Just ordered new barrel .308. .340 neck question

[fm1947]

I ordered this yesterday of course it will be months before I get it, I'm thinking loaded round should be .337 or .336 for this .340 neck. my loads now are .33750, so I'm thinking won't take much to get them right.

 

[Keith Glasscock]

Tell me more about your intended shooting environment. Dusty, rain, etc.

Also how is it going to be used? F-class, etc.

All are considerations in setting neck clearance.

 

[fm1947]

yes 600 f class and benchrest, if I have the time.

 

[Keith Glasscock]

I use .0025 clearance for my FTR rifle.

 

[fdshuster]

fm1947: You did not say what brass you are using. My 308 loaded Lapua necks are .338" and Winchester brass is .333". I'll be specing a new chambering reamer from PTG & will go with a .340" chamber neck.

pm sent

 

[fm1947]

I have many types of brass, I measured some lapua that I necked up from .260, was close to .338, my Rem brass was Right on .336, I plan to order some palma brass , what is the neck wall thickness of your lapua?

busdriver, so basically little to no clearence is that common for a match 308? because if I don't have to turn the necks other than to clean them up I will be real happy.

 

[Laurie]

Standard Lapua 308s that I've bought in recent years run in the 0.014 to 0.015 thickness ranges, some lots in the bottom half of that thou' range, some in the upper half. I have seen such brass exceed 15 thou', but not recently.

My current Palma lot runs at 0.0143" to the high 14s, none hitting 15 thou'. A clean-up neck turn takes them to 0.0144-0.0145", some cases cut down 100%, some at maybe 75% of the neck area at that turner setting.

Uniformity around necks is good, although I've seen Lapua lots in other calibres that were better still. Very few ofr my Palma cases have a greater variance than a half thou' if measured at three points around the neck.

Water capacity for my two lots of Palma brass and the most recent lot of standard 308 that I have are identical, so they appear to be made on the same machines from identical dimension brass 'coins', the only change being in the primer pocket size and flash-hole diameter.

 

[fm1947]

Laurie, great thanks, I may only need to clean up , I just measure loaded round on Win Brass, is .333, how much clearence do you run and what size neck do you have.

 

[Laurie]

Laurie, great thanks, I may only need to clean up , I just measure loaded round on Win Brass, is .333, how much clearence do you run and what size neck do you have.

My Lapua brass ammo runs at 0.337 - 0.338 depending on brass lot and whether I've done a clean-up neck-turn. I also use a good deal of elderly Norma brass that runs at 0.013" neck-wall thickness or even less. Some of the rounds I've loaded with these cases will be as small as 0.332" O/D after neck-turning. I use them as (a) I already own many hundreds having acquired them in a time many years back, and (b) being thin-walled they have larger capacity than Lapua and so can provide slightly better MVs with heavy bullets. In this respect, thyey're similar to Winchester cases, but are much, much more consistent and need less work with fewer rejected during measurement and preparation.

My F/TR rifles have all been built with minimum SAAMI chambers which means the neck section dia. will be somewhere ~0.343". That gives a total clearance of 0.005-0.006" with Lapua and 10 or even 11 thou' with Norma or Winchester cased stuff.

The GB F-Class Association 'threatens' GB league F/TR competitors with a chamber clearance test, an F/TR equivalent of the GB NRA Rule 150 in UK 'Target Rifle'. If an inert standard test cartridge doesn't chamber in a TR competitor's rifle, he or she is DQ'd on safety grounds. If it were to happen to an F/TR shooter, he or she would be moved into 'Open' as using a 308 Win rifle with a non-compliant chamber. The former likely uses a maximum dia. SAAMI / CIP neck O/D, while I'd imagine the F/TR equivalent is based on the minimum SAAMI cartridge neck O/D figure.

Personally, I've never seen any great disadvantage in having relatively generous clearances. My Norma case ammo shoots no differently from thicker wall large primer Lapua cased stuff. It will work harden the brass faster though even with minimal sizing using a bushing die, so case life will likely be reduced or the benefits of regular annealing enhanced. In fact, that's how I got these cases in the first place. Many years back my local gunshop got thousands of rounds of factory Norma .308 Win 150gn PSP hunting ammo and sold it very cheap as being 'unsuitable for reloading', users having found that a couple or three firings in slack sporting rifle chambers and sizing in standard full-length dies produced neck splits. I bought maybe 600 rounds, pulled and sold the bullets, used the Norma 201 or 202 powder in other handloads and put the primed brass on one side, finding it again when I took up F/TR.

