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Decrease in velocity with increase in powder? Any explanation?

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I never really understand this need for speed. To me accuracy is WAY more important. I have NEVER found that the most accurate round is ever loaded anywhere near a recipe max.

 

But I realize I am strange! :tongue:

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I never really understand this need for speed. To me accuracy is WAY more important. I have NEVER found that the most accurate round is ever loaded anywhere near a recipe max.

 

But I realize I am strange! :tongue:

Speed is great but accuracy is final beyond a doubt. Most barrels will exhibit at least two accuracy nodes at different speeds.

 

You need to try some of these Black Hole barrels. I have found in many of mine that the faster I load them the better they shoot. Like you have found most of my factory barrels do respond to backing down somewhat.

 

Greg

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One thing that has not been mentioned (and is not mentioned very often in reloading forums) is metallurgy. It is a known fact (at least I think I've known it for many years) that when using most powders...there will nearly always be a point reached where you will get decreasing amount of velocity increases for each increment of powder...Then, at some point,..you will start to get negative returns or..at minimum..sporadic returns. I think this is more true for rifle powders than handgun,...but it still true to a certain extent with handguns.

 

Steel will not stretch until it reaches a certain pressure point. When it reaches that point it will be at the same pressure each time. As the pressure increases beyond that point the steel will start to temporarily stretch...but since steel is very elastic,..the still will spring back when the pressure is relieved...So...no harm done,..and you've now increased the pressure beyond the steel stretching point and gotten a little more out of your weapon. (incidentally...the torque values listed for bolts are usually the point at which an engineer has determined that the steel is at that point stretching..and therefore pushing back...with less of a change of coming loose).

 

HOWEVER....you can only go a certain amount past the stretching point before your stretch NO LONGER returns to it's original shape...and, of course,..a bit beyond that "beyond" and you have blown up your chamber. It is my opinion that when your amount of return per increase in powder starts to fluctuate a bit,..you are now at the "stretching" point..

 

In VERY OLD ancient reloading manuals,.. I believe they used to state that the best way to find your max load is to slowly increase your powder (with all other things equal) and in the beginning you have a straight line on your graph (velocity vs. amount of powder).. But the top of the graph will start to level out..it will look like the top of a bell. You can find the top...and then back off a little to be safe. I believe this is no longer in any type of manuals and hasn't been for way over 50 years. I'm guessing there were too many guys that wanted to make sure there wasn't another top of the bell curve that they hadn't seen yet..but I digress).

 

Of course,...the above is just an added dimension to all of the different variables in reloading. Your powder is a greater variable. Some powders start to give you more return (per given amount of increase in powder) when they are compressed..... And it is well known that some of the faster pistol powders are very dangerous if you start to compress them (usually the faster ones..not the slower ones like H110 or 4227).,

 

Ok, take what I say with a grain of salt...but it is an overlooked variable... Even though we'd all like to think that there are ansi standards for pistols requiring the weapon to burst at a minimum of 4x the stated safe pressure...pistols don't work that way. I believe (when a manufacturer will actually admit it) that most of them will blow sky high not long after you are around double the stated safe pressure..if not sooner.)...I would expect that you should be more careful if you are not using an american gun. I know most semi auto's don't necessarily blow up..they just bust slides, etc.,.. I mic'd the chamber walls on my Ruger p90..45 once,... And I think they were within a couple thousands of an inch of some of my 44 mags...So,..basically, within 1 or 2 percent. Also mic'd a 1911 or two but can't remember how thick the walls were..

 

OK, Just my 2 cents.

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One thing that has not been mentioned (and is not mentioned very often in reloading forums) is metallurgy. It is a known fact (at least I think I've known it for many years) that when using most powders...there will nearly always be a point reached where you will get decreasing amount of velocity increases for each increment of powder...Then, at some point,..you will start to get negative returns or..at minimum..sporadic returns. I think this is more true for rifle powders than handgun,...but it still true to a certain extent with handguns.

 

Steel will not stretch until it reaches a certain pressure point. When it reaches that point it will be at the same pressure each time. As the pressure increases beyond that point the steel will start to temporarily stretch...but since steel is very elastic,..the still will spring back when the pressure is relieved...So...no harm done,..and you've now increased the pressure beyond the steel stretching point and gotten a little more out of your weapon. (incidentally...the torque values listed for bolts are usually the point at which an engineer has determined that the steel is at that point stretching..and therefore pushing back...with less of a change of coming loose).

