Flatline bullet review

[Darkker]

Anyone who follows the "Precision" blogs or shooters of the world have read the hype.
Ultra-high BC, able to be pushed faster than traditional, leaps tall buildings in a single bound....

I bought a box of the .308. 155.5gr bullets. Let me say that Mr. Warner, who builds them is a fine gentleman. The Precision buffoons who promote them are another story.

Bullet length = 1.447"
Front driving band width = .093"
Back band length = .205"
Shank diameter = .301"
Driving band Diameter = .309" - which is the same as my 175 SMK's.
Cartridge OAL to lands = 3.227"** this is ROUGHLY, simply because I didn't get a really good "feel" for the lands and this was seated about the same width as the front driving band. So I called it close enough, seated the bullets the standard .03125" deeper and called it game.
Due to this, they benefitted immensely from using my FCD.



The middle picture is against a 175SMK that I shoot to a mile.
The bottom is a line up of:
175SMK -308
140SMK -264
142SMK -264
140 Berg Hybrid -264
155 FLATLINE 308

In the original Precision blog I read about these, it was suggested that due to the general magic associated with them, you would need to step up to a fast powder and load as though it were a whole class lighter bullet. So load for a 130-class bullet. Specifically it has been said anything short of 4895 is too slow and would produce very low velocities. So I used a load of CFE that I have very detailed info on, used behind 150gr SMK's; "slow is bad" bedamned. On a 6 shot average(Same powder lot) the FL bullets were very consistent in being only about 30fps slower than the 150SMK's.

Short of a strain guage system, the best way to tell pressures is velocity, so this isn't looking good for the magic.
These do happily stabilize in my 10-twist, however.
I have a bunch of Pressure testing with them in progress, so a wee bit O'time will confirm. And will be able to confirm or debunk this claim about speed with 4895.

The tail angle and CG/CP will almost certainly prevent them from safely crossing Trans-sonic, but I will also test that very shortly.

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[Darkker]

The Pressure results are in. This time tested against Sierra's 150gr Pro Hunter, in another rifle. Again Same jump, same load.

 

[Bon Sauvage]

Friend, you know how to post!

 

[Morpheus]

Great write up. With that type of length, I assume you are not using any sort of magazine feed system?

And are these solid copper lathed rounds?

 

[Darkker]

Single loading, far too long to fit a mag.
They are some solid copper alloy, turned in a lathe, Yes.

Was also told this alloy won't play well with standard jacket fouling. This also turned out to be hooey.

 

[JustShoot]

You are running a 10 twist for high BC 155's ?
and what is your length of barrel Bore ?

Why you loading (stretching out) such a Long Cartridge OAL ? . do you have a Super long throat-cut ?
you can use a Reamer specifically for 155's and keeping within Mag. Box dimensions .

( imho ) . Your FPS Vel. is still a tad bit on the conservative side for running 155's . . 2800 fps range is OK . as long as you have find a good node for accuracy, it will work .
Small Bering surface, high BC 155's can be pushed hard and you can push the 155's with 308 up to even the 3100 fps areas without over pressure, with only sacrificing Primmer Pockets for wear & tear .
.

 

[JustShoot]

also dont understand the comparison your making with them to the 150 grn. prohunt ?
They share nothing in common . The 155's high BC bullets are meant to be F-Class screamers and running longrange target steal .
Weights are similar yes . but the bullets are night & day in design .

edit add:
maybe better choice for comparison might be Sierrs's 155 palma or Bergers VLD or match hybrids ? . in Pressure and Vel. with powers ?
Even the lapua Scenar 155's are a little doggy in comparison to the Flatliners and vld's or hybrids .
.

 

[Darkker]

1) You are running a 10 twist for high BC 155's ?
2) what is your length of barrel Bore ?

3) Why you loading (stretching out) such a Long Cartridge OAL ? .
4) do you have a Super long throat-cut ?
5) you can use a Reamer specifically for 155's and keeping within Mag. Box dimensions .

