Intrinsic Accuracy of the .308 round.

[Bart B.]

broncman, about spinning bullets in a collet. . . . .

One of Sierra Bullets' machinists (Ferris Pindell or Arvin Martin?) in 1971 made an end mill shaped to precicely match the ogive and body of those Lapua D46 bullets. They had previously looked at their shape with an optical comparitor and noticed four distintly different ogive shapes; probable evidence that four different pointing dies were used at Lapua to make those bullets. Only one shape lot was used for the test. That cherry made a cup in a collet with its shank sized to fit a Dremel Moto Tool. Then it was spun empty in the tool with an amp meter inline with the power cord to measure current. The collet was ground off a bit in a few places until the meter read the lowest consistant current. To them, that meant the collet was perfectly balanced as it spun at 30,000 rpm. When fired in the 1:11 twist barrel they would spin almost 170,000 rpm.

Bullets were put in the collet point down, spun up to speed and the current noted. The perfect ones with minimum current were put in the test box. Others drawing more current due to the centrifugal force loading the tool's bearing with more force required more current to spin it up to speed. Some flew out and those were probably going to shoot in the 9 ring at 600 yards in competition which sometimes happened using those bullets in matches. Sometimes 3 or 4 out of a box of 100 would do that.

Anyway, those perfect ones shot amazingly accurate. Which is a testament to the accuracy attained by pre-64 Win 70 based rifles and the Hart barrels fitted to them conventionally epoxy bedded in wood stocks. It also gave credibility to full length sizing .308 Win. cases for best accuracy in SAAMI spec chambers; lots of room around the front part of the case but they all centered perfectly up front in the chamber when fired.

 

[Keith Glasscock]

Were any of the spin-tested bullets run on a juenke machine by chance? I'd be interested in any correlations.

 

[Bart B.]

Were any of the spin-tested bullets run on a juenke machine by chance? I'd be interested in any correlations.

No, just that collet in the Moto Tool. I don't think the Juenke ICC tool was available back then.

I think and good machinist could make the collet and bore a straight wall cavity in it about .0001" larger than bullet diameters. That may well work.

 

[dreever]

In my .308 GA Precision Hospitaller with 24 inch Bartlein 11 twist barrel I use:

Lapua large primer pocket brass neck turned and prepped to the best of my ability.
Bullet choice's are Berger 175 Tactical OTM and Berger 185 Juggernaut if the wind's up.
Powder Varget, by all means not a max load but one that is super accurate in my rifle
Primers CCI250 I saw no advantage over the chrono or in actual use using the more expensive BR2's.

Since my rifle uses AI magazines I'm limited to a 2.890 OAL. Both bullets and loads have a MV of 2615 fps with an ES of 12 fps. It's not a benchrest rifle but I treat my prep and loading as if it were. IE: sorted bullets, neck turning, weighing every powder charge, etc. This is imperative regardless of the rifle, caliber, or discipline if you really want to see the maximum potential.

Off the bench using front rest rear bag setup I've shot some fantastic groups at my ranges 840 yard maximum with the edge going to the 175's in good conditions. Even though the loads are almost identical the 185's do have more noticable recoil. In a blind test I can identify the 185's every time. I have shot both these loads at 1000 yards on my secret "ahem" (can you say powerline) range and both have performed well.

Danny

 

[Bart B.]

Here's what my .308 Win. Palma rifle did in a test of Sierra's then new 155-gr. Palma bullets at 800 yards.

Paramount action with a 3.5 pound trigger, Kreiger 32", 1:13 twist .2950" bore & .3075" 4-groove, SAAMI chamber, unprepped WCC60 cases full length sized, 45.3 gr. IMR4895, bullet runout .003", soft-seated bullets set back about .010" in case when chambered. Rifle scoped for accuracy test with a Weaver T20. Tested at 6 AM when the wind was calm.

Two sighters used to get a zero then clean the barrel before shooting 20 rounds for the test. Numbers 1 and 2 were the first ones shot and the rest went a bit higher; that barrel shot bullets a bit faster after a few rounds of barrel fouling. Shots fired about every 25 to 30 seconds slung up in prone with a rice bag under my front hand and another under the toe of the stock.

 

[stool]

2015 fps ?????

In my .308 GA Precision Hospitaller with 24 inch Bartlein 11 twist barrel I use:

Lapua large primer pocket brass neck turned and prepped to the best of my ability.
Bullet choice's are Berger 175 Tactical OTM and Berger 185 Juggernaut if the wind's up.
Powder Varget, by all means not a max load but one that is super accurate in my rifle
Primers CCI250 I saw no advantage over the chrono or in actual use using the more expensive BR2's.

Since my rifle uses AI magazines I'm limited to a 2.890 OAL. Both bullets and loads have a MV of 2015 fps with an ES of 12 fps. It's not a benchrest rifle but I treat my prep and loading as if it were. IE: sorted bullets, neck turning, weighing every powder charge, etc. This is imperative regardless of the rifle, caliber, or discipline if you really want to see the maximum potential.

Off the bench using front rest rear bag setup I've shot some fantastic groups at my ranges 840 yard maximum with the edge going to the 175's in good conditions. Even though the loads are almost identical the 185's do have more noticable recoil. In a blind test I can identify the 185's every time. I have shot both these loads at 1000 yards on my secret "ahem" (can you say powerline) range and both have performed well.

Danny

 

[Down South]

2015 fps ?????

In my .308 GA Precision Hospitaller with 24 inch Bartlein 11 twist barrel I use:

Lapua large primer pocket brass neck turned and prepped to the best of my ability.
Bullet choice's are Berger 175 Tactical OTM and Berger 185 Juggernaut if the wind's up.
Powder Varget, by all means not a max load but one that is super accurate in my rifle
Primers CCI250 I saw no advantage over the chrono or in actual use using the more expensive BR2's.

Since my rifle uses AI magazines I'm limited to a 2.890 OAL. Both bullets and loads have a MV of 2015 fps with an ES of 12 fps. It's not a benchrest rifle but I treat my prep and loading as if it were. IE: sorted bullets, neck turning, weighing every powder charge, etc. This is imperative regardless of the rifle, caliber, or discipline if you really want to see the maximum potential.

Off the bench using front rest rear bag setup I've shot some fantastic groups at my ranges 840 yard maximum with the edge going to the 175's in good conditions. Even though the loads are almost identical the 185's do have more noticable recoil. In a blind test I can identify the 185's every time. I have shot both these loads at 1000 yards on my secret "ahem" (can you say powerline) range and both have performed well.

Danny

Typo im sure.

 

[dreever]

Typo yep, changed to 2615 fps. Sorry I didn't catch that.

Danny

 

[CaptainMal]

Ken Hunt used a 308 to fight the wind at the Manatee Shoot this morning. He tied for first and lost out in a shoot-off to a Dasher.

308's can be made to shoot well, especially in the 600 yard range.

 

[Sray53TXTN]

Ken Hunt used a 308 to fight the wind at the Manatee Shoot this morning. He tied for first and lost out in a shoot-off to a Dasher.

308's can be made to shoot well, especially in the 600 yard range.

6 Dasher?

 

[Bart B.]

amlevin, the barrel's harmonics, or frequencies it whips and wiggles at, are probably the most repeatable thing in the whole shooting system comprising rifle, ammo and shooter. They don't change from shot to shot for each one's profile and chamber/bore dimensions. The amount may be microscopically different, more with heavier loads, less with lighter ones, but for a given load they are 100% repeatable from shot to shot.

I must add that if case heads and bolt face are out of square, bolt lugs are not lapped to full and even contact with their receiver lumps and the case body's clear of any contact with the chamber except at the back end where its pressure ring's against the chamber from being there from extractor pressure against its groove for it, and there's room for the barrel to whip and wiggle without touching any part of the stock, that barrel will not be repeatable in direction and amount in all its wiggling and whipping. External things have physically altered its behaviour. But its basic resonant frequency and harmonic multiples thereof are still the same.

 

[Mr. Ten-X]

Although I feel like I have stepped back in time to the usenet groups, info like this is invaluable.

 

[cmillard]

if one has a premium barrel of fairly heavy diameter with a good trigger and all around solid set up with a good trigger puller behind the glass, there is no reason why it can post groups near bench rest level accuracy. I would say though, if shooting long range and shooting the 175+ grain bullets (why anyone would shoot lighter is beyond me--unless it is the 155 palma style), I would definitely shoot 10 to 11 twist barrels. from my understanding, the 12 twist is barely enough (when shooting shorter barrels--24 inch) for 1000+ yard shooting and shooters tend to see their groups open up a bit, which "could" be due to stability issues. if you look at USMC m40-a3 which has a 1-12 twist vs Army m24 which has a 1-11.25, the M24 shoots tighter groups at 1000+ yards with the same ammo. Take that for what it is worth, as I have only read about that on multiple occasions, but that does not sound out of reason.

