Powders for 308

[Bart B.]

If I was building a pressure test barrel, it would be a two piece one. The chamber section would be threaded into the rifling section. Re-rifle as needed. One chamber section for each pressure system; best for comparing CUP to PSI with the same freebore, and throat plus rifling dimensions.

[Shadow9mm]

Originally Posted by Reloadron

Shadow9mm and kilotanker22, how are you guys planning to measure chamber pressure? While I would be curious as to the results I am wondering what method you plan to use to get the data.

Ron

To be clear. I am testing for pressure, not measuring pressure. Meaning I run the load from start to max looking for things like flattened or cratered primers. Ejector swipes on the brass. Or stick bolt/extraction.

My goal is to get to max with no pressure signs. then I work back down from max, testing for good SD and ES. After that is the seating depth testing.

[kilotanker22]

Originally Posted by Reloadron

Shadow9mm and kilotanker22, how are you guys planning to measure chamber pressure? While I would be curious as to the results I am wondering what method you plan to use to get the data.

Ron

I do not actually test chamber pressure. I guess, a more appropriate term would have been "testing for consistent pressure".

To accomplish this I simply measure velocity in ten round strings. I record velocity spreads and adjust my powder charge and primer choice until I am able to achieve what I consider to be a tight velocity spread. To me an acceptable velocity spread means an extreme spread of less than 20 fps.

My theory is that inconsistent pressure will not yield consistent velocity spreads. While doing this, I also watch for signs of excessive pressure. For excessive pressure, I watch for the obvious signs along with velocity. So I do not actually measure the pressure. I only measure velocity as an indicator of pressure consistency.

[Bart B.]

I've shot proof loads in Garands developing about 67,500 CUP (82,000 PSI) that most people thought "pressure signs" looked maximum and safe. Others thought a bit warm but safe like their regular service ammo. Normal pressure is 50,000 CUP (60,000 PSI).

[Shadow9mm]

Originally Posted by Bart B.

I've shot proof loads in Garands developing about 67,500 CUP (82,000 PSI) that most people thought "pressure signs" looked maximum and safe. Others thought a bit warm but safe like their regular service ammo. Normal pressure is 50,000 CUP (60,000 PSI).

That is why I do not exceed published max data. I will go to max, but not beyond. Each gun is somewhat of an individual so I test start to max when working up a new load, just to make sure I am not getting any odd pressure signs.

[Reloadron]

Kilotanker22 and Shadow9mm, thanks for sharing that. I was just curious.

Bart, if I were to invest in doing it I would only go with the piezo transducer method. When doing other forms of pressure testing I spoke with and looked at the equipment Piezotronics uses for ballistic testing. Really nice stuff and I only spoke with them briefly about ballistics since that was not quite what I was supposed to be discussing with them. While the CUP method is fine and served for decades I really like looking at an actual pressure curve with respect to amplitude and time in a plot. I can't get that measuring a copper pellet before and after. While nowhere on par with the piezo transducer method I hope to try using the method that pressure trace uses since I have the stuff laying around to do that.

While SAAMI proof testing ammunition can exceed max load pressures for rifle by 30 ~ 44% I have never had any desire to push things that far. Doing it right not only involves firing proof test ammunition but after firing disassembling the complete rifle and measuring every part for changes brought about by stress. They also get into round counts of how many proof rounds were fired. Julian Hatcher did a lot of work with proof testing on 1903 Springfield rifles.

Like most I remain below maximum loads but have no problem loading max and working down and observing velocities looking for good accuracy and small standard deviation numbers. Keeping it simple.

Ron

[hounddawg]

That depends on how you evaluate the group. If you track each shot's location, then a large group evaluated by radial standard deviation is best. If you track only the group diameter as determined by the two furthest-spaced shots in your groups (group diameter) it turns out that firing 7-shot groups and averaging the diameters of several of them get's you to statistical nirvana with the fewest number of rounds fired. A paper covering this and how many groups of 7 you need to get certainty within different percentages is here. It says the average diameter of 6 groups of 7 shots (42 shots fired altogether) gets you to within 15% error expected for an infinite group count with 90% confidence.