6) Your FPS Vel. is still a tad bit on the conservative side for running 155's . . 2800 fps range is OK .
7) Small Bering surface, high BC 155's can be pushed hard and you can push the 155's with 308 up to even the 3100 fps areas without over pressure, with only sacrificing Primmer Pockets for wear & tear .
.

1) Yes, the claim is that they stabilize in a standard 10-twist, and in fact they do!
2) Mine was a 24". the Pressure Testing rifle has a 22". In either case the velocities were all but identical.
3) Because if you don't load them long enough to have an equal amount of jump to the lands(equal with both bullets) the pressure testing and velocities are not real. Seating long bullets deep in the case allow for MUCH more gas bleed-off. More bleed-off would have you think that more powder doesn't equal more pressure, which is false.
4) No, standard Savage and Ruger. The length of the nose is why you can seat the bullets "long".
5) Seating the bullets deeper are what would keep it within mag length. To ream the throat such that the FL bullets were seated to box length would have a HORRIBLY short throat, and prevent any factory ammo being chambered safely.
6) Not true, look at the Pressure Traces. These loads are just under 60,000 psi. from other testing, to gain approx 100 fps more velocity, you will need 10-15,000 psi additional.
7) Again that is simply not true, and the entire point of this testing. ANYONE who tells you primers and brass are a reliable way to know pressures, has no clue what they are talking about. These "Small bearing surface" 155's had the EXACT same jump to lands, powder charge, powder lot, primer lot, and case lot; as the 150 SPH's. The velocities and pressures are not statistically any different. The claim was that you must use a rather fast powder, specifically listed 4895, and can load to speeds from the 130gr-class bullets. That is NOT true. Back to the cases, anyone here know what alloy and hardness spec their cases are built to??? Nope! The last time any of that was publicly listed was WAY back in the 40-50's from Olin in the 30-06. That alloy was C260 and was spec'd to a tensile strength of about 85,000 psi. Well when you get to that pressure range is when the brass streches and pockets get loose. So your comment about sacrificing pockets, IF your current brass was the same C260, you know that you are approaching the yield strength of that brass and FAR over-pressure when the pockets get loose. From more testing we noticed that as a generality, production rifles tend to "show" classic pressure signs(hard lift, primers, etc) in the neighborhood of 75,000psi+


For your follow-up post/questions:
The 150gr Pro-Hunter IS a perfectly valid test. By the load data between Hornady(9th) and the current Nosler data, this load of 4895 falls between min and max. IF a standard 150gr hunting bullet gets pushed to(in this case) about 2800 fps. Then IF the super-duper voodoo claims of small bearing surface uber-match bullets were true, the velocity AND pressure would be lower at the same charge. Since the charge/jump/etc were the same, AND the pressure/velocity was the same; the claims of magic are BS. The same load produces identical pressures and velocities, so in order to produce the claim of 3,000-ish fps, you MUST increase the pressure dramatically. So can you get that velocity out of this bullet? Certainly. CAN you get it safely, and without going over-pressure? Absolutely NOT.

On another board, over the winter we Pressure Traced some Creedmoor loads. We in fact did compare Berger VLD's and the New hybrids, against SMK's and custom comps. The notion that with Berger's having a lower bearing surface you can push faster safely, was also false.

The only way we found you could get higher velocities at lower pressures, was relatively speaking and in a range only. So if you used a standard burning curve powder, we used H-4350, and pitted it against a VERY progressive burn curve like Superformance; you could see a window. What we found is that running them at lower pressures, in the low 50,000's; the progressive nature of Supr allowed higher velocities at THE SAME pressure levels. Ultimately at max SAAMI pressure the total velocities were the same. Progressive propellants curves become more "typical" when pushed to higher pressures, and lose the efficiency provided at lower pressures.

 

[Dan Warner]

You wanted this is an open forum, here you go....
http://www.scout.com/military/snipe...ftr-bc-test-results/ms/182017337?s=541&page=2

 

[Darkker]

You wanted this is an open forum, here you go....
http://www.scout.com/military/snipe...ftr-bc-test-results/ms/182017337?s=541&page=2

Actually this is an open forum, but thanks for the link. Let everyone read it, please.