Here is a link to another topic on this subject from last year. You'll see that not everybody is convinced that sub-SAAMI chamber neck dimensions add to 308 Win precision.

http://forum.accurateshooter.com/index.php?topic=3794300.0

 

[mysticplayer]

Played with tight neck chambers years back. What a PITA. Any case growth or dirt and zingo, you had a pressure spike thus a tossed shot.

It became a battle to keep necks thinned properly

Ultimately, I went back to more standard sized chambers and my accuracy didn't change but my piece of mind improved greatly.

Now in F class, the chance of rain where I live is very high. Water and tight neck chamber can be a bad mix. Even ammo being damp can take up enough "slack" to cause issues.

My chambers are generous enough that a fired case neck is wide enough a bullet can wiggle a bit. No chance of contact with the chamber.

I anneal and not found neck splits to be a problem. Other benefits have resulted so I am happy to add this step.

Looking at the firing process, I have to believe that the bullet is moving or already left the neck long before the neck actually expands. What happens to the neck afterwards had no affect on the bullet.

So I lean towards reliability and tight necks are not reliable under all match conditions in my opinion.

YMMV.

Jerry

 

[Keith Glasscock]

I have many types of brass, I measured some lapua that I necked up from .260, was close to .338, my Rem brass was Right on .336, I plan to order some palma brass , what is the neck wall thickness of your lapua?

busdriver, so basically little to no clearence is that common for a match 308? because if I don't have to turn the necks other than to clean them up I will be real happy.

I just do a cleanup pass on my Winchester 308 brass it comes out at .3325 and the chamber is .335. The clearance controls a number of things. Primarily, it controls the amount you work your brass, and ultimately, the total runout. Everybody does it differently. My way may not be the best, but it certainly works for me.

Just a note on safety: I NEVER fire a piece of brass on its first or second firing without running a .334 bushing over the loaded neck -or- micing it in 3 locations to verify that I have clearance. I also keep a close eye out for donuts.

YMMV,
Keith

 

[fm1947]

Thanks everyone

Laurie, that answered my question about lapua , the ones I necked up measure .337 close to .338 , that is alot of rules in UK

The Rem brass looks good at .336 and Win is .333 so I have a good choice of brass clearence , I have started seperating by weight, I haven't shot my current 308 in several years it is a Rem 700 SS, 5R, Mil Spec, so I shot it today, shot pretty good at 200 yards .4 Moa with 150 SMK and 168 SMK

Thanks again, I wanted to see what was some clearence everyone was useing, I wanted to try a little tighter neck and twist rate of 13 , just for the heck of it.

 

[jsthntn247]

I have a ptg reamer with .339 neck and will be trying for a .336 loaded round. I hope that's enough clearance.

 

[Laurie]

Glad to help a little.

Our NRA Rule 150 goes back to when 'issued' milspec 7.62mm NATO ammunition was the norm in UK 'Target Rifle'. Some of this stuff was terrible and gunsmiths took all sorts of measures to reduce the downsides and produce enough velocity to shoot it to 1,000 yards - 'tight bores', 1-13 or even 1-14 inch rifling twist rates and suchlike. A few started reducing the chamber neck dimensions too .... And then one sunny day, the NRA bought a large amount of imported 7.62mm which had an outside neck dia. that was right on, or maybe a bit above, the maximum allowed tolerance, and the rifles with tight and/or slightly short chambers produced excessive pressures. Since Musgrave and Swing actions are pretty (very!) strong, I don't think anything broke or anybody got hurt, but there were fired cases that didn't want to be extracted and people using cleaning rods on the firing line to get them out. It soon became obvious that there was a potentially dangerous situation developing, so Rule 150 was introduced and inert cartridge gauges used before major matches to ensure everybody's rifle had enough clearance.

PT&G has a 'Bisley 150' reamer that meets the minimum spec and which is nevertheless a very good chamber for 308 match use with the original 155gn Sierra MK. Looking at my PT&G produced 'The Gunsmith Book of Chamber Prints', I see it's officially called "308 Palma Bisley (Bisley 150 Rule)" and the neck is shown as 0.3435" dia.

