Adventures in OAL determination: A front-line report for the first-tim

[ChemistShooter]

This one is not a question. It's for all the first-timers out there like me. (Everyone here has been extremely helpful. I'm trying to give back a little.)

I am determining Maximum Overall-length (OAL, aka COL, aka COAL) for Hornady 115grain Full Metal Jacket Round-Nose bullets (115gr FMJ RN). Maximum Overall Length will be DIFFERENT for each particular chamber-and-bullet combination and must be determined by the user each time.

I am making dummy rounds---no powder or primer---in order to find max OAL for my particular gun with this particular bullet, a 9mm XDM 3.8 Full-Size. Note the SAAMI OAL specification for 9mm is 1.169 inches. I make the dummy bullets by carrying them through the full cycle on my RL550B. (Note: The bullets have to be crimped (or "deflared", which is a more accurate description for 9mm) in position 4, or they will move when you try to measure the length.)

Shortening things a little, I discover 1.173 inches will pass the plunk test easily on my chamber for this particular bullet-and-chamber combination. A little bit of a surprise since I am over the SAAMI specs by .004 inch. But nope, there's not the slightest hitch anywhere.

(A "plunk test" is where you remove the barrel from your gun, drop a round into the barrel's chamber and see if it passes two tests. 1. The round must fall out when the barrel is inverted. 2. The round must spin in the chamber without effort. Try it with a factory round to see how it works.)

1.183 inches, however, does NOT work.

Now the question becomes "WHY is this round not passing the plunk test?" I can solve this by using a method I found posted by somebody who apparently works for Dillon. (Don't have the link, or I'd post it.) The method is to take the sticking round, paint it black all over with the Sharpie, put it back in the chamber, and turn it. (My .02. You won't be able to turn it with your fingers. I had to use a pair of pliers.)

Pull the round out. Where the round is sticking will have a bright line scored around it. I hereby quote from the post (saved it to a reloading file I'm compiling)

1) scratches on bullet--COL is too long

2) scratches on edge of the case mouth--insufficient crimp

3) scratches just below the case mouth--too much crimp, you're crushing the case

4) scratches on case at base of bullet--bullet seated crooked due toinsufficient case expansion (not case mouth flare) or improper seating stem fit

5) scratches on case just above extractor groove--case bulge not removed during sizing. May need a bulge buster.

When I pulled the round out, I had the cutest little circle around the bullet. I attach a picture. The arc you see on the bullet goes all the way around. Case 1, the bullet is too long. Presumably it's hitting the lands.

Conclusion. 1.183 is too long. 1.173 works. Max OAL for this particular combination is therefore somewhere between 1.173 and 1.183.

9mm magazines won't feed longer than 1.169". Therefore the OAL I actually use can only be 1.169" or less. I have selected 1.150" to allow for variation. I am informed, and some testing has shown, OAL variation on a 550B can be as much as 0.005".

Also: The process of feeding the round causes the bullet to be knocked back deeper into the chamber and therefore decrease OAL. (Anything besides seating that knocks a bullet back deeper into the chamber is called "setback.") On my gun, feeding setback is around 0.001"-0.002".

Next: After determining Max OAL, load dummy rounds into magazine and see how well they feed. A lot of the time Max OAL will not feed properly.

Edited December 30, 2015 by ChemistShooter

[superdude]

Some of what you have described is at this link: http://www.shootingtimes.com/reloading/reloading-tips-the-plunk-test/

Different bullet profiles will have different maximum overall lengths. An example can be found here at figure 13: http://38super.net/Pages/Bullet%20Design%20and%20Feeding%20Reliability.html

[amokscience]

Do the magazine test after the plunk test. Load your magazine(s) full with dummy rounds. It will often be shorter than your Max OAL.

[ChemistShooter]

Post edited with above information. Thank you, superdude, amok, live long and prosper.

[Southpaw]

There's an easier way to measure a chamber's max OAL than loading a bunch of dummy rounds: find a fired case that a bullet will easily slide into. Place the bullet in really long and then slowly press it into the chamber. Remove round and measure, that's your max OAL for that chamber and bullet, back at least .005" off this when loading. Someone has a link better explaining this than me.

