THR Group Project - PISTOL - Advanced Reloading Concepts and Discussions

[Rule3]

In reference to bds fine post and pictures above, I would like to add this,

The Lyman manual #49, beginning on page 62, Chapter 7 has a very good explanation pf powders. Characteristics, Burn rates and types. It lists many of the common brands and a lot more.

It may help some decide on what powder to buy (if and when it ever becomes available)

Unfortunately a lot of "new" reloaders miss this type of information as they use manuals only as recipe books

 

[LiveLife]

Rule3, good point. Having a sound reloading foundation to start out will help produce more accurate loads later. I think learning the proper "basics" of reloading principles is key to producing more consistent and safer loads.

- MATCH LOAD VS RANGE PRACTICE/PLINKING LOAD

Repost from another thread - http://www.thehighroad.org/showthread.php?p=9892605#post9892605

Match loads:

- Montana Gold/Winchester FMJ/JHP bullets
- Sorted brass / headstamp
- Separately resized and hand primed cases
- Primer pocket checked/cleaned
- CCI/Winchester primers
- Specific powder that metered with less than .1 gr variance
- Tighter finished round dimension QC criteria

Range practice/plinking loads:

- Cheapest plated/lead bullets
- Mixed range brass / headstamp
- Resized and press primed cases in progressive mode
- Primer pocket not checked or cleaned
- Cheapest primers
- Cheapest available powders, even with up to .2+ gr variance like Promo
- Less finished round dimension QC criteria

 

[Toprudder]

I agree, read a good reloading manual, and try to understand it all, before you seat your first bullets. After you have reloaded some, go back and read it all again, so it all makes more sense.

 

[LiveLife]

OK, here's an update of topics:

Reloading Practice:

Open - MAX VS WORKING OAL/COL
Open - WORKING OAL/COL VS CHAMBERED OAL/COL
Open - SEATING DEPTH - OAL/COL
Open - STEPPED RN VS NON-STEPPED RN FOR 9MM KKM/LONE WOLF BARRELS
Open - WHEN TO USE SHORTER THAN MAX OAL/COL
Open - USING LONGER THAN SAAMI MAX LENGTH
Open - COMPENSATE FOR MIXED RANGE BRASS CASE LENGTH VARIATION
Open - CALCULATING BULLET SEATING DEPTH TO DETERMINE MAX CASE FILL
Open - CALCULATING POWDER CASE FILL TO AVOID COMPRESSED LOADS
Open - DECREASING OAL/COL TO INCREASE NECK TENSION/INITIAL CHAMBER PRESSURE (9mm FMJ/RN SPECIFIC)
- CRIMPS (Taper vs Roll)
- WHEN TO DOWNLOAD BELOW PUBLISHED START CHARGES

Reloading Components:

Open - POWER TYPES (Shape/Burn rate/Coating)
Open - BRASS CASE (Head stamp)
Open - BULLETS (design/weights/cannulas/gas checks/lube)
- PRIMERS BRANDS/SIZE DIFFERENCE/SEATING DEPTH

Reloading Equipment:

- POWDER CHARGE DROP VARIANCE
- ACCURACY OVER CHRONOGRAPH (MV/ES/SD)
- BARREL TWIST RATE/BULLET WEIGHT
- USING RESIZED/HAND PRIMED CASES IN PROGRESSIVE PRESSES
- HOW TO OBTAIN MORE CONSISTENT OAL/COL
- TUNING A BALANCE BEAM SCALE
- WHAT DIGITAL SCALES ARE NOT SUITABLE FOR RELOADING

Range Testing:

- POWDER WORK UP
Open - EVALUATING PISTOL LOADS

 

[LiveLife]

- POWDER TYPES (Shape/Burn rate/Coating)
- CALCULATING BULLET SEATING DEPTH TO DETERMINE MAX CASE FILL
- CALCULATING POWDER CASE FILL TO AVOID COMPRESSED LOADS

Continuing from post #74 regarding powder types - http://www.thehighroad.org/showthread.php?p=9890280#post9890280

Continuing from post #67 regarding bullet seating depth - http://www.thehighroad.org/showthread.php?p=9889263#post9889263

Comparison picture below shows max powder charges for 185 gr jacketed bullet / 45ACP case. As you can see, different powders require different amount of max charges for the same weight bullet. -

Now the question is, if you are using near max/max charges and/or bullets with long bullet base seated shorter, will the finished rounds end up with compressed powder charge? My thinking is that once pistol powder charges get compressed, chamber pressure will spike and burn characteristics will change affecting initial/peak/average chamber pressures and accuracy. When case length variation is factored in (from mixed range brass), different bullet seating depth will stack to reloading variables and produce greater deviations in muzzle velocities and shot group size.

