[TwoMorrow]

So I have been learning all I could about loading 9mm for a couple of months now, from this site and my lyman's and a few messages to fred. (Thanks fred)
I loaded up the most nervous 11 rounds I have ever shot, even more nervous than the first time I ever shot my xdm. Everything went well so I made a minor tweak to my recipe and loaded up 50 more, then 100. Everything appears to be of to a good start. The only thing I have noticed is a few and I mean maybe 5 small bits of powder left in the barrel after shooting each round. They don't accumulate, always just a few bits. I am loading 5.3 gr of Power Pistol under a 124 gr FMJ. The rounds appear to function perfectly. No FTE's, no FTF's no KB, no squibs, every one has cycled and shot without a hitch or hiccup. All the spent cases and primers appear normal. Is the powder in the barrel a problem? I know PP is on the medium to slow side, as far as burn rate maybe that is the reason?
Also I was just wondering how many rounds some of the rest of you test fire before going all out on a new recipe? I have about 1500 cases to do and enough components for about 800 of those and I would like to get loading. I just need a bunch of plinking ammo so working up the perfect load at this point doesn't concern me I just need safe and reliable.
One more question, and maybe my dumbest yet, I purposely set up my press so that a double charged case is basically impossible to do. But a case with no powder at all is pretty easy to accomplish. Will the force of a primer and no powder cause a squib? I can't imagine it would but, I am guessing that I have a better chance surviving a load a little too hot with all my digits in tact than, shooting the next bullet into a barrel obstruction.

 

[scooterj]

Most slower powders will not give a complete burn unless loaded toward the upper end of the data.
A primer does produce enough energy to launch a projectile into the barrel. If you hear "pop" instead of "bang", stop and check the barrel for an obstruction.

 

[fredj338]

Your PP load is a bit soft for that burn rate. Medium burners for me start @ Unique & end about HS6. So medium burners run best above midrange levels. The lower pressures don't allow complete combustion in shorter bbls. Using 6.1gr of PP under a Rem 124grJHP @ 1.145"OAL, I am only running around 1100fps in a G17, so 5.3gr is pretty enemic, maybe 1000fps, maybe? Get the charge wt up a bit & the unburnt powder should go away. Speer#14 calls for 6.4gr as max @ 1160fps in a 4"bbl, pretty close to what I get.
I work up loads 0.1gr at a time to max average using a chronograph. I load in 5rd lots, shoot them in order & note vel & accuracy, of course reliability. If I see any pressure signs or the vel increase flatten out, then I take that as max, back of 0.1gr & that would be my working load, or choose the most accurate, clean running reliable load of the test group. All powder/bullet combos have sweet spots for accuracy.
As to squibs. IMO, almost as dangerous as a double charge, particularly in revolvers but also semis. It is possible to stick a bullet into the bbl & with a modified gun running a light recoil spring, to have the slide cycle, not likely, but possible. Pull the trigger on a full power round behind that & it could take your gun apart. Most shooters easily recognize a squib, one benefit of NOT shooting super light bunnyfart loads, but some do not. Very easy to do in revolvers for gun games. Always verify your powder charges, always. Carry a 8-9" length of 1/4 brass rod just in case you do get a squib, yes it has happened to me.

 

[Cranium]

When developing my loads, I will do 10 rounds at various powder weights. For slower burning powders that require larger volumes and have a greater spread between the recommended starting and max loads, I will increase my loads by .2 gr each time. For faster burning powders like TiteGroup and N320, I will increase my loads by .1 gr each time.

I load these test loads using my Hornady Lock-N-Load Auto Charge Powder Scale and Dispenser in cases of the same headstamp. I then seat and crimp each round individually. This removes several variables that can throw off results.

I then chrono each of these batches and record the results on-going in a spreadsheet for future analysis. When firing, I look for signs of over-pressurization and lack of accuracy; however, more intensive accuracy testing is done subsequently. The chrono testing I do has always been at 7 yards.