 

[Bart B.]

A bit of history regarding 24" long, 1:12 twist barrels and 190-gr. Sierra HPMK's atop 44 grains of IMR4320 in a new, primed M118 7.62 match ammo case. That bullet left at just under 2600 fps

That was the most accurate long range load in USN and USAF Garands so chambered in the late '60's and early '70's. In spite of slightly out of square new case heads and bolt faces, the Springfield Armory (in MA) broach-rifled standard profile M1 barrels with about .3078" groove diameters, and .003" bullet runout, the best of those rifles would shoot that load in less than MOA at 1000 yards. Some folks testing that same ammo in bolt guns got under 3/4 MOA at 1000.

The US Army Team pulled the 172-gr. bullet from M118 ammo then replaced it with a Sierra 180 HPMK. From their 1:12 twist 22" barrels, it left close to 2600 fps. And shot good enough to equal what the Garand's 190 load did and they set their share of records with it.

Note also that 7.62 NATO Garands shooting the nororious M852 match ammo with Sierra 168's, they drove tacks at 1000 yards shot from 24" barrels tight enough for more muzzle velocity and best accuracy at long range. It was the M14's 22 inch barrels that too often didn't push those 168's out fast enough to stay stable and supersonic through 1000 yards; the reason Lake City arsenal had Sierra design a 175-gr. match bullet with the same boattail their old 180-gr. HPMK had. The 50 fps difference in muzzle velocity was enough to make a difference. That old 180 had its boattail changed to the short one like 168's have and the Army's M14's never shot them all that great just like the 168's. So the Marksmanship Unit at Fort Benning contracted Sierra to use the old bullet dies for 180's making their boattail like the 190's and early 180's have so their M14NM's would do well at 1000 yards.

 

[amlevin]

Although I feel like I have stepped back in time to the usenet groups, info like this is invaluable.

Nah! Usenet groups usually got spammed with porn in no time at all.

 

[cmillard]

I wonder how those bullets would have performed past the 1000 yard mark.

 

[Chris F]

As much as I appreciate Mr Bobbit's historical perspective, I will revive this thread to offer a correction to his statement;

It was the M14's 22 inch barrels that too often didn't push those 168's out fast enough to stay stable and supersonic through 1000 yards; the reason Lake City arsenal had Sierra design a 175-gr. match bullet with the same boattail their old 180-gr. HPMK had. The 50 fps difference in muzzle velocity was enough to make a difference. That old 180 had its boattail changed to the short one like 168's have and the Army's M14's never shot them all that great just like the 168's. So the Marksmanship Unit at Fort Benning contracted Sierra to use the old bullet dies for 180's making their boattail like the 190's and early 180's have so their M14NM's would do well at 1000 yards.

The 175 Sierra was borne out of the M118 improvement project that resulted in the M118LR cartridge being fielded. In the 1990's, the USMC Sniper Section tried working with Lake City to improve the quality of the M118 round. The highpower community, was very aware that the accuracy of the M118 round had slipped substantially and it yielded to M852 out to 600 yards as the favored round. However M852 with the 168 Sierra was deemed not adequate for USMC Sniping purposes as it would not reliably stay supersonic out to 1000 yards out of the M40A1. WTBN sent folk over to Lake City to work with them to improve the quality of the 173 gr projectile, but it was deemed a lost cause. They turned to Sierra to design a 173gr analog in their Match King line. The result is the 175gr Sierra. It was ultimately fielded as M118LR and came with a directive that it was not to be shot out of the M14's as it was loaded quite hot. The other services had no such restrictions and M118LR won multiple Long Range service rifle championships in the hands of other branches. Ultimately LR was toned down. M118LR remains one of the few instances where the fielding of a round was done by the USMC.

 

[XTR]

 

[ebb]

What does Intrinsic mean?

 

[SheepDog]

Intrinsic means natural or built in. In this case it means that the 308 is naturally more accurate. It is an easy cartridge to get to shoot well with a number of different components.