Determining OAL of 9x19mm with Different Bullet Shapes

[9mmepiphany]

I don't have a lot of reloading experience, so I approached it from a mathematical and basic reasoning POV.

If I'm loading a 9mm 124gr RN bullet and I switch to a FPRN bullet, I reasoned that I should maintain the same seating depth to keep the case volume constant...the same amount of bullet should be pressed into the case.

Seating a shorter bullet to the same depth, should result in a short OAL. That difference in OAL should be the difference in the length of the bullets themselves.

As an example:
1. The 124gr RN bullet has a length, from base to tip, of .580"
2. The 124gr FP RN bullet has a length of .525"
3. The difference in length is .055
4. OAL of the RN cartridge is 1.160
5. Subtracting .055" from this should result in a new OAL of 1.105" for the FP RN cartridge

If I normally seat my RN bullets to 1.140", where I'm getting consistent velocities, I should be seating my FP RN bullets to 1.085"

I know my math is correct, asking if my reasoning for determining OAL sounds right to more experienced reloaders.

The powder being used shouldn't make any difference, as the volume stays the same, but I'm working with BE-86

 

[jcwit]

I normally go by what the reloading manual tells me the OAL should be for the bullet being used.

 

[readyeddy]

Sounds like a good idea. I never bothered measuring my bullets. I just used the same OAL and loaded at least 10% below max.

But your approach sounds more logical.

 

[CZ9shooter]

I calculate the approximate internal case volume (OAL minus bullet minus web thickness) on each of my loads. I also then compare that with the amount of powder and come up with how "dense" the powder charge is in each paricular load (charge weight divided by case capacity).

However, I do not really use this information to set OALs when working with a new bullet. That is usually determained by the fit and function in the gun I am loading for. It is just another data point I like to record. Sometimes it is interesting to see how different loads with the same powder act with varying levels of case fullness.

 

[rcmodel]

A more important consideration is if they will Feed, Fire, and Function Freely.

You determine that by taking the barrel out of the gun and using it to 'plunk test' your OAL at the reloading bench.

Different bullet ogive shapes will hit the rifling if loaded the same OAL as a different shape.

And chambers vary considerably between brands of guns on what OAL with each bullet shape will fit in them without getting into the rifling leade.

Forget internal volume.
Concentrate on the plunk test, and load as long as you can.
Long generally feeds better then short.

rc

 

[egd]

I'm new to reloading too. But from all I've read how can you forget internal volume. Doesn't that affect the pressure-an all important factor in the whole process?
I've wondered the same thing as OP. But I only have one bullet type so far to ply with soo I haven't tried it yet. I notice in my manuals they give different oal for different bullet types.
BTW, what is fprn?

 

[9mmepiphany]

I normally go by what the reloading manual tells me the OAL should be for the bullet being used.

There isn't any data for this specific bullet shape or I would have. I did look at 124gr JHP for a similar profile, but the math just seems like a more qualitative method.

The closest in the Lyman (49th Ed) is the 125gr JHