Question for expert reloaders.

[zZ_denis]

Thanks for all the great replies, guys. Lots of good info in this thread.

Load 'em to the cannelure. Trace isn't loaded to different pressures than ball. The bullet is longer to make room for the trace element. Mind you, you won't be able to shoot 'em on a range.

The cannelure is for .30-06. Loading them to cannelure in .308 would make the cartridge way too long for .308.


There is no reason to try and push the tracer bullet at maximum velocity. I just used that bullet as an example of a long bullet of same weight.

 

[H4831]

Sure it will. What do you think keeps it from "over-expanding" and rupturing on the first firing? If it expands over time, then it is subject to pressure upon firing, and is being contained by the chamber and bolt face.

I've been enjoying these posts and Jordan, you have come up with some good assessments, but Stubblejumper is 100% on this one.
"Normal," case head expansion is by very small amounts and when primers go back in with less pressure than they should, it is a certain sign of very heavy, or overloading. I have blown one primer in my reloading career and it is not something you want to happen.
I agree that flattening of primers is the poorest method of all to judge overloads by. In the first place "primer flattening," is subjective. One says they're too flat, next one says, "No, that is just normal."
When the bolt handle sticks on lifting it, that is a heavier load than one (me, anyway) wants. But I have found that a moderately sticking bolt will not expand the primer pockets in one or two shots on any combination of components I have used.

 

[stubblejumper]

Sure it will. What do you think keeps it from "over-expanding" and rupturing on the first firing?

Have a look at some bolt faces. In bolt faces like the Mauser design, there is no ring of steel surrounding the case head. Even in designs like the Remington 700, there is plenty of clearance around the case head, even after many firings. Suppose the case head diameter did expand outward against the bolt face for support, how would you ever size it back down to fit the gun? Not with a sizing die, because this part of the case head never enters the sizing die, it is being held in the shellholder during the sizing process.

 

[Ron AKA]

If you do a ladder test of loads in your gun, and lack confidence in being able to read pressure, I suggest you line up all the cases in load order and take a close up photo of the primers. This will give you a good reference for future on what pressure does to those specific brand of primers. They do change. You just have to develop the eye for it. And, yes it is specific to your gun and those primers.

 

[Jordan Smith]

The bolt face and the chamber do support the case head to some extent. I'm not suggesting that it's a tight crush fit, but it does contain the brass from expanding outward excessively (which it would if there were nothing there to offer support).

You cannot accurately judge pressure by case head expansion or primer pocket tightness. Some brass is softer than other brass. You may not see excessive expansion because you're using a hard lot of brass, but the pressure may be beyond safe. In this case, you need to make sure that your velocities are not higher than expected based on pressure-tested data. You cannot safely judge pressure by brass/primers alone.

 

[stubblejumper]

The bolt face and the chamber do support the case head to some extent. I'm not suggesting that it's a tight crush fit, but it does contain the brass from expanding outward excessively (which it would if there were nothing there to offer support).

Would you care to explain just how the bolt face shown below supports the case head to keep it from expanding in the radial direction? Notice that it is completely open on the side shown, so there is nothing to keep the diameter of the case head from increasing due to expansion. So if the bolt face is totally open on one side, what do you call an oversized bolt face, and how does it cause excessive primer pocket expansion as you previously claimed?

 

[Jordan Smith]

When the rifle is fired, the casing is tightly pressed against the bolt face, and that pressure gives some resistance to radial movement by the brass head. Like I said, this probably isn't the largest factor at play here, but it does have SOME effect.

More importantly, can you please explain how primer pocket expansion is a reliable metric of chamber pressure based on the fact that brass hardness varies so much, to extremes in some cases?

We could go back and forth on this ALL day. We might just be better off, and waste less time bantering back and forth, if we agree to do things differently

 

[stubblejumper]

When the rifle is fired, the casing is tightly pressed against the bolt face, and that pressure gives some resistance to radial movement by the brass head. Like I said, this probably isn't the largest factor at play here, but it does have SOME effect.

You specifically mentioned an oversized bolt face, but you still can't explain what it is, or how it supposedly effects case head expansion. The picture that I posted proves that the size of the bolt face has no bearing at all on the radial expansion of the case head.

 

[Jordan Smith]

More importantly, can you please explain how primer pocket expansion is a reliable metric of chamber pressure based on the fact that brass hardness varies so much, to extremes in some cases?

My comment obviously doesn't apply to that bolt design as much as it does to some others. But some designs do help contain expansion. Please respond to the above quotation, since it is obvioulsy more applicable to the discussion and the OP than the degree to which bolt face dimensions influence case head expansion...

 

[Andy]

...Secondly, can i use velocity as a pressure indicator? Lets say im working up a load for one of these odd-length bullets. I load it to 2900 fps. I know that the shorter bullets of the SAME WEIGHT can be fired safely in this caliber at ~3000fps. Does this mean i can keep adding more powder until i reach ~3000fps with the longer bullet? (lets assume i don't see any obvious signs of excessive pressure).

Yes you can, although we're talking about estimates, not absolutes.

Even commercial pressure testing equipment provides an estimate (margins of error, differences in equipment, etc.), and the estimate is for that day, with that powder lot, with that primer, with that chamber and bore, in those climatic conditions, etc. "Pressure Signs" are notoriously deceptive and unreliable, and cannot be trusted, although I'd say a blown primer pocket is a sure sign of very high pressure and to back off (but I can't estimate what the pressure might have been very accurately). Casehead expansion could provide a good estimate, but only if you possess baselines to measure against, consistent brass to measure, and a very accurate and consistent measuring technique.

Muzzle Velocity (MV) however, can provide a useful, reliable and practical estimate for anyone with a Chrony, and the thought process you are following is sound - I've followed it many times.

Once we have a published load (including pressure), we are free to substitute slower powders, and we have a benchmark to let us know when we're moving into higher pressure territory. We know that if you require more of Powder A to produce the same MV as Powder B, that the Powder A load is operating at a lower peak pressure. If the load book shows a load for H4831, but not for H1000, I can try the H4831 load in my gun with my components, note the MV, and then safely substitute more H1000, knowing that for the same MV, the peak pressure is lower. Conversely, if I want to use Reloder 15, if the MV is the same as for H4831, then the peak pressure is higher. You won't know what it is, but you will know where it falls relative to H4831. You can't do that by looking at primers, nor by measuring casehead expansion.

We also know that a heavier bullet will generally produce a higher pressure and lower MV than the same load with a lighter bullet. Even bullets of the same weight, over the same load, will operate within an MV range, but not necessarily the same ranges, e.g. one might show 2850-2925, and the other 2890-2965. There's a lot of overlap there, but the one range is notably higher. Higher pressure is but one explanation, others include less friction due to less bearing surface or a more "slippery" coating. In this case, if the published load had a slower MV than that for the substituted bullet of the same weight, I'd back off the load a bit for the substitute. You can't do that by looking at primers, nor by measuring casehead expansion.

Some guys will just say "If it's not in the load book, don't use it!" or something dramatic like "It's your face!". Those guys should stay safely within what their books say (but books vary, so which book?), but a thoughtful, careful reloader can safely do what you have suggested.