My goal is to achieve a power factor between 125-130 on my loads with accurate results. Once I determine what powder charge to use, I then load 50 rounds of mixed brass on my AP press and chrono about 10 rounds then fire the rest at distances of 15 and 25 yards. If I'm happy with the results, I will mark this as a load ready to mass produce. I'm not as experienced or accurate as many shooters so my criteria for a load being accurate enough is a bit relaxed. At 25 yards if I can get them in a 8" diameter ring, I'm happy.

The weekend before last, I tested loads with 3 different powders. 4 different weights for each powder and 10 rounds per weight meant there were 120 rounds loaded by hand and it took a while to complete these. I used a sharpie to mark each casing with a number and recorded each batch on a piece of paper to ensure that I did not get any batches mixed up.

I use an RCBS Lockout Die to try to eliminate the possibility of double charges or squib loads. I say 'try to eliminate' because I have, on more than one occasion, had the die stick in the upper position essentially disabling it. It is still important to be mindful of what you are doing first and relay on your equipment as a second layer of protection.

I will also add that the 125-130 power factor is used for jacketed bullets. For my lead cast bullets, I'm currently averaging 122 power factor and 1019 fps to minimize leading.

 

[fredj338]

My goal is to achieve a power factor between 125-130 on my loads with accurate results. Once I determine what powder charge to use, I then load 50 rounds of mixed brass on my AP press and chrono about 10 rounds then fire the rest at distances of 15 and 25 yards. If I'm happy with the results, I will mark this as a load ready to mass produce. I'm not as experienced or accurate as many shooters so my criteria for a load being accurate enough is a bit relaxed. At 25 yards if I can get them in a 8" diameter ring, I'm happy.

The weekend before last, I tested loads with 3 different powders. 4 different weights for each powder and 10 rounds per weight meant there were 120 rounds loaded by hand and it took a while to complete these. I used a sharpie to mark each casing with a number and recorded each batch on a piece of paper to ensure that I did not get any batches mixed up.

I use an RCBS Lockout Die to try to eliminate the possibility of double charges or squib loads. I say 'try to eliminate' because I have, on more than one occasion, had the die stick in the upper position essentially disabling it. It is still important to be mindful of what you are doing first and relay on your equipment as a second layer of protection.

I will also add that the 125-130 power factor is used for jacketed bullets. For my lead cast bullets, I'm currently averaging 122 power factor and 1019 fps to minimize leading.

I have to admit, I would be very unhappy w/ ammo that made 8" groups @ 25yds. Even if you are not capable at the moment to take advantage of a higher degree of accuracy, you should strive for it if possible. A load that will group into 3" @ 25yds gives you just that much more margin for error when shooting. a load that groups 8" means at your best day, you will barely be able to hold the A zone.
As to cast bullets, the lower PF has nothing to do with leading. It's a pure myth that you can't run lead bullets to high vel. Ask any rifle shooter using cast bullets. They are running to 2000fps+ w/o leading. Shooting lead bullets actually requires a bit more work than jacketed bullets for best results. Leading is almost always a bullet fit issue, sometimes alloy, rarely the lube. I shoot lead bullets almost exclusively in all my guns. In most cases, leading is minimal to none at vel from 800-1600fps. Whne it comes to the 9mm, it's one of the more diff rounds to get to run lead bullets well. A slightly undersized bullet, even 0.0005" can cause leading, especially if it's a hard alloy & running @ low pressure/PF.
With lead bullets, everything matters wjen it comes to accuracy & lack of leading. Fit is king, but diff lubes & powders can have ana affect on leading. Get the bullet fit right though & the rest is fine tuning. Pistols are easier to get right than revolvers, one chamber & one throat. Get it right though, lead bullets can be really accurate, cheap to shoot & offer little more cleaning than jacketed.

