Powder PSI
 

I am wondering about PSI(pounds per square inch) on reloads regarding the powder. We see so many reloading charts about type of powder, grain of bullet, primers, crimp, etc. But when a bullet is seated while reloading and compresses the powder is there a measurement on the PSI pressure on the actual powder. And is it different in different loads? Is the actual PSI calculable or is it just "load by the chart".

:confused::confused:

I get what you are asking but I don't think most rounds actually compress the powder when seating the bullet. I will have to get the calipers out and do some figure'n but any specific load you are thinking about???

Am thinking about the .308. When seated, the compression of the powder. The bullet will not fire efficiently without compressing the powder, but is there a general PSI that the powder is compressed to to max it out while being safe?

I get ya... I will ask my FIL about this. He is a rifle guy and been loading longer than I have. You are the first person to ever ask this on a forum that I am aware of. You must be one of those thinkers or something:D

hehehehe...always need to know the specifics.

Most loads aren't compressed. Usually they will have an abbreviation CL or something to indicate it is compressed as compression can increase the PSI quickly and dangerously. Some types of powder may take up more space in the case but very few actually squeeze the bullet down far enough to compress the powder. When creating a compressed load you fill the powder according to the weight of the charge which will fill above where the bottom of the bullet would seat. Then the projectile being seated will compress the load when seated to the OAL.

So there can be airspace between the powder and the bullet?

Depending on the load yes. Sometes a lot,msometime a a little. I have some Trailboss that is a much fluffier powder to take up more space because 231 loaded in a 38-40 case woul only fill to about a third of the case. Then the powder sits on the bottom of the case and may not ignite correctly. Not enough to Squibb but maybe a lower velocity.

I loaded some .32 Magnum and could double charge the load without over flowing the case. That means single charge would take less than half of the case.

Yes many times there is a bit of space between the top of the powder and the bottom of the bullet. So a compressed load would be over filled with powder and squeezed or compressed down. VERY DANGEROUS with a powder that the burn rate is not appropriate for a compressed load.

For example, we load powder by weight. But 1 grain of W231 and 1 grain of AR Comp and 1grain of Trail Boss would all take up different volumes. Then compound the faster burn of the AR comp and you could have a high pressure spike than if you loaded the same volume of Trail Boss.

^this. Pressure in a firearm is measured in CUP (copper units of pressure). Some powders are meant to be compressed, most are not. Some powders are position sensitive (i.e. if they lay along the bottom of the case, ignition will suffer). Some powders characteristics are such that free space causes pressure spikes. In that case, OAL is reduced, or fillers are used. That is why loading manuals always list minimum and maximum overall length for each bullet and powder combination

I never thought about the powder laying along the bottom of the case. Now ya really got me going....some of this comes from a round, any caliber, being chambered over and over, lowering the OAL and then the round damaging the gun upon firing.

Interesting discussion. Tagged.

If there isn't you're likely to get a BIG surprise. :D

And this is a reason I asked about powder compression. Reading the boards some guys complain about using powders that require them to damn near jam the bullet in to get the desired OAL. So, as I'm reading this, I'm thinking about the PSI of packed powder. I'm sure this all has to do with burn rates in some way to max out the load.

I keep chambers loaded with the guns in rotation. Not having to unload sd round/s to shoot to practice, having dedicated practice guns. No need to worry about set back from constant chambering. I worry more about mucking the rim up so the extractor doesn't get a solid a purchase as it should on a new round. Making sure to load the round back in the mag [ to rechamber it ] with a clean spot on the rim, not on a gouged/deformed areas previously grabbed by the extractor :)

I get that, Brownie....but why are fillers used when reloading?

In the case of position sensitive powders, to keep the powder in proximity to the primer to ensure uniform ignition, which it would not achieve if laying on one side of the case

So some sort of compression or uniformity of the powder is necessary?

Remember you are talking about 3 different variables here.

1 Powder
2 Bullet
3 OAL

Not all 150 ge bullets are the same length. Not all powders have data for all calibers and OAL is dependent upon the bullet length and the powder charge. That is why different powders have different OAL for one bullet and may have a different OAL for the same bullet with a different powder charge.

^this

And I've never heard of fillers used in pistol reloading

No compression with fillers, but with some loading real powder puffs, depending on powder used, it can be so little compared to case capacity ignition is spotty and I've been told as dangerous as a double charge.

Ohhhhhh yes you have....I bitched about it on FCC when my new Springfield Black Stainless had "grit" in the chamber.....

