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9mm, OAL vs. Powder Weight

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I'm setting up 1050 to start reloading 9mm (have .40 and 38SC setups) and am running into simple, but frustrating issue: OAL and powder weight create two dimensional parameter space, where I can vary either one of them to adjust the peak pressure and bullet velocity.

 

With my .40 setup, I got the OAL from the gunsmith who built the gun (SVI) so I could just adjust the powder measure to get the velocity and power factor I need. With 9mm, it seems that the OAL is all over the place both in manuals and online. I understand that the shape of the bullet defines how much space is left in the case which significantly affects the pressure, but so does the amount of powder in the case. Even if I pick a good starting point, I get to play with two variables now - length and charge. 

 

So, are there any tricks about picking a good starting OAL? If I look at the manual, I'm seeing same bullet weight but slightly different shape listed with quite different OALs. If I interpolate and pick a good starting point, do I now try to adjust the OAL in addition to the charge, or do I just stick to a "good enough" OAL, look for the overpressure signs and adjust the charge? 

 

For reference, I will be using N320 and 147 Blue Bullets, but also have a batch of MG 130 FMJ that I would like to use up. I would want to use the same ammo (if possible) in everything from S&W 929 to SA 1911. 

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Have you done the plunk test on your barrel/barrels to determine the maximum OAL without hitting the grooves?  That would be a good starting point.  Then depending on what of bullet you are using determine charge weight and test for accuracy and pressure signs,  You can make changes in both OAL and charge weight depending on what your guns like.

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I agree with Stick.  Pick your bullet first, find the OAL for this bullet using your gun.  Once this is done OAL is fixed and your only variable is charge weight. 

 

Using a chrono and visual inspection of your fired cases you'll be able to determine where to set the charge.  Of course this is assuming you have a powder in mind.  If you haven't selected a powder then you really have 2 variables to deal with after setting OAL, that is powder and charge.

 

I'm developing a 9-major load.  I selected a bullet, set OAL and worked up loads using 3 different powders.  I'm now at the point where I'm comparing each of the loads for accuracy and dot movement.  Definitely not a quick task if you're considering more than 1 powder, however I enjoy reloading and learning how different powder perform in my gun.  Plus I have time as I don't plan to shoot Open this year or next.

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Stick and Muncie have hit it on the head     :cheers:

 

You are loading 9mm Minor, with Very Little Powder in the case -

your OAL is going to have almost Zero effect on pressure or

velocity.

 

You've picked the bullet (147 gr BB's) which is a great choice, and an excellent

powder.

 

First, take the barrel out of your gun, and run some empty cases with 147 BB's

loaded to 1.13" and drop them into the barrel - IFF they Plunk (sound made when

they hit bottom, or are solidly seated in the chamber), and they can easily spin

and drop out when you invert the barrel, then you know you can load as long as))

1.13".    If NOT, shorten, and try again.   If 1.13" is good, why not try 1.135" and

see how long you can seat the bullet (making sure they also fit through the

magazine).

 

Determine the longest OAL you can use With THAT Bullet (if you switch to the

130 gr FMJ, you'll have to do The Plunk Test Again).

 

Now that you have the OAL determined, vary the powder until you get what 

you want in terms of feel, velocity and accuracy.  

 

Good luck and have fun.    :) 

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Posted (edited)

N320 will show almost zero velocity difference between 1.100” and 1.150” in a 9mm load. Perhaps a few FPS. You’re already so low in case volume that our friends above are very much correct. It barely matters with titegroup, prima V, or N-320.

 

Set your crimp so that when you pull a bullet there’s only a faint trace of the case mouth on the side of it. Remove the flare but do NOT crimp into a coated bullet in 9mm.

 

Find a charge weight that gets you 130-133 pf in both guns.

 

Play with OAL to tune your 25yd group sizes.

 

Then re-chrono, and tweak your powder load if needed.

 

(I do find in some guns that pushing 147s a little faster has a dramatic effect on accuracy. Think 135pf vs 128pf.)

 

Edited by MemphisMechanic

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4 hours ago, IVC said:

I'm setting up 1050 to start reloading 9mm (have .40 and 38SC setups) and am running into simple, but frustrating issue: OAL and powder weight create two dimensional parameter space, where I can vary either one of them to adjust the peak pressure and bullet velocity.