 

[Cranium]

I have to admit, I would be very unhappy w/ ammo that made 8" groups @ 25yds. Even if you are not capable at the moment to take advantage of a high degree of accuracy, you should strive for it if possible. A load that will group into 3" @ 25yds gives you just that much more margin for error when shooting. a load that groups 8" means at your best day, you will barely be able to hold the A zone.
As to cast bullets, the lower PF has nothing to do with leading. It's a pure myth that you can't run lead bullets to high vel. Ask any rifle shooter using cast bullets. They are running to 2000fps+ w/o leading. Shooting lead bullets actually requires a bit more work than jacketed bullets for best results. Leading is almost always a bullet fit issue, sometimes alloy, rarely the lube. I shoot lead bullet almost exclusively in all my guns. In most cases, leading is minimal to none at vel from 800-1600fps. Whne it comes to the 9mm, it's one of the more diff rounds to get to run lead bullets well. A slightly undersized bullet, even 0.0005" can cause leading, especially if it's a hard alloy & running @ low pressure/PF.

I only started shooting about 8 months ago and believe me, I do strive for better accuracy and it has improved greatly over the past couple of months since I joined a private range. 8" is happy....I can usually get better than this but I still occasionally have flyers from anticipation or rushing it that throws it all off. I also typically shoot 10 rounds for measurement and sit at a bench but don't use any supportive rest to help consistency besides the bench top.

The loads I've been working for the lead bullets have continued to be a work in progress. I've tried various alloys and various loads that have peaked as high as 1200 fps down to where I am now using Power Pistol from 5.7 gr down to 4.8 gr and alloys from straight range lead to quenched Lyman #2. So far, the 4.8 gr works the best for my 96/2/2 alloy unquenched bullets (~12 BHN) shot from my Sig P226. I've also recently started sizing to .357" instead of the .356" I previously sized at to see if that helps out as well.

 

[ChaoP]

Not trying to hijack the thread, but I have a quick question

I know nothing about reloading

How much $$ do you save by reloading your own ammo? if I shoot 1000 rounds of WWB vs 1000 rounds of ammo I reloaded myself, whats the cost differential going to be?

And how long would it take to reload 100 rounds myself once I get good at it?

9mm btw

 

[Cranium]

These are my personal numbers. Others mileage will vary:

Cost comparison calculations (taking into account use of any consumables I may use):

• Buying PMC 115gr ammunition in bulk: $0.23 per round ($11.50/box)
• Reloading with Speer Gold dot 147 gr hollow point bullets: $0.20 per round ($10/box)
• Reloading with Berry's or Precision Delta bullets: $0.13 per round ($6.50/box)
• Reloading with purchased lead for bullets: $0.08 per round ($4/box)
• Reloading with free wheel weights for bullets: $0.06 per round ($3/box)

 

[fredj338]

Buy components in some bulk, free cases that you have been saving from factory ammo, your cost using FMJ will be right at half ($10-$11/100 for 9mm) of most cheap factory ammo like WWB or Tula. The larger the caliber, the more the savings. You gear cost will depend on time, the higher the volumn/hr, the greater the cost. Lee turret, maybe 150rds/hr, about $350 for one caliber. A Hornady LNL or Dillon 550B, 400rds/hr+, about $650. A LNL or 650 w/ case feeder, about 600rds/hr+, figure $800-$1000 respectively.
So if you shoot a lot, have little time to reload, then a progressive gives you minimal time & max output, but longer payback to your gear. Figure shooting 6Krds/yr of 9mm only, you would save $600/yr so pay for your gear in 1-2yrs depending on which way you wanted to go. I run a 550B & a 650. I can go into the garage & load 100 45acp in less then a10min from start to finish. Over an hours time, 600rds is pretty easily done for a sustained hour.

 

[Keltyke]

Will the force of a primer and no powder cause a squib?

YES! It'll stick a .40 S&W about an inch into the barrel. If you don't catch it, the next round you fire will be a KABOOM.

Don't EVER rely on the press to do your checking. I VISUALLY check all cases for powder before seating the bullet.

 

[TwoMorrow]

Not trying to hijack the thread, but I have a quick question

I know nothing about reloading

How much $$ do you save by reloading your own ammo? if I shoot 1000 rounds of WWB vs 1000 rounds of ammo I reloaded myself, whats the cost differential going to be?

And how long would it take to reload 100 rounds myself once I get good at it?

