175 SMK + 20" barrel = low velocity?

Accuracy nodes are the byproduct of more than just length. the bullet, Powder burn rate, barrel rigidity+harmonics and the tightness of bore are all parameters that impact accuracy nodes. 308's are easier to keep within their envelope of optimal barrel time (for the burn rate of the powder) with 18-20"+ barrels, but it is still entirely possible to have highly accurate 18" 308's and entirely $hitty 30" barrels. Furthermore, velocity does not follow a strict X-fps per inch for its entire length. I would rather have a quarter-minute load doing 2500 than a half minute load doing 2700, and sub-sonic does NOT mean the bullet starts flying off at 45 degrees to its original path.

The OP need not change anything in his recipe to achieve accurate 1000 yards results if his current load is accurate.
 
Agreed. The only bullet that is known to tumble when it goes subsonic is the 168 SMK and Bryan Litz does an excellent job of explaining why in his book. He also states that it is not the case with other 168 gr. bullets.

Ballistic analysis of the 175 SMK shows that it is going transonic or subsonic (depending on conditions) by the time it gets to 1k, when fired in the low 2600's. Yet, people are still winning with it.
 
Cartridge : .308 Win.
Bullet : .308, 175, Sierra HPBT MatchK 2275
Cartridge O.A.L. L6: 2.800 inch or 71.12 mm
Barrel Length : 20.0 inch or 508.0 mm
Powder : Hodgdon VARGET

Predicted data by increasing and decreasing the given charge,
incremented in steps of 2.0% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step Fill. Charge Vel. Energy Pmax Pmuz Prop.Burnt B_Time
% % Grains fps ft.lbs psi psi % ms

-06.0 99 42.30 2467 2364 51569 8723 97.0 1.108 ! Near Maximum !
-04.0 101 43.20 2517 2462 54926 8892 97.6 1.077 ! Near Maximum !
-02.0 103 44.10 2567 2561 58511 9050 98.2 1.047 ! Near Maximum !
+00.0 106 45.00 2617 2661 62343 9196 98.6 1.018 !DANGEROUS LOAD-DO NOT USE
 
Oh please... Quickload is only a program.


Example:

Cartridge : .308 Win.
Bullet : .308, 175, Sierra HPBT MatchK 2275
Cartridge O.A.L. L6: 2.820 inch = 71.63 mm
Barrel Length : 22.0 inch = 558.8 mm
Powder : IMR 3031

Predicted data by increasing and decreasing the given charge,
incremented in steps of 0.746% of nominal charge.
CAUTION: Figures exceed maximum and minimum recommended loads !

Step Fill. Charge Vel. Energy Pmax Pmuz Prop.Burnt B_Time
% % Grains fps ft.lbs psi psi % ms
+00.0 94 40.20 2539 2506 48616 7611 100.0 1.206



And here is what it looks like in real life, with a real rifle, real chrono and real pressure measurement system:

3031.jpg


Quickload is horribly inaccurate at times. I've found that it exaggerates the effects of things like barrel length and seating depth tremendously. Some of the powder profiles, like RL-17 are off by a mile. Further, it doesn't distinguish between match and non-match barrels or even primer brands, which can make a HUGE difference in pressure and velocity.

If you want to know the performance of a load, you need to work it up in real life. Period.
 
I know QL is a program but it has been quite accurate for me once proper parameters are entered. It at least gives a good idea of where a certain load SHOULD fall into and is a good starting point.
 
I've calibrated is for several loads only to find it off again in different loads with the same powder, primer and case. I like the program, but it isn't as glorious as many make it out to be and it really doesn't prove or disprove anything. It's a starting point at best.
 
kombayotch said:
Oh please... Quickload is only a program.
Click to expand...

As I understand your post, Quickload predicted 48616psi and 2539fps, your measurements gave 52307psi and 2614fps?

That pressure prediction seems pretty much spot-on to me (within 4000psi), pretty much as good an agreement as one might expect. The velocity difference of 75fps is a bit wide, but not outrageously so (i.e. some nominally identical barrels can differ by that much).
 
There are many variables that it cannot account for. IMR3031 is one of the more accurate powders in QL. Try RL-17. It was off by more than 200 fps in my 6mm loads. With H4895 and Scenars, QL was nearly 10k psi to low in its pressure prediction. N540 was also way off, which was a surprise since its available in Europe where the author lives. I only chose that specific load because I have very limited data with the 175 SMK (for any barrel length) as I don't like the bullet. Most of the data I have captured for it is from friend's barrels, and I only save my data... usually.

Agreed about the barrels, that was one friend's 22" Broughton. A different friend's 20" Rock bested it by 30 fps. with that load. I've also seen two supposedly identical Kreiger barrels, chambered with the same reamer that shoot around 40 fps different from each other with the same load. That was on a switch barrel rifle, swapping them, and using the same batch of components, through the same chorno. The owner wanted to have an "identical" backup.

Point is: a QL simulation does not prove or disprove anything. It can only be relied on as a ballpark estimate. I have seen many 20" barreled 308s (all match grade bbls) shooting the 175 SMK over 2600 fps. and the 155 Scenar over 2900 fps. The custom builders on here have probably seen many, many more...
 
Shooter ----/ said:
Jamie, have you had problems with the 168's??

I will rebarrel to 26 or better when this one burns out.
Click to expand...

168s work fine but at rnges past 600 they start to not work too good


the 155lapuas are what i wanted my gun to love..... sadly it dont:(
 
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