Neck size only for semi auto?

[Palmetto-Pride]

I know for bolt action some people neck size only already fired brass for the same gun, but do some people neck size only for semi autos (ARs) from brass that has already been fired in the same rifle they plan on using the ammo for?

[jwrowland77]

Most folks that use semi-auto rifles FL resize to avoid loading issues.

I guess you could neck size if you plan to load one round at a time though, don't know. I mainly use a bolt rifle.

[Brian Pfleuger]

Won't work unless you're using it as a single shot...

[AllenJ]

The people I know who reload for AR platforms usually use small base full length dies. They want accurate and reliable reloads as failures to load/eject can be a pain.

[hodaka]

Yes, it does work. I tried it for a while when I was trying to squeeze the last bit of accuracy out of a heavy barreled AR. I never had any failures to chamber but neither did I see any improvement in accuracy. I probably tried a box of bullets (100) before giving up.

[Brian Pfleuger]

I suppose it should be properly said that it may or may not work. It might work for one cycle through, highly unlikely to work the second time. It might work in one gun and not another one with a tighter chamber. It might work with some brass and not other brass. It might work with some loads and not others.

Generally speaking, it's asking for reliability issues.

It's also a safety issue in firearms with a floating firing pin. If the round fails to chamber properly, the sudden stop can slam the firing pin into the primer and ignite the round out of battery. A "slam fire". These are very bad juju. This is why people use CCI military spec primers (#41) even when brass is properly sized.

[Palmetto-Pride]

Thanks for the info guys. So it sounds like any little accuracy gain isn't worth the cons. I do it for my bolt 308 and was going to try it for my AR10 308, but I don't think I will now.

[Bart B.]

Full length sizing bottleneck cases has produced the best accuracy for decades. Most benchresters have switched from neck only to full length sizing. Their smallest groups are still the same size. But their largest ones are a lot smaller. Why it took them almost 50 years to figure that out is beyond me. Sierra Bullets figured it out in the 1950's.

[reynolds357]

Some still have not figured it out. I shoot with a current world record holder and he still neck sizes. He also still reloads with a nylon hammer instead of a press. Having said that, I agree; neck sizing is obsolete. The main reason I do it is because I can make brass last and last and last and last.

[Bart B.]

It's easy to get several dozen reloads on a .308 Win case by properly using a full length sizing die. And that's with a standard die with its neck opened up a little and cases from a SAAMI spec chamber.

Been there. None that.

[waveslayer]

Depends on your chamber. Just anneal your brass and you will be fine

[SpringOWeiler]

It's a big no no in a M76.

[pathdoc]

Having said that, I agree; neck sizing is obsolete. The main reason I do it is because I can make brass last and last and last and last.

Ditto, and especially germane to myself and others who are .303 British shooters. The other reason I neck size is because I don't need to bother lubing the cases, so that skips a case-prep step (probably two, because I don't need to worry about getting the lube off afterwards either). The full-length die comes out for range pickups and my leftover brass that was previously fired in a different chamber.

I have also made it policy to obtain a Lee loader in every calibre I load for. This way when I get around to having a holiday house, I can take my reloading "on the road" without too much trouble.

[Unclenick]

The main idea behind neck sizing-only is to better align the bullet by having a perfect chamber fit. There are a couple of issues with that. One is that since most cases are not perfectly uniform in wall thickness all the way to the head, they don't expand evenly. As a result, if you don't get the headstamp oriented the same way in the chamber every time, you actually introduce an alignment variance. This is one reason people look for "good" cases that they nurse through up to 50 reloads or so. These are ones that turned out exceptionally concentric, I believe, in addition to providing similar bullet pull. Full length sizing that just barely moves the shoulder back, still narrows the case body. That allows self-centering of the case by the taper and hole principle where the case and chamber shoulders meet. That works regardless of head stamp orientation.

I did see posts by a fellow from Finland, I think it was, who was neck sizing for an M1A. If you use a Lee loader, the scoop that comes with it usually throws a pretty conservative charge and the brass may spring back enough to let you get away with it for awhile, but not usually indefinitely. And the OOB fire hazard is real.

[Bart B.]