9mm btw

I am just getting started, but here is the run down even if you don't buy in bulk.

I bought a used progressive press with all the other equipment (Manual, Calipers, Scale, Tumbler, etc.) and spent $450. It costs me right under $25 for one hundred rounds of WWB at my local wally world. That same one hundred rounds costs me $12.50 and I only bought enough to do 1000 rds .
I think my press will do more once I become more proficient but right now I can do 150/200 rounds per hour

 

[fredj338]

I am just getting started, but here is the run down even if you don't buy in bulk.

I bought a used progressive press with all the other equipment (Manual, Calipers, Scale, Tumbler, etc.) and spent $450. It costs me right under $25 for one hundred rounds of WWB at my local wally world. That same one hundred rounds costs me $12.50 and I only bought enough to do 1000 rds .
I think my press will do more once I become more proficient but right now I can do 150/200 rounds per hour

What press did you buy? The LNL & 550B w/o case feeders are tapping out around 450-500rds/hr sustained. Placing the case & bullets eats into the production, not the manual advance of the 550B. Add a case feeder to the LNL, you can get over 600rds/hr, 750+ for the 650. I haven't used the feeder on the 550B, many report issues, so I don't bother. At 500rds/hr, plenty fast for any but the most die hard match shooter. At one point I was loading upto 3K 45colt a month for the wife & I to shoot competition & then other calibers for me shooting diff comps, metsil, IPSC, etc. That is when the rime savings of a progressive come in very handy.

 

[TwoMorrow]

Your PP load is a bit soft for that burn rate. Medium burners for me start @ Unique & end about HS6. So medium burners run best above midrange levels. The lower pressures don't allow complete combustion in shorter bbls. Using 6.1gr of PP under a Rem 124grJHP @ 1.145"OAL, I am only running around 1100fps in a G17, so 5.3gr is pretty enemic, maybe 1000fps, maybe? Get the charge wt up a bit & the unburnt powder should go away. Speer#14 calls for 6.4gr as max @ 1160fps in a 4"bbl, pretty close to what I get.

I am so confused on recipes. It seems every manufacturer has a different idea and only experience or a chrono, can tell you which is correct. I sent Fred a note before making my first eleven, with 6.1gr as my start. He thought it sounded good. But I always double check, so I wrote Alliant in search of more than is listed on their website and got this, along with my other sources, as a result.

Lymans #49 125gr FMJ 5.1-5.7
Blue Pistol book 125gr FMJ Max 6.6
Hornady 124 gr 4.3-5.7
Alliant 124/125 gr jacketed 5-5.5
Only half these even suggested an OAL

I realize there are a lot of factors at work here. OAL, companies covering their *ss,etc. But I am starting to think this process is next to impossible for a beginner with no chronograph.

I kind of averaged out all the sources to come up with my 5.3 to start. I realize this is a process. I guess I will just keep trying. I am frustrated by the fact that I at this point I have little way of knowing if I'm approaching danger. Now I realize that the danger is on the min. and the max. side of these loads.
I already wondered if too little powder was the cause of my unburned powder, but I still don't understand if it is a problem? Is the problem that being on the under side of the load I am approaching squib territory or accuracy problems, or both, or wasting powder, harming my weapon in some way?
Thanks to everyone who is trying to help, and by the way what is the process for using that 1/4 brass rod JIC. Push it out in the direction it should have went in the first place I would assume?

 

[TwoMorrow]

I bought a Hornady pro-jector old and heavy as hell. It works great though. Auto indexes, Auto ejects, does rifle and pistol. Going to be a real pain if I start doing more than one caliber but a great press I think to get me started and I only paid $206 including shipping! The 150/200 rnds/hr I'm sure is me and not the press plus I don't have a case activated powder drop yet. I have to pull a second lever on every up stroke.

 

[fredj338]

I am so confused on recipes. It seems every manufacturer has a different idea and only experience or a chrono, can tell you which is correct. I sent Fred a note before making my first eleven, with 6.1gr as my start. He thought it sounded good. But I always double check, so I wrote Alliant in search of more than is listed on their website and got this, along with my other sources, as a result.

