COL question 9mm

[Kip.D]

I've seen a lot of discussion about COL in relation to "clunk" dimension. There is similar issue in rifle precision reloading where we want the COL to be at least 0.010" less than the COL dimension when a specific bullet ogive is just starting to touch the rifling lands in a specific rifle. How far back from the "just touching" COL is recommended with pistols?

Using HAP 125gn bullets in my HK P2000 9mm pistol (3.66" barrel), the COL is about 1.095" when the ogive touches the rifling. I'm using Vihtavuori N330 and CCI 500 primers. VV shows that specific bullet and powder (3.9 to 4.5 gn) in their online reloading data with a COL of 1.102". I guess this difference of 0.007" is acceptable considering variations in different weapons. But I believe I still need to subtract some more to get the ogive a little further back.

I'm using Gordons Reloading Tool internal ballistics program to model this load as well. It has data on that specific bullet and powder- and as I input different COLs, the generated bullet seating depth changes accordingly, and is pretty close to dimensions I'm actually seeing including percentage fill. I didn't know how much difference COL mattered till I saw the drastic pressure increases that show up in GRT with shortened COLs. So I'm paying a lot more attention to COL/seating depth. I have not fired any of this ammo yet.

Thanks, Kip......

 

[Bcwitt]

Most handguns have the lands well foreward of the chamber. If in doubt, drop a flat based bullet in the chamber backwards & measure to muzzle.

 

[Misplacedtexan]

I set mine at 1.090

 

[joneb]

I guess this difference of 0.007" is acceptable considering variations in different weapons. But I believe I still need to subtract some more to get the ogive a little further back.

I would try post #3's recommendations, when doing the plunk test you should be able to rotate the loaded round in the chamber.
Depending on case neck tension .02 should be about right
I load a dummy round to determine the end of chamber to land length.

 

[LiveLife]

HAP 125gn ... HK P2000 9mm ... COL is about 1.095" ... Vihtavuori N330 ... powder (3.9 to 4.5 gn) ... reloading data with a COL of 1.102". I guess this difference of 0.007" is acceptable considering variations in different weapons. But I believe I still need to subtract some more to get the ogive a little further back

If you load for multiple pistols, use the shortest "working" OAL that will reliably feed/chamber from the magazine. Using the barrel to "plunk test" will give you "max" OAL but that OAL may not reliably feed from the magazine and you need to function check with dummy round (No powder, No primer) fed from the magazine and letting the slide go without riding it. If the dummy round won't reliably feed, incrementally decrease the OAL until it does.

For reference/comparison, from "Barrel vs Bullet Max/Working OAL" thread - https://www.thehighroad.org/index.p...col-for-reference.848462/page-2#post-12249361

• Glock 22, KKM 40-9 conversion barrel - Hornady 125 gr HAP: 1.125"
• M&P Shield 9mm - Hornady 125 gr HAP: 1.120"
• Glock 22, Tactical Kinetics 40-9 conversion barrel - Hornady 125 gr HAP: 1.070"
• Glock 23, Lone Wolf 40-9 conversion barrel - Hornady 125 gr HAP: 1.045"

NOTE: 9mm is high pressure cartridge and due to small internal case volume, small changes like reduction in OAL can significantly increase chamber pressure.

As to adjusting powder charge for shorter than OAL published in the 9mm load data, I usually reduce my start/max charges by .2-.3 gr depending on how significant OAL reduction is.

 

[243winxb]

Taurus G3C tight chamber. COL 1.045" Speer starting load data for 125 gr lead works well for tested powders.
Bullseye, Unique, 700X, HS-6 & 244 Powder. Bullet- Lee cast- 356-120-TC.
Diameter .3562" to Maximun of .3568"


https://www.thehighroad.org/index.php?media/albums/taurus-g3c-9mm-luger.317/

 

[rfwobbly]

To expand upon LiveLife's excellent explanation a bit....

Cartridge OAL for the auto pistol is actually not a single, fixed dimension, but rather an acceptable range within which you’ll be safe. This “range” is defined by 2 sets of measurement “limits”. Some of these limits are set by the realities of reloading, other limits are imposed by SAAMI physical limits. Both these limit sets represent hard boundaries which the reloader MUST obey, and thus work within.

• The outer limits are set by SAAMI. The 9x19 Luger cartridge cannot be longer than 1.169” or it may not physically fit into the magazine. SAAMI also advises that the cartridge should not be shorter than 1.000” due to feeding issues.
  
  
• The inner limits are defined by the bullet-to-barrel fit for the longer dimension. The shorter dimension should be the shortest published OAL you can find in your load manuals. (Of course with calculation, you can always compensate and go shorter. But if you don’t have the means or the experience, then stay with the book OAL.)

Taken together these 2 sets of limits result in a graphic that looks like this…

​

Within these safe limits the final chosen OAL to build your cartridge will be determined by experimentation concerning what works best with your dies and gun's feed ramp.

Also realize:
► The OAL shown in your load manual is NOT a suggestion. It is part of the Load Data used in the manual, and the lab crew is merely reporting the OAL they used during testing.