IMO, with large volume lower pressure cases like 45ACP, this may be less of an issue but with small volume higher pressure cases like 9mm, this is more of an issue.

Here's an example with Promo and MBC 124 gr RN (SmallBall) bullet seated to 1.100" OAL/COL - http://www.thehighroad.org/showthread.php?p=7679116#post7679116

1.100" is the max OAL and length of resized case is 0.750" with bullet length at 0.565".

That means 0.565" - (1.100"-0.750") = 0.215" of bullet base gets seated inside the case neck. The picture above of 4.0 gr of Promo inside the case shows the powder is 0.260" below top (and 4.4 gr is 0.220" below top). So, 4.0-4.4 gr of Promo should be fine with 1.100" OAL using MBC 124 gr RN (SmallBall) to not compress the powder.

My working OAL is 1.080" and I "try" to use 4.0 gr as max charge as I get upto .2+ gr variance with Promo.

Fluffy powders like Unique/Red Dot/Promo may tolerate slight compression of powder charges enough to not affect chamber pressures/accuracy. With Herco and 115 gr FMJ/Berry's HBRN-TP, 124 gr HBRN-TP and 124 gr ZCast lead RN, I used 1.155"-1.160" OAL with 5.8-6.1 gr to not compress the powder charge - http://www.thehighroad.org/showthread.php?t=745656

When I tested RMR 124 gr HM RN with WST/BE-86 @ 1.160", 4.0 gr of WST and 5.2 gr of BE-86 were determined to be charges before I started compressing them - http://www.thehighroad.org/showthread.php?p=9655361#post9655361

So what do you think?

Will compressed pistol loads affect accuracy?

 

[Blue68f100]

Maybe. It all depends on the powder burn properties. Some powders are sensitive to this and some not. To accurately test this you need to weight each charge then shoot over a crony. For accuracy of weight it needs to be as consistent as it can possibly be. A 0.05 gr powder charge change has more impact at the upper end than when in mid charged. Some say you don't need to measure powder to the 0.01gr. But this is one of the variables that can have a large impact on velocity/pressure. The percentage change deviation is higher on the small pistol charges vs rifle. Most say their scales are dead on but accuracy is only ±0.1gr. This standard deviation can be a 10% change. Most powders burn more complete when at the upper end so small changes show up there. Getting the most accuracy applies to all steps needed to get the same/identical properties as you can every time. This is one of the reasons BE shooters normally shoot reduced loads. Pressure changes are not as great when running lower charges.

Good topic for discussion. This is where having a pressure chamber to test in would find it's usefulness. But then you have to determine how much change is acceptable. A static condition like a test chamber will give a different results than a dynamic's of a pistol, simi-auto or revolver.

 

[LiveLife]

- TUNING A BALANCE BEAM SCALE

While this repost from another thread is specific to Ohaus 10-10, steps outlined could be used to check sensitivity to .1 gr and properly clean/tune other beam scales - http://www.thehighroad.org/showthread.php?p=9893627#post9893627

If you want to properly clean and tune beam scales, inspection and cleaning of agate stones and posts so they can "free float" is crucial for proper zero and repeatability.

Ohaus 10-10 scale ... got an RCBS Standard Weight Check set.

I zero the scale with nothing in the pan, dial in a weight I want to test, and drop the appropriate weights in the pan. The result isn't bang on. It's pretty close but not bang on. I've done a few measurements in the 2-5 gr ranges and others in the 20 gr range.

