Max Load question

[Jamie6.5]

Me too!
When I see the broken thumb lever on someone else's Auto-Prime I always make a mental note NOT to be around when they are seating primers.
Almost 20 years and probably over 1k rounds and my A-P still has the original thumb lever.

 

[civilian75]

I've never tried TAC. But I noticed you may not be able to fill the case to 100% capacity w/o reaching max pressures. As said above, 308Win likes a full case. My best loads are compressed a little bit. With the right component selection, you should be able to get subMOA accuracy, and sub 10fps standard deviation. It is just harder to obtain the latter w/o a full case.

Also, beware of temperature sensitivity. If TAC is temp sensitive, (I am sure there has to be something on this topic somewhere on the Web), do not be discouraged. RL15 is very temp sensitive, but, it is very accurate in 308Win. And with the right load it is accurate at different temperatures, too. What you won't get is the same mean mv at all different temperatures. But, if you know what your mv will be for a given temp, that's all you need to put shot after shot on the same vicinity.

I noticed TAC is a bit faster than other powders commonly used for 308Win. You may be able to get more mv with a slower powder in your 26" bbl, if that is desired.

I am sure you will find a lot of useful info on SniperHide.com

 

[deadshot2]

Also, beware of temperature sensitivity. If TAC is temp sensitive, (I am sure there has to be something on this topic somewhere on the Web), do not be discouraged. RL15 is very temp sensitive, but, it is very accurate in 308Win. And with the right load it is accurate at different temperatures, too. What you won't get is the same mean mv at all different temperatures. But, if you know what your mv will be for a given temp, that's all you need to put shot after shot on the same vicinity.

If competing, one can overcome the temperature sensitivity somewhat by "warming up the rifle". Shoot several fouling shots and get a little heat into the action. Then develop a routine where your cartridge sits on the magazine follower for 30 seconds or so then in the chamber for about the same amount before it's fired. If you are spacing your shots by a minute or so the temperature will remain fairly constant. Loads worked up this way will not be as sensitive to ambient temps as the action temp will always be warmer than ambient.

This method doesn't work all that well for a hunting round and there I would select a powder known for it's performance at a wider range of temps.

 

[Spitpatch]

"Then how does one account for the wide variations in velocity from the same load/case/bullet/primer out of two different rifles of the same brand and barrel length?
A well worn barrel with a long throat may allow another 100-200fps over a short throat barrel that has very few rounds through it, and is on the tight side of the groove diameter spec."

Two different rifles of same brand, etc. may shoot markedly different velocities with the same load because something in one of the rifles is creating more pressure than the other, resulting in a higher velocity. Manufacturing tolerances are pretty tight and consistent these days, but not perfect. The list of possible differences between two guns (even consecutive serial numbers!) that may affect pressure (therefore, velocity) is not a small one.

Identical rifles very often show different velocities (as you rightly noted). Identical rifles of different wear stages (as you rightly noted) may show even greater differences in velocities. This is because the pressures generated during ignition/bullet travel in the barrel are different. It sounds simple because it is.

 

[Jamie6.5]

I agree Spitpatch, but to say that more pressure always equals more velocity isn't true, because that obviously isn't always the case.

 

[deadshot2]

More pressure WILL always equal more velocity PROVIDED that the breech and barrel remain intact. That's the problem.

 

[Spitpatch]

A meeting of a mind. DS2, you get the credit, since my contribution was not being received in all completeness. I considered going elswehere to ask "experts" about this axiom, but felt those that contended otherwise might better expend the energy to defend their contentions. John Barsness might be a good source to consult (on the Campfire Forums). I know from my own experience it cannot be doubted.

Having said that, and having been wrong in my strong convictions before (and still have personal improvement work to do toward having an open mind), I invite illustration of a scenario when it might not be the case.

 

[Gunner3456]

Be sure that you're at least 10' from your chrony. Be sure the chrony is level and square with the bullet path.

We had this discussion in another thread, but you shoot through, not over the chrony. The sensors are at each end of the box, on top. Ideally the bullet passes about 4" above the sensors, but with a scoped rifle it's easy to shoot the box, LOL. I tape a piece of paper to the back of the chrony to see where the bullet is for height, and then adjust my aim accordingly before taking measurements.

If not used correctly, you can get some really inaccurate readings.

 

[rrojohnso]

Thanks everyone, for all the great information. I will continue to work up the loads .5 gr, but will reload two other slower sets (of 5) to check for consistency. It's not that I am loading for speed as much as I am loading for consistent groups. I will also check where the lands begin to make sure the COL is where it should be. I appreciate all the insight.

 

[Spitpatch]

Fire up your printers, go to BiMart and get a frame and find a place on the wall, because you will need to glance up at this frequently when you tire of endless debates where no one gives any ground.

Jamie6.5 is right with his postulation that more pressure does not ALWAYS result in more velocity. I was wrong. My great error was in utilizing an absolute and all-encompassing statement to describe scenarios based on the OP's specific problem: My absolute only applied to his activity: adding more of the same powder under the same bullet, in the same gun. Absolutes should never be applied to specifics. Different specifics will almost always disprove an absolute.