► Given: 1. All chambers are cut differently. 2. All bullet makers produce a bullet of slightly different dimensions. The inner limit Max OAL is a result of how the unique bullet fits into your unique barrel. Only the person with both the bullet AND the barrel can determine this dimension with any precision. IOW, no person here can answer your question; each individual reloader must make these measurements for themselves.

► In some special cases, a bullet-to-barrel fit may allow a Max OAL of (say for instance) 1.220”, which of course exceeds the SAAMI Max of 1.169”. In this case, the useful OAL range is then defined by the SAAMI Max as the longer limit, and then the load manual OAL as the Min OAL limit.

Hope this helps.

 

[Kip.D]

Thanks all. I crashed after getting off work and have just now returned to this thread.

 

[Kip.D]

I would try post #3's recommendations, when doing the plunk test you should be able to rotate the loaded round in the chamber.
Depending on case neck tension .02 should be about right
I load a dummy round to determine the end of chamber to land length.

Thanks for reply.

I believe you are saying you determine your "clunk" COL and subtract 0.020- correct?

 

[Kip.D]

If you load for multiple pistols, use the shortest "working" OAL that will reliably feed/chamber from the magazine. Using the barrel to "plunk test" will give you "max" OAL but that OAL may not reliably feed from the magazine and you need to function check with dummy round (No powder, No primer) fed from the magazine and letting the slide go without riding it. If the dummy round won't reliably feed, incrementally decrease the OAL until it does.

For reference/comparison, from "Barrel vs Bullet Max/Working OAL" thread - https://www.thehighroad.org/index.p...col-for-reference.848462/page-2#post-12249361

• Glock 22, KKM 40-9 conversion barrel - Hornady 125 gr HAP: 1.125"
• M&P Shield 9mm - Hornady 125 gr HAP: 1.120"
• Glock 22, Tactical Kinetics 40-9 conversion barrel - Hornady 125 gr HAP: 1.070"
• Glock 23, Lone Wolf 40-9 conversion barrel - Hornady 125 gr HAP: 1.045"

NOTE: 9mm is high pressure cartridge and due to small internal case volume, small changes like reduction in OAL can significantly increase chamber pressure.

As to adjusting powder charge for shorter than OAL published in the 9mm load data, I usually reduce my start/max charges by .2-.3 gr depending on how significant OAL reduction is.

Excellent advice.

The four guns you show specs for have a range of 0.080" COLs. I suspected that there would be differences, but not that much. I though manufacturing tolerances would be more uniform.

 

[Kip.D]

I want to put a finer point on my original question. I need to clarify some issues to see if we're on the same page.

Assuming that one has correctly determined a clunk "COL" dimension for their unique bullet and chamber, is there a consensus on how far back (if at all) from that dimension one should use as they build their rounds for that unique bullet and chamber? My inexperienced hunch is that building rounds right at the clunk COL might be dangerous.

(I am relying less on "clunk" technique and more on technique of pushing a dummy round with loose case neck tension into the chamber to determine the COL when the ogive touches the lands for this specific bullet and barrel/chamber combination. I came up with 1.094-1.096" after several different trys. To me, this seemed a more precise way to approach choice of final COL choice. This is a technique I've observed in the precision rifle reloading world, but it seems to me pretty much the same issue as the "clunk" test. I'm guessing that clunk testing might come up with a COL dimension slightly shorter [0.003"?]. I also used the "clunk" method by gradually seating the bullet deeper until it would spin freely in chamber, and the results were similar/same.)

Thanks......

 

[243winxb]

(I am relying less on "*plunk*" technique and more on technique of pushing a dummy round with loose case neck tension into the chamber to determine the COL when the ogive touches the lands for this specific bullet and barrel/chamber combination. I came up with 1.094-1.096" after several different trys.

A perfect method when bullet diameter is .355" or .356" & throat is larger.
A COL less then 1.094" will work well.
How much less depends on the seating depth variation. This may be as much as .010" after seating.

No loaded round COL should be longer then 1.090" The will allow the action to always full close, when a round is chambered.

**Best to have an Case head to bullet ogive measurement to control COL.**

https://www.thehighroad.org/index.php?media/9mm-oal-case-head-to-bullet-ogive.4640/

 

[LiveLife]

Assuming that one has correctly determined a clunk "COL" dimension for their unique bullet and chamber, is there a consensus on how far back (if at all) from that dimension one should use as they build their rounds for that unique bullet and chamber? My inexperienced hunch is that building rounds right at the clunk COL might be dangerous.

I am relying less on "clunk" technique and more on technique of pushing a dummy round with loose case neck tension into the chamber to determine the COL when the ogive touches the lands for this specific bullet and barrel/chamber combination. I came up with 1.094-1.096" after several different trys. To me, this seemed a more precise way to approach choice of final COL choice.

This is a technique I've observed in the precision rifle reloading world ... I'm guessing that clunk testing might come up with a COL dimension slightly shorter [0.003"?]