I have two Ohaus 10-10 beam scales and they are accurate and repeatable to Ohaus ASTM class 6 stainless steel check weight set (BTW, do not touch the check weights with your fingers and only use tweezers to handle them and place them back in the storage pouch as soon as you are done to reduce contamination) - http://www.thehighroad.org/showthread.php?p=9875559#post9875559

You can test the sensitivity of the 10-10 scale by using 1/4"x1/4" pieces of 20 lb copy paper. Both of my 10-10 scales will detect one piece of paper and read slightly over .1 gr with two pieces of paper consistently. - http://www.thehighroad.org/showthread.php?p=9614543#post9614543

If your 10-10 scale won't detect and consistently read the 1/4"x1/4" pieces of paper, your scale may need cleaning, especially the agate stones the knife edge pivots on (they are supposed to be free floating and dirt/debri could be preventing them from not allowing the scale to zero/read consistently). I outlined the "basic tuning" of 10-10 scale and proper use on this post - http://www.thehighroad.org/showthread.php?p=9683211#post9683211

"I bought both of my Ohaus 10-10 scales used (second one was new old stock) and had similar issue of scale not maintaining zero. Good cleaning of agate stones and posts solved the problem.

I found the repeatable zero resulted from the knife edges pivoting on the free floating agate stones. Can you inspect the beam/knife edges to make sure they are not bent and at 90 degrees? FYI, I do the following to clean/tune the scale.

- Remove the bearing covers with a Phillips screwdriver (see pictures below)
- Make sure the posts the agate bearings free float on are clean
- Clean the agate bearings, especially the "V" notches
- Re-install the covers
- Clean the knife edges
- Level the bench surface using a bubble level at 90 degrees
- Turn HVAC/vent off and close the window/door to the room as any ambient air movement will affect scale reading/zero
- Place the powder pan on the pan support
- Set both large and micrometer poises to zero
- Lock the micrometer poise with the nylon bolt
- Adjust the leveling foot so the pointer is at the zero line"

Ohaus 10-10

RCBS 5-0-5

 

[LiveLife]

- TESTING FOR PROPER NECK TENSION

apparently, I am the only one who measures bullet pull in auto-loaders when working up a load. it indicates a lack of bullet tension. if present, it needs to be eliminated (imho).

I agree that lack of neck tension should be eliminated.

When using mixed range brass with different reload history and condition of brass, you may end up with differing amount of neck tension.

I used to test for neck tension by pushing on the bullet against the bench top. I found this method limiting as finished round feeding/chambering from the magazine and slamming against the feed ramp undergo different "shock force" than gradual linear pressure against the bench top - think impact wrench vs socket wrench.

So now I test neck tension by measuring bullet setback after feeding/chambering dummy rounds from the magazine. If you want to expand your sampling, you could check bullet setback of different headstamp cases. While no bullet setback is ideal, when using mixed range brass, some bullet setback is a reloading variable we may have to address to an extent or live with.

For me, if the bullet setback is more than a few thousandths, I will review my reloading practices and components to eliminate as much of bullet setback as possible.

Once I found a bad batch of once-fired PMC 45ACP brass and I culled the entire lot and problem went away.

 

[blarby]

When using mixed range brass with different reload history and condition of brass, you may end up with differing amount of neck tension.

So, I hate to jump in on the middle of this one... but its such a common problem, and one of the easiest answers is so clear that it begs the question;

Why not ?

If we as handloaders can't even be bothered to headstamp sort brass, why do we expect anything other than less than stellar results ?

I mean, comeon guys........ This part isn't rocket science. Its also not difficult, its friggin stamped on the dang head of the case !

Consistency is the one universal factor we're striving for in all of the subfactors we're researching and discussing. Brass is one of the major concerns in functionality and uniformity, so why not do the easy stuff ?

 

[LiveLife]

blarby, so far the take away from the discussions for me is if you have enough time to sort brass by headstamp, you should instead be sorting by resized case lengths as some suggested.

Headstamp won't tell you how many times brass has been reloaded.

Length of case perhaps is more pertinent to the number of firings and condition of the brass in terms of malleability which IMO translates to neck tension and will directly affect consistency of bullet seating depth and chamber pressures/high pressure gas leakage.

Of course, the contribution to final accuracy on paper may not be much but someone did mention stacking of tolerances and who knows, these small improvements in accuracy may "stack" together to actually show as smaller shot groups on target.

 

[blarby]

Then while you're at it, sort to length.

I just blurted it out, because my experience has been that you'll find much more variations in a pile of say, seven brands, than you will in a pile of one brand. Length and weight.

I just don't get the premise of continuous workaround effort for something that's just easier to do correctly.

I just don't believe that there is one of us who can say, with a straight face, that their bag of mixed range brass shoots equally as well as sorted casings.

The techniques we're discussing aren't all that valuable with mixed components, when we're splitting hairs. Did I miss some angle I should be catching ?

