Neck turning or Concentricity gauge?
- Thread starter rayatphonix
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I'll add ........
Those tiny groups benchrester's win matches with are shot from free recoiling rifles resting on slippery top bags touched only by their owner's index finger on their hair trigger. They're extremely repeatable in their movement shooting bullets out their barrel.
If that rifle is held by its owner's hands against his shoulder as it rests on anything, those groups will be much, much larger. Us humans cannot hold any rifle perfectly repeatable while its ammo shoots bullets through its barrel.
Which often means our rifles and their ammo are really more accurate than we shoot them as we hold and aim them.
Those tiny groups benchrester's win matches with are shot from free recoiling rifles resting on slippery top bags touched only by their owner's index finger on their hair trigger. They're extremely repeatable in their movement shooting bullets out their barrel.
If that rifle is held by its owner's hands against his shoulder as it rests on anything, those groups will be much, much larger. Us humans cannot hold any rifle perfectly repeatable while its ammo shoots bullets through its barrel.
Which often means our rifles and their ammo are really more accurate than we shoot them as we hold and aim them.
spitballer
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...yes, and in fairness I've cheated by adding ballast to help minimize that movement. I also took some advice from the late great rcmodel and put a small tuft of polyfill in the neck. Nevertheless, I can still detect a 1/2 moa split with a couple of later rounds dropping straight down the middle and if I thought I could get away with it I'd be inclined to bump up the charge. Do FMJ's tend to produce this same pattern?
Yes. Why not?
Only the bullet jacket touches the rifling, so there's no difference across all types of jacketed bullets. The rifling doesn't know what the rest of the bullet shape is so its engraving the jacket is the same for all jacketed bullets and changes only with the jacket thickness and metal properties. Good lots of Lapua FMJBT bullets with open rebated bases shot as accurate as Sierra HPMK's. Arsenal 30 caliber 172-gr FMJBT match bullets from a good machine would shoot as accurate as Sierra's original 30 caliber 180-gr FMJBT match bullets with hollow base exposing the lead.
Back in 1970 when Sierra Bullets introduced its first 7mm match bullets, when shot in the 7mm Rem Mag, they sometimes split apart having been engraved too deep which weakened the jacket. The Hart barrel (in the rifle owned by Sierra's ballistic technician) my friend used to set the Wimbledon 1000-yard record with them that year had shallower grooves along with a very uniform lot of jacket material in his bullets from Sierra. I've seen a few fly apart about 100 yards down range shot in some barrels. Obermeyer Barrels started using a 5R style of rifling which more mildly engraved those 7mm bullets and they stayed intact. Sierra made some of those match bullets with thicker jackets, but they didn't have as good of thickness uniformity and didn't shoot as accurate as that first batch of .284" 168-gr HPMK bullets.
What type of surface coating does that burned polyfill residue put on the lands and grooves? Is it 100% even all the way around the bore?
Are you implying the rifle's movement during barrel time is minimized by stuffing stuff behind the bullet in the case? What's the difference in recoil energy against the shooter's shoulder? Doesn't adding the mass of the polyfill add to the mass of the bullet so with a given powder charge, recoil will increase?
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spitballer
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Jim Watson
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Arsenal 30 caliber 172-gr FMJBT match bullets from a good machine would shoot as accurate as Sierra's original 30 caliber 180-gr FMJBT match bullets with hollow base exposing the lead.
I don't doubt that but there were a lot of 172 gr military match bullets replaced with open tip SMKs as "Mexican Match." Were those shooters wasting time and money?
I don't doubt that but there were a lot of 172 gr military match bullets replaced with open tip SMKs as "Mexican Match." Were those shooters wasting time and money?
No. All M118 ammo lots had bullets from a few machines. Cases, primers and powder was single lot stuff.
I shot thousands of rounds of Mexican match. Some I made, others by a good Mexican friend or someone else at the Unit made for USN teams. All the military teams used M80 ball and M118 match ammo re-bulleted with 168's. Some used Sierra 180's in M118, Army usually.
It shot in tests near half MOA at 600 yards from M1 and M14 rifles.
I shot thousands of rounds of Mexican match. Some I made, others by a good Mexican friend or someone else at the Unit made for USN teams. All the military teams used M80 ball and M118 match ammo re-bulleted with 168's. Some used Sierra 180's in M118, Army usually.
It shot in tests near half MOA at 600 yards from M1 and M14 rifles.