Unclenick's right; the main reason most folks neck size is the idea that they'll fit the chamber more perfectly. That's based (in my opinion from their explanations as to why) on the belief that chambered rounds rest in the bottom of the chamber until fired. Neck only sized case body's are a bit larger in diameter than a full length sized fired case from the same chamber; an easy thing to measure and prove. So that better centers the case neck and the bullet it holds in the chamber neck so it's better centered to the bore. A full length sized case, being a little smaller in body diameter, will end up with its bullet a tiny bit lower in the chamber; very sound reasoning and a fact of life. But things change when the bolt's closed on both types of reloads and the round's fired.

When the bolt's closed and its got a spring-loaded ejector in its face, that ejector pushes the cartridge full forward in the chamber. While it was resting in the chamber bottom as the bolt pushed it most of the way in, that ejector pushes it full forward until the case shoulder stops against the chamber shoulder. If there was a couple thousandths head clearance on that case (difference between chamber and case headspace), it would be a couple thousandths short of full forward in the chamber as it rested on the chamber bottom. Those last couple thousandths forward movement made the case shoulder slide up the chamber shoulder until the case shoulder was in full contact with the chamber shoulder all the way around where it's perfectly centered. The bottom of the case is now above the chamber bottom. And the case's front part is centered in the chamber with a thousandth or two clearance all the way around it.

Same thing happens with a full length sized case except that there's more clearance around it; its shoulder's perfectly centered in the chamber shoulder exactly like the neck only sized case. There's no difference in the neck centering precision of either type.

Bolts with Mauser type extractors may not push the case full forward in the chamber when the bolt's closed. Some have an in-line ejector whose spring will do that. The extractor lip typically has enough clearance to the bolt face that the case rim's front will not touch it when the case is full forward in the chamber anyway.

Meanwhile, at the back end of the case, it's been pushed against the chamber wall opposite the extractor. It's at the top of the chamber in rifles with a sliding extractor on the bolt side locking lug, at the left side with external Mauser type extractors pushing it to the left. So there's no way the back end of the case will rest on the bottom of the chamber when its fired. And finally, the firing pin comes along and touches the primer. . . . .very, very hard.

The force of the firing pin drives the case shoulder hard into the chamber shoulder where its forward movement is stopped; momentarily. And it's very well centered there, too, as both case and chamber shoulder angles are the same. More often than not, that force sets the case shoulder back a thousandth or more before the primer fires. The lesser shoulder angles and smaller shoulder area cartridges have more shoulder setback than cases with more of each.

Finally, the primer fires, powder burns, case expands to chamber dimensions then shrinks back a little bit. It length is usually a couple thousandths less than before it was fired.

One should surmise from this that the better centered the case neck is on the case shoulder, the better centered it would be when the round fires. That's reality. The other reality is that when the case is resized, a one-piece die with its neck perfectly aligned with its case body that minimally reduces both body and neck diameters as well as setting the shoulder back a thousandth or two ends up producing what's needed. Neck sizing dies don't hold the case body aligned with their neck axis when they're sized down. Only full length sizing dies do that. The difference is how much clearance there is around the case to the chamber wall. And when neck only sized cases get body diameters large enough to start touching the chamber body walls, they won't do it evenly all the way around; neither's perfectly round. When that happens, the case neck starts getting positioned off center in the chamber neck; it's fixed on the case shoulder and takes the bullet off center with it. Such stuff never happens with full length sized cases.

One other thing about resizing fired cases from semiauto rifles. The US Army Reserve Rifle Team tried to reload their fired cases from M14NM semiauto match rifles. New cases, especially good commercial .308 Win. match ammo, shot into 4 inches at 600 yards in the best of those rifles. CWO4 Billy Atkins (team captain) had his reloading crew try all sorts of resizing stuff to get at least that good of accuracy, Never happened. Their rifle's bolt faces were never squared up and fired cases from them had out of square heads. Resizing them didn't fix that problem. Best accuracy they got with full length sized commercial and arsenal match cases was about 8 to 12 inches at 600 yards. They quit reloading fired cases and shot only new ones whose heads were quite square to start with. This same issue was observed by the other military rifle teams shooting match conditioned M1 and M14/M1A rifles.

[Jim243]

but do some people neck size only for semi autos (ARs) from brass that has already been fired in the same rifle they plan on using the ammo for?

Can't say that some don't do this, but the idea of neck sizing only is to improve accuracy. Since most of our AR's are 5.56 and the only dies I have seen around are 223 the chamber & throat of a 5.56 will be just a hair longer than that of a 223 and I doubt that the shoulder of the case will be set back properly. As Brian has already said you will face the issue of a slam fire or a stuck case.