 

[LiveLife]

- 9MM BULLET SEATING DEPTH AND NECK TENSION

Another factor to consider regarding bullet seating depth and neck tension is the construction of the case wall. Most case wall becomes thinner as you get close to case mouth and the thinning is so gradual with most semi auto caliber cases that bullet seating depth has less affect on neck tension which is friction between bullet base and case wall.

Since 9mm is a "tapered" case, this is more of an issue. 243winxb's picture in this thread illustrates this - http://www.thehighroad.org/showthread.php?p=9895615#post9895615



Picture above shows case wall getting thicker as you move down from the case mouth. As discussed on post #33, using longer OAL/COL with shorter base bullets like 115 gr FMJ/RN will result in less bullet base seated inside the case neck which will produce less neck tension. And as discussed to death in many threads, increasing taper crimp WILL NOT increase neck tension rather decrease neck tension by reducing the diameter of the bullet and brass spring-back.

So with 9mm case and shorter base bullets, seating the bullet deeper is one solution to produce greater neck tension for more consistent initial chamber pressure build, especially with lower powder charges. More consistent initial chamber pressure build will produce more efficient powder burn and more consistent gas pressure which will produce more consistent average/peak chamber pressures that will translate to more consistent muzzle velocities and lower SD numbers.

Many complain 9mm is more difficult caliber to load accurately than other calibers and I think a good balance between using longer OAL to reduce high pressure gas leakage vs using deeper bullet seating depth for consistent chamber pressures will produce greater accuracy, especially when using below max powder charges with 115 gr FMJ/RN bullets. Match barrels with shorter leade/free bore and quicker start of rifling angle address this issue and perhaps is the reason why Lone Wolf decreased the leade and increased the rifling angle on newer 9mm barrels. While KKM 9mm barrel does have longer leade/free bore but IMO the slower barrel twist rate of 1:20 is the greater contributor for accuracy than Lone Wolf with 1:16 twist rate that most aftermarket barrel makers use but this is for another discussion topic.

FYI, some 9mm cases have "internal step" as shown in the picture below which reduces internal volume of already small volume case so if you are using bullets with longer base like 124/125 gr SWC or non-step RN, using shorter working OAL will be limited by compression of powder charge

 

[LiveLife]

I just don't believe that there is one of us who can say, with a straight face, that their bag of mixed range brass shoots equally as well as sorted casings.

The techniques we're discussing aren't all that valuable with mixed components, when we're splitting hairs. Did I miss some angle I should be catching?

Yes, yes and yes.

I started this thread to help with reloaders that are beyond the basics but won't pursue the extreme reloading practices of bullseye match shooters like sorting brass by headstamp/resized case lengths - http://www.thehighroad.org/showthread.php?p=9878562#post9878562

The theoretical concept question is "Given the variation in case length of mixed range brass, how do we compensate to maximize our accuracy?"

The extreme reloading practices used to produce utmost accuracy and eliminate flyers were discussed in another thread and use of new brass was the best way to reduce flyers and I doubt any of us will order 5 gallon bucketful of new brass (and even then, the same headstamp brass will quickly become once/multi fired and become "mixed" unless you keep track of firings ) - http://www.thehighroad.org/showthread.php?p=9606640#post9606640

Yes, so the limiting criteria for this thread is maximizing accuracy with mixed range brass that most of us use.

 

[blarby]

Got it.

Pm to follow after work !

're-rails the train in the appointed direction

 

[LiveLife]

update of topics

Reloading Practice:

Open - MAX VS WORKING OAL/COL
Open - WORKING OAL/COL VS CHAMBERED OAL/COL
Open - SEATING DEPTH - OAL/COL
Open - STEPPED RN VS NON-STEPPED RN FOR 9MM KKM/LONE WOLF BARRELS
Open - WHEN TO USE SHORTER THAN MAX OAL/COL
Open - USING LONGER THAN SAAMI MAX LENGTH
Open - COMPENSATE FOR MIXED RANGE BRASS CASE LENGTH VARIATION
Open - CALCULATING BULLET SEATING DEPTH TO DETERMINE MAX CASE FILL
Open - CALCULATING POWDER CASE FILL TO AVOID COMPRESSED LOADS
Open - DECREASING OAL/COL TO INCREASE NECK TENSION/INITIAL CHAMBER PRESSURE (9mm FMJ/RN SPECIFIC)
Open - 9MM BULLET SEATING DEPTH AND NECK TENSION
Open - TESTING FOR PROPER NECK TENSION
- CRIMPS (Taper vs Roll)
- WHEN TO DOWNLOAD BELOW PUBLISHED START CHARGES