I think you are trying to transfer "off the lands" reloading practice for bottle neck rifle cartridges for straight wall 9mm reloading (Well, 9mm is "technically" a tapered case ... but more on this later) and there are some differences to produce finished rounds that will actually fully chamber reliably from the magazine and to produce greater accuracy rounds.

Load development steps are: Determining the Max OAL, then Working OAL and incrementally seating the bullet deeper to increase neck tension to reduce group size.

With bottle neck rifle cartridges operating at much higher chamber pressures than 9mm, case "grows" longer as case base wall "thins" from pressure pushing on the bottle neck portion of the case with subsequent reloading and eventually will require trimming the case neck or discard the case when case base wall thining is too much to safely contain the chamber pressure (Incipient case head failure).

Although 9mm is a "higher pressure" cartridge than say 45ACP, it is a "straight wall" case (Well, technically a "tapered case") and like most other straight wall semi-auto case, case length actually grows shorter with subsequent reloading.

Why?

Because most resizing dies' carbide sizer rings do not resize all the way down to case base. With each firing and resizing of case, downward force on the case neck will gradually push brass/metal towards case base that continues to very gradually expand but since sizer ring do not reduce this portion of case, over time case will grow shorter.

Step 1 - Maximum OAL/COL:

9mm and other "straight wall" semi-auto cases headspace off the case mouth meaning during "clunk" test (Actually called the "plunk" test due to "plonk" noise the round makes when dropped in the barrel), case mouth drops down and contact the chamber to make the "plonk" sound. And when we determine the "Maximum" OAL, we identify the OAL that will allow the finished rounds to drop in the chamber freely with a "plonk" and spin freely without contacting the start of rifling for that particular bullet ogive and barrel combination.

BUT, what happens when you load to Max OAL with a shorter case? More bullet nose protrudes above the case mouth. And when you perform the barrel test, more bullet nose (ogive) sticking above case mouth will contact the start of rifling. So when I am determining Max OAL, I will measure samples of resized case length and use shorter cases as longer cases will allow less bullet nose to stick above the case mouth.


Step 2 - Working OAL/COL:

Depending on bullet nose profile (ogive)/barrel/magazine/pistol, rounds loaded to Max OAL can reliably feed from the magazine in some cases but usually, Working OAL is shorter. To determine the Working OAL, we load dummy rounds (no powder, no primer) and feed them from magazine and release the slide without riding it. If dummy rounds feed reliably, this is your Working OAL. If not, I incrementally reduce the OAL by .005" until it does.


Step 3 - Powder work up and accuracy trending:

If you can find the same bullet/powder/primer published load data, you can use the same start/max charges. But if you cannot find the published load data for same bullet/powder/primer combination, I reference all available load data and use the most conservative start/max charges for my initial powder work up (As you can always go higher). If I can't find load data for the particular bullet weight, I will reference load data for bullet weight that is slightly heavier.

And if my Working OAL is significantly shorter than published (Let's say more than .010"), I will compensate by reducing my start/max charges by .2-.3 gr (As you can always go higher).

During initial powder work up range test, I will first identify the powder charge that will reliably cycle the slide and extract/eject spent cases then I will monitor accuracy trends to identify charge that will produce smaller groups. (If start charges reliably cycle the slide/extract/eject spent case while producing accuracy, often with faster burning powders, I will "Work Down" from start charge in .1-.2 gr increment to identify lighter target loads)

If I am pursuing greater accuracy (Say to develop match loads) and using mixed range brass, I will sort by same headstamp case and maybe same resized case length and test for neck tension and perhaps thicker case wall brass to eliminate bullet setback during chambering - https://www.thehighroad.org/index.p...neck-tension-and-bullet-setback.830072/page-4

Why?

Even though you may produce consistent OAL with .001" variance, if you experience bullet setback during round chambering, your "Chambered OAL" will vary with different bullet seating depth to produce different chamber pressures that could translate to greater muzzle velocity variance (SD numbers) and increase scatter of groups size on target.

And with "no bullet setback" rounds, if I am not at max published load data, I will test for accuracy of group size by incrementally decreasing the OAL (Say by .005") to see if group size gets smaller. If yes, I will use shorter OAL. If no, I will use longer OAL. (I have done enough tests to show that compared to longer 1.150" OAL used for most 115/124 gr FMJ/RN bullets, shorter 1.130"-1.135" OAL produced greater accuracy from greater neck tension. And for 115 gr FMJ/RN with shorter bullet base sized .355", I used even shorter 1.115" OAL to produce greater accuracy)

Of course, since you are using HP bullet with longer base and shorter nose than FMJ/RN, your Max/Working OALs will be shorter around 1.045" - 1.120", depending on the barrel's leade length/start of rifling angle.

These steps are outlined in the 9mm load development - https://www.thehighroad.org/index.p...-and-discussions.778197/page-10#post-11419509

I hope this helped.

 

[Kip.D]

I think you are trying to transfer "off the lands" reloading practice for bottle neck rifle cartridges for straight wall 9mm reloading (Well, 9mm is "technically" a tapered case ... but more on this later) and there are some differences to produce finished rounds that will actually fully chamber reliably from the magazine and to produce greater accuracy rounds.

