Boat Tails and Bearing Surface? (.308Win)

[WrongHanded]

I got a new rifle and had some perplexing issues. I started a thread about it. here is (hopefully) the relevant post to this thread: https://www.thehighroad.org/index.php?threads/accuracy-irons-vs-ier-scope.873360/#post-11606107

Basically, I tested three types of 150gr .308/7.62 ammo. Two were using boat tail bullets and performed poorly. One was with the Remington Core-Lokt PSP, and performed as expected.

I believe this particular Core-Lokt bullet (and probably others) are a flat bottom design. That, to my mind, means these bullets probably have a larger bearing surface than a boat tail of the same weight. And I'm wondering if maybe this is where the accuracy issue with the other two types of ammo is coming from. Maybe that combined with a shorter barrel of 18.5" isn't stabilizing the bullet well?

I realize that some barrels are picky, and that I may even see increased accuracy with a heavier bullet. But I'm trying to wrap my head around this issue first, mainly because I don't want to buy what won't work decently.

If you have thoughts on it, please share.

 

[Varminterror]

The distinction that the Core-lokt is flat based and the others are boattailed is but one of many variables you have changed between these bullets. More often than not, this particular distinction will have absolutely nothing to do with the difference in accuracy you are seeing.

The distinction between the powder charges used in each of your respective factory munitions tested will have far, far greater influence than the bullet base design. The ogive profiles and jump length relative to your individual rifle chamber will have far, far greater influence than the base design. The consistency of neck tension, jacket uniformity, powder charge, brass internal capacity, etc will all have far greater influence on accuracy than the base design.

This is kind of like, “I heard an unfamiliar sound in the woods, it must have been Bigfoot.”

 

[JFrank]

I feel comfortable saying that Core lokt / SP are not your issue.
My advice is to select good components and develop a load.
vvv this is 200 yards with a hunting rifle

 

[WrongHanded]

I feel comfortable saying that Core lokt / SP are not your issue.
My advice is to select good components and develop a load.
vvv this is 200 yards with a hunting rifle

The Core-Lokts weren't a problem. They did what I expected. It was the other ammo that performed poorly.

One day, I may start reloading bottle necked rifle cartridges. But not any time soon.

 

[WrongHanded]

The distinction that the Core-lokt is flat based and the others are boattailed is but one of many variables you have changed between these bullets. More often than not, this particular distinction will have absolutely nothing to do with the difference in accuracy you are seeing.

The distinction between the powder charges used in each of your respective factory munitions tested will have far, far greater influence than the bullet base design. The ogive profiles and jump length relative to your individual rifle chamber will have far, far greater influence than the base design. The consistency of neck tension, jacket uniformity, powder charge, brass internal capacity, etc will all have far greater influence on accuracy than the base design.

This is kind of like, “I heard an unfamiliar sound in the woods, it must have been Bigfoot.”

I understand what you're saying. It's one of many factors. I totally understand.

Perhaps you or someone else could recommend a 150gr factory load using a boat tail, that is known to perform well for many people in various rifles, and I could try that out. Something between $1 and $2 per round seems a reasonable price point right?

 

[JFrank]

I must’ve misunderstood your question.
I’m getting old and need my meds..lol

 

[JFrank]

Finding a box Ammo that shoots well in a rifle is trial and error, I’ve had limited success doing so and the question of bearing surface was never
part of the equation but twist rate definitely should be.
Box Ammo is a crap shoot at best IME

 

[jmr40]

I have seen some tests showing that a flat based bullet CAN be more accurate than a boat tail bullet, at least at closer ranges. But the differences were very, very small. We're talking about a few 1/100" And easily offset by the better ballistics of boat tail bullets.

There are many variables that go into an accurate load and rifle. The flat base vs boat tail is only one. I'm thinking that it is just a coincidence in this case.

 

[Nature Boy]

To add another variable to your test, changing components in a back to back comparison can often unsettle the results. I’ve seen it happen enough that I always clean the barrel between tests when changing power, bullets or primers to eliminate that variation

 

[skeeterfogger]

I use Privi Partisan 165spbt in 06 and they work great. You might dive them a try.

 

[WrongHanded]

To add another variable to your test, changing components in a back to back comparison can often unsettle the results. I’ve seen it happen enough that I always clean the barrel between tests when changing power, bullets or primers to eliminate that variation

I can understand where this could be an issue. However, one load didn't even stay on the 8" target at 100 yards. I'm not claiming to be a particularly good shot, but I'm not quite that bad. I'm not sure the variances I was seeing can be attributed to a dirty bore.

 

[illinoisburt]

Flat based bullets tend to shoot accurately in my experience as well. I've heard it explained as to gas seal in the barrel (slight variations in pressure on any given side) and muzzle crown as it leaves with boattails being much more senstive to crown damage. Might take a quick look at your crown to see if there is a small nick.

 

[redneck2]

This^^^^^

Think of the boat tail as it leaves the muzzle. The tail is wedge shaped, pointing downward. If there is a nick, groove, or the crown is off center, the gas escapes there first and squirts past the bullet base, kicking it off to one side

IIRC, Bench rest shooters use flat base bullets at ranges up to 300yards

There are a ton of variables, this is just one

 

[Nature Boy]

I can understand where this could be an issue. However, one load didn't even stay on the 8" target at 100 yards. I'm not claiming to be a particularly good shot, but I'm not quite that bad. I'm not sure the variances I was seeing can be attributed to a dirty bore.

I think a lot of what you’re seeing can be attributed to the fact that the ammo you’re testing falls into the general category of range fodder.

 

[WrongHanded]

I think a lot of what you’re seeing can be attributed to the fact that the ammo you’re testing falls into the general category of range fodder.

That's pretty fair. I was just pretty amazed because I've never seen ammo perform that poorly.

Regarding the crown, it doesn't appear to have any defects. I took the flash hider off and installed the included thread cap before I ever shot it. The cap is not loose btw. I only mention it to say that I can clearly see the muzzle.

 

[Varminterror]

I think a lot of what you’re seeing can be attributed to the fact that the ammo you’re testing falls into the general category of range fodder.

This is really the answer.

Comparing boattails and flat based bullets, and describing the mechanics for each is wholly overlooking the simplest answer: your rifle doesn’t shoot well with the other factory loads, and shoots better with the Remington load. The unique combination of variables which lead to that outcome is largely coincidental. That’s why the answer to, “which factory ammo shoots best?” is always “you have to try a lot of different factory loads and figure out which shoots best in your rifle.

So going into the minutia of comparison between flat based bullets used in short range benchrest competition and boattails used in long range competition simply isn’t apt. Your car was outside in a hailstorm, and now has dents. You might be interested to realize your neighbors’ car, with fiberglass body panels took more paint damage than your steel bodied car, while the body panels on yours are physically dented more than theirs - but the real answer is simple: if you don’t want dents, Park in the garage during hailstorms...

 

[Nature Boy]

I was just pretty amazed because I've never seen ammo perform that poorly.

Oh, I have. Picked up some of that Turkish ZQI .308 win from Wally World on a smiley-face-falling-prices-special.

Even going in with rock bottom low expectations I was utterly disgusted with how god awful the accuracy was. It made the stuff you're testing look like pending world record bench rest quality in comparison.

I actually feared for the safety of my fellow shooters at the range. There was the potential that the herculean effort these bullets exerted to miss the target might impart enough force to cause them to circle back and kill someone on the firing line!

(sorry, I took a few liberties with my prose )

 

[WrongHanded]

This is really the answer.

Comparing boattails and flat based bullets, and describing the mechanics for each is wholly overlooking the simplest answer: your rifle doesn’t shoot well with the other factory loads, and shoots better with the Remington load. The unique combination of variables which lead to that outcome is largely coincidental. That’s why the answer to, “which factory ammo shoots best?” is always “you have to try a lot of different factory loads and figure out which shoots best in your rifle.

I think by now it's pretty obvious that I don't know that much about what makes rifle ammo accurate in a particular rifle. Therefore I've been looking at the problem (at least partly) from the perspective of the knowledge base I have, which is mainly pistols. So my assumption had been that the projectile was the problem more so than the overall cartridge. Thankful you and others have pointed out that this is not the case.

I will simply try other types of ammo and see what works.

 

[Varminterror]

@WrongHanded - the ocean is a lot deeper than folks give it credit. Welcome to rifle shooting! There are two sides to every coin; there is a convenience in picking factory ammo off of a shelf, but we’re then beholden to the powder choice, charge weight, neck tension, crimp force, seating depth, etc the manufacturer chooses, which may or may not suit our firearms. Alternatively, there’s a convenience in CONTROL over our reloads, such we can tailor loads to coax a dozen different bullets to shoot small groups from our rifle, but we’re burdened with the saddle of self-sustaining our ammunition supply.