Reloading Components:

Open - POWER TYPES (Shape/Burn rate/Coating)
Open - BRASS CASE (Head stamp)
Open - BULLETS (design/weights/cannulas/gas checks/lube)
- PRIMERS BRANDS/SIZE DIFFERENCE/SEATING DEPTH

Reloading Equipment:

- POWDER CHARGE DROP VARIANCE
- ACCURACY OVER CHRONOGRAPH (MV/ES/SD)
- BARREL TWIST RATE/BULLET WEIGHT
- USING RESIZED/HAND PRIMED CASES IN PROGRESSIVE PRESSES
- HOW TO OBTAIN MORE CONSISTENT OAL/COL
Open - TUNING A BALANCE BEAM SCALE
- WHAT DIGITAL SCALES ARE NOT SUITABLE FOR RELOADING

Range Testing:

- POWDER WORK UP
Open - EVALUATING PISTOL LOADS

 

[LiveLife]

- BRASS CASE (Head stamp)

Repost from another thread - http://www.thehighroad.org/showthread.php?p=9896140#post9896140

What is "commercial" brass?

To me, anything that doesn't have military/NATO marking.

I like buying "military" .308 brass with Lake City headstamp "LC" that has cross inside a circle for "NATO" spec ammunition. The crimped primer pocket tells me it's once-fired.

The difference between "military" vs "commercial" is thicker wall of military brass that will reduce internal case volume and I will use less powder charge at the top than what was developed for thinner walled commercial brass. But I found this is not always the case as when I sort resized/trimmed brass, sometimes I find military brass to weigh comparable to commercial brass so using water to determine the internal volume is the only sure way to ensure consistency.

With .223/5.56 brass with crimped primer pockets, I don't think this is the case and I don't separate military brass with NATO markings from commercial brass and use the same powder charge as commercial brass.

With 9mm NATO marked brass, I simply remove the primer pocket crimps and reload like other commercial brass.

 

[Toprudder]

FYI, some 9mm cases have "internal step" to prevent bullet setback as shown in the picture below so if you are using bullets with longer base like 124/125 SWC or non-step RN, using shorter OAL will be limited by the depth of the "step"

I personally don't believe the purpose of that "step" is to prevent bullet setback. I measured some Ammoload and IMT cases, and the depth of that step is much further down in the case than where the rear of a bullet would be seated.

Titegroup is known to be a powder with a very low charge volume. I looked up the lowest charge recommended for 147gn bullets, dropped that much into a stepped case, and the powder covered the step. I believe that internal step is a manufacturing shortcut. The stepped cases have a constant wall thickness down to the step, and a relatively constant wall thickness after the step. I think this is easier to manufacture than a true tapered wall thickness. JMHO. If this internal step was indeed intended to stop bullet setback, I think we would see this feature in some of the NATO headstamps, where they are used in full-auto weapons.

I did take various 9mm headstamps and analyze them for wall thickness. Quite a few of them had a constant wall thickness down to about 0.25" from the case mouth, then started to taper. The distance to where the taper started varied slightly between headstamps. The one headstamp that I remember, off the top of my head, that tapered from the case mouth was Hornady.

 

[LiveLife]

Good point. I revised my post #87 from:

FYI, some 9mm cases have "internal step" to prevent bullet setback as shown in the picture below so if you are using bullets with longer base like 124/125 SWC or non-step RN, using shorter OAL will be limited by the depth of the "step"

To now read:

FYI, some 9mm cases have "internal step" as shown in the picture below which reduces internal volume of already small volume case so if you are using bullets with longer base like 124/125 gr SWC or non-step RN, using shorter working OAL will be limited by compression of powder charge.

 

[Blue68f100]

Has anyone actually measured the case volume in the step vs non?

The reason I ask this is I measured some in a crude method and the volume was the same. I just used tape to cover the primer pocket weighted the empty brass for a tare then added water. But since water can actually go over the rim case you have to be very careful not to over fill. I have no idea if I kept my test data on this for this was over a year ago that I did this.