Load development steps are: Determining the Max OAL, then Working OAL and incrementally seating the bullet deeper to increase neck tension to reduce group size.

With bottle neck rifle cartridges operating at much higher chamber pressures than 9mm, case "grows" longer as case base wall "thins" from pressure pushing on the bottle neck portion of the case with subsequent reloading and eventually will require trimming the case neck or discard the case when case base wall thining is too much to safely contain the chamber pressure (Incipient case head failure).

Although 9mm is a "higher pressure" cartridge than say 45ACP, it is a "straight wall" case (Well, technically a "tapered case") and like most other straight wall semi-auto case, case length actually grows shorter with subsequent reloading.

Why?

Because most resizing dies' carbide sizer rings do not resize all the way down to case base. With each firing and resizing of case, downward force on the case neck will gradually push brass/metal towards case base that continues to very gradually expand but since sizer ring do not reduce this portion of case, over time case will grow shorter.

Step 1 - Maximum OAL/COL:

9mm and other "straight wall" semi-auto cases headspace off the case mouth meaning during "clunk" test (Actually called the "plunk" test due to "plonk" noise the round makes when dropped in the barrel), case mouth drops down and contact the chamber to make the "plonk" sound. And when we determine the "Maximum" OAL, we identify the OAL that will allow the finished rounds to drop in the chamber freely with a "plonk" and spin freely without contacting the start of rifling for that particular bullet ogive and barrel combination.

BUT, what happens when you load to Max OAL with a shorter case? More bullet nose protrudes above the case mouth. And when you perform the barrel test, more bullet nose (ogive) sticking above case mouth will contact the start of rifling. So when I am determining Max OAL, I will measure samples of resized case length and use shorter cases as longer cases will allow less bullet nose to stick above the case mouth.


Step 2 - Working OAL/COL:

Depending on bullet nose profile (ogive)/barrel/magazine/pistol, rounds loaded to Max OAL can reliably feed from the magazine in some cases but usually, Working OAL is shorter. To determine the Working OAL, we load dummy rounds (no powder, no primer) and feed them from magazine and release the slide without riding it. If dummy rounds feed reliably, this is your Working OAL. If not, I incrementally reduce the OAL by .005" until it does.


Step 3 - Powder work up and accuracy trending:

If you can find the same bullet/powder/primer published load data, you can use the same start/max charges. But if you cannot find the published load data for same bullet/powder/primer combination, I reference all available load data and use the most conservative start/max charges for my initial powder work up (As you can always go higher). If I can't find load data for the particular bullet weight, I will reference load data for bullet weight that is slightly heavier.

And if my Working OAL is significantly shorter than published (Let's say more than .010"), I will compensate by reducing my start/max charges by .2-.3 gr (As you can always go higher).

During initial powder work up range test, I will first identify the powder charge that will reliably cycle the slide and extract/eject spent cases then I will monitor accuracy trends to identify charge that will produce smaller groups. (If start charges reliably cycle the slide/extract/eject spent case while producing accuracy, often with faster burning powders, I will "Work Down" from start charge in .1-.2 gr increment to identify lighter target loads)

If I am pursuing greater accuracy (Say to develop match loads) and using mixed range brass, I will sort by same headstamp case and maybe same resized case length and test for neck tension and perhaps thicker case wall brass to eliminate bullet setback during chambering - https://www.thehighroad.org/index.p...neck-tension-and-bullet-setback.830072/page-4

Why?

Even though you may produce consistent OAL with .001" variance, if you experience bullet setback during round chambering, your "Chambered OAL" will vary with different bullet seating depth to produce different chamber pressures that could translate to greater muzzle velocity variance (SD numbers) and increase scatter of groups size on target.

And with "no bullet setback" rounds, if I am not at max published load data, I will test for accuracy of group size by incrementally decreasing the OAL (Say by .005") to see if group size gets smaller. If yes, I will use shorter OAL. If no, I will use longer OAL. (I have done enough tests to show that compared to longer 1.150" OAL used for most 115/124 gr FMJ/RN bullets, shorter 1.130"-1.135" OAL produced greater accuracy from greater neck tension. And for 115 gr FMJ/RN with shorter bullet base sized .355", I used even shorter 1.115" OAL to produce greater accuracy)

Of course, since you are using HP bullet with longer base and shorter nose than FMJ/RN, your Max/Working OALs will be shorter around 1.045" - 1.120", depending on the barrel's leade length/start of rifling angle.

These steps are outlined in the 9mm load development - https://www.thehighroad.org/index.p...-and-discussions.778197/page-10#post-11419509

I hope this helped.

That's an s-load of info! Thanks.


And some things that I need to consider that hadn't occurred to me- like significance of case length. My current understanding of clunk (OK, plonk ) max OAL determination is the point at which the forward movement of the round is no longer stopped by the bullet contacting the rifling- but rather the case mouth contacting the ridge in the chamber. So if case lengths are not uniform, there can be a situation where the bullet contacts the rifling if a case is significantly shorter than the dummy test rounds. So I will be using same head stamp cases and checking their length uniformity- and be using a working OAL set-back that can more than accommodate potential variations.