I often share this anecdote in times like this: about 10 years ago now, I mentored a close friend into rifle shooting and reloading. We found that his newly built rifle shot very well with many bullets, but exceptionally well with 55grn Vmaxes. He called several months later and said something was wrong - he had shot at a coyote at 250yrds and missed completely. So he checked the rifle at home - it was spraying 3” groups a couple minutes off of his zero. In troubleshooting over the phone, he revealed he had bought some Hornady factory 55 vmax ammo instead of reloading with the load we had developed for his rifle. The next weekend, I met him with boxes of HSM, Remington (Accutips), Underwood, and Hornady factory ammo - and a box of the pet load we’d developed... all 5 of these shooting the exact same Bullet - the Hornady 55 Vmax. The pet load shot to his POA, and grouped sub-MOA, as they had in development and his training sessions. The factory loads all shot between 2-4moa, and impacted a few minutes outside of his POA in one direction or another. Given only that factory ammo, he likely would have assumed his rifle were a lemon, and would have certainly believed the rifle didn’t care for the 55 Vmax.

 

[JFrank]

At this point in my reloading journey I feel comfortable saying that your rifle didn’t like that ammunition.

 

[WrongHanded]

@WrongHanded - the ocean is a lot deeper than folks give it credit. Welcome to rifle shooting! There are two sides to every coin; there is a convenience in picking factory ammo off of a shelf, but we’re then beholden to the powder choice, charge weight, neck tension, crimp force, seating depth, etc the manufacturer chooses, which may or may not suit our firearms. Alternatively, there’s a convenience in CONTROL over our reloads, such we can tailor loads to coax a dozen different bullets to shoot small groups from our rifle, but we’re burdened with the saddle of self-sustaining our ammunition supply.

I often share this anecdote in times like this: about 10 years ago now, I mentored a close friend into rifle shooting and reloading. We found that his newly built rifle shot very well with many bullets, but exceptionally well with 55grn Vmaxes. He called several months later and said something was wrong - he had shot at a coyote at 250yrds and missed completely. So he checked the rifle at home - it was spraying 3” groups a couple minutes off of his zero. In troubleshooting over the phone, he revealed he had bought some Hornady factory 55 vmax ammo instead of reloading with the load we had developed for his rifle. The next weekend, I met him with boxes of HSM, Remington (Accutips), Underwood, and Hornady factory ammo - and a box of the pet load we’d developed... all 5 of these shooting the exact same Bullet - the Hornady 55 Vmax. The pet load shot to his POA, and grouped sub-MOA, as they had in development and his training sessions. The factory loads all shot between 2-4moa, and impacted a few minutes outside of his POA in one direction or another. Given only that factory ammo, he likely would have assumed his rifle were a lemon, and would have certainly believed the rifle didn’t care for the 55 Vmax.

I guess I've just been pretty lucky with factory ammo up until this point. I can't recall having used anything in any rifle I've owned that didn't shoot fairly well considering the sighting system and my own abilities. Although I suppose I haven't expected too much from my rifles, all things considered.

At some point I'll begin reloading bottle necked rifle cartridges, which will likely be quite eventful. For now, I just want to find a few factory loads I can rely on. Thanks for the information!

 

[gotboostvr]

Outside of Federal Gold Medal Match I've had very poor success with most factory ammo. FGGM is the only factory fodder that's ever turned in <1 MOA groups for me. My 308win R700 shoots both the 168gr and 175gr FGMM equally well.

My handloads with the same 168gr Serria Match King bullet do about as well. The 165gr Serria Game King is just a little bigger group, but is cheaper and a better hunting bullet.

 

[DoubleMag]

Federal GM Match (mentioned previous post) is a Sierra 168gr BTHP Match bullet. And, as is the name, many consider it to be the 'gold standard' for accuracy out of a factory box of bullets.

You have a new rifle and it's a child which really likes chocolate milk, and, all Dad has is strawberry. It may be that simple. Fortunately the rifle DOES in fact operate correctly i.e. group. Also, you stated you 'took the flash hider off' is this an auto? AR-10? 1:10 twist?

 

[WrongHanded]

Fortunately the rifle DOES in fact operate correctly i.e. group. Also, you stated you 'took the flash hider off' is this an auto? AR-10? 1:10 twist?

It's a Ruger Scout Rifle. The flash hider just seemed unnecessary. And yes, I believe it is a 1:10 twist.

I ordered 3 boxes of Federal Sierra Match King Gold Medal 168gr yesterday. Now I'm very interested to see how it works.

 

[JFrank]

Good for you, @WrongHanded
Box ammunition is notorious for huge variations in powder weight from case to case, as much as 1 full gr in some Ammo.
I’m not claiming to know what dispensers they use and all that jazz BUT I know for a fact that even 2 tenth’s of a grain will cause point of impact variations , keep in mind that a barrel is an oscillating whip that when charges ( combustion) changes so does exit timing of the projectiles sending then in any direction until timing is consistent . I’ve attached a reference photo of just .2 gr increments in powder to further make my case. No pun intended