 

With my .40 setup, I got the OAL from the gunsmith who built the gun (SVI) so I could just adjust the powder measure to get the velocity and power factor I need. With 9mm, it seems that the OAL is all over the place both in manuals and online. I understand that the shape of the bullet defines how much space is left in the case which significantly affects the pressure, but so does the amount of powder in the case. Even if I pick a good starting point, I get to play with two variables now - length and charge. 

 

So, are there any tricks about picking a good starting OAL? If I look at the manual, I'm seeing same bullet weight but slightly different shape listed with quite different OALs. If I interpolate and pick a good starting point, do I now try to adjust the OAL in addition to the charge, or do I just stick to a "good enough" OAL, look for the overpressure signs and adjust the charge? 

 

For reference, I will be using N320 and 147 Blue Bullets, but also have a batch of MG 130 FMJ that I would like to use up. I would want to use the same ammo (if possible) in everything from S&W 929 to SA 1911. 

 

Great points so far on starting with OAL and making sure it plunks OK in your gun.

 

As I re-read your post, I see that your examples are all minor PF and you mention a 929 & SA 1911.

Big thing to consider with the OAL & your 1911 is how the loaded ammo fits in your magazines.

After you determine the max OAL by plunk test, then determine what works best in your mags & feeds good in your gun.

 

My SS 1911's feed great with 1.120-1.150 OAL loads using RN profile. Well short of max OAL from plunk test in my barrels

 

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IVC, the reason you find such a variance in OALs is different manufactures chamber their barrels differently.  European firms typically chamber with a very short leade.  That's why you see so many astonishingly (to us) short OALs from European reloading tables.

 

SAAMI length is 1.169" OAL with a round nose bullet.  I load 115gr HAPs to 1.161" and have no trouble feeding in 2011 or 1911 mags.

 

You got a lot of good info above.  Personally, I'd develop a load for your revolver first.  If it proved too long for the 1911, I'd have that barrel throated.  That's exactly what I did with both my auto barrels.  There wouldn't plunk anything over 1.150", so I had them throated for 1.165" and load to 1.161"

 

Another powder you might try is Alliant Sport Pistol.  A twin to N320 and great for coated bullets.

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great advice by the above posts.  I did this many years ago, with the exact same load.  I was experimenting with my Glock however.  I found that 147gr coated bullet at 1.135" with 3.2gr on N320 was excellent.  Actually this would chrono at a 2 standard deviation.

 

I first started by experimenting with OAL first.  I loaded 20 rounds at 0.005" increments from 1.120" - 1.150", I shot every group of rounds through a chrono and into a target so that I could measure accuracy spread and velocity spread.  It resulted in a very obvious bell curve type data.  It was fun to do and I learned a lot from it.  I think you should give it a try.

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6 hours ago, stick said:

Have you done the plunk test on your barrel/barrels to determine the maximum OAL without hitting the grooves? 

 

6 hours ago, muncie21 said:

I agree with Stick.  Pick your bullet first, find the OAL for this bullet using your gun.  Once this is done OAL is fixed and your only variable is charge weight. 

 

3 hours ago, Hi-Power Jack said:

First, take the barrel out of your gun, and run some empty cases with 147 BB's

loaded to 1.13" and drop them into the barrel - IFF they Plunk (sound made when

they hit bottom, or are solidly seated in the chamber), and they can easily spin

and drop out when you invert the barrel, then you know you can load as long as))

1.13".    If NOT, shorten, and try again.   If 1.13" is good, why not try 1.135" and

see how long you can seat the bullet (making sure they also fit through the

magazine).

 

That's perfect and exactly what I was looking for - thank you.

 

I pulled out two barrels, SP01 (should be short) and SA 1911 (could be anything), as well as 929. Since I have Redding micrometer seating die, I set it up for 1.169 as the starting point, seated a bullet (130 MG FMJ) in an empty resized case (no primer/powder), crimped it and tested it - both barrels felt "sticky" so I know the bullet was touching the rifling. Then, I kept adjusting depth by 0.010 on the already crimped blank and found out what you were talking about. I could feel the proper "plunking" in the 1911 at about 1.150 and in the SP01 at about 1.130 (I recorded the actual measurements, both the OAL where it passed and the last one where it failed). All of the OALs worked in 929. 