The radial standard deviation method will do that in 15 shots with 95% confidence, so probably about 13 shots for 90% confidence, which is just one more than the number of holes you are including in your measurements of the extreme spread of six groups of 7. The radial SD method is the most ammunition-economical method, but you do need to know where each round lands to use it.

I roll with the CEP method myself, if I can keep my CEP below .5 MOA then all I have to do is read the wind and put crosshairs in the right place. Simple huh

https://military.wikia.org/wiki/Circular_error_probable


Bart - I establish my scopes windage zero when I first install the scope and waterline @100, chrono for ammo velocity and work up a dope card. At a match however the wind speed and direction can change radically through a 8 -9 hour match. You have to adjust and adapt, changing POA or clicks accordingly

For the curious this link explains why a fishtailing head or tail wind is the most difficult to call and can push a shot out of the X and into the 8 ring. I'll take a 15 mph crosswind over a 5 mph headwind any time

Not about reloading but a good read for both short and long range shooters.
https://bisonballistics.com/articles...han-crosswinds

[Bart B.]

A 5 mph headwind from 12 o'clock has the same effect as a 7.3 fps slower muzzle velocity. Bullet will strike only a tiny bit lower. There's no wind to move the bullet horizontally.

[hounddawg]

and what if that headwind is veering between 0°, 375°, and 15°
Bart, try reading the link I provided and learn

It's NOT the Vertical

[Bart B.]

Originally Posted by hounddawg

and what if that headwind is veering between 0°, 345°, and 15°

Then it's a fish tailing headwind whose maximum effect on windage equals the sine of 15° (.259) times the wind drift from 90° or 270°.

[hounddawg]

you are determined not read that link. aren't you LOL

[Bart B.]

I read the link.

[hounddawg]

great then now you know that a small headwind does more than cause a tiny drop in bullet impact. Headwinds and tailwinds are rarely if ever direct they will always shift back and forth. In the link they use a 10 mph wind shifting a measly 3° and it caused a 2 MOA shift. In F class terms that would move you from the X ring to the 8 ring.

[Bart B.]

Sine of 3 degrees is .05233.

A 10 mph wind from 3 degrees either direction of LOS will move shots horizontally a bit over half an inch if the drift rate is 10 inches (1 MOA) per mph at 1000 yards.

https://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

[7.62 man]

If you want to have max velocity rounds & save money check into the Shooters World Powders. Good powder for much less $$$.
I use the Match Rifle or the AR Plus for my .308.

[Reloadron]

This is a good day out to 200 yards.


The flags are placed at 25 yard intervals. A constant wind is often non-existent and it's not unusual to have a variable wind out of one direction 25 yards down range from the line of fire and a totally different direction and velocity 175 yards down range and this says nothing for the 500 yard line. On a breezy day it's the shooter who can gauge the wind all the way downrange that takes the match. To believe the wind is a constant is just plain foolish. All the formulas are about useless for a changing wind.

The above was actually a shooters dream but even with the breeze out of one direction The velocity changes all the way out to 200 yards.

Ron

[hounddawg]

don't take this the wrong way Bart but I trust Damon Cali more than I trust you on this, once gain read the link. I have recently observed this phenomena myself, Damon is not making this up

https://bisonballistics.com/articles...han-crosswinds

@ reloadron. yep when all the flags are blowing in one direction it is indeed a good thing, due to a 35 ft berm on the right and a 50 ft tree line on the left my range gets a swirling effect

back to topic this morning I tested out BLC-2 in my new .308 bolt build. I was shooting 45.0 gns topped with a 168 gn Nosler CC. I had loaded these for my AR10 a while back, charges were thrown not weighed, Remington 9 1/2 primers, LC mixed year cases. The barrel is 24 inches and fluted and it was pulled from a Savage 10 FP10 several years back and has appx 500 rounds down it. Once I had the scope dialed in I was hitting a 1 MOA plate consistently shooting prone from a bipod and bunny ear bag @ 200. Recoil seemed mild and I had no problem remaining on target through recoil but I had a muzzle brake on it.