Also: while bearing in mind overpressure issues, increased seating depth increases round concentricity.


Though I have not finalized my reloading specification decisions for this round at this point, I’m pretty much on the same general track I had been considering: max working OAL 1.089” or less depending on case length uniformity. And reducing starting charge masses relative to VV data (OAL 1.102”) because of reduction of OAL of dimensions in my rounds and pressure considerations.


Your above post made me look deeper into effect my sizing die is having on case dimensions. I believe my findings differ to some degree from your observations.


While trying to decide which 9mm Luger reloading die set to buy recently, I looked at many options and reviews- and did not limit my considerations based on cost. I settled on an inexpensive set from my LGS: Lee Deluxe Pistol 4-Die Set ($70). Here are my findings. I checked several dimensions of once fired cases before and after sizing. Brass is Winchester WMA 20- findings consistent for four cases checked.


Mouth OD: .378 to .374 (-4K)

Diameter at approx. middle of case: .391 to .387 (-4K)

Diameter right above extraction groove: .388 to .388 (no change)

Length: .741 to .747 (+7K)


Looking at diameters at middle of cases, it appears the fired cases are about 3K wider at middle compared to dia just above extraction groove. But I did not notice any extraction problems. The new cases do not have this bulge and are .381 at middle. My novice hunch is that, apparently, the explosion has a greater expansive effect on the middle of the case where the wall thickness is less. The Lee sizing die appears to be "full length", and the sized cases do not have the bulge, and an adequate taper is restored. However, the sized cases are still larger around the middle compared to new by about 5K.


Also, apparently the cases did grow approx. 6K. I’m OK as long as they stay below .754 and have consistent length, I believe.


Your above post is saved as a PDF to my reloading files- as will be some of the posts in the links you provided. Awesome info. As a novice, this info will take me a considerable time to digest.

On a slightly different topic: how much crimping do I need (if any)? The bullets in my dummy rounds seem plenty tight. See if there is any movement of bullets in dummy rounds while being chambered with full slide velocity?


Thanks much to LiveLife and all for this info .

 

[LiveLife]

My current understanding ... forward movement of the round ... stopped by ... case mouth contacting the ridge in the chamber. So if case lengths are not uniform, there can be a situation where the bullet contacts the rifling if a case is significantly shorter than the dummy test rounds

Actually forward movement of round during chambering is stopped by:

• Bullet base/bearing surface (part of bullet that rides the rifling) contacting start of rifling
• Case mouth contacting chamber ridge
• Case rim contacting extractor
• Case contacting chamber wall

Determining Maximum OAL using the barrel/"Plunk Test":

As already posted, Walkalong's thread on "plunk test" will provide a lot of information during load development - https://www.thehighroad.org/index.p...rel-find-a-max-o-a-l-with-your-bullet.506678/

With the barrel held upright, notice the hood of the barrel is what contacts the breech wall face of the slide during slide returning to full battery/lock up (From right to left):

1. Case rim above barrel hood - Picture on the far right shows too long of OAL/COL where the bullet nose/ogive sticks above the case mouth enough to contact the start of rifling which can prevent slide from returning to full battery. If round spins freely, resized case is headspacing off case mouth but is too long and needs to be trimmed. If round does not spin freely, bullet base/bearing surface is hitting the start of rifling and bullet needs to seat deeper in the case neck. (Another cause of finished round sticking above barrel hood is case not being full-length resized, case neck elongation due to bullet tilt during seating, case wall thickness/bullet diameter combination bulge of case neck too "fat" for chamber and/or case mouth flare not returned back flat on the bullet and parts of case contacting chamber wall - This could cause the slide to lock up requiring great force to free up the slide)
2. Case rim flush with barrel hood - Second picture from right. If round spins freely, case is headspacing off case mouth and slide will return to full battery. If round does not spin freely, bullet base/bearing surface is hitting the start of rifling and bullet needs to seat deeper in the case neck.
3. Case rim slightly below flush with barrel hood - Third picture from right shows typical situation reloaders will find with mixed range brass that grows shorter with subsequent firing and reloading. If round spin freely, case is headspacing off case mouth but may start to headspace off extractor depending on the resized case length. If round does not spin freely, bullet base/bearing surface is hitting the start of rifling and bullet needs to seat deeper in the case neck.
4. Case rim is really below flush with barrel hood - Picture on the left. If round spins freely, resized case is too short and round likely will headspace off extractor. If round does not spin freely, bullet base/bearing surface is hitting the start of rifling and case is ready to be tossed/recycled.

I will be using same head stamp cases and checking their length uniformity- and be using a working OAL set-back

Bullseye match shooters have found using same headstamp cases will often reduce flyers. Using uniform resized length cases could improve consistency of neck tension and could reduce group size further.