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spitballer
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...right, and this is why I don't understand why ball ammo doesn't have a reputation for accuracy. With a closed tip even a thick jacket made of a hard enough alloy can be made highly accurate with enough pressure, right? Please excuse my ignorant interjection here, but isn't the military simply eschewing lubricants and coatings by using tougher jackets at higher pressure?
Ball ammo’s made with material with loose specs for uniformity. It has to work to an acceptable level in the worst of combat environments. Which is why military ball ammo bullet diameters are smaller than the rifle barrel’s smallest groove diameters so barrels in worst condition, wear or fouled, would still shoot good enough for combat use. It’s got heavily crimped in bullets so OAL specs are met for reliable operation in autoloading weapons, powerful but not too uniform primers, bullets unbalanced to some degree but durable in handling, 60 to 70 fps spread in muzzle velocity and case necks not to straight overall on case shoulders. And their quite out of square case heads make barrels point at all the numbers on the clock when the bullets leave; mostly right angles to the bolt locking lug axis. All devastating for best accuracy.
It's like picking the best tool to use for chopping down a tree and brain surgery when the only two tools available are an axe and scalpel.
That said, Lake City arsenal’s lot 12638 of M80 ball ammo made with IMR4475 powder and bullets miking .3078" diameter shot almost as accurate as their M118 match ammo thru 300 yards with bullets miking .3085" diameter in the USN Garand barrels whose groove diameter was also .3078". Those barrels were selected from a few hundred made by Springfield Armory in MA air gauging them for groove uniformity. All those .3078" uniform and smaller were set aside for match grade Garands. The others gauging up to .3085" were set aside for normal service use at Recruit Training Commands. Such is life when a rifling broach is used to cut the grooves in several barrels before it gets worn out. Barrels made at the end of the broach life were the most accurate.
Radway Arsenal in Great Britain made M80 ammo for the Kindom’s Fullbore long range rifle matches shot from 300 to 1000 yards. Their rules required issued arsenal ammo be used by all competitors; no handloads allowed. They used to issue rifles to everyone based on their belief that that would “level the playing field” and the best shot would win the match. That stopped in the 1960s when they used 7.62 NATO ammo instead of .303 British in their SMLE’s as well as Mauser 98 type bolt action rifles after realizing that all rifles of the same make and model don’t shoot the same accuracy wise. Their 7.62 NATO M80 bullets were often .307" diameter and barrel makers made the groove diameters .3065" so best accuracy was at hand. Best lots of Radway arsenal M80 ammo would shoot MOA through 300 yards and about 2 MOA at 1000. When Great Britain and its Commonwealth countries allowed the Swing 4-lug bolt action to be used, Radway M80 ball ammo shot even more accurate; it was the best thing going for out of square case heads; nobody was allowed to use reloads with very square once fired cases with squared up heads.
Nope.
The most uniform jackets in bullets are made with the thinnest jacket material. It’s easier to shape to uniform dimensions than thicker stuff. All of which is why match bullets usually have thinner jackets than hunting or military bullets.
Yes, good FMJBT match bullets can be made. Sierra and Western Cartridge Company made very accurate ones up through 1958 and were favored by all the 30 caliber match rifle shooters to produce the best scores. Western Cartridge Company used FMJBT 200-gr. match bullets in their 1958 lot of ammo made for the US Olympic Teams 300 metre free rifles; .3088" diameter. They shot very accurate in Winchester 70 broach rifled match barrels with .3085" groove diameter. Two years later and benefitting from Sierra’s very accurate 168-gr. International 30 caliber hollow point match bullet, WCC60 match ammo made for the US teams were 190-gr. BTHP bullets made with precision dies like those used to make their Open Point Expanding hunting bullets. The label on the white boxes holding them said ‘197 grain OPE Bullet.” They also shot very nice in those same barrels. A .30-06 shooting reduced loads with these 197's won the Palma Match at the Nationals in the late 1980's. I’ve shot several of each in post '64 Win 70 hammer forged match barrels about MOA at a thousand yards. Norma 139-gr. FMJBT 6.5mm nickel plated match bullets were favored by 300 meter biathlon and Olympic competitors shooting the 6.5 Swede round for years before Sierra’s 308 168's hit the market.
Lapua has also made their 30 caliber D46 185-gr. FMJ rebated hollow base match bullet very precisely. A friend shot a few dozen of them from the same lot at 600 yards getting 10-shot groups all under 1.5 inches with a couple as small as .7 inch. Then put 40 of ‘em inside 1.92 inch. (For all the big, round heavy single shot action aficionados: He used a box magazine pre '64 Win 70 action, Hart barrel, wood stock and full length sized cases.)
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