I hope you have a blown case removal tool, just in case the head of the case has been compromised by stretching. Otherwise I can't see any problem except maybe an over sized case every 3rd or 4th round out of a mag.

Me, I small-base full length re-size each and every round of 223 and have great accuracy with them and no feeding or extracting issues.

Jim

[bfoosh006]

Post #6 from Brian Pfleuger has a lot of merit.

Remember most gas guns are designed to work in harsh environments... so having a case freely feed is more important than any possible "1/4 moa" improvement in accuracy.

That "1/4 moa" improvement can easily be made up by other means. Finding the right charge weight that your rifle likes is a good example.



( the "1/4 moa" is just a example, not an actual, measured gain... )

[chiefr]

Hats off to Nick again.
I have reloaded for many autos, Garands, FN 49, ARs, HKs, M1As, to name a few. Autos like FL size and SB dies.

[Slamfire]

One other thing about resizing fired cases from semiauto rifles. The US Army Reserve Rifle Team tried to reload their fired cases from M14NM semiauto match rifles. New cases, especially good commercial .308 Win. match ammo, shot into 4 inches at 600 yards in the best of those rifles. CWO4 Billy Atkins (team captain) had his reloading crew try all sorts of resizing stuff to get at least that good of accuracy, Never happened. Their rifle's bolt faces were never squared up and fired cases from them had out of square heads. Resizing them didn't fix that problem. Best accuracy they got with full length sized commercial and arsenal match cases was about 8 to 12 inches at 600 yards. They quit reloading fired cases and shot only new ones whose heads were quite square to start with. This same issue was observed by the other military rifle teams shooting match conditioned M1 and M14/M1A rifles.

These guys are a lot better shots than I will ever be. I understand why case heads would be out of square in a Garand action, but when I measured multiple fired cases out of my Garand I don’t see it. The Garand bolt is asymmetrically loaded, (bending a piece of paper, hopefully will get this right) the bottom is under compression and the top under tension. Load is not applied directly through the centerline of the bolt or the bolt would fall out. Given this asymmetric loading, case heads should be a bit bent.

As for AR10’s, don’t have one (yet) but Stoner’s bolt design is very symmetrical and very stiff. Any load should be nicely distributed and assuming bolt face is in line with the bore, case heads ought to be as square as any good bolt gun.

I am not God’s true Archer, I struggle at long range. I also am a sling shooter, so things F Class shooters see in their ammunition that is lost in my hold and heartbeat. However I recently shot a midrange match with small based sized 223 ammunition in my match AR. My last stage I shot a 196 with 75 Hornady’s, one eight due to a change up and two nines that I have no idea where they came from. I doubt fatter cases would have improved anything, and would likely have created malfunctions. I shoot small based ammunition because I want ammunition that is closest to factory dimensions that I can have in my semi autos. For a well designed semi auto the amount of case clearance upon extraction is carefully studied. Neither the 223 nor the AR15 were well studied, I found a DTIC chart that showed case interference upon extraction with the 5.56, and that assumed new ammunition. The report “Understanding Extractor Lift in the M16 Family of Weapons” provides a good explanation for this phenomena. Basically, friction between case and chamber will defeat the desired residual blowback effect. Once the bolt is unlocked and the pressure low enough (and this is carefully studied and designed into the mechanism timing) there is enough pressure to basically pop the case out of the chamber but not rupture the cartridge.










All figures from Vol IV Chinn's "The Machine Gun".


If you notice in the report http://www.dtic.mil/ndia/2003smallarms/din.ppt the Ordnance Depart had to grease their case to prevent extractor lift. A dry case in a dry chamber produced so much friction that the case did not stay in the bolt face.

So given that even with factory dimensioned cases there is some friction and interference between case and chamber, fatter cases are more likely to have extraction malfunctions. Now I think the AR10 might be more tolerant as the 308 round was well studied by real experts, but, why risk it. Size to the factory dimensions for best function reliability.

[Bart B.]

Slamfire, I could easily see .308 Win. case head out of round conditions only when I stood fired ones on their heads against the "V" of a steel square, put a 10X loupe over the mouth then twist the case. The out of round circle the case mouth made as the case spun was 10 times the amount of case head out of square. I chose this method as case bodies taper down forward from case heads and as the case axis is pretty well aligned with the chamber axis when fired, any case whose body, shoulder and neck axis was not square with the case head would cause the mouth center to spin around a line perpindicular to the case head flat.

Case head's flat area's about .400" diameter. Case length is about 2.000. So, for a .001" further back one side of the case "flat" is from the other, the case mouth will tilt .010" to the side. New cases, or fired ones from my bolt gun's squared bolt face, showed zero or barely measurable out of square issues.

After checking several new commercial and military cases for head squareness this way, I was facinated by how square they all were. Military ball ammo from arsenals and commercial suppliers was the worst; some were .002" out. Lake City match brass and regular commercial ammo were very good. One lot of Western Cartridge Company match cases (WCC60) and Winchester's first Palma cases made in 1991 (PALMA 92) had the best; zero out of square new case heads for all practical purposes.

Fired cases from M1's and M14's had a .002" or so out of square issue with their heads.

I borrowed a 12mm diameter optical flat to put on a stripped bolt face to chamber in a rifle with a light spring against the chamber shoulder and it pressing it fully against the bolt face. Looking down through the muzzle with a wand light poked into the muzzle showed the muzzle's reflection off that flat. In a Win. 70 .30-06 factoy barreled action, the muzzle's reflection from that flat was not aligned with the bore. In my .308 match rifle, the muzzle's reflection was well aligned with the bore as its bolt face had been properly squared up.

[jeager106]

Short answer.
NO.
Neck sizing only is good IF you are using a target grade rifle.
In a semi neck sizing only won't do much for you.
Even in a dedicated target rifle neck size only, inside neck reaming, outside neck turning, & such is chasing your tale unless you need to shave thousanths of an inch off a group size.
Have a gun like that? Want to shoot one hole groups?
Go for it.

[Slamfire]

Slamfire, I could easily see .308 Win. case head out of round conditions only when I stood fired ones on their heads against the "V" of a steel square, put a 10X loupe over the mouth then twist the case. The out of round circle the case mouth made as the case spun was 10 times the amount of case head out of square. I chose this method as case bodies taper down forward from case heads and as the case axis is pretty well aligned with the chamber axis when fired, any case whose body, shoulder and neck axis was not square with the case head would cause the mouth center to spin around a line perpindicular to the case head flat.

I highly suspect your measuring technique and tools were better than mine. I have a RCBS Master concentricity gage, I shoved the base against the rear post and rotated the cases. I did not see anything unusual when I rotated the case.


Garands and M14's were primarly designed as service rifles. Target shooting was something later. The military never intended its Soldiers to reload and what I saw on the military teams, they got to shoot new ammunition. These rifles met their primary purpose: they were great combat rifles. Attempts to make them something different can only go so far.

I do think the AR action is a better basis for a semi auto target rifle than the Garand action, but I trust my M1a more than an AR15.

[Bart B.]

I've also used a Wilson case trimmer case holder clamped in a vise, dropped a case in it, layed a mirror from a dentist's tool on its head, then shined a laser pointer anchored up at a 45 degree angle on it. Where the laser beam refleced off of it onto the wall was an indicator of case head squareness. Rotating the case in the holder moved the beam around in a circle; bigger for cases with more out of square case heads.

[Unclenick]

You can also trim the case head with the Wilson by reversing the holder. If you tweak the stop so the cutter only just kisses the case, you can see where it starts taking metal off first.

Chucking the Wilson holder and case in your lathe will also let you indicate the breech end of the head. But by either method, keep an eye peeled for brass not only high but high at a specific location at the rim, rather than just the whole plane of the head being tilted. That can be caused by rim bend at the extractor. You can also indicate in forward flat surface of the rim inside the extractor groove to find that.

It would be interesting to resize and then trim a few case heads flat in the Wilson to see how the accuracy compares to new brass.

[Bart B.]

I did that , Unclenick.

Took 20 Remington once fired cases from a 7.62 Garand, full length sized them about .004" too long in headspace, then squared up their heads in my Wilson trimmer with the case holder reversed. Took off just enough head brass to make case headspace 1.629" and clean up the entire head. They had very slightly better head squareness than new cases.

Loaded these rounds along with 20 new cases and 20 once fired ones resized to the same headspace number with 44 grains of 4064 over Remington primers and Sierra 168's. Put an aperture front sight on the rifle the went out to the 200 yard range early one morning along with my bags of rice to rest the Garand on shooting prone with a sling.

The new cases and squared head ones shot about 1.5 MOA; 3 inches with most shot holes in the middle. The reloaded rounds with original slightly out of square case heads shot well over 4 inches, 2+ MOA, and sorta strung from 7 to 1 o'clock.