'Afternoon gents,

A simple question if I may, how far should one back off from a load that generates pressure signs to avoid short case life, loose primer pockets, safety in different temperatures etc?

Say I have an 06 sized case, a 08 sized case and a .223 sized case for your examples unless you want to use percentages.

I have a load that is giving me pressure signs at 57.5 grains of powder, the 56.5 grain load shows no such signs, is it likely to be safe or is it still too much at only around a 2 ans a bit percent reduction?

With thanks,

A

Not answering the way you want me to (sorry), but I'd back off to the accuracy node below your current (too hot) load.

For example, if I had worked up from 42 to 46 grains in half grain increments, and started seeing trouble, I'd go back down to the most accurate load below 46.

If the accuracy or velocity at that node is unacceptable, I'd try a different powder/bullet combo.

-nosualc

Not at all, that's a great answer.

That seems logical but in several loads things just seem to tighten up the higher the load, what about in those cases for example?

With thanks,

A

For me I take into consideration ambient temperture when working up loads . If it's a load that is going to be used for hunting in cold weather and I'm developing it in cold weather I back off .2 Gr . till the pressure signs have stopped . If it's a load that I intend to shoot year round , I'll back it off .5 Gr. and then find my accuracy load , there or below . It's not uncommon for a load developed in cold weather to show pressure signs , when fired in warm-hot weather .

What pressure signs are you talking about?? Flat primers and dimpled primers can be a result of the primer itself, sticky extraction can be a dirty chamber, etc. It's been stated that by the time you get to stiff bolt lift, you are off the chart with regards to pressure. How does your load compare with a load book in comjunction with a chrony? That's where you should be getting your information.
Basically, what you're saying is "how much can I push the envelope?" And if you end up with smoking, hot shards of steel sticking out of your brain, you can say "it's not my fault, the guys at AR said it was okay".
IMO, motoring anything at the top edge of performance is exponentially harder on the item than a more moderate pace. That is to say, things are much more apt to go wrong when you're running at the top end. This can range from minor irritations to more serious things.

Thanks guys,

For example the 57.5 grain load is the book max of h4350 under a 180 grain bullet and is giving me slightly difficult bolt lift and faint extractor marks.

Primers can be misleading but if the cases are neck sized or P-FL sized can be a good indicator.

I've noticed that with faster powders, say H4895 one gets sticky extraction before one gets extractor marks or cratered primers but with slower powders it's the other way around.

Makes sense from the point of view that the faster burners obturate the case faster to grip the chamber faster and give sticky extraction where as the slower powders cause more bolt thrust before they obturate the case fully but it may just be co-incidence.

Has anyone else noticed this?

quote:

Originally posted by wasbeeman:
What pressure signs are you talking about?? Flat primers and dimpled primers can be a result of the primer itself, sticky extraction can be a dirty chamber, etc. It's been stated that by the time you get to stiff bolt lift, you are off the chart with regards to pressure. How does your load compare with a load book in comjunction with a chrony? That's where you should be getting your information.
Basically, what you're saying is "how much can I push the envelope?" And if you end up with smoking, hot shards of steel sticking out of your brain, you can say "it's not my fault, the guys at AR said it was okay".
IMO, motoring anything at the top edge of performance is exponentially harder on the item than a more moderate pace. That is to say, things are much more apt to go wrong when you're running at the top end. This can range from minor irritations to more serious things.

No no, I'm asking "how far do you back off when you discover the bounds of the envelope".

I do not go over reloading manual maximums as a rule, the recent RL 17 30.06 are an exception because of the unusual fact that pressure data and corroboration is available.

Sometimes when working up to the book max one encounters pressure signs before reaching the published maximum.

At that point, what is going on pressure wise in the rifle?

Ghubert You asked why you sometimes see pressure signs before you get to book max loads. Well not all chambers are cut exactly the same. If you have a slightly tighter chamber or a short throat (no freebore) and bullet seating depth all can have effects on pressure. Loading manuals are just a guide. Max for a particular rifle may be a couple grains less or a couple grains more. Rather than trying to get every last foot per second of velocity I think one is better off trying to obtain the best accuracy. Also regarding a max load, it is great to watch for sticky bolt lift,flattened primers and extractor marks on the case head (all signs of too high a pressure). I would suggest you consider a load to be safe and not too much pressure if you can load that 3 times without loosening the primer pocket.If the primer pockets loosen after 2 or 3 firings you need to back off a little more.

If one is experiencing sticky extraction he really is likely three grains over the 65,000 PSI threshhold.

quote:

Originally posted by snowman:
Ghubert You asked why you sometimes see pressure signs before you get to book max loads. Well not all chambers are cut exactly the same. If you have a slightly tighter chamber or a short throat (no freebore) and bullet seating depth all can have effects on pressure. Loading manuals are just a guide. Max for a particular rifle may be a couple grains less or a couple grains more. Rather than trying to get every last foot per second of velocity I think one is better off trying to obtain the best accuracy. Also regarding a max load, it is great to watch for sticky bolt lift,flattened primers and extractor marks on the case head (all signs of too high a pressure). I would suggest you consider a load to be safe and not too much pressure if you can load that 3 times without loosening the primer pocket.If the primer pockets loosen after 2 or 3 firings you need to back off a little more.

Thanks Snowman, I did have a vague idea as to why maximum loads differ in different rifles but that's good to know.

I like your idea about reloading for tightness of primer pockets.

quote:

Originally posted by vapodog:
If one is experiencing sticky extraction he really is likely three grains over the 65,000 PSI threshhold.

So the 54.5 grain load doing 2550 fps is at 65Kpsi?

doesn't seem right to me.

You should be ok backing off 1-2 grains,just to be safe in hot weather,as long as the rifle still shoots like you want it to.
If you can get some RL-17 it might get you the speed you want without the high pressure.It does seem to work somewhat differently than the 4350 powders.

The "pressure signs" all tell you that the
brass is begining to yield and has little
strength left. If you think about it you will back off. If your primers loosen after only three loadings you are skipping along the edge.

quote:

Originally posted by Ghubert:
things just seem to tighten up the higher the load, what about in those cases for example?

In my experience, the most accurate load is usually below max for a particular rifle. This has been the case for me, with my f-class rifle being a notable exception.

IMO, when you've found your max, work down to find your best load, then further tune your load with OAL. You'll probably be pleasantly surprised, and will never miss the small loss of speed.

If you can't find an accurate enough load, change bullets, change powder, change primers. If you can't find a load that is fast enough to suit you, change cartridges.

If the only way your rifle shoots accurately is at or above max pressure, that's really unusual, and ultimately unfortunate.

Living on the "max" edge, will stress your brass, your rifle, and perhaps your skin. No reason to, especially in a hunting rifle, where reliability should strongly influence your decisions.

-nosualc

so, you have found max load ... i, personally, backoff a couple percent, and if vel isn't what i want, i change powders.

Ghubert,

If you've decided to load HOT, say for hunting purposes, I suggest only using modern first-rate bolt-action rifles, such as Remington, Winchester, Kimber, Dakota, and the like. Do not load HOT for automatics, semiautomatics, pumps, or refurbished military rifles.

With a modern strong bolt-action rifle, the rate limiting factor in high-performance reloading is the brass case, which begins to yield rapidly after you pass ~65,000 PSI. Brass is an imperfect elastic metal, never returning to 100% its original shape and size after being hammered by PSI - the higher the PSI the more it stretches and more and more deformed it becomes post firing.

At PSIs over 65,000 the primer pockets loosen fairly quickly, within 3-5 reloadings, and become unuseable. If I can push the primer back out with finger pressure, for me, that case is done and thrown away. At 75,000 PSI and above you're likely to get a blown primer after one shot. When this happens, you're at risk of getting escaping gases in your eyes, hence always wear eye protection. I wear eye glasses when hunting.

Modern bolt-action rifles will take in excess of 150,000 PSI, so you're not likely to blow-up the gun. Some worry about "metal fatique", but I shoot these HOT rounds only for hunting, and thus, less than a dozen shots per year. I load way down for "killing" targets - why stress the gun for target practice?

If you're using a HOT load, you must take into consideration ambient temperature - that is, a safe load at 70oF may become too HOT at 95oF. Also, HOT loads are subject PSI excursions, which can be a bit difficult to predict, so I use only the very best components available, I use match primers, I weigh every charge, and I employ the slowest-burning powder that will bring my load up to the desired pressure. Slow-burning powders tend to be more forgiving. Remember, as PSI increases the burn rate of the powder tends to increase - that is why only a one grain increase in powder may increase PSI 5,000 PSI or more - and go from a safe load to one that might produce a blown primer or stuck case.