Checking for bullet setback is a good quality control reloading practice for improving accuracy as deeper seated bullets will increase chamber pressure which could widen group size. If you experience significant or sporadic bullet setback, you can use thicker wall cases/different headstamp and/or use slightly larger sized bullet from .354"/.355" to .3555"/.356" - https://www.thehighroad.org/index.p...neck-tension-and-bullet-setback.830072/page-4

cases and checking their length uniformity ... while bearing in mind overpressure issues, increased seating depth

You will discover during your load development/powder workup/range tests that often, optimal accuracy is not produced with max load data. And depending on powder burn rate, faster burn rate powders (I use W231/HP-38 as reference mark) can also produce accuracy at lower powder charges to identify ligher target loads while slower burn rate powders tend to produce optimal accuracy at high to near max load data.

And you can address overpressure concern with deeper than published load data by decreasing powder charge.

working OAL 1.089” ... And reducing starting charge ... relative to VV data (OAL 1.102”) because of reduction of OAL ... and pressure considerations.

Reducing start/max powder charges when working OAL is shorter than published OAL is a good reloading practice.

While trying to decide which 9mm Luger reloading die set to buy recently ... I settled on ... Lee Deluxe Pistol 4-Die Set

Mouth OD: .378 to .374 (-4K) ... Diameter at approx. middle of case: .391 to .387 (-4K) ... Diameter right above extraction groove: .388 ... Length: .741 to .747

Good choice. Your measurements are showing the "taper" of 9mm case. Lee resizing die carbide sizer ring is tapered (Not all brand resizing dies are tapered) with round radiused mouth opening to produce smooth resized surface that follows the "taper" of the 9mm case.

Also, I have found Lee resizing dies to reduce OD of cases slightly more and further down towards case base than other brand dies. (Lee actually makes undersize/"U" dies for other companies and their regular resizing dies are essentially slightly "undersize" dies )

Looking at diameters at middle of cases, it appears the fired cases are about 3K wider at middle compared to dia just above extraction groove. But I did not notice any extraction problems. The new cases do not have this bulge and are .381 at middle. My novice hunch is that, apparently, the explosion has a greater expansive effect on the middle of the case where the wall thickness is less.

While priming compound "detonates", most smokeless pistol powders "burn" at similar rate as match head compound. (In a snap when there is no powder to reload, match head compound "could" be used to reload pistol rounds. But usual THR disclaimer applies here ... Do this at your own risk )

Your measurments/observations about fired case is correct but consider this additional information. Brass (Alloy of copper and zinc) was chosen for firearm cartridge for many reasons with this factor, brass spring back. Thinner case mouth area expands quickly to seal high pressure gas with the forward part of chamber wall which is usually tighter in ID to finished round's OD (According to SAAMI max dimensions). Usually, barrel manufacturers (More so with factory barrels than aftermarket/match barrels) cut chamber walls more generous to SAAMI max dimensions so rounds can more reliably feed and chamber from the magazine.

When powder charge is ignited by primer detonation, case as a whole experience expansion with thinner case mouth/case neck as expanding the most to seal the high pressure gas. But after bullet exits the barrel, brass spring back allows the spent case to readily release away from chamber wall to be extracted from the chamber and eject from the pistol.

So, depending on the barrel chamber cut, expansion of case neck and body will follow the dimensions of the barrel chamber. With tighter aftermarket/match barrels, expansion of case neck/body is often less than most factory barrels.

Also, apparently the cases did grow approx. 6K. I’m OK as long as they stay below .754 and are consistent

Case length will grow with firing from case expansion but will grow shorter after resizing. With some barrel/chamber, case length will actually get longer after resizing. Eventually, after many resizing of brass, case length of straight wall semi-auto cases will tend to get shorter. And repeated firing and resizing will make the brass "work hardened" and affect mealeability of brass spring back and eventually will lead to split case neck.

Chances are, you will find most mixed range brass and even once-fired brass over time growing shorter than .754" so no worries.

how much crimping do I need (if any)? The bullets in my dummy rounds seem plenty tight. See if there is any movement of bullets in dummy rounds while being chambered with full slide velocity?

When we say "apply taper crimp to 9mm", we essentially mean return case mouth flare back flat on the bullet.

Since straight wall semi-auto pistol calibers headspace off case mouth, you do not want to appy too much taper crimp to the point where case mouth gets inserted past chamber ridge during "plunk test" (Actually when chambered in pistol, extractor will prevent round from going too far forward).

For me, I determine taper crimp amount by thickness of case wall and diameter of the bullet. Taper crimp is typically applied at case mouth around .100" below case mouth. Most headstamp brass thickness at this portion of case is around .011" and I add .022" to the diameter of bullet to arrive at my taper crimp amount.

So for .355" sized bullet, I use .377" taper crimp (.355" + .011" + .011" = .377"). And for .3555"/.356" sized bullets (Speer Gold Dot HP/TMJ, RMR/ELEY FMJ/JHP, Zero, Berry's, HAP, etc.) I use .378" taper crimp - https://www.thehighroad.org/index.p...re-sized-the-same.818806/page-2#post-10567453

And if case wall is slightly thicker, adding .022" to diameter of bullet will apply skosh more taper crimp to bullet which is OK - https://www.thehighroad.org/index.p...nd-bullet-setback.830072/page-3#post-10712225

Keep in mind not all barrels have same chamber dimensions. And if particular factory/aftermarket barrel chamber is cut with SAAMI minimum dimensions, you may need to apply slightly more than "just return flat back on bullet".