 

[LiveLife]

- WHEN TO USE SHORTER THAN MAX OAL/COL
- 9MM BULLET SEATING DEPTH AND NECK TENSION

I did take various 9mm headstamps and analyze them for wall thickness. Quite a few of them had a constant wall thickness down to about 0.25" from the case mouth, then started to taper. The distance to where the taper started varied slightly between headstamps.

This is the reason why for 115 gr FMJ/RN bullet with shorter base, I load at shorter 1.135" OAL even though my working OAL is 1.169+". The thickening of case wall provides greater neck tension to produce more consistent initial chamber pressure build and IMO compensates for less neck tension from using mixed range brass with varying degrees of case neck length and condition of brass.

I think this is a major contributing factor why many claim heavier 124/125 gr bullet is more accurate than 115 gr bullet for 9mm when using mixed range brass.

While I load 115 gr FMJ/RN at near max/max load data (even at 1.135" OAL) with W231/HP-38 to reliably cycle the stiffer recoil springs of compact/subcompact Glocks; with 124/125 gr FMJ/RN bullets at 1.135" OAL, I can use mid range load data and still produce accuracy. Using bullets with longer base like SWC and non-step RN (like MBC SmallBall), depending on powder type, I can even use lower powder charges to produce accurate loads.

 

[LiveLife]

- BULLET SEATING DEPTH AND INTERNAL CASE VOLUME
- WORKING OAL/COL VS CHAMBERED OAL/COL

Has anyone actually measured the case volume in the step vs non?

The reason I ask this is I measured some in a crude method and the volume was the same. I just used tape to cover the primer pocket weighted the empty brass for a tare then added water. But since water can actually go over the rim case you have to be very careful not to over fill.

I think more pertinent method of measuring internal volume is determining bullet seating depth and fill water to this depth. This will better duplicate internal case volume as loaded and I think you will see greater difference from non-step cases.

Of course, if you want to be "true to life", you would also need to determine the bullet setback you average from using mixed range brass and subtract this average from bullet seating depth to arrive at true "chambered OAL" and bullet seating depth.

 

[egd]

I'm basically new to reloading so take what I say with lots of salt. But what BDS is saying about seating depth, I think, is probably as much if not more a factor in accuracy as powder charge. I've been following this thread from the beginning trying to learn from it. At about the same time as the part about seating depth started showing up I was just running out of the Berrys 124 plated bullets I had, and started using some RMR 124 plated.
The whole subject of OAL has had me baffled since I started. I see lots of different lengths listed for the same weight and style bullet (not to mention that especially for a newbie how is one to know the exact shape of bullets listed in manuals).
When I first started I used the Berrys 147 grain, cause that's what the store had. Then when they ran out I got some 124. I hadn't thought much about how much of the bullet goes into the case until I switched to the 124 and saw that the bullet itself was much shorter. OK, now the wheels were turning and I brilliantly deduced, shorter bullet-shorter OAL.
Now, back to where I've just switched to the RMR. When I got them and was reading this thread I decided to measure them and compare them to a few of the Berrys I had left. (and here's another factor-the variation even within the same brand of bullet, both the Berrys and the RMR). If I remember right (I was too dumb to write it down and I've used the last of the Berrys now), the RMR averaged about .1or .2 grain heavier and were about .005 shorter. Again I may have the length reversed. But the point is, this affects the OAL AND the amount inside the case. And that affects the pressure.
What caused me to post this rambling thing is that today I went to shoot some. I had three bullets that I thought I had screwed up on and loaded them to about 1.125 instead of the 1.133/4 I was trying for. I decided to shoot them anyway just to see and they were the most accurate of the day. Is that the result of the neck tension/initial pressure BDS talks about, or did I just get lucky. IDK.
Anyhow, I'm going to load up some at 1.125, or maybe 1.127 and see what they do.
I hope this post didn't ramble too much.

 

[LiveLife]

If decreasing OAL from 1.134" to 1.125" improved accuracy, you could have considered using same OAL but increasing the powder charge to make the chamber pressure more consistent.

IME, you get optimal accuracy from using longest OAL to reduce high pressure gas leakage.
This is why we conduct a full powder work up from start to max charge once we determine the max/working OAL.

With 115 gr plated RN at 1.160", I was .1 gr from max charge (1999 lead RN load data) and I did not want to increase the powder charge. I suspected lack of neck tension and decreasing OAL to 1.135" was a good compromise between gas leakage vs chamber pressure.

If you are not at near max load data, IMO using longer OAL and higher powder charge would be ideal. Also, if you are using less dense powders, using shorter OAL may not be an option as you would be compressing the powder charge and would need to use longer OAL with higher powder charges.

 

[egd]

OK. Man, this really gets complicated. Like I said, it could have just been a fluke that those three did that good. That's why I was going to load some more up just to try.

You know, I just re-read your last post and some things partially clicked with me, and some questions come to mind also.
Do I have this right? when fired, the case expands to form a seal in the firing chamber so no gas goes backward, right? But it's not 100% and some gas does escape? Or does all this mean that when there's more space between the end of the bullet and beginning of the rifling (due either to shorter OAL or manufacturer just making it a bigger chamber or both) there's more space for that energy(gas) to expand and therefore less to push the bullet down the barrel? Is this what you mean by gas leakage?
BUT, there must be sufficient bullet length down inside the case to hold the bullet there long enough so that powder can completely burn and pressure build up to "explode" the bullet out of there. That's your point about sufficient seating depth and the compromise. Right? Am I on the right track with all this?
I also beginning to understand when I've read that reloading is part science and part art.

 

[50cal]

when fired, the case expands to form a seal in the firing chamber so no gas goes backward, right? But it's not 100% and some gas does escape? Or does all this mean that when there's more space between the end of the bullet and beginning of the rifling (due either to shorter OAL or manufacturer just making it a bigger chamber or both) there's more space for that energy(gas) to expand and therefore less to push the bullet down the barrel? Is this what you mean by gas leakage?

Let’s just not worry about gas leakage… If after testing and tweaking ammo, you have the optimal results for your equipment and components, do you care? Point is, your loads will be developed for performance and gas leakage isn’t bad or good. It’s a fact and one that is outside our means of measurement.

I had three bullets that I thought I had screwed up on and loaded them to about 1.125 instead of the 1.133/4 I was trying for. I decided to shoot them anyway just to see and they were the most accurate of the day.

Friend, there is simply too much to consider here to make any determinations as to why you have an anomalous (call it interesting result) after 3 shots with nothing else to go on. I do like your approach though - shooting various loads and observing results.

We don't even know what you are shooting (revolver/auto/what barrel length/compensator?). Factors worthy of considering (i.e. not gas leakage) are :
actual powder charge - how accurate is your scale? If digital, was it warm - cold electronics and strain gauges will fall short of claimed accuracy. By the way ,virtually all scales under $800 dollars are insufficient for truly accurate reloading. If you get serious buy a MFR scale. How accurate is your powder drop - we can't make the assumption the bullet is travelling faster. You may have also been shy a few granules and it’s going slower. Twist makes a difference too. Too fast or too slow for the bullet weight will impact accuracy - the faster the fps (in barrel), the faster the rpm. Perhaps you stumbled on the best velocity for that bullet in that barrel... but I doubt it. Again, only 3 shots. Was the brass fresh?

OAL is limited by things like cylinder length, magazine, feed-ramp angle and AOA of cartridge. In revolvers, having the bullet closer to the forcing cone is probably better but not because of 'chamber pressure'. It’s because the bullet has a better chance to enter the barrel with less effect from contacting the forcing cone off the center line (advantage autos and rifles… and line bores) - the bullet has less velocity and will incur less deformation which affects its flight. If you have an auto maybe your neck tension was tighter do to seating deeper, so when it contacted the feed ramp and subsequently the top-inside of the barrel, the bullet didn't move, and perhaps your other rounds were a little looser (being longer) and the bullet actually got forced down even further than the suspect rounds so the energy was even greater and thus lost accuracy due to recoil and gun torque... (getting a bit silly right?). In autos, the bullet should be pretty darn close to the lands – you can seat to achieve this if you know the headspace of your gun – but I wouldn’t sweat it as long as your brass is getting support.

Bottom line (and perhaps my moral obligation), IMO this thread is a train-wreck of reloading information and should be taken very lightly. Most reloaders have done some experimenting, found what they like and happily churn-out better-than-manufacturer ammo at a huge cost saving. And, they do so without over-complicating things. Secondly, if you want ultimate accuracy, buy top-of-line components and skip the range scraps. If you are not obsessed with peak performance and just love to shoot a lot, grab any brass that works (almost) and have at it. Most consumer guns today are very tolerant (they have to be).