How do you know when you've hit the wall with a specific powder

[Alan Adamson]

I've been playing with Autocomp for a 9mm Major load... I really like it's feel... BUT here's the rub.

my starting load was very close...

7.0gr of Autocomp at 1.175 oal behind a 124gr MG JHP

8 shots gave me a very good ES and a PF of 166, average velocity 1334

I decided that 7.1gr would offer a little more pucker factor room, so I loaded up 8 more round with 7.1gr

The ES was just as low, but the velocity was *exactly* the same 1334.

As a note, I hand loaded each of these rounds, individually weighing out the loads on a .02gr scale

Nothing else changed, except I saw no additional velocity.

A friend of mine suggested that I had hit the wall with this powder and this load and that jacking up the charge would more than likely put me in *critical* territory.

With either load no visual sign of over pressure, nothing significant on the primers, etc. I always figured that the wall would show up as a wildly fluctuating ES as a starting point and then go bad from there (assuming your increment was small that is).

I don't think many have played with this powder. Most have ignored it based upon prelim info... at this PF, in a 5" open gun, it shoots very soft, tracks very well and was just a pleasure to shoot. I simply wanted something around 170pf to be safe, but perhaps I can't get there...

Any ideas?

Alan

[MoNsTeR]

There's a non-trivial probability that two 8-unit samples of different charges could produce the same mean by sheer chance.

[kaiserb]

There's a non-trivial probability that two 8-unit samples of different charges could produce the same mean by sheer chance.

Statistically speaking the larger sample you test the lower your margin of error. Testing a sample size of 5 is very low and has an error rate of 40-50%, thus a 40-50% range in which you could chrony the same value(s). Small sample sizes can cause misleading results. This is why many recommend chronying at least a 10 round string and if possible a 20-30 round string. If one loads 500 rounds and tests 5 of them across the chrony you are testing 1% of the population.

Looking at a shooting match example:

Given

500 rounds [population]

Typical chrony procedure requires 80% rounds meet PF [margin of error determine from this]

Lets say we want to be 90% certain of the results [confidence level].

With a 500 round population to chose from we randomly select 5 rounds for testing [sample size], which yields

Ave PF 166

StDev 15

A quick calculation shows the confidence interval is +/- 11.04. One could expect within another sample a PF range of 154.96 PF - 177.04 PF

Using the same data but a sample of 30 rounds tested yields a confidence interval of +/- 4.51 so one could expect with another sample a PF range of 161.49-170.51 PF Additionally with the larger sample one could expect the SD to narrow giving an even greater confidence level in the results.

Edited September 4, 2009 by kaiserb

[XRe]

In other words... you're probably OK, and a change of one tenth in the charge weight without change in velocity is probably not something to get too worked up over.... yet... If I were in your shoes, I would probably bump it another tenth and see what happens. If the velocity stays the same, or worse, gets lower, then its probably time to consider bailing out. I would feel safe doing this because its highly unlikely that one tenth would cause a catastrophic situation in a power in that speed range. I'd be a lot more wary if we were talking about, say, loading Clays behind a 200gr .40 bullet, say... You may see pressures ramping up more quickly, but its been my experience that the relatively gradual change in these medium speed powders would start to show you more signs before doing something drastic.

I take no responsibility for what you decide to do, of course

[RiggerJJ]

try a 1# heavier recoil spring...

jj

[the duck of death]

Why will that help?

[XRe]

Why will that help?

I had the same question....

[G-ManBart]

A couple of things come to mind. Adding a tenth may not show up as a consistent increase because most powder measures vary that much. Not only that, but two cartridges loaded "identically" will frequently vary more in velocity than the change you'd theoretically see from increasing a tenth of a grain. If you were to use a sample size of 50 or 100 rounds, get a good average there, then increase by a tenth and average another 50-100 rounds you might see the average go up a slight amount...say 10-15fps, but that doesn't mean that a slower round in the batch that's a tenth higher won't be down near the lowest velocities seen from the batch that's a tenth lighter.

I guess the short version is that a tenth isn't enough to really rely on a noticable, consistent increase. Some of that is a function of the powder itself, the charge weight and the burn rate. The slower the powder, the more of it you need and the more it takes to cause a change.

Second, if you're at 166pf, you need a heck of a lot more cushion than you're going to normally get from a tenth or two. I've said this many time before, but last year I loaded a batch of ammo for Nationals, Area-2 and a Sectional. It was one lot of 1,000 new cases, one lot of powder, bullets from the same box from MG and a full box of primers from the same sleeve. That batch went 171PF the first time I chrono'd it, but I didn't get to put as many rounds over the chrono as I usually do (20x2). At Area-2 it went 174PF. After I came back from Nationals I had some left over (still have 100 left) and I ran it over the chrono again and got 175PF. I recently tried it again, two strings, and got 174 and 175PF. At Nationals it was 166.1PF

I had a solid load, using a powder not known for temperature sensitivity, it was over 170PF every time I tried it, and it still just squeaked by at Nationals.

I recently loaded up my Nationals ammo using the same lot of powder as last year (bought a bunch of it), bullets from the same shipment (different box), new cases (same brand etc) and slightly different primers (FSPM instead of FSR) and it ran 174PF and 175PF both times I tried it (20 round strings). I can't wait to see what this runs over the Nationals chrono because it's been pretty consistent except for the 08 Nationals and the first abbreviated chrono session.

You can bet I'm not going to a big match with anything that doesn't consistenty run well over 170PF now!

Back to the original question. Each powder will show different signs when you hit the wall. Some will get wild fluctuations in velocity, some will show no gain at all and some will show a decrease in velocity. At that point it's likely you'd be seeing primer signs, but not guaranteed. Certainly, seeing no gain is cause for concern, but I wouldn't be too worried just yet.

I'd load up 40 at 7.0gr and 40 at 7.2gr and chrono all of them using two 20-round strings for each load. That should give you a pretty reliable average. If the 7.2gr isn't clearly faster and over 170PF I would start looking for another powder. R,

[G-ManBart]

Why will that help?

I had the same question....

He's suggesting that the heavier spring will keep the gun in battery for an instant longer which will delay unlocking and loss of pressure....so you get higher pressures and an increase in velocity. I think that's one of those things that works in theory and might apply to cannons, but not handguns in the real world.

In reality the recoil spring is at it's weakest when fully extended so even going up in spring weight isn't going to make a big difference in how much force it's applying to hold the slide closed. I'd guess that changing the firing pin stop geometry and using a heavier mainspring might make more difference in how the gun unlocks than the recoil spring. Still, I can't see any of that helping the OP. R,

Edited September 5, 2009 by G-ManBart

[wide45]

The bullet is long gone when the barrel unlocks. I'd be astonished to see chrono results showing a significant repeatable increase in muzzle velocity by going to a heavier spring.

[kamikaze1a]

I would say the variables greatest with the chronograph. Change the chrono, change the distance from muzzle, change the lighting...

[kamikaze1a]

And I'm with wide45 on this one...I believe the bullets out of the muzzle before the slide starts moving. If not, accuracy would be affected by the barrel movement...

[G-ManBart]

The bullet is long gone when the barrel unlocks. I'd be astonished to see chrono results showing a significant repeatable increase in muzzle velocity by going to a heavier spring.

That's what I've always said as well. I'm waiting on some crazy fast high speed video of a Glock being shot out of a Ransom Rest to help clear that up. I've seen it before, but didn't get a chance to break it down and go frame by frame. I recall the bullet being gone before the slide moved even the smallest amount. The funny thing was watching the guide rod hit the bottom of the barrel and seeing daylight (clearly) between the frame and slide

[GrumpyOne]

I think the recoil spring thing and barrel lockup have been discussed at length in another thread. Wide45 and Kamakaze are right. If the barrle started it's downward/rear ward movement before the bullet left the barrel, no auto would be worth a penny.

[rhyrlik]

And I'm with wide45 on this one...I believe the bullets out of the muzzle before the slide starts moving. If not, accuracy would be affected by the barrel movement...

If you look at slow motion video of a 1911, the barrel and slide recoil together for about a sixteenth of an inch before the bullet exits the muzzle.

[GrumpyOne]

And I'm with wide45 on this one...I believe the bullets out of the muzzle before the slide starts moving. If not, accuracy would be affected by the barrel movement...

If you look at slow motion video of a 1911, the barrel and slide recoil together for about a sixteenth of an inch before the bullet exits the muzzle.

I think what you are seeing is the very miniscule take up of the barrel link before the slide comes out of lock. The only way for the slide to move really is for it to drop out of lock. When it drops from lock, the barrel tilts down at the chamber, allowing the slide to move rearward. What holds the barrel and slide together in lock when being fired, is the pressure of the brass case against the walls of the chamber, the only way for the slide and barrel to come out of lock is when the pressure subsides, I.E., when the bullet leaves the barrel. The slide will not move when being fired because the extractor is in the groove of the case, which is still locked tight against the chamber walls by the pressure of the gasses. The link on the barrel (through which your slide stop pin is inserted), acts as the pivot, to pull the barrel downward, away from the locks. While the slide and barrel may move rearward (it won't be 1/16th of an inch, unless the barrel link is wore out, probably much less), a heavier recoil spring would have absolutely no effect on keeping the gun in lock longer, only a slower bullet can do that...

[rhyrlik]

I'm not talking about the barrel unlocking. I'm talking about the slide and the barrel recoiling to the rear together for about a sixteenth of an inch while locked together, then unlocking after the bullet has left the muzzle.

[XRe]

I think what you are seeing is the very miniscule take up of the barrel link before the slide comes out of lock. The only way for the slide to move really is for it to drop out of lock.

The slide and barrel move rearward together somewhere in the neighborhood of 1/16" before the barrel begins to drop.

When it drops from lock, the barrel tilts down at the chamber, allowing the slide to move rearward. What holds the barrel and slide together in lock when being fired, is the pressure of the brass case against the walls of the chamber, the only way for the slide and barrel to come out of lock is when the pressure subsides, I.E., when the bullet leaves the barrel.

Wrong again... what holds the two together in lockup - what keeps the locking lugs of the barrel firmly engaged in the locking lugs of the slide - has nothing to do with some kind of sliding friction pressure of the brass case against the chamber walls. If that were the case, you'd never see a stuck case in the chamber - the gun wouldn't cycle at all, then.

What keeps the gun locked up is simply physics - the barrel moving down the barrel pulls the barrel forward, pulling the barrel's locking lugs forward surfaces against the rear surfaces of the slides locking lugs. Once the bullet has cleared the barrel, that force is no longer present, and the pressure against the lugs is gone, allowing the two to separate.

There's a nice thread archived here on the forum of a discussion between a couple of smiths that goes through the whole thing, and its apparently also well documented in Kuhnhausen's books (including details on why that 1/16th of inch of movement is important, etc...

The slide will not move when being fired because the extractor is in the groove of the case, which is still locked tight against the chamber walls by the pressure of the gasses.

Its also very demonstrable that, upon unlocking, the extractor has no where near enough strength to keep the slide from moving rearward. Again, stuck cases prove you wrong. You would never see a stuck case (due to high pressures, or sometimes rough chambers) if this were the case - you'd have to beat the gun open instead.

The link on the barrel (through which your slide stop pin is inserted), acts as the pivot, to pull the barrel downward, away from the locks. While the slide and barrel may move rearward (it won't be 1/16th of an inch, unless the barrel link is wore out, probably much less), a heavier recoil spring would have absolutely no effect on keeping the gun in lock longer, only a slower bullet can do that...

I agree with the bit I bolded here.

[CocoBolo]

The non visual clue I get is by feel, it starts with little minute particles of burned powder hitting you in the face. With Auto Comp I started to feel it wasn't going to make major at 7.4 gr behind a 125gr Zero JHP in my 38 Super. I would recommed it for Minor 9, if you have a Steel Master its the perfect powder.

I had a similar expierece with TruBlue once I went beyond 8.3gr with a 125gr in 38 Super. Which was about 168 pf but my gun likes 174-175pf its an old school open.

Most of the local Major 9 guys I know prefer RAM Shot Silloutte. (never could spell). One die hard old timer swears by HS6 which is way lound and abrupt in 38 Super. A few are using TruBlue.

There aren't a lot of choices in 9 mm major, you can spend years trying different powders in 38 Super.

[GrumpyOne]

I think what you are seeing is the very miniscule take up of the barrel link before the slide comes out of lock. The only way for the slide to move really is for it to drop out of lock.

The slide and barrel move rearward together somewhere in the neighborhood of 1/16" before the barrel begins to drop.

When it drops from lock, the barrel tilts down at the chamber, allowing the slide to move rearward. What holds the barrel and slide together in lock when being fired, is the pressure of the brass case against the walls of the chamber, the only way for the slide and barrel to come out of lock is when the pressure subsides, I.E., when the bullet leaves the barrel.

Wrong again... what holds the two together in lockup - what keeps the locking lugs of the barrel firmly engaged in the locking lugs of the slide - has nothing to do with some kind of sliding friction pressure of the brass case against the chamber walls. If that were the case, you'd never see a stuck case in the chamber - the gun wouldn't cycle at all, then.

What keeps the gun locked up is simply physics - the barrel moving down the barrel pulls the barrel forward, pulling the barrel's locking lugs forward surfaces against the rear surfaces of the slides locking lugs. Once the bullet has cleared the barrel, that force is no longer present, and the pressure against the lugs is gone, allowing the two to separate.

There's a nice thread archived here on the forum of a discussion between a couple of smiths that goes through the whole thing, and its apparently also well documented in Kuhnhausen's books (including details on why that 1/16th of inch of movement is important, etc...

The slide will not move when being fired because the extractor is in the groove of the case, which is still locked tight against the chamber walls by the pressure of the gasses.

Its also very demonstrable that, upon unlocking, the extractor has no where near enough strength to keep the slide from moving rearward. Again, stuck cases prove you wrong. You would never see a stuck case (due to high pressures, or sometimes rough chambers) if this were the case - you'd have to beat the gun open instead.

The link on the barrel (through which your slide stop pin is inserted), acts as the pivot, to pull the barrel downward, away from the locks. While the slide and barrel may move rearward (it won't be 1/16th of an inch, unless the barrel link is wore out, probably much less), a heavier recoil spring would have absolutely no effect on keeping the gun in lock longer, only a slower bullet can do that...

I agree with the bit I bolded here.

The slide and barrel move rearward together somewhere in the neighborhood of 1/16" before the barrel begins to drop. I can agree with this. It does move, the point was, it doesn't move enought for a heavier spring to be of any use.

Wrong again... what holds the two together in lockup - what keeps the locking lugs of the barrel firmly engaged in the locking lugs of the slide - has nothing to do with some kind of sliding friction pressure of the brass case against the chamber walls. If that were the case, you'd never see a stuck case in the chamber - the gun wouldn't cycle at all, then

I disagree with this. Think of just a plain old Remington Model 742 auto rifle. What holds the bolt closed is the pressure between the case and the chamber wall when being fired. If it didn't, the bolt would come smashing back the exact instant you pulled the trigger. The case/chamber wall pressure thing is also why you don't oil your ammo before shooting. When the case expands against the chamber walls, it displaces 99.9% of whatever oil you had on the case, but the other .1% acts like a suction, holding the case to the chamber walls, even after the pressure has been released.

Its also very demonstrable that, upon unlocking, the extractor has no where near enough strength to keep the slide from moving rearward. Again, stuck cases prove you wrong. You would never see a stuck case (due to high pressures, or sometimes rough chambers) if this were the case - you'd have to beat the gun open instead.

While I do agree with this, the original quote was not entirely what I meant. "The slide will not move when being fired because the extractor is in the groove of the case, and the locking lugs are engaged, which the case is still locked tight against the chamber walls by the pressure of the gasses" Only when the pressure releases, and the case "shrinks" from the chamber walls, can the locking lugs disengage.. Anyway, enough of this thread drift!

Edited September 6, 2009 by GrumpyOne

[rhyrlik]

A heavier recoil spring will delay the slide and barrel assembly from recoiling to the rear. This delay will change the barrel harmonics and may affect accuracy.

[RiggerJJ]

try a 1# heavier recoil spring...

jj

A heavier recoil spring will delay the slide and barrel assembly from recoiling to the rear. This delay will change the barrel harmonics and may affect accuracy.

I don't know about changing accuracy, but I do know that a slightly heavier recoil spring WILL, IN SOME CASES, help add a few PF to a load that you don't want to add more powder to...

thats why I made the suggestion, try it, and see what you find. you may be golden, you may be still scratching yer head, but at least you are trying things. (instead of arguing with the peanut gallery)

jj

Edited September 6, 2009 by RiggerJJ

[G-ManBart]

I don't know about changing accuracy, but I do know that a slightly heavier recoil spring WILL, IN SOME CASES, help add a few PF to a load that you don't want to add more powder to...

thats why I made the suggestion, try it, and see what you find. you may be golden, you may be still scratching yer head, but at least you are trying things. (instead of arguing with the peanut gallery)

jj

The problem with that, well the first problem anyway, is that he really needs more than "a few PF" to be safe (at least 5 more) so we wind up back and the same place....either more of the current powder or an entirely different powder.