And what do you mean by "decrimp". You bell/flare the case and then de-bell (i.e., crimp)

Do the magazine test after the plunk test. Load your magazine(s) full with dummy rounds. It will often be shorter than your Max OAL.

Yup, doesn't matter what the chamber will take if it won't fit in the mag Edited December 29, 2015 by Southpaw

[9x45]

OP, I think you are overthinking OAL. I run 9mm (all 125 grains) in my Glocks from 1.165" 10 1.060" depending on the bullet shape and don't see any significant change in accuracy. OAL is far more important in a rifle. Most shots in competition are only 3-15 yards anyway. And it's not a crimp, it's just enough to remove the bell. Try the wipe test, mark a round before after seat and check how much is wiped. Should only be about .005" on average (mixed cases). Left to right, Montana Gold JHP, Bayou TC, Hornady XTP (.357RemMag) and Bear Creek RN.

By the way, measure a factory 115 FMJ, they are nowhere near 1.170"

Edited December 29, 2015 by 9x45

[ChemistShooter]

First-timer here. I am trying to understand the process thoroughly before I start actually producing rounds. So I am going a bit farther than is usual.

My concern really isn't accuracy at this point. It's NOT blowing my ass up. :-)

I measured 50 stock Blazer 9mm before I did all of this. 1.145", IIRC, SD .002". Again, just to see how things were in the real world.

"De-crimped" was wrong and has been changed.

Edited December 29, 2015 by ChemistShooter

[IDescribe]

OP, you're test is determining the chamber's max OAL with a particular bullet. The SAAMI spec of 1.169 is the industry standard max for 9mm that almost all 9mm pistols are designed around in terms of the maximum length that the magazine will allow.

There is a space between where the case mouth is supposed to headspace and where the lands of the rifling begin. That space is often referred to as the leade or throat. Your maximum OAL with a particular bullet and chamber is the OAL where the shoulders of the bullet just make contact with the lands, or as you're making the determination, just shy of where the shoulders touch the lands.

Now, different bullet profiles stick out different distances forward of the shoulders, so different bullets will produce different maximum OALs for a specific chamber. A full wadcutter, which is essentially cut off at the shoulders, is going to produce a very short OAL while RN bullets that narrow and extend well in front of the shoulders will have long OALs, and flat points and hollowpoints will fall in between. Because of this, RN bullets often are capable of loading longer than the magazine will allow. The nose just sticks out that far. But you're still limited by your magazine. If you're plunk test shows a max OAL longer than 1.169, just figure that your max OAL is 1.169, or for that matter, make it 1.160 or 1.150 -- it's not going to matter. The differences in accuracy you get from fine-tuning OAL don't really show up at the distances at which we shoot pistols in a readily quantifiable way. For rifle, YES, it matters. For pistol, not so much, not inside 30 yards anyway.

There will also be minor variances in throat/leade from one barrel to the next of the same manufacture, probably not more than a few thousandths. But when you go from one manufacturer to the next, the throats/leades can differ dramatically in length. I can load the Montana Gold 124gr JHP to 1.13 for my HK VP9. But for my 9mm CZ pistols I have to load the same bullet to 1.080. This suggests that my VP9's throat is about .05 longer than my CZ pistols' throats. Why would a pistol manufacturer produce an especially short throat? Because in some countries, it's illegal to shoot anything other than RN, and RN doesn't need a long throat. This is the case in the Eastern European countries where my CZ pistols and your XDm are manufactured.

Welcome to the short-throated Eastern European pistol club.

[9x45]

OP, you won't blow your gun up by loading long at minimum published powder weights. Now if you have bullet setback, watch out, the pressure can double from just a .050" setback. You should be looking for accuracy and function, that's all. If you don't shoot competition, there is not even a need to meet power floor. +/- .002" is really tight for OAL variance. Most progressives will go +/- .005". What loader are you using? And like ID already said, welcome to the short Euro's. The XD is the old HS2000 (Hrvatski Samokres (Croatian Pistol). Springfield bought the rights in 2012 and changed the name.