 

This makes quite a bit of sense now. I can find the longest OAL that would work, either for one specific gun or for a bunch of them, then adjust the charge. Much like with rifles, playing with bullet jump (effect of OAL) will affect accuracy. So, it looks like the process is: (1) find a good OAL based on the specific bullet and barrel (give or take, based on how generic I want the ammo to be), (2) find a good charge weight to get in the vicinity of the desired PF, (3) adjust OAL for accuracy and charge for PF. 

 

Does that sound about right? 

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5 hours ago, Hi-Power Jack said:

Determine the longest OAL you can use With THAT Bullet (if you switch to the

130 gr FMJ, you'll have to do The Plunk Test Again).

 

Another good point - just for fun, I measured some factory Federal ammo and it was 1.152, which is above the OAL that would pass the plunk test I was just doing. I was confused for a second, but when I thought about it I realized it's all about the bullet shape. Federal has much more pointy FMJs, so the bullet will engage rifling at different OAL. 

 

Again, it all makes much more sense now. 

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5 hours ago, racer-x said:

After you determine the max OAL by plunk test, then determine what works best in your mags & feeds good in your gun.

 

My SS 1911's feed great with 1.120-1.150 OAL loads using RN profile. Well short of max OAL from plunk test in my barrels

 

That's another considerations. Longer normally feed better, but I'll have to test it. I have Tripp Cobra magazines for my 1911 and a bunch of factory stuff for my other 9mm guns. 

 

Looks like it's a trade-off between how generic the ammo is and how well it works in the particular race gun. Isn't it always like that in life... ? 🙂

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1 hour ago, Butterpuc said:

great advice by the above posts.  I did this many years ago, with the exact same load.  I was experimenting with my Glock however.  I found that 147gr coated bullet at 1.135" with 3.2gr on N320 was excellent.  Actually this would chrono at a 2 standard deviation.

 

I first started by experimenting with OAL first.  I loaded 20 rounds at 0.005" increments from 1.120" - 1.150", I shot every group of rounds through a chrono and into a target so that I could measure accuracy spread and velocity spread.  It resulted in a very obvious bell curve type data.  It was fun to do and I learned a lot from it.  I think you should give it a try.

 

That's the charge I was thinking about - load a small batch of 3.0, 3.1, 3.2 and 3.3 to see how it works. 

 

I really like the idea of sticking to a single charge and varying OAL (particularly since I can do it easily with the micrometer seating die) to see what works best for the specific gun. The only downside is that it will likely be different for different guns, so I'll have to have an array of different loads and either find a compromise that works well overall, or adjust it every time I load for a particular gun. Choices, choices... 

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5 hours ago, MemphisMechanic said:

Set your crimp so that when you pull a bullet there’s only a faint trace of the case mouth on the side of it. Remove the flare but do NOT crimp into a coated bullet in 9mm.

 

I have the crimp currently set to 0.377. Should I actually look at the finished round, or just go by the calculation and measurement? 

 

(Also, I spent some time studying and researching, so I completely understand how and why too much crimp on lead bullets will decrease neck tension and be counterproductive.) 

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1 hour ago, IVC said:

 

I measured Federal ammo at 1.152", which is above the OAL that would pass the plunk test I was just doing. I was confused for a second, but when I thought about it I realized it's all about the bullet shape.  

 

Right.  Each bullet shape can come in a different OAL.    :) 

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1 hour ago, IVC said:

 

I have the crimp currently set to 0.377. Should I actually look at the finished round, or just go by the calculation and measurement? 

 

(Also, I spent some time studying and researching, so I completely understand how and why too much crimp on lead bullets will decrease neck tension and be counterproductive.) 

 

I have no idea. You see... I work with these kinds of measurements for a living.

 

Your digital calipers are accurate to +\- .001” on a good day. Unless you’re using a micrometer to measure the crimp, your tool doesn’t have enough resolution for really fine tasks.

 

Given that, I’ve always set the crimp by feel and with a straightedge first, getting rid of all of the belling, and then pulled a bullet to verify I’m set correctly.

 

My crimp has never caused issues and I’ve loaded 50k+ coated bullets in 9mm. Simple process, and it works.

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