.308 questions, so chime in please

[Trickymissfit]

getting ready to bite the bullet and order in three barrels. I've pretty much decided on Pacnor pre-fit tubes for a couple Savages and one Remington 700.

Barrels will be:
* .223 N.M. with a .246" neck (Remington) at 22" long in a #5 contour or maybe a #7
* 6mm/250 Ackley with a .264" neck 25" long in a #7 contour
* .308 N.M. 24" long in a #7 contour

Now back to the .308 a bit. They offer so many chambers that it's almost confusing! The one that caught my eye was the .308 Obermeyer chamber. I assume it's a national match chamber with a different throat. The rest has got to be standard. Has anybody here came across the .308 Obermeyer chamber?
gary

 

[Michael Eichele]

Jerry,

I'm not familiar with the Obermeyer chamber.

When it comes to the 308, I prefer to do two things.

1: Keep it simple (that's the whole point of using a 308).
2: Move brass as little as possible when re-sizing.

I like to have a snug chamber with tight 'no-turn' neck. I have my smith keep the headspace to a minimum as well. This allows for very easy resizing that doesn't stress or work harden the brass anymore than it has to be. Since I shoot 308s more than any other cartridge, and do a lot of it, keeping brass in good shape for a long time is important to me. Again, that's the point of a 308 right? Longevity is key for my 308 barrels. Longevity is also key for my 308 brass.

You never said what you plan on doing with this 308. What loads are you looking at? What is the application? What is the twist?

 

[Trickymissfit]

Jerry,

I'm not familiar with the Obermeyer chamber.

When it comes to the 308, I prefer to do two things.

1: Keep it simple (that's the whole point of using a 308).
2: Move brass as little as possible when re-sizing.

I like to have a snug chamber with tight 'no-turn' neck. I have my smith keep the headspace to a minimum as well. This allows for very easy resizing that doesn't stress or work harden the brass anymore than it has to be. Since I shoot 308s more than any other cartridge, and do a lot of it, keeping brass in good shape for a long time is important to me. Again, that's the point of a 308 right? Longevity is key for my 308 barrels. Longevity is also key for my 308 brass.

You never said what you plan on doing with this 308. What loads are you looking at? What is the application? What is the twist?

mostly long range targets. Thinking of bullets in the 165 grain thru 180 grain range in a ten twist barrel.
gary

 

[Michael Eichele]

Oops! Sorry, I got the name wrong. Confused you with someone else. If you're interested in a 308 for long range targets, I'd try and talk you out of the 24" barrel. In many respects, you only loose about 30-40'sec between 26 and 24" tubes. The difference though is a 26" barrel handles slower powders much better such as H4350 RL17 and N540. A 26" tube, Palma cases, 205 primers and H4350 with 180-215 grain pills is magic in a 308.

Also, if 180 grains is the max weight you intend to run, I'd also try and talk you out of the 10 twist. With 175-190s and even many of the 200 grain varieties, 11 to 11.25 is a definite sweet spot. Not that 10 is bad but 11 to 11.25 is a sweet spot. 11.25 also handles the 210 and 215 very well too if you decide to go that route. Despite all the buzz about tighter twists and maximizing BC, you cannot argue with the length of time that the 308 utilizing 11-11.25 twist barrels and the success they've had. BCs run normal as well.

I'd also like to try and talk you out of the 165-180 range to widen the range to 155 to 200. The 155 TMK has shaped up to be a fantastic 308 bullet. I haven't had a chance to check the real BC but Sierra is probably close. With the short bearing surface they flat rock and roll in a 26" tube. I have no trouble hitting 3000-3025'sec with 4064 and 2950-2980 comes easy with VARGET. Both are incredibly accurate. This offers a light recoiling load with reasonable wind values. The 155 Hybrid also theoretically has great numbers though I've never tried them.

If you really want to step it up, the 185 Hybrid has phenomenal numbers with Bryan's .576 G1 value. Over 51.0 of H4350 in the Palma case at 2.975" (feeds in a Wyatt box perfectly), they're rocketing out at 2781'sec with accuracy with zero high pressure signs. I'm of the opinion that you cannot get enough H4350 in any 308 case to create harm but you need more than 24" of barrel and heavier bullets to utilize it. And to not have high muzzle blast with a shorter barrel and slower powder. This combo is quite possibly one of the best all around loads I have ever worked up.

Right now my favorite loads are the 155 TMK but I like the 175 TMK a bit better and the 185 Hybrid. The 190 VLD shouldn't be overlooked but the 185 can be pushed faster and has a higher BC. It's an F/TR bullet from hell. The 178 ELDX might be another great option. The 178 Amax is a great bullet in the 308 but after 750 yards they peeter out pretty hard. The ELDX may fix that. If it works as advertised, it may become my only 308 bullet. Great balance of recoil, retained energy, wind drift and a lower expansion threshold.

