F-Class rifle in 6.5-.284 the risks would be a lot lower. If I make up a reamer so that I can use "no turn" Lapua 6.5-.284 brass, say, perhaps about the most exotic thing that's going to happen is that somebody will try using Norma 6.5-.284 brass. It's not like there is a bunch of weird milsurp 6.5-.284 out there that might mistakenly be used. Even if somebody is forming brass from .284 Winchester, there is a better chance of a reloader doing a calibre change operation to a piece of brass paying attention to and catching the neck diameter of the chamber.

I suppose I must sound like a safety ninny warning people away from using tight necked .308s. I guess what makes me push just a bit harder on this warning is that there is a modest safety risk to it, with absolutely no accuracy benefits to be had. You can win an F-TR match using a chamber that has a SAAMI min spec neck diameter.

And what Jerry said about the important parts being throat diameter length and leade angle, he's right, that's by far the more important part to fuss about. That can let you optimize your .308 to the bullets that you plan on using.
 
.004" total clearance, or .002" a side. Lots of experiments have been run on this topic and most eventually come back to the notion of a tight neck for BR purposes. Even the no turn necks made a brief appearance in BR over the last few years, and have now disappeared. The trend now is to light turn necks, but still tight necks. Preference being to getting the tight neck on only 1 neck turning, instead of the 2 neck turnings the thinner necks require. Saves time!

A few general comments. This oversize neck issue shows up in most BR shooters exploits eventually. It may be donuts, bad calipers, fat bullets, bad math at work, but it happens. Symptoms are usually along the lines of erratic shots and/or hard bolt closing. Since the rifles don't blow up, and there are no weird pressure signs it can be difficult for shooters to figure out what the problem is. Eventually the brass will become the leading suspect, and voila, an interference fit is discovered, screwing with the release of the bullet!

Tip for everyone using tight necks. Super fast and easy way to check for this issue is to buy a sizing bushing the same size as the chamber neck and slip it over a loaded round to see if you have clearance. For example if you have a .269 neck get a .269 bushing and a .268 as well and slip over the loaded rounds. Much faster than calipers.

FYI I still would not advocate a tight neck for Fclass or TR, not really for safety, but the shear volume of brass preparation and the potential inability to borrow or shoot factory ammunition at a distant shoot should it be necessary.

We may have 2 disciplines colliding here on this topic, since in BR the tight neck issue is the norm and everyone is accustomed to it, vs the Fclass world where other issues dominate the choice of reamers.

My .002 if you will.
 
According to Kiff, .263 and .269 are running neck and neck in sales these days. Pun intended! This is for the 220 Russian by Lapua.

If you go the new Norma 6PPC brass, you will need the .262-263, as it is much thinner than Lapua.

Of course there are still many .262 reamers floating around. Point of history here, the .262 became fashionable because that was how thin you had to carve the old Sako brass to clean it up for a tight neck. Once the Lapua 220 Russian showed up gunsmiths already had the 262 reamers on hand and they stuck with them. Slowly the 269 is creeping in.

FYI the 263 reamer is popular today because the leading Hall of Fame points man (Tony Boyer) likes the 263.
 
FYI I still would not advocate a tight neck for Fclass or TR, not really for safety, but the shear volume of brass preparation and the potential inability to borrow or shoot factory ammunition at a distant shoot should it be necessary.

We may have 2 disciplines colliding here on this topic, since in BR the tight neck issue is the norm and everyone is accustomed to it, vs the Fclass world where other issues dominate the choice of reamers.

I think that's exactly it. The fullbore world (TR/Palma and F-Class) is one of the most accurate forms of rifle shooting, and there's always good reason to look for a bit more exploitable accuracy. There is only one game out there with higher levels of accuracy and that is BR, so it is only natural to look to the BR world to see which of their tricks ad techniques can be imported to our game. Many can, but not every thing that BR shooters do ends up being useful in fullbore. Advanced techniques involve many subtle tradeoffs. Sometimes a given technique is overall beneficial in BR (and is therefore commonly done and it helps people win) but because of the tradeoffs involved it can be not helpful (or even worse off overall) in fullbore.

When trying to figure out what to do and what to not bother doing, it's useful to consider the relative importance of things. For example let's say you want to get decent accuracy out of a factory hunting rifle. Based on knowledge from fullbore and Benchrest, you know that bullet quality matters and so does brass quality. But before you worry about getting some Lapua brass for your hunting rifle you should realize that the accuracy effects of mediocre brass are *far* smaller than the accuracy effects of middling bullets (brass is at least ten times less important that bullet quality). So while it is *definitely* worthwhile trying out top quality bullets in your factory hunting rifle, quite honestly any old piece of junk brass will do the trick just as well as the very highest quality brass that you can get. It's not that the good brass isn't better, it's just that the improvement it gives you is so small that it will always and forever be complete lost in the inaccuracy "noise" from the other parts in the system that are less-than-perfect (e.g. bedding, barrel quality, action lockup squareness etc). Using good bullets is a big enough improvement to be worthwhile and it can give you improvements bigger than the "noise"; using good brass isn't.