 

[rfwobbly]

Assuming that one has correctly determined a clunk "COL" dimension for their unique bullet and chamber, is there a consensus on how far back (if at all) from that dimension one should use as they build their rounds for that unique bullet and chamber? My inexperienced hunch is that building rounds right at the clunk COL might be dangerous.

I'll answer your questions in reverse order...

► Your hunch is correct, and here's why... All manufacturing has tolerances; some due to the human element and some due to the machinery. So while the reloader may plan to make cartridges to 1.094", measurement of 50 finished products might show that finished OALs actually measure anywhere between 1.092 to 1.098". A tolerance of 1.094" -0.002/ +0.004 . If the maximum was 1.094" then any cartridge longer than that is a serious concern. Why? Because those are the cartridges that may allow the pistol to fire Out Of Battery (OOB). That is to say, allow the firing pin to fall on a cartridge BEFORE the slide and barrel "lock up". In short, longer cartridges create a safety hazard for the shooter.

► I very much doubt you'll find any "consensus". Reloaders tend to be a fairly independent lot and each will have their own 'back off" number that time and experience have proved safe to them. The problem with this is that every independent human generates their own unique "human error" AND each of these individuals is also using different reloading machinery. Some of this machinery is 50 year old Rock Chuckers that haven't been oiled since the 1980's, and some is ultra modern, precision machined presses that get lubricated before each loading session. There can be no consensus in that environment.
However, a number that I teach and that seems to work fairly well across a wide swath of people and machines is 0.015". So your 1.094" measurement would then translate to a target OAL of 1.079". And if you should generate cartridges with a +0.007" tolerance, in other words a cartridge that was 1.086", then you're still a long way from worrying about the danger of firing OOB.

Hope this helps.

 

[Kip.D]

I'll answer your questions in reverse order...

► Your hunch is correct, and here's why... All manufacturing has tolerances; some due to the human element and some due to the machinery. So while the reloader may plan to make cartridges to 1.094", measurement of 50 finished products might show that finished OALs actually measure anywhere between 1.092 to 1.098". A tolerance of 1.094" -0.002/ +0.004 . If the maximum was 1.094" then any cartridge longer than that is a serious concern. Why? Because those are the cartridges that may allow the pistol to fire Out Of Battery (OOB). That is to say, allow the firing pin to fall on a cartridge BEFORE the slide and barrel "lock up". In short, longer cartridges create a safety hazard for the shooter.

► I very much doubt you'll find any "consensus". Reloaders tend to be a fairly independent lot and each will have their own 'back off" number that time and experience have proved safe to them. The problem with this is that every independent human generates their own unique "human error" AND each of these individuals is also using different reloading machinery. Some of this machinery is 50 year old Rock Chuckers that haven't been oiled since the 1980's, and some is ultra modern, precision machined presses that get lubricated before each loading session. There can be no consensus in that environment.
However, a number that I teach and that seems to work fairly well across a wide swath of people and machines is 0.015". So your 1.094" measurement would then translate to a target OAL of 1.079". And if you should generate cartridges with a +0.007" tolerance, in other words a cartridge that was 1.086", then you're still a long way from worrying about the danger of firing OOB.

Hope this helps.

I think I will adopt your max OAL minus 0.015" working OAL protocol. I am somewhat hesitant in reducing working OAL because of its deviation from the VV published online reload data (OAL 1.102") which is guess can be accurately attributed to differences between my HK P2000 and their test weapon. I wanted to stay as close as possible to that recipe.

Though I believe my reload process to have less drift than you describe, that's my ego speaking and may not be realistic. And if there's no downside to a shorter working OAL, why not use it?

Are there downsides to shorter working OAL? Obviously, increased pressures which will be mitigated with lower starting powder masses.

Are there other downsides?

In addition to added safety, are there additional upsides to shorter working OAL? Two that come to my mind are less air space in cartridge and more round concentricity.

Thanks for your info. The input from this thread is definitely helping.

 

[rfwobbly]

I think I will adopt your max OAL minus 0.015" working OAL protocol. I am somewhat hesitant in reducing working OAL because of its deviation from the VV published online reload data (OAL 1.102") which is guess can be accurately attributed to differences between my HK P2000 and their test weapon. I wanted to stay as close as possible to that recipe.

1. First I am deeply flattered and honored. Thank you for your trust.

2. Please refer to my previous graphic. I am not suggesting that 1.079" become your OAL, simply the upper limit of a RANGE of OAL. However, since that number is shorter than your lowest published load, you do find yourself in an dilemma wrapped in an enigma. This is not the normal course of events. I can suggest the Hornady 3rd Edition which has loads as short as 1.040". I will also write you privately to describe alternate methods you can use. Check your PM.