I hope that helps.

 

[Trickymissfit]

Oops! Sorry, I got the name wrong. Confused you with someone else. If you're interested in a 308 for long range targets, I'd try and talk you out of the 24" barrel. In many respects, you only loose about 30-40'sec between 26 and 24" tubes. The difference though is a 26" barrel handles slower powders much better such as H4350 RL17 and N540. A 26" tube, Palma cases, 205 primers and H4350 with 180-215 grain pills is magic in a 308.

Also, if 180 grains is the max weight you intend to run, I'd also try and talk you out of the 10 twist. With 175-190s and even many of the 200 grain varieties, 11 to 11.25 is a definite sweet spot. Not that 10 is bad but 11 to 11.25 is a sweet spot. 11.25 also handles the 210 and 215 very well too if you decide to go that route. Despite all the buzz about tighter twists and maximizing BC, you cannot argue with the length of time that the 308 utilizing 11-11.25 twist barrels and the success they've had. BCs run normal as well.

I'd also like to try and talk you out of the 165-180 range to widen the range to 155 to 200. The 155 TMK has shaped up to be a fantastic 308 bullet. I haven't had a chance to check the real BC but Sierra is probably close. With the short bearing surface they flat rock and roll in a 26" tube. I have no trouble hitting 3000-3025'sec with 4064 and 2950-2980 comes easy with VARGET. Both are incredibly accurate. This offers a light recoiling load with reasonable wind values. The 155 Hybrid also theoretically has great numbers though I've never tried them.

If you really want to step it up, the 185 Hybrid has phenomenal numbers with Bryan's .576 G1 value. Over 51.0 of H4350 in the Palma case at 2.975" (feeds in a Wyatt box perfectly), they're rocketing out at 2781'sec with accuracy with zero high pressure signs. I'm of the opinion that you cannot get enough H4350 in any 308 case to create harm but you need more than 24" of barrel and heavier bullets to utilize it. And to not have high muzzle blast with a shorter barrel and slower powder. This combo is quite possibly one of the best all around loads I have ever worked up.

Right now my favorite loads are the 155 TMK but I like the 175 TMK a bit better and the 185 Hybrid. The 190 VLD shouldn't be overlooked but the 185 can be pushed faster and has a higher BC. It's an F/TR bullet from hell. The 178 ELDX might be another great option. The 178 Amax is a great bullet in the 308 but after 750 yards they peeter out pretty hard. The ELDX may fix that. If it works as advertised, it may become my only 308 bullet. Great balance of recoil, retained energy, wind drift and a lower expansion threshold.

I hope that helps.

not cutting you off, but there's more info than I can digest all at once! So this response can be divided into a couple three parts. Yet I did pick up on a couple things that interest me.

The barrel twist rate set at ten twist has always kind of confused me as the Palma twist is twelve. This brings in bugga boo number two. The gap between a 150 grain bullet and a 200 grain is enormous. Perhaps I'm thinking too much, but I'd like to think that an ideal throat for a 150/165 grain bullet would be too short for a two hundred grain bullet. Perhaps I'm wrong. Then there's the issue with the 150 grain group of bullets. Love to be able to use Palma bullets, and yet be able to move up to the 175 grain area bullets.

This all falls back to my lack of understanding in throat design and why. Mr. Ackley never covered that part all that well in his writings. Still when I think of 190 and heavier bullets in the .308, I kind of see that the case is marginal at best. Perhaps a .257x57 improved case necked up to .308, or better yet a 6.5x55 improved necked up to .308 (.308Vias?). Either of these two cases will fix the one problem the 7.62x51 has. Yet I'd rather have a standard case, as I'm tired of wildcats in my old age.

With the above aside, I have a virtually inexhaustible supply of 7.62x51 N.M. once fired cases as long as I take them in two or three hundred round bags. So I'd say the generic .308 is the way to go for me. The good thing (unlike a Remington short action) is that I plan on using a Savage. They are about .150" longer than the Remington 700. Means a lot with long bullets as it helps to keep the bullets out of the shoulder. The other barrels will be easy!
gary

 

[AZShooter]

I enjoyed reading about Bryan Litz's recent F-TR win using his 308 win with 215 berger hybrid target bullets. His barrel is a 1 in 9. Read the story linked below for the rest of the details:

Litz Dominates His First-Ever F-TR Match with Pierce-Built Rifle « Daily Bulletin

 

[SidecarFlip]

FYI, John Pierce & company built my last 2 308's. Like Brian's FTR rig, they have Bartlien barrels.

I discussed with John what would be the best chambering for medium to long range 308 shooting. He said without hesitation to chamber with a Bisley reamer so thats what I did.

Can't go wrong with experience. BTW, both sticks shoot sub MOA at 200 yards with 168 Bergers. How about consistently 3 in the same hole and 2 within 1/2" in a 5 group.

I'm happy.

Running exclusively Lapua brass and I don't see much brass working between loads. Better add that I had John Whidden build a custom bushing die based on 3 once fired cases in that chamber.

One thing I noticed about the Bartlien barrels is they prefer to run slightly fouled. Cleaning with BTE and then firing, the groups spread somewhat until the rifling builds a bit of copper, then they tighten right up. Takes about 5 down the tube.

 

[Darkker]

I'd try and talk you out of the 24" barrel. In many respects, you only loose about 30-40'sec between 26 and 24" tubes. The difference though is a 26" barrel handles slower powders much better such as H4350 RL17 and N540.

With the short bearing surface they flat rock and roll in a 26" tube.

If you really want to step it up, the 185 Hybrid has phenomenal numbers with Bryan's .576 G1 value. Over 51.0 of H4350 in the Palma case at 2.975" (feeds in a Wyatt box perfectly), they're rocketing out at 2781'sec with accuracy with zero high pressure signs. .

I agreed with you and the KISS advice earlier, but this is wrong.
The reason, just as you stated, that there is no velocity difference of note between length; is because it doesn't matter. You get more velocity ONLY because you are over-loading, has nothing to do with burning rate.

The bearing surface argument is also false, as is the "signs" comment. Just like the stories we're told about low bearing surface on the FlatLine bullets. When I Pressure Trace them, they are statistically identical to an equal weight flatbase. Same story when i've Traced Berger, SMK, or Scenar.

You may not "see" signs of Pressure, but you are over SAAMI limits.

The FlatLine 155's we are told, can be pushed to 130gr velocities "without signs" of Pressure. However when you use instruments that are actually capable of accurate measurement, you see it's a lie.

My point here is only about info. I don't care whether or not anyone wants to run higher pressures. Just know the truth about what is going on. Uncalibrated cases and primers do not accurately report pressures when a handloader stares at them.

 

[Michael Eichele]

It has nothing to do with burn rate?

Have you pressure traced H4350 in the 308?

More of a slower powder doesn't necessarily mean overloading.

I've compressed H4831SC (51.0 grains) under 190 VLDs at 2570 which is typically about SAMMI spec velocity for VARGET. I assure you, there is less pressure with 4831. It has much to do with burn rate.

That fancy chart does nothing to prove that my 185 loads are over pressure.

German Salazar pressure traced 185s at over 2700'sec at under SAMMI max pressure with R17. Yes, burn rate matters.

 

[Michael Eichele]

Duplicate post.

 

[SidecarFlip]

I agreed with you and the KISS advice earlier, but this is wrong.
The reason, just as you stated, that there is no velocity difference of note between length; is because it doesn't matter. You get more velocity ONLY because you are over-loading, has nothing to do with burning rate.

The bearing surface argument is also false, as is the "signs" comment. Just like the stories we're told about low bearing surface on the FlatLine bullets. When I Pressure Trace them, they are statistically identical to an equal weight flatbase. Same story when i've Traced Berger, SMK, or Scenar.

You may not "see" signs of Pressure, but you are over SAAMI limits.

Inconsequential. SAMMI specification is only a guideline for ammunition manufacturers to follow...and inexperienced handloaders.......

I load consistently over SAMMI spec, if grouping warrants it (and I can get the charge in the case ((which I usually can by jumping the pills followingthe Berger regimen)), which can be applied to all manufacturers of bullets.

No issues here at all.

 

[Darkker]

Remember the standard was Lead Crushers, until it was discovered that with the increasing operating pressures they weren't accurate. Enter the Copper Crushers. Then it was discovered that like their predecessor, they had a shortcoming. Over around 45,000 psi very carefully calibrated crushers would report variances on the EXACT same reference load, on the order of 20,000 psi.
Measuring your brass means you can "assure" it's dimensions, not what pressures you ran.
I have Traces of both 4350's and RE-17 in the 308 & Creedmoor. Here are a few in the 308.
Please look at the "fancy charts" from the Pressure Traces. Notice the barrel exit times, pressures and velocities across the burning rates.

 

[Trickymissfit]

I think I've found the difference between Boot's chamber and the standard factory Winchester chamber. The Obermeyer chamber throat is shorter, and the case dimensions are a little tighter. Yet not by a great amount other than throat length. The chamber seems to be popular with the FT-R guys.
gary

 

[SidecarFlip]

So's the Biesley. Thats what Brian won the FTR championship with btw.