[ChemistShooter]

Oh, so that 1.169" spec comes from the MAGAZINE? This is gold. Okay, I will set OAL to 1.150"---basically the same as the Blazer---record the test results for future reference, and consider this particular task done.

I've read about short-throated Eastern European pistols elsewhere on this forum. Probably you wrote it, I imagine.

[ChemistShooter]

I know what "setback" is. This shouldn't be a problem.

Not to worry. I'm gonna start with 3.9gr Titegroup. That's a minimum load for 115gr RN listed in one of my reloading manuals. If that works, I'll just stop right there until I can afford a chronograph.

I'm not sure what you mean by "loader"? I'm using a Dillon RL550B with all-Dillon dies.

.005", great, another piece of information I was looking for hard.

Thanks to all.

[IDescribe]

Your Dillon 550 is what he meant by "loader".

The 1.169 standard came first, but because 9mm Luger is supposed to have a 1.169 maximum OAL, almost every firearm made chambered for it is going to be designed to take a magazine with a maximum 1.169 OAL.

When you are measuring your own bullets for OAL consistency, be warned that the bullets you are loading are themselves not all the same length. Dillon seating dies have a reversible anvil where one "flat" side pushes right against the nose of the bullet and the other side is hollow and so makes contact down on the ogive. Using the flat side of the anvil will result in a more consistent OAL. HOWEVER, because most of the variation in the bullet occurs in the nose, using the hollow side of the anvil takes the nose out of the equation, and results in a more consistent depth at which the bullet base is seated into the case, and a more consistent distance between the bullets' shoulders and the lands. And those latter two things are more important than actual OAL when it comes to the precision with which the cartridge will shoot. We're still in the realm of it not mattering a whole lot at the distances we typically shoot pistol, but when it comes to seating, the consistency you get from the hollow side of the anvil is more valuable than what you get from the flat side. Use the hollow side.

[ChemistShooter]

Yeah, I have the Dillon reloading video. (Not bad, but needs better editing. YouTube is actually more helpful.) They discuss the seating die reversible anvil.

Hollow it is. I will be creating dummy test rounds tonight at 1.150" and doing initial setback and chambering tests.

Hmm, yeah, you know, it makes sense from a chemical perspective. A more consistent seating depth means a more consistent chamber volume means a more consistent pressure profile when the charge deflagrates.

[Southpaw]

I found the link I mentioned earlier that explains the easier way to measure max OAL, see post #4: http://www.czfirearms.us/index.php?topic=34225.0

"De-crimped" was wrong and has been changed.

I see you're now saying, "(Note: The bullets have to be crimped (or "deflared", which is a more accurate description for 9mm) in position 4, or they will move when you try to measure the length.)"

Why is the bullet moving before you crimp it? I'm assuming you're referring to bullet setback? The crimp die on a straight walled pistol cartridge doesn't prevent setback, it just removes the flare. Neck tension from the sizing die prevents setback. If you're getting setback after seating there's likely something wrong with how you set up your sizing die. Of course you likely still will need to crimp your dummy rounds to do a plunk test or else the flare will prevent the cartridge from fitting in the chamber.

[ChemistShooter]

Nah, I was referring to movement when I tried to caliper it. It would wiggle a little if you weren't careful.

[d_striker]

Oh, so that 1.169" spec comes from the MAGAZINE? This is gold. Okay, I will set OAL to 1.150"---basically the same as the Blazer---record the test results for future reference, and consider this particular task done.

I've read about short-throated Eastern European pistols elsewhere on this forum. Probably you wrote it, I imagine.

Don't assume that 1.150" will work. Figure out max OAL for each bullet type you plan on using. Use the method that Southpaw outlined above. It takes very little time or effort to do it. Max OAL will be different from gun to gun and different for each bullet type.

[IDescribe]

Don't assume that 1.150" will work. Figure out max OAL for each bullet type you plan on using.