My main concern, when loading HOT, is with these PSI excursions, which could freeze the bolt and prevent reloading as you watch that trophy of lifetime walk over the hill!! (If I need to push a stuck case back out of the chamber, I alway carry a cleaning rod with me that can broken down into parts for easy transport, although I've never had to do this in the field.)

I load until I begin to see the very faintest ejector impression and STOP! When this happens, there won't be a bright shiny spot, but you may notice your primer pockets getting loose after 5 reloadings.

The best way to measure loosening primer pockets is by hand priming your cases - you can feel the drop in finger pressure needed to seat the primer. Hotcore recommends using PRE and CHE for this, and this works but IMO, one can do it with hand primer pocket seating just as easily. PRE and CHE can be used at the range, while primer pocket feel requires returning to the loading bench.

The bottom line - how much risk can you live with? Happy and safe reloading.

Regards, AIU

Thanks for all the replies guys, I fear I have given the wrong impression here.

I'm not out to load as hot as possible, rather I'm asking that if one sees pressure signs working up a load in the normal way, by what percentage ( To avoid examples like Vapodog's above ) in order to be "safe" and or maintain case life?

Is there a rule of thumb or must one do a shakedown test on say one case until failure?

With thanks,

A

quote:

For example, if I had worked up from 42 to 46 grains in half grain increments, and started seeing trouble, I'd go back down to the most accurate load below 46.

If the accuracy or velocity at that node is unacceptable, I'd try a different powder/bullet combo.

+1

My rule of thumb is basically back down one full grain from where I see pressures signs, assuming I still get aceptaqble acuracy. It has worked for me across a broad caliber spectrum for years.

Ghubert, I usually go back, look at my brass, look at my targets, and see what makes sense. Typically in a midsize case like an 30.06, I will try to back off at least a full grain from where I see an extractor mark.

As a rule of thumb, a .02% reduction in your p[owder charge should result in a .04% reduction in pressure. If your load is showing obvious high pressure indications, a .04% reduction in pressures still leaves you on the ragged edge. For cases the size of 30/06 a 2 grain reduction in your powder charge would be advised for a hunting rifle.

quote:

Originally posted by fredj338:
My rule of thumb is basically back down one full grain from where I see pressures signs, assuming I still get aceptaqble acuracy. It has worked for me across a broad caliber spectrum for years.

I've found this^^^^^^ works good too.

quote:

04%

I do believe your decimal point is off. 4% maybe

2grs in most 06 loads would be more like 3.5% or higher.

quote:

how far should one back off

Till there is no pressure sign.

It depends on what you mean by "pressure signs".. If all it is is a flattened primer then anywhere from 1/2 gn to 1.5 gns. If you are getting a sticky bolt then I agree with Vapo that you may have to back up as much as about 3 gns..

Then as mentioned there are variables to consider like temps, different brass and even a new lot of powder..

I usually watch for flattened primers then go back about 1 gn if the accuracy is good..

Thank you again for all of thought-provoking replies.

I have had a play with quickload and looked M98's excellent data and decided that there is no such thing as a rule of thumb in this case....

I've done some reading and if I've understood it correctly, the burn rate of a given powder is proportional to the pressure at which it burns.

This makes sense considering the "lumpiness" of the pressure traces I've seen, from various source, as the charge is increased.

What I mean when I say lumpiness is that the relationship between charge weight and maximum mean chamber pressure does not appear to be linear at the extremes of the working pressure envelope.

It seems, from my admittedly limited, research and experience that pressure seems to "spike" as one approaches maximum.

The H4350 load above was worked up from load data on the Hogdon website.

I used the same OAL (3.250"), a Hornady 180gr BTSP Interlock and loaded three of each at half grain increments from 52 to 57.5 grains.

I shot these loads over a chronograph and worked up from 2450 at 52 grains, to 2650 at 56.5 grains, well I did shoot the 57.5 grain loads but I'll deal with that in a moment.

Between this velocity the relationship was fairly linear, rising about 50 fps per grain until the 57.5 grain load, where the velocity jumped 100fps in one grain charge weight increase.

If I try and make a 100fps, or 3.7%, increase with Quick Load, which incidentally cannot and did not predict the pressure spike, to make it work the pressure is increased by 6Kpsi or 10%.

M98's data seems to bear this rough principle out also.

What this all means from the point of view of my original question, I'm not quite sure.

I need to think about this some more.

Cutting through the mass of information I would back off one grain....You didn't have any pressure signs there! and your sure not losing anything in velocity or trajectory by backing off a grain. Keep your life simple you can overload and explode when handloading!