 

[savageshooter86]

I like the idea of having 3-4 neck clearance. Just to help not over work the brass. Don't know/think if it adds accuracy to the 308 win

Sounds like you will be spot on with what you have

 

[6BRinNZ]

(b) being thin-walled they have larger capacity than Lapua and so can provide slightly better MVs with heavy bullets.

Hi Laurie - do you find the Norma brass primer pockets hold up to the pressures ok? I have heard in the 6mm class that brass life and fps is ultimately better in Lapua due to the ability for the pockets to hold up to high pressures compared to Norma.

I am asking as a wholesaler we deal with has picked up the Norma dealership and is keen for us to try the brass - I'm keen because Norma seems to have a reputation for consistency and the slightly larger case capacity.

Have you found a noticeable improvement in MV? or in FTR terms is it a bit of a wash?

TIA

 

[Laurie]

This Norma 308 brass is very strong and gives a lot of firings. I used it last year with the 168gn Hybrid over Varget at around 2,925 fps which isn't quite as hot as some people run their loads for F/TR in the UK - ME wise, it's equivalent to the 155.5gn Berger at ~3,040 fps which is almost what I now run this bullet at in small primer Lapua Palma brass. So far, nothing has worn out despite some cases having five or six firings.

However, this stuff dates from the mid 1980s, so isn't probably much use for predicting anything with current brass. (I have 200 current 308 Norma cases, but they've yet to be loaded.) I do know that Norma had a bad spell 10 or maybe more years ago with rather soft case-heads.

My experience with recent Norma is with 6XC which is very strong indeed and with .204 Ruger, but the latter using soft match loads. Both of these calibres are very consistent and look excellent quality. The only fault I've found is that my lot of 6XC brass has slightly shallow primer pockets which need reaming before the first loading otherwise primers sit slightly proud. A lot of our F-Class competitors shoot the 7mm/270 or 7mm/300 WSM and Norma brass is the usual starting point for these very hot rounds.

So far as the extra capacity goes, the velocity gains aren't that great, although it does depend on the powder. With some slower burners, Lapua might not hold quite enough to get maximum pressure, or does so with a heavily compressed charge. We've now largely shifted to Lapua 'Palma' brass for the heavies in F/TR as these cases offer enhanced velocities and reduced extreme velocity spreads in this application. This doesn't just apply to F/TR. Norma brass was used by some British and British Commonwealth 'Match Rifle' competitors until the Lapua Palma case appeared. (MR is a 1,000 to 1,200 yard discipline in the UK and out to yet further distances in Australia for .308 Win rifles - see http://nrcofs.org/MatchRifle.html

 

[fm1947]

I'm putting this barrel on my Savage Target action, I had Bruno true it up, I have a 30BR Krieger on it now , but I had Shilen build me a new 30BR with thier action and trigger and barrel, So I'm going to put this new 308 on my Savage, I am also having a muzzle brake on it, being retired I shoot almost everyday in my backyard where I have a 200 yard target, and I have some shoulder problems and trying to avoid an operation, so recoil is hard on me at 66 years young, I shoot free recoil with my 30BR but my 308 Rem 700 will jump of the bench if I try that, so I'm going to add some weight to the new setup some how because I know in Bench Rest you can't use a muzzle brake, our F-Class is not a sanctioned match so I believe I will be able to leave the brake on it, today and yesterday was the first time I shot my 308 Rem in 3 years or better, you might be wondering why shoot a 308 if I have shoulder problems, long story , but it's all about sales.

 

[Mr. Ten-X]

In my conversations with Mr Kiff on a 308 reamer set for neck-turned Lapua, he steered me toward .003" minimum clearance and felt that I'd likely see no accuracy difference with .004" clearance. My initial test loads will be a loaded diameter of .3365 give or take a smidgen. The reamer is a 340NK.

 

[mysticplayer]

New Norma is wonderful stuff. Packaged in egg crate box for 25 cases.

THE nicest brass I have ever shot out of the box and it is strong.

When you get the box, see where it is manufactured.

Does NAMMO ring any bells?

Very expensive but if you can accept the costs, great stuff.

Jerry