He did figure out the max OAL for the chamber and the bullet he is using, but it was longer than the 1.169 SAAMI lists as max, so he was confused. He's straight on that now. The 1.15 came from my telling him not to come down to exactly 1.169, but to go all the way to 1.16 or even 1.15. He's opting for 1.15, but he knows to do the push and plunk tests to verify fit for other bullets in that chamber.

[ChemistShooter]

Guess what.

Feeding from the magazine in my gun causes .001"-.002" of setback. (For the first-timers: "Setback" is when something besides seating pushes the bullet deeper into the case.) The sources I read said this is what happens in semi-automatics, but I really didn't believe it. It seemed like too much force.

This might actually be a good thing. Shows I don't have too much crimp on the bullet, which is something I was scared of doing.

[9x45]

OP, if your' going to be a shooter, don't use chemistry terms like "deflagrates" Just say when it goes bang. Also you cannot compare mixed cases when it comes to volume. Has to be the same case head stamp, and bullets that are the same length and weight, then with the same OAL, you can chrono them form velocity, not pressure. You should just get going with a starting load, Hodgdon data, says 4.5 grains TiteGroup at 1.125", then get out to the range and check for accuracy and function. Reloading is only a necessary part of getting to the part where it goes bang, that's the object. What's far more important is mastering the fundamentals of pistol: stance, grip, sight picture and trigger control. Running a $5,000 STI Open gun with super match grade ammo won't make up for the fundamentals. By the way, TIteGroup will throw about +/- .1 grains on a 550, thats what I load on

[9x45]

Setback occurs every time you chamber a round, and it can occur in the magazine during firing. For example the first round in the magazine is subject to the recoil event each time you fire a round. It can end up shorter by the time it chambers. Normally not something to worry about but you will find the occasional bullet that wants to drop into the case at the seating station, throw that case away. And it's more dangerous with heavier than lighter bullets. Check a round by chambering it several times, the bullet will move back.

[9x45]

Reloading is only a means to an end, and this is the end you want, doubles, about 15 yards, although 2 Alphas are much better than 2 Charlies, G31 Limited Major 9. Montana Gold 125JHPs on top of 7.8 grains of BE-86 at 1.140" going about 1,420 fps.

[ChemistShooter]

Setback occurs every time you chamber a round, and it can occur in the magazine during firing. For example the first round in the magazine is subject to the recoil event each time you fire a round. It can end up shorter by the time it chambers. Normally not something to worry about but you will find the occasional bullet that wants to drop into the case at the seating station, throw that case away. And it's more dangerous with heavier than lighter bullets. Check a round by chambering it several times, the bullet will move back.

A bullet can just drop into a case at the seating station? Another valuable datum. Okay, noted and recorded in my reloading SOP. When I see it, I will pitch it.

1420 fps? Ouch.

Edited December 30, 2015 by ChemistShooter

[Beastly]

Quick unscientific test:

Measure bullet COAL. Using thumbs on case head, press bullet tip into wood bench as hard as you reasonably can. Lean into it. Soft wood will be dented. Remeasure COAL. Hopefully there is < 0.001 setback.

[9x45]

.

A bullet can just drop into a case at the seating station? Another valuable datum.

Chem, you gotta quit talking like your'e still in school and get on like a shooter does. First you datum then you marry-m.....

SOP means (S)tarfire (Op)tical Range. So instead of saying that, you say "Stuff to know about reloading"

Starfire is like LegoLand, only with lasers... for shooting down ICBM's

Edited December 30, 2015 by 9x45

[Alan550]

.

A bullet can just drop into a case at the seating station? Another valuable datum.

Chem, you gotta quit talking like your'e still in school and get on like a shooter does. First you datum then you marry-m.....

SOP means (S)tarfire (Op)tical Range. So instead of saying that, you say "Stuff to know about reloading"

Starfire is like LegoLand, only with lasers... for shooting down ICBM's

Don't rag on him too hard. At least he didn't start the post with "What's up peeps?" as did another newbie on here.