I did Jamie's homework for him, and gained enlightenment in that process. Here's a thread that shows he is right (and so am I to a smaller degree, but only toward the OP's experiments). The handle "Mule Deer" is John Barsness. Mine on that thread (as the OP) is "Tahnka". I would like to believe that John would be hesitant to call himself an "authority" or "expert". Even Jack O'Connor stated specifically that he did not like those terms applied to himself, and never sought them to be, but both gentlemen have gathered more experience than I ever will:

Higher pressure equals higher velocity: any exceptions? - 24hourcampfire

 

[Jamie6.5]

I think you did "Jamie's homework" for yourself.
I scratched my head extensively over this issue many many years ago. The physics of hydraulics says it MUST be right,...
But it ain't always true.
Why?
Damifiknow, but there it is.
I *think* DeadKenny over there hit the nail on the head with his post:

The key here is to clarify whether you are talking about just the pressure peak, or the overall pressure curve. The velocity should be proportional to the area under the pressure curve. So, it is in theory possible to have a sharp 'spike' in pressure that produces a higher peak pressure while actually having a lower velocity than another case with a 'flatter' pressure curve.

Lower pressure over a greater duration results in more overall acceleration of the projectile.

A similar phenomenon results in a longbow shooting a 36" arrow vs a crossbow shooting a 14" bolt (arrow).
The crossbow exerts more force on the arrow, but does so for a much shorter duration.

BTW, there is NO animosity here, hopefully we are all here to learn from one another's experience.
I was just relating mine. Hopefully it was enlightening.

 

[Spitpatch]

Once again, you are right considering my motivation toward self-enlightenment. (I actually thought you'd beat me to the homework.)

 

[Gunner3456]

Actually you guys are certainly right in guns which are sealed between the firing chamber and barrel. The increasing pressure accelerates the bullet down the bore.

However, consider the revolver which "leaks" pressure between the cylinder and the bore. There is a distinct reduction in pressure behind the projectile once the projectile enters the barrel, although the pressure is still significant. Those and other types of guns which leak pressure always use a faster burning powder with a higher pressure peak. There really isn't as much time or place to take full advantage of a "pressure curve."

To a smaller degree, the same is true of any really short barrel, and to a lesser degree, any pistol.

That's speaking in generalities of course.

 

[Jamie6.5]

Spitpatch, if I ever win the lottery, (read: have the $$) and decide to buy the necessary equipment to find the ABSOLUTE(S) of why this occurs, I'll get a hold of you and we'll get to the bottom of it.
Gun by gun, and load by load.

 

[Jamie6.5]

That's speaking in generalities of course.

While I agree with *some* of what you said there Gunner,...
When one is concerned with ALWAYS, generalities suck.
Generally speaking of course

 

[deadshot2]

Spitpatch, if I ever win the lottery, (read: have the $$) and decide to buy the necessary equipment to find the ABSOLUTE(S) of why this occurs, I'll get a hold of you and we'll get to the bottom of it.
Gun by gun, and load by load.

You dont' need to even win a big lottery. A Pressure Trace System is only about $500 or so without their fancy analytical software. You can equip several guns to show pressure curves. Jut plug in (on) the cable when you want to test a round for pressure. You will need a laptop however with "bluetooth" capability.

RSI - PressureTrace

I'm not one to merely fill the safe with "Safe Queens" so I'll be buying one of these next year for my annual contribution to my "gadget" collection instead of another gun like many do.

 

[Blitzkrieg]

One thing to also consider is winchester brass has a larger case capacity by up to 1-2 grains. As always check for pressure signs as indicated, if you are not seeing any I would continue to load up. This is my recipe

Winchester Brass
Varget 44.9 Grain (similar to RL 15, I will swap next month)
CCI Large Rifle Primer
Nosler Custom Competition 175 grain BTHP
O-give 2.293

I was going to say.. every brass is different and you work up max loads with one brand and one lot of brass, do NOT mix N match brass for max loads !

If you want more power go to a larger caliber, NEVER hotrod any caliber!

 

[deadshot2]

I was going to say.. every brass is different and you work up max loads with one brand and one lot of brass, do NOT mix N match brass for max loads !

If you want more power go to a larger caliber, NEVER hotrod any caliber!

Are you talking Caliber or Cartridge? The way I see it is there are lots of calibers that have been "hotrod'ed". Just look at the list of all the "cartridges" that use a "30 Caliber" bullet

 

[Blitzkrieg]

Me too!
When I see the broken thumb lever on someone else's Auto-Prime I always make a mental note NOT to be around when they are seating primers.
Almost 20 years and probably over 1k rounds and my A-P still has the original thumb lever.

I can guess you never seated lots of primers in ex crimped military brass.. I broke 3 of them before I gave up on the system

 

[Blitzkrieg]

Are you talking Caliber or Cartridge? The way I see it is there are lots of calibers that have been "hotrod'ed". Just look at the list of all the "cartridges" that use a "30 Caliber" bullet

I am talking about exceeding recommended charge weights and loads found in loading manuals.. do it at risk of your face and hands