The second "problem" is that changing springs sets off a whole chain of events. It changes how the gun cycles and it might not be the right spring for his shooting style/timing. It can cause reliability issues as well. If the gun is reliable, tracks well for you, and doesn't meet power factor with your ammo you don't change the gun, you change the ammo, powder, powder charge or bullet until it makes PF with a nice cushion and avoid all the other potential pitfalls out there. R,

[XRe]

Wrong again... what holds the two together in lockup - what keeps the locking lugs of the barrel firmly engaged in the locking lugs of the slide - has nothing to do with some kind of sliding friction pressure of the brass case against the chamber walls. If that were the case, you'd never see a stuck case in the chamber - the gun wouldn't cycle at all, then

I disagree with this. Think of just a plain old Remington Model 742 auto rifle. What holds the bolt closed is the pressure between the case and the chamber wall when being fired. If it didn't, the bolt would come smashing back the exact instant you pulled the trigger. The case/chamber wall pressure thing is also why you don't oil your ammo before shooting. When the case expands against the chamber walls, it displaces 99.9% of whatever oil you had on the case, but the other .1% acts like a suction, holding the case to the chamber walls, even after the pressure has been released.

Wow, man, you are really off in the weeds.

The 742 is a gas operated rifle. What holds the bolt closed is the locking lugs on the bolt rotated into the locking lugs on the barrel. If you remove the action tube, or plug the orifice, the gun wil remain locked up until pull back on the operating handle. The locking mechanism is similar to the AR-15 (though the operating mechanism is not quite the same). Still has exactly zero to do with the brass or pressure within the chamber. The gun design is carefully timed (in the case of a gas operated gun, the placement of the gas port vs. the expected operating pressure, etc) so that it doesn't unlock the bolt while chamber pressure is too high. In fact, in the case of gas operated guns, you don't have the recoil lug phenomenon that you have in the 1911 style gun - you can, in fact, unlock the gun while the bullet is still in the barrel and cause a very serious problem, if you don't design the gun properly.

While I do agree with this, the original quote was not entirely what I meant. "The slide will not move when being fired because the extractor is in the groove of the case, and the locking lugs are engaged, which the case is still locked tight against the chamber walls by the pressure of the gasses" Only when the pressure releases, and the case "shrinks" from the chamber walls, can the locking lugs disengage.. Anyway, enough of this thread drift!

It has less than zero to do with anything involving the case pressing against the chamber walls... And... the above bolded text is not at all what you said - still doesn't matter, though. The extractor has zilch to do with keeping a 1911 locked up, either.

As far as the recoil spring contributing anything to when the slide unlocks, you're correct there. That's total bunk. Any change in velocity seen when changing recoil spring by 1# is sheer coincidence. Period.

[Alan Adamson]

Well, I bit the bullet so to speak.

I took what advice was offered and I retested a couple of loads.

I started with what I had originally done a 7.0gr load of Autocomp behind a 124gr MG JHP at 1.175. All the below were hand trickled and hand loaded.

Got these results

High: 1323.0 164

Low: 1304.0 162

E.S.: 19.0

Ave.: 1314.3 163

S.D.: 5.9

final column is PF btw

Then I'll insert the 7.1grs that I did prior, these showed no increase over some other 7.0gr versions (however, those were loaded on a different scale)

High: 1337.0 166

Low: 1328.0 165

E.S.: 9.0

Ave.: 1334.4 165

S.D.: 3.2

And finally the 7.2gr versions that I did along with the above 7.0's.

High: 1363.0 169

Low: 1336.0 166

E.S.: 27.0

Ave.: 1352.8 168

S.D.: 10.8

As you can see, it appears I hadn't actually hit the wall with this powder. And in looking at the individual rounds, I think it's actually closer to the 169 PF in a broader sample that this small sample would show.

Couple of notes... at this 7.2gr, there is a little bit of primer flattening and primer flow... I had to look really close to see the very slight outline of the firing pin hole surrounding the firing pin strike point. However the edges of the primer as still rounded. These were all CCI SP primers as a point of reference.

These are in a 9mm Major open gun and it's a full length with Storm Lake Barrel

My summary is as follows.

a) I originally loaded some 7.0gr on one scale, and then did the 7.1's on a different (same make, model) scale

in redoing all the loads on the same scale, the original 7.0's seem to behave similar to the 7.1's that I loaded, leading me to believe that one or the other scale is slightly different from the other (these are .02gr resolution scales btw)

c) looking at everything loaded from the same scale, the 7.0, 7.1, and 7.2 show incremental increases with no significant negatives from just a numbers perspective

d) in this case, it appears that either 7.2 or possibly 7.25 will be a major (with fudge factor) load for this open gun

e) a larger sample with heightened inspection for pressure signs in the cases will be conducted

Anyway, YMMV with any of this information, but I figured I'd share what I found out.

Thanks for the advice,

Alan