Must use faster or slower propellant?

[Rule3]

Obviously it's startling to hear of such pressure from a minimal load of varget, but despite extenuating circumstances like the thinner cup of a regular CCI #400 primer and seating to touch the lands it's just as obvious to me that the larger issue here is prudent powder selection when working with a barrel that's significantly longer than a 24" test barrel.

With all due respect, seating a few thousandths off the lands isn't going to be especially helpful to the young new owner of a savage.223 target rifle with a 30" bbl who's made an imprudent propellant selection. Published load data is extremely valuable, and a lot of work and sweat has gone into these tables, but I found out the hard way that when you get into over-length barrels all bets are off - some of these propellants can really pack a wallop if they're given enough running room. There are those of us who still use old fashioned long rifles and FWIW I just hope we're not obscuring the very real issues associated with reloading for them.

Your original post indicated you had a blow primer and mushroomed case. From the get go you seem to want it to be the "powder"
There are several, if not many other things it can be, but you want to belive it is "the powder" or the barrel length.

You seem reluctant to look at any other possible cause, you will not indicate trim length or COAL. So there is not much others can help with other than speculation.

Hope you figure it out.

As your signature states:

"Theories require facts, Captain."

 

[Walkalong]

Cutting off six inches of barrel will do nothing to reduce pressure. The very question of this thread inclines me to believe you do not understand burn rates and pressure.

 

[Jim Watson]

Beats me.
I have loaded up to 25 gr Varget and a 90 gr Berger or JLK VLD with no drama.
Accuracy is better at 24 gr, though.
Barrel is a 28" 6.5 twist Krieger. Seating is .01" off lands.
CAUTION This is over Hodgdon Maximum but necessary to hold supersonic at 1000 yards.

I don't know the effect of a polygon bore on pressure but will point out that there is a SAAMI spec on minimum cross sectional area.

 

[Dudedog]

Food for thought, not the length but the barrel, tight chamber etc.
Weatherby rifles generally have quite a bit a free bore. Loads listed for Weatherby Mag ammo account for this. Lyman for example cautions against using the loads
they list for Weatherby mag ammo in custom chambered guns without the free bore found in commercial Weatherby rifles.
So different barrel, different pressures.

2 barrels off the same line will probably have different peak pressures, bigger difference with 2 same length barrels from different makers.
Shorter barrel A could run higher pressures than longer barrel B.
That is why you start at start charges and work up watching for pressure signs.
Every manual I have seen mentions that what they show as the MAX charge may be over what is the MAX charge for your firearm.

IMO Something is causing your pressure issue other than the type of powder or barrel length, you need to correct it if possible or just accept the fact that you will have to use less powder.
Listed loads from a manual are not something on a stone tablet that came down from the mountain top.

When the bore was new and rough I could get consistent 1/2 moa groups with 55 grain bullets at 26.7 grains of H414, traveling around 3025 fps. But after break-in I couldn't keep the velocity down, even with wadding. I wonder if I were to stick with the same 26.7 grains of H414 and simply use the weight of a heavier 64 grain bullet to keep it around 3025 fps - this is what I'm mulling over at the moment.

Wadding???
Heavier bullet same powder charge = more pressure, not a good idea if you are having pressure issues in the fist place.
Very easy way to reduce velocity reduce the powder charge.

Brass can be an issue, not all brands of brass have the same internal volume. Not all lots of brass of the same brand will have the same volume.
Less case volume=more pressure.
Dirty bore=more pressure
Case not trimmed to correct lenght for the chamber/chamber not correct=more pressure
the list goes on
I am just concerned that instead of a pierced primer your pressure issues could lead to something worse.
I'll leave it at that,
I hope you get it worked out safely.

 

[spitballer]

Strong argument ATLDave and I'm not sure how to explain why I differ with this opinion, but I'll try:

even though we all know that peak pressure occurs fairly close to the chamber there is also seems to be an effective pressure involved, and maybe this is why cuP readings are so different. I suspect that even though peak pressure may only reach a certain level, if it's sustained for any length of time it leads to an increase in effective pressure. Exactly why this occurs I can't explain, but (and I'm theorizing here) I suspect that a certain elasticity or buffering may occur if the pressure peak is brief enough.

 

[ATLDave]

I can understand that as a conjectural notion... if we were talking about a 1" versus 10" barrel. I find it extremely implausible that the difference between a 24" and 30" rifle barrel is doing this. Try doing a little research on how little extra time the bullet is going to be in the barrel... it is already moving very fast, so the extra duration will be very short compared. It will also be at decreasingly low pressure compared to the first 5" of travel. If you're summing the area under the pressure curve, the last 6" of a long barrel are adding a very small portion of the total pressure compared to everything that happened before. I think if the brass and primer can stand up to the much, much, much higher pressures of the earlier part of the internal ballistics, the chances that they're going to break down over the last 6" are nil.

I could be wrong. I have not studied this issue in detail. But I have never seen your conjecture supported by any data or other analysis.

There are several possible explanations for your experiences that are consistent with fairly conventional and well-understood internal ballistics phenomena. You have suggested an explanation that would, to my (incomplete and amateur) knowledge be novel. I think if you are interested in solving your problem, working through the more conventional explanations first would make more sense.

But what do I know? I'm no ballistician.

 

[Jim Watson]

Port pressure for an M16, 13" down a 20" barrel, is 12800 psi, muzzle pressure just as the bullet exits the 20" barrel is 9900 psi. It only declines more as the gas expands down a longer barrel. I doubt that sub 10000 psi for about a millisecond longer than GI is going to pierce primers.

 

[outlawjw]

I don't like to talk like this , but I think your biggest problem with this rifle is between your ears. Or maybe that's , just behind your eyes. To op.

 

[spitballer]

I don't like to talk like this , but I think your biggest problem with this rifle is between your ears. Or maybe that's , just behind your eyes. To op.

You're right and I should have taken the first cue from our esteemed moderator who's been exceedingly patient. I've been wrong before, most notably concerning the large flash holes designed for unleaded primers. Obviously safety comes first.

Request this thread gets the lockup

 

[Walkalong]

As you wish.

If another question pops up, do ask it, and we'll try to answer it.