Lymans #49 125gr FMJ 5.1-5.7
Blue Pistol book 125gr FMJ Max 6.6
Hornady 124 gr 4.3-5.7
Alliant 124/125 gr jacketed 5-5.5
Only half these even suggested an OAL

I realize there are a lot of factors at work here. OAL, companies covering their *ss,etc. But I am starting to think this process is next to impossible for a beginner with no chronograph.

I kind of averaged out all the sources to come up with my 5.3 to start. I realize this is a process. I guess I will just keep trying. I am frustrated by the fact that I at this point I have little way of knowing if I'm approaching danger. Now I realize that the danger is on the min. and the max. side of these loads.
I already wondered if too little powder was the cause of my unburned powder, but I still don't understand if it is a problem? Is the problem that being on the under side of the load I am approaching squib territory or accuracy problems, or both, or wasting powder, harming my weapon in some way?
Thanks to everyone who is trying to help, and by the way what is the process for using that 1/4 brass rod JIC. Push it out in the direction it should have went in the first place I would assume?

This was part of my reply:
I think your starting load should be fine. I ran some w/ Rem 124grJHP, a RN JHP version, very sim to FMJ in profile. With 6.1gr @ 1.145"OAL, I was getting 1106fps in my G17. Going to 6.2gr went to 1130fps. A big jump for 0.1gr, telling me I am pushing the top end.
We also talked about the importance of OAL. W/O OAL, powder charge info is vague @ best. Yes, every powder manuf is using diff bullets & pay close attention to their OAL, especially in short high pressure rounds. I think we also talked about working loads up to that, but maybe you or I wasn't clear. What works in my gun may not in yours, so always work up the load, drop at least 5% from anything approaching upper end loads & work them up.
Yeah, it's one of the most confusining issues for the newb reloader. What data to use? They all vary because they all use diff components & test platforms. Some use actual guns (Speer), some universal recievers (Lymans) & some don't say (most manuf web sites). So it does matter. A UR doesn't have to cycle an action. So min loads may not run your gun.
When working w/ a new powder, I'll average data from all my manuals, seat to the longest OAL, start w/ middle avg & work up in 5rd lots @ 0.1gr at a time. Shoot them in order, note vel (if you have a chrono), accuracy, reliability & any pressure signs, high or low. There is almost always a sweet spot where eveything runs great, powder burns well & accuracy is exc.
It is more diff to develope good reloads w/o a chorno, you are really only guessing. Educated guessing, but still guessing. Can still be done, but then it's best to stay w/ published data & use components as close to the data as you can. If you avg the max data from Lyman, Speer & Hornady, you get 5.95gr as max. Loading to a longer OAL buys you some pressure room. Using a med powder like PP buys you a more linear pressure curve. I am quite confident in the data from the Speer #14 (6.4gr @ 1.135"OAL), it mimics what I get in almost every caliber & load, but again, doesn't mean it will be safe in your gun w/o you working it up. I still cross ref other sources, then as always, the person reloading is the final safety check. Hopefully that clears it up a bit.

 

[Cranium]

Here are my chrono results collected for Precision Delta 124gr JHP using various amounts of Power Pistol with my SIG P226 (4.4" barrel):

Grains	OAL	Vel	PF	Ft Lbs	Spread
5.7	1.12"	1102	137	335	54	<--9 rounds averaged
5.5	1.115"	1090	135	328	62	<--28 rounds averaged
5.5	1.12"	1086	135	325	39	<--10 rounds averaged
5.4	1.12"	1081	134	322	79	<--30 rounds averaged
5.2	1.105"	1047	130	302	48	<--10 rounds averaged

This data was collected over the past 2 months. My OAL started at 1.12 with these bullets and worked fine with my SIG but was too long for my Springfield XDM. I later decreased it to what I use today (1.105") so it would work in both firearms. Other bullets were as high as 1.15" OAL (115 gr Berry bullets)

Here is the data collected for Montana Gold 121gr IFP using Power Pistol with my SIG P226:

Grains	OAL	Vel	PF	Ft Lbs	Spread
5.4	1.105"	1075	130	311	41	<--32 rounds averaged
5.3	1.105"	1079	131	313	84	<--10 rounds averaged

Many of these rounds were measured with mixed case stamps so this will throw off the data a little and will be more accurate with a larger number of rounds averaged (which is why I included # of rounds). Another thing throwing off the data a bit will be how tightly I hold the gun from round to round (ransom rest would be nice). I have data collected for other bullets and other powders that I've tested as well but these seem to be closest to what you are using. I also have date/time/temp/humidity data but don't think this really helps.

 

[fredj338]

Here are my chrono results collected for Precision Delta 124gr JHP using various amounts of Power Pistol with my SIG P226 (4.4" barrel):

Grains    OAL    Vel    PF    Ft Lbs    Spread
5.7    1.12"    1102    137    335    54    <--9 rounds averaged
5.5    1.115"    1090    135    328    62    <--28 rounds averaged
5.5    1.12"    1086    135    325    39    <--10 rounds averaged
5.4    1.12"    1081    134    322    79    <--30 rounds averaged
5.2    1.105"    1047    130    302    48    <--10 rounds averaged

This data was collected over the past 2 months. My OAL started at 1.12 with these bullets and worked fine with my SIG but was too long for my Springfield XDM. I later decreased it to what I use today (1.105") so it would work in both firearms. Other bullets were as high as 1.15" OAL (115 gr Berry bullets)

Here is the data collected for Montana Gold 121gr IFP using Power Pistol with my SIG P226:

Grains    OAL    Vel    PF    Ft Lbs    Spread
5.4    1.105"    1075    130    311    41    <--32 rounds averaged
5.3    1.105"    1079    131    313    84    <--10 rounds averaged

Many of these rounds were measured with mixed case stamps so this will throw off the data a little and will be more accurate with a larger number of rounds averaged (which is why I included # of rounds). Another thing throwing off the data a bit will be how tightly I hold the gun from round to round (ransom rest would be nice). I have data collected for other bullets and other powders that I've tested as well but these seem to be closest to what you are using. I also have date/time/temp/humidity data but don't think this really helps.

Note the very short OAL, dramatically increases pressures/vel in the 9mm. So comparison to a sim wt bullet seated out to 1.150" is diff.
BTW, what does how loose or tight you hold your gun have anything to do with vel????? FWIW, Ransom rest is a great tool, had one for years, but you can shoot just as well off a good bench support for short periods of time out to 25yds. Where the Ransom is great is long strings or further distance. It's why I sold mine. Sent this test to TM.
Keep in mind that OAL has a huge affect on pressures in small volumn/high pressure rounds like the 9mm & 40. I ran a little test using some 115grFMJ & 5.5gr of Unique, comperable to PP in burn rate, a bit faster. All I did was change OAL:
@ 1.140" = 1092fps
@ 1.120" = 1119fps
@ 1.090" = 1193fps

 

[Cranium]

what does how loose or tight you hold your gun have anything to do with vel?????

I've noticed apparent differences in velocity with how consistently I've held my gun. If I am very relaxed and let the recoil cause more movement in the gun then tighten up my grip, I tend to see larger extreme spreads in a string.

I have not tested specifically for this effect so will admit that it could be coincidence with some other unknown factor. But I've noticed large spreads before in strings that I've matched cases, individually dispensed powder into, and individually seated the bullets into and crimped.

Looking at it scientifically:
The ignition of the powder causes recoil as it applies pressure to the bullet which is Newton's 3rd Law of motion or "the law of reaction" that states: Forces are always produced in pairs, with opposite directions and equal magnitudes.
The bullet accelerating as well as the amount of recoil is Newton's 2nd Law of motion: When a force is applied to an object, it accelerates. The acceleration a is in the direction of the force and proportional to its strength, and is also inversely proportional to the mass being moved.

So in this case, assuming that all other variables are the same, firing a bullet will produce a certain amount of energy that is available to disperse by various means (pressure, heat, light, etc). Limp wristing a shot will absorb more energy resulting in less energy being available to accelerate the bullet.