If a good target rifle can shoot 1 MOA at 500 yards with crappy brass and your hunting rifle is shooting 3 MOA at 100 yards, using better brass is not going to help your hunting rifle. Whatever it's problems are, they are *much* bigger than any brass problem might be. Go find and fix something that will improve your accuracy by 1 MOA or 1.5 MOA (e.g. bullets barrel or bedding), don't waste your time with something that *might* be worth 0.1 MOA (quality brass) or 0.02 MOA (turned necks).

While fullbore rifles are more accurate than 99% of the rifles out there and they are built to very high standards, they still have "noise" of their own. While this noise is pretty small, it's still enough to overshadow and completely bury a whole bunch of really-tiny improvements that are out there, are real, and are being successfully used in the BR world.


My .002 if you will.

Ha! (Colour me slow, I didn't get that the first time around....! ;-)
 
Dan I think you are absolutly right about the *noise*. I'm definatly guilty of doing things because they can't hurt, and quite honestly, I fall into the camp that thinks if I think it helps, it sure can't hurt.

As for the necks, I don't neck turn because of the numbers involved. Keeping 200 pcs ready to go for a rifle is bad enough, but 500 is pretty much needed if one doesn't want to sit in a hotel room loading ammo during a week long match. The only real reason I can see doing it would be if one were stuck using brass with inconsistant necks. I feel that consistant necks should give more consistant neck tension case to case, and therefore should help to produce smaller ES/SD's which are a big deal at long range. With the numbers involved in Fullbore and F class, you are probably further ahead buying good quality brass, checking to verify the necks are consistant, use top quality bullets, and make damn sure your powder charges are consistant.

Insidentily Dan, do you size your necks from .344 to .334 in one step? If you do how do you keep the runout down? Seems like size down 0.010" in one step could induce some pretty spectacular runnout...
 
[....neck turning....] The only real reason I can see doing it would be if one were stuck using brass with inconsistant necks. I feel that consistant necks should give more consistant neck tension case to case, and therefore should help to produce smaller ES/SD's which are a big deal at long range. With the numbers involved in Fullbore and F class, you are probably further ahead buying good quality brass, checking to verify the necks are consistant, use top quality bullets, and make damn sure your powder charges are consistant.

I think the #1 brass prep step to be done is to.... buy good brass. If it is available for your calibre, get Lapua (or equivalent quality-level) brass.

For many, many shooting games, that's all the brass prep needed. For TR shooting, I used unprepped Lapua .308 brass and also unprepped Winchester brass.

For higher levels of accuracy needed e.g. F-Class it may well be worthwhile to do some very light neck turning for the purpose of making the neck tension more uniform. Personally I think that before investing the time in doing this, it is a good idea to have invested the money in good brass to start with. Neck turning will make necks uniform and concentric but it will not fix any non-concentricities in the body of the cases.

Insidentily Dan, do you size your necks from .344 to .334 in one step? If you do how do you keep the runout down? Seems like size down 0.010" in one step could induce some pretty spectacular runnout...

My fired brass is 0.343". My Lapua brass I size in one step with a .335" Redding Bushing (so 8 thou not 10). Concentricity is pretty good. This is with a "Competition" sizer die, whose micrometer adjustment I have always disparaged as being useless bling. Perhaps the sliding sleeve that it has has been helping me all along, keeping my necks reasonably concentric with this one-step sizing?

I don't have a bushing small enough for my Winchester brass, so I use a regular fixed Redding neck sizing die (which just _barely_ gets it down to the .333" or so that is needed).

With both Winchester and Lapua brass, sized as above, my runout for my .308 ammo is typically 2 thou total indicated runout, with some rounds as high as 3 thou. No idea if you would consider this "ok" or "awful"....?


- Daniel
 
It's nice to hear that simple sizing steps, taken w/ good quaility dies, can top quality ammo. I don't consider 0.002-003 awfull at all. I cna't tell the difference in perfornce between no detectable runnout, and 0.003 with the barrel I'm currently shooting.
 
Even at BR levels, the accuracy advantage shown by a tight neck is related to the chance of misalignment of the neck during the sizing operation more than to anything that happens during firing. At accuracy levels of 3/8 moa or greater, it is unlikely one could tell the difference between a tight neck and a loose one.
Again, the great asdvantage to a tighter neck is that there is less chance of misalignment when sizing when you size less. Regards, Bill
 
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