Don't make me come out there Brownie.....funny

Yup, I remember that now Joe. But how many 10's of 1000's of rounds have you fired that didn't produce that? Forget the maker of that ammo you used, but it's not the norm to add fillers to pistol cases.

Yah, you got a point.....ALOT of rounds from that the maker...I can't complain.....


Now, back to compressing powder.....

Yep, some IMR powders are more dangerous with an undercharge than an overcharge. And some pistol powders ARE position sensitive and require filler to hold the charge in place. I wish Dave was still here, he could quote it off the top of his head as to which ones. Joe, if you got filler debris out of a batch of ammo and never got it before, likely that ammo maker was using what they could get during the shortage, and its characteristics called for a full case due to position sensitivity

If you are compressing powder, you have more guts than I do. Generally not a good idea.

Talkrd to fil today he said he won't compress powder. If it doesnt fit he either finds different piwder or redesgns load with better options.

Definitely had filler, but it wasn't during the shortage. I suspect it was a $$$$ profit matter. Still, the ammo functioned fine. Brownie, me and a few other students fired over 3000 rounds of it in one weekend. Zero malfs. I still have over 2K of .45 from that batch. Maybe I'll bust a few open and see what's in there.

Another reason to miss Dave....

Okay, so I’ve been reading this thread for a while now… I’m not aiming to piss you all off, but I probably will.

We are peering into some serious science here.
1st- NO OPINIONS on this subject, PERIOD! Practicing an opinion here can get you killed.

Way back when our government actually did stuff for the benefit of the people they established SAAMI (Sporting Arms and Ammunition Manufacturers' Institute) later “Inc.” and invited all our countries gun and ammo manufactures to join and create standards for the industry. These guys have made careers out of pushing the envelope so you don’t have to.
www.saami.org

In the old days it was trial and error test methodology which required some poor dolt to pull the trigger and couple of saps to clean up the mess, while the smarter guy observed from a distance. The army figured it was better to keep the dolts for collecting enemy bullets rather than blowing them up in testing so they developed a method for estimating chamber pressures for launching projectiles which became known as C.U.P. courtesy Wikipedia- Copper units of pressure or CUP, and the related lead units of pressure or LUP, are terms applied to pressure measurements used in the field of internal ballistics for the estimation of chamber pressures in firearms. The key here is “estimation” though accurate it was still an educated guess.
In the late 50’s and early 60’s the advent of the strain gauge and transducers allowed measurement and recording of actual instantaneous pressures through the entire firing cycle. But enough history, the full read, http://en.wikipedia.org/wiki/Copper_units_of_pressure

So to answer Joe’s original question, No the “air pressure” increase when seating a bullet in such a small volume is inconsequential in the big picture. Air as an inert gas neither adds nor detracts significantly to the overall reaction ratios during ignition. Unfortunately the thread has grown to include “Powder compression” and “fillers” known as suspension or balancing agents.

Now we are talking some serious science, head exploding science. There are powders designed for compression and there are some that have been tested to be used under light to moderate compression. These will be listed in your loading manual as designated or permissible. If not then “DON’T DO IT”! If you have changed bullet types or weight and are encountering this problem I suggest contacting the bullet manufacturer or saami.

Fillers- This is bad Juju… this practice is a follow on from the black powder days in an effort to insure ignition of a load that may be kept in a gun over an extended period with a piss poor ignition system. With the invention of the modern internal primer cartridge it is unnecessary. It is now used as attempt to control burn rates in hot short barreled loads (Pistols) primarily and is not considered a good practice. IE; if a manufacturer can’t get there normal powder or is trying to cheapen things up.

Hope I didn’t piss you off.

Didn't piss me off. I have eight sisters and three young kids, pissing me off is an impossibility.:D
So why do we ram a wad down the barrel of a black powder rifle. To hold stuff in place, compress the powder, or both?

I have seen a drunk Marine forget the wad and the ball roll out the end of the barrel. I about pis*sed my self for a week laughing.

Lol...didn't piss me off. I never said fillers were a good idea, just stated they are used in some applications

Well… yes to holding stuff in place. It would seem the ball is just as important. The powder needs to stay in the base of the chamber in close proximity to the primer charge or cap orifice. You’re basically building a modern round in the bottom of your barrel each time you shoot. Powder compression is still relatively minor, the more wadding between the powder and the shot the less compression you will achieve.

I load ALOT for 45-70 and using under min charge data (cat fart loads) and with certain Powders will use Dacron for filler But always remember compresed loads even Dacron compressed can cause Havoc
Always use caution stuffing Xtra anything in a Case
No chamber ringing going on Here with Under Min loading
DOGG!!!