3. This may come as a shock and you may not want to hear it... but it needs to be said: When a bullet-to-barrel fit renders such a short OAL number, you may be better off to simply conclude: that specific bullet should not be loaded for that specific barrel. Just because a bullet is offered for sale does not mean it's a good match for every gun on the market. That's a hard pill to swallow at the price of components these days, but it is true. Not every bullet can be used to reload into every barrel. Sometimes admitting defeat is the safer, more prudent course of action.

Though I believe my reload process to have less drift than you describe, that's my ego speaking and may not be realistic. And if there's no downside to a shorter working OAL, why not use it?

Everyone's ego believes they are God's gift to reloading.... until they sit down and lay a caliper on 50 pistol rounds they just reloaded. The only guys achieving extremely tight OAL tolerances are the bench rest guys, and they may take 1 hour per round... which isn't fun or feasible with auto pistol reloading. If your ego can stand a humbling moment (which can be very conducive to a moment of quiet prayer), I sincerely urge you to measure your next batch of 50 to 100 rounds. In reloading there is Guessing and there is Knowing... and only one of those is Safe.

Are there downsides to shorter working OAL? Obviously, increased pressures which will be mitigated with lower starting powder masses.

Would I be warning you about loading below published loads if it weren't dangerous ? Yes, you need to pay attention like a hawk when your OAL goes below published loads. As was pointed out previously, 9x19 Luger is already a high pressure cartridge. Its pressure rises dramatically with even slightly shorter OALs. As a rule of thumb I would not go shorter than -0.007" under published loads and expect anything good to happen. Most modern guns are built to absorb +P, and that's what saves you at minus 0.005 / 0.0006" OAL during normal reloading screw ups.

In addition to added safety, are there additional upsides to shorter working OAL? Two that come to my mind are less air space in cartridge and more round concentricity.

Its is the set amount of powder burning inside the reduced case volume under the bullet that creates the higher pressure. If you shorten the OAL, then you must also lower the amount of powder. In reloading EVERYTHING we do is to CONTROL chamber pressure. I can't express it any clearer than that. Think about it... power choice, powder weight, type of bullet, bullet OAL, use of chronometers, beginning at Starting Load... everything is to control chamber pressure.
Rule #1: Chamber pressure is the devil we live with.
Rule #2: Always err onto the side of caution.

Thanks for your info. The input from this thread is definitely helping.

Good, I'm glad. Look for a PM.

 

[jonas66]

Holy carp.
This is why I love this place.
I would have to pay money I don't have to go to a school (where?) to be taught like this-- and at that, I don't know that I would be able to find the depth of knowledge and breadth of perspective found here so often.
Thanks guys.

...sorry to interrupt; please continue...

 

[rfwobbly]

Holy carp.
This is why I love this place.
I would have to pay money I don't have to go to a school (where?) to be taught like this-- and at that, I don't know that I would be able to find the depth of knowledge and breadth of perspective found here so often.
Thanks guys.

...sorry to interrupt; please continue...

You're only saying this because you haven't received my bill !!
.

 

[rfwobbly]

Considering the amount of OAL reduction, I agree with LiveLife's suggested charge reduction of 0.1 to 0.2gr. So whereas the VV manual suggested 3.9gr, your Starting Load should be shifted downward to 3.7gr or 3.8gr. And you most definitely want to begin loading at the Starting Load.

If you have a chrono, then your velocity figures for Starting Load should match favorably with those listed in the VV Load Manual. That will be the proof that the reduction estimation is correct. But don't believe me. Trust your chrono !

As an aside, I would not expect issues with N330 because it is a "single-base" powder. The more common "double-base" powders contain nitroglycerin which tends to make them less predictable. This is a subject you may wish to research. I only mention it to ease any concerns you may have.

Hope this helps.

 

[BJung]

This is my opinion on the topic. Handgun OAL does affect accuracy. I did a test in the Spring with a determined 9mm accuracy load with a given OAL in the load manual. Various test loads were made with different OAL were shot and one OAL testload grouped the best. I did a similar test with my .45 a year earlier. At 1.272", the handloads would just barely feed from the magazine. Ken Waters' Petloads recommended an OAL of 1.272". I had to slam my slide to make it lock in place. With 1.270", I didn't have to release the slide from the back position and allow it to slam in place. I'm getting a 2" group with this 5.0gr BE load.225 RN Cast, at 18 yards with this OAL from a factory Kimber Compact. The groups open up when the OAL is less. Case length also might affect accuracy too. I read an article from a cast bullet forum (I lost the source) with test to prove the claim. I have made test loads made with different case lengths to see if the claim is true. I just have shot the test loads tests. Yes, many claim that using the same headstamp will improve accuracy. I think it has to do with the neck tension on the bullet tot the charge. I have cast 38-148wc Lee bullets loaded with 2.9gr BE (my accuracy load) seated to the mouth of various cases from Remington, Winchester, Federal, Speer, Star, and PMC. Whichever load groups the best, I will dedicate that brass to that load combination. I just haven't shot the test loads yet.