 

HOWEVER....you can only go a certain amount past the stretching point before your stretch NO LONGER returns to it's original shape...and, of course,..a bit beyond that "beyond" and you have blown up your chamber. It is my opinion that when your amount of return per increase in powder starts to fluctuate a bit,..you are now at the "stretching" point..

 

In VERY OLD ancient reloading manuals,.. I believe they used to state that the best way to find your max load is to slowly increase your powder (with all other things equal) and in the beginning you have a straight line on your graph (velocity vs. amount of powder).. But the top of the graph will start to level out..it will look like the top of a bell. You can find the top...and then back off a little to be safe. I believe this is no longer in any type of manuals and hasn't been for way over 50 years. I'm guessing there were too many guys that wanted to make sure there wasn't another top of the bell curve that they hadn't seen yet..but I digress).

 

Of course,...the above is just an added dimension to all of the different variables in reloading. Your powder is a greater variable. Some powders start to give you more return (per given amount of increase in powder) when they are compressed..... And it is well known that some of the faster pistol powders are very dangerous if you start to compress them (usually the faster ones..not the slower ones like H110 or 4227).,

 

Ok, take what I say with a grain of salt...but it is an overlooked variable... Even though we'd all like to think that there are ansi standards for pistols requiring the weapon to burst at a minimum of 4x the stated safe pressure...pistols don't work that way. I believe (when a manufacturer will actually admit it) that most of them will blow sky high not long after you are around double the stated safe pressure..if not sooner.)...I would expect that you should be more careful if you are not using an american gun. I know most semi auto's don't necessarily blow up..they just bust slides, etc.,.. I mic'd the chamber walls on my Ruger p90..45 once,... And I think they were within a couple thousands of an inch of some of my 44 mags...So,..basically, within 1 or 2 percent. Also mic'd a 1911 or two but can't remember how thick the walls were..

 

OK, Just my 2 cents.

I think you're undercharging for your opinion, I think it's worth considerably more. Back when I did reload, I found many of the same things to be true. Maximum, and above maximum loads did not always return the fastest velocities. I think that the steel "stretch" theory is sound, and I agree. My experience playing with engines mimics my experience playing with guns. Head bolts stretch, which is why in many applications, they're replaced after each use (Cadillac 4.6 IIRC is that way). They've been taken to the point where there is no more stretch left, and they're at the ragged edge of breaking under the stress.

 

Ever twist a bolt off when you were working on something? You push, and push, and it gets tighter and tighter, and then it starts to get easier, and then you have two pieces of a bolt. If you push the envelope, you may get to right before it gets easier to turn, and the next one blows the gun. Turning fine firearms into shrapnel is not fun, and I can't figure out the guys who push that hard all the time. To me, a $500+ gun, my hands, and my eyesight is worth much more than wringing the last few fps out of a given load.

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...Steel will not stretch until it reaches a certain pressure point. When it reaches that point it will be at the same pressure each time. As the pressure increases beyond that point the steel will start to temporarily stretch...but since steel is very elastic,..the still will spring back when the pressure is relieved...

 

 

A good reason to measure case head expansion and base bulge when working up maximum loads! When the case head exceeds the SAAMI .425", you know the brass is flowing due to over pressure. I've found in my Glock G40 stock barrel that fired case head measurements of .426" and case bulge of .436" (.434" chamber) did not show any obvious signs of overpressure/stress, such as cratered/pierced primers, Glock smilies, case head cracks, or case mouth splits...and, did not result in expected velocity for the charge weight.

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Hello and welcome to the 10mm communtiy

 

I've run into this also with P.P. and other powders as well. I just attributed it to two possibilities after playing around with different primers and seating depth.

One, is the powder doesn't like to burn as efficiently at that higher pressure as it would with a lower charge. PP has not impressed me as a powder to use for 100% loads... More like 85-90%

The other thing is that with the increased powder charge you just ran out of barrel to burn all the powder. There is probably a good reason why Alliant lists 9.3grs with a 180gr bullet.

The load my G20-SF likes very much is 9.0 of PP with a Hornady 180 FMJ. Makes for a good solid all-around load. After 9.0grs I run into the same phenomenon. My barrel is only 4.6".

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slow is smooth and smooth is slow. The need for speed is ok as I have gotten older and developed arthritis in my hands I like the gentler loads that don't pound my hand.

Edited by gshayd

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