I've heard of extreme limp wristing causing a failure to eject and I've also heard of holding the stock of a rifle against a wall can cause a jam as well (and saw it demonstrated on the show Sons of Guns).

So while scientifically, I can say without a doubt that how tight you hold a gun will result in bullet speed changes, until I actually test for it or read a study of someone who has, I can't say for sure if it is significant enough to be able to notice.

I like getting into the science of it all. But I also realize it is sometimes very difficult and sometimes impossible to align the science with the real world due to the immense number of variables that have to be taken into account; which is why we have reloading suggested start and max load data rather than fixed reloading rules.

 

[Cranium]

FWIW, Ransom rest is a great tool, had one for years, but you can shoot just as well off a good bench support for short periods of time out to 25yds.

Replace the "you" with "I" in that statement. Not everyone can shoot just as well at 25 yards. I certainly cannot. The ransom rest is attractive to me from the aspect of removing multiple variables of the possibility of human error. The more of these I can remove, the better.

But I don't see myself buying one any time soon and hope that my bench rest shooting will improve to the point that, like you, it won't be needed. I need to get some bags or something to see if it will help. I have a Shooters Ridge Handgun Rest but haven't seen any improvement using it. It isn't ideal for shorter barrel guns but it could, again, just be me.

 

[fredj338]

I've noticed apparent differences in velocity with how consistently I've held my gun. If I am very relaxed and let the recoil cause more movement in the gun then tighten up my grip, I tend to see larger extreme spreads in a string.

I have not tested specifically for this effect so will admit that it could be coincidence with some other unknown factor. But I've noticed large spreads before in strings that I've matched cases, individually dispensed powder into, and individually seated the bullets into and crimped.

Looking at it scientifically:
The ignition of the powder causes recoil as it applies pressure to the bullet which is Newton's 3rd Law of motion or "the law of reaction" that states: Forces are always produced in pairs, with opposite directions and equal magnitudes.
The bullet accelerating as well as the amount of recoil is Newton's 2nd Law of motion: When a force is applied to an object, it accelerates. The acceleration a is in the direction of the force and proportional to its strength, and is also inversely proportional to the mass being moved.

So in this case, assuming that all other variables are the same, firing a bullet will produce a certain amount of energy that is available to disperse by various means (pressure, heat, light, etc). Limp wristing a shot will absorb more energy resulting in less energy being available to accelerate the bullet.

I've heard of extreme limp wristing causing a failure to eject and I've also heard of holding the stock of a rifle against a wall can cause a jam as well (and saw it demonstrated on the show Sons of Guns).

So while scientifically, I can say without a doubt that how tight you hold a gun will result in bullet speed changes, until I actually test for it or read a study of someone who has, I can't say for sure if it is significant enough to be able to notice.

I like getting into the science of it all. But I also realize it is sometimes very difficult and sometimes impossible to align the science with the real world due to the immense number of variables that have to be taken into account; which is why we have reloading suggested start and max load data rather than fixed reloading rules.

You are over thinking this big time. Free recoil has nothing to do with vel readings. The position of the powder does. So for best vel readings, raise the muzzle vert before every shot. It's why slightly compressed charges give more uniform vel results, the powder is in the identical spot everytime prior to ignition. IMIO, the mixed headstamps is accounting for your spreads. Diff brass, fired a diff number of times has diff neck tension & slightly diff internal capacity. That has a huge affect on std dev in vel.
The limp wristing issue is a product of the shooter absorbing some slide force that is needed to run the gun reliabley, after allit is a recoil operated stystem. The cartridge has fired, you can not affect the powder charge ignitition by limp wristing. So I can say w/o a doubt, how loose or tight you hold the gun has NO afect on consistant vel. Powder location inside the case, yes, grip strength, no. In the same thought, if you throw the gun at the target as you press the trigger, like the old western movies, it doesn't make the bullet go faster. Yes I am poking fun at you a bit. Sometimes A+B does not equal C.