[Reloadron]

Powders for 308

Oh right, back on topic. My choice of powders for .308 Winchester varies depending on rifle. For my M1A and AR10 I really like powders like IMR4895, Hogdon4895, Accurate Arms2495 and while I am not fond of it Varget but nothing slower than Varget for any of my gas guns. That includes an M1 Garand I have chambered in 7mm-08 which could easily be a .308 Winchester.

With my bolt gun in .308 Winchester I like the VihtaVuori powders like N135 and N140, Varget, Alliant RL15 and a few others.

My best suggestion as to a .308 Winchester Powder is try several in your rifle with several bullet weights and types. Since I haven't hunted in years most of what I shoot are match bullets or common 150 grain FMJ bullets. Suggestions are fine but you need to find what works for you in your gun(s).

Ron

[Unclenick]

The trick is matching the powder to the bullet weight. The heavier the bullet, the better it will play with slow powders. I like the 4064 range of powders, and Varget was originally designed by ADI (as AR2208) to compete with 4064. With the 175-ish-grain bullet weights, the 4064s and Varget do very well. If you are going to shoot 125s and 150s, you may well discover your gun is happier with N135 or, sometimes, even with 3031. All you can do is try it.


Regarding the wind debate, the fishtailing wind simulated in the article isn't shifting 3°. The article says the standard deviation of the fishtailing is 3°. So the total error span for twenty shots will average 11°. Hence the bigger error.

You can use Didion's old formula from 1858 as an approximation. The sine of 11° is 0.19 on my calculator times 5 mph is 0.954 mph, times 1.46666… gives 1.399 ft/s, times 12, gives 16.8 inches per second for the span of the shift in crosswind velocity component. It's more precise to do ±5.5°, but at these angles, the error is less than half a percent, so I took the shortcut. If the bullet leaves the muzzle at 2800 fps, the vacuum TOF flight would be 3000 ft / 2800 fps, or 1.07 seconds. If the bullet has the equivalent of a G1 BC of 0.5 all the way to 1000, then the TOF in an ICAO standard atmosphere is 1.598 s (from an exterior ballistics calculator I wrote; cheating, but the only other way is measurement and Didion would have had a stepped sequence of ballistic pendulum measurements for this). The difference will be 0.528 s. Multiply that times 16.8 inches per second, and you get 8.704 inches of total shift in the horizontal plane. My ballistics software puts it at 8.69 to 8.91 inches, depending on if it is a tailwind or a headwind, but Didion's estimate still does pretty well for its age.

[hounddawg]

I don't think I would know what to do with a steady crosswind. All the ranges I shoot at reassemble bowling alleys, the wind is either a tail wind, head wind or is playing ping pong bouncing off the tree lines and berms. Maybe up in the plains states or out in the desert they get a steady crosswind but in the pine forests and swamps of the south there aint no such thing

[Unclenick]

The calculation is for a single 5 mph wind vector whose deflection spans the expected extreme range from one side of the target to the other for 20 shots, -5.5° to +5.5° off the bore axis. Mind you, those values are for the expected two most extreme shots out of the 20, while the others will all be in between. There's no break from watching flags or, with pulled targets, seeing where the spotters appear on the other targets to reveal the action of wind not present all the way back at the firing point.

[Bart B.]

Remember that winds in the first third of target range have much more effect on the bullets impact on target than the last third.

[hounddawg]

according to Kestrel

at 200m, the first third accounts for 56% of the
influence, the middle contributes 33%, with the third closest to the target roughly 12%. As the
distance increases to 1000m, the influence of the first third drops to 44%, the middle third
increases to 39%, and the last third grows to 17%.

https://kestrelinstruments.com/mwdow...d/link/id/100/