which has more value- powder charge or velocity

[ericf]

TO clarify my question, I'm dropping a "minimum recommended" powder charge as starting point, But my measured velocities are almost at the maximum. I;m trimming cases to .008 under "sierra" manual. Should I be concerned about bullet depth (OAL)? I'm not sure where to look.
Thanks

 

[ckirkc]

Re: which has more value- powder charge or velocity

look for pressure signs in your fired cases, flattened primers, ejector marks, excessive cratering of the primer. these signs will let you know when it is time to back off. if you are at minimum charge my guess is you are not seeing these signs and you probably have room to increase velocity.

 

[Greg Langelius *]

Re: which has more value- powder charge or velocity

Neither, worry instead about pressures and accuracy. The goal is to achieve the latter before the former becomes excessive.

Powder selections which accomplish this with a relatively fuller case tend to work more consistently.

OAL becomes an issue when a) it's in the 'nether region' where some contact the lands and some don't, and b) when bullets are jammed enough to create pressure spikes. Powder burn rates vary with pressures, and the higher they spike, the faster they burn, and the faster they burn, the more they spike, and...

You get the idea.

If you have a borescope, I good way to tell if you are going faster than optimal is to find copper fouling that extends a long way back along the bore from the muzzle. You don't need to go fast to be accurate, and going faster may be more accurate, but it can cause new problems as well; like excessive copper fouling, which degrades accuracy faster.

Accuracy comes from driving the bullet so it gets where it's going while it's still going fast enough to maintain it's good stability range; which typically occurs above 1300fps. Faster than that can help a shooter who's counting on velocity to cover deficiencies in wind reading skills, but it's also rough on the bore, and defeats the goals of good efficiency and moderation.

The good shooter recognizes the wind, accomodates, and uses the wind to <span style="font-style: italic">help</span> drop them in ontarget. Other shooters fail to see the wind as an ally, and fight it, which is a losing battle. When a shooter fails to employ the wind effectively, they need to work on that friendship. Like a really beautiful woman, the wind can be fickle, but respect and friendship will always help.

Greg

 

[Victor N TN]

Re: which has more value- powder charge or velocity

I agree with BOTH the different statements made above.

 

[MitchAlsup]

Re: which has more value- powder charge or velocity

I agree with Greg. Accuracy is the goal, and whatever charge weight is required to get accuracy and avoid dangerous pressure situations is what you ar elooking for.

There will be several accuracy nodes from minimum charge weight and maximum safe charge weight (typically 4 or 5). For benchrest shooting, where accuracy is everything, you will want to investigate every single accuracy node to see which one is the least sensitive. For long range shooting, you will be looking for the accuracy node the is definately inside the safe pressure window, and accurate enough. For tactical shooting of less than 600 yards or so, any of the accuracy nodes will work just fine.

Sometimes you can use a bore brush to feel where the copper fouling deposits are. But you must develop a light, firm, steady pace to feel the slight roughness in the bore from the copper grains.

IF you develop the ability to listen to your gun, it will tell you what it wants. To the OAL question: after you find an accuracy node with acceptable pressure (i.e. no pressure signs), then run the bullet depth experiment* and see if you gun, with that bullet, and that powder cares. If it does, then believe what the gun prints. In may cases, there will not be any useful change, in others its massive.

(*) if you investigate the bullet touching or "into" the lands, be darned sure that you are not at/near pressure limits.

 

[Grump]

Re: which has more value- powder charge or velocity

If your barrel length is the same as for the published loads, I would be very cautious about exceeding the published velocities, regardless of the charge weight. I have a nice and accurate IMR 4064 load that is going about 130 fps faster than the Sierra Book's max speed, out of a barrel that's 4 inches shorter. The charge weight is a full half-grain less than the Sierra max load, too.

I'm NOT using that one. My very hard-headed cases are not showing pressure signs, either.

Case make and bullet make can also have a large influence.

 

[Greg Langelius *]

Re: which has more value- powder charge or velocity

Barrel length is only partly determinant in achieving a given velocity. Bore friction is at least as significant.

If the bullet's acceleration is retarded by a tighter, or rougher, or clean/dry, unfouled bore, the same pressure spike cycle occurs as we see with bullets that are jammed into the lands. The difference is that this occurs repeatedly during the bullet's transit down the bore.

Anything which increases friction will likewise increase pressure and burn rate, thus delivering a higher velocity, regardless of the barrel's shorter overall length. The opposite is also true.

Though counterintuitive, it is the way things work in relationship to bores, bullets, burn rates, pressures, and velocities.

Greg

 

[LoneWolfUSMC]

Re: which has more value- powder charge or velocity

Velocity only really comes into play when you are reaching out there. Then the more velocity you start with, the longer you can go without dropping trans-sonic.

When I do load development if I have to accuracy nodes that are almost the same I will choose the higher velocity one. This will give me greater accuracy at long range.

I have only been reloading for a couple years, and only for .223 and .308 so I am still learning some of the tricks. This is just what works for me.

 

[ericf]

Re: which has more value- powder charge or velocity

The published max vel. for the 168 smk is at 2712. I was at 2660, in a variety of different cases. I never saw any pressure signs on the fired cases, except for in one rifle I had fired brass sticking in the chamber. I backed down the charge for a vel. of 2550, which approximates factory loads and no further problems. And is very accurate. but I'm concerned that this vel. won't have enough charge behind it to make it to 600-900 yrds. My range only goes to 300, so testing becomes a problem. And I don't desire to "discover" a problem once in west Texas.

 

[Grump]

Re: which has more value- powder charge or velocity

Unless you have a long barrel or you want to push loads to barrel-burning hotness OR you're shooting at a high enough altitude that your bullets are still above at least Mach 1.1 (the only safe and reasonable alternative in my book), then 168s are not really the bullet to use.

175s go slower but have a nice BC to get you past 900.

155s *can* go enough faster to still be okay past 900.

Some people make 168s work to 1,000, but it's rarely below 3,000 ASL. If you can make the search function here work better than I can, then you can learn more about the edges of performance on this.

168s are fine to about 800 out of just about any rifle at any altitude, especially at the old standard GI velocity of 2550 at 78 feet, about equals 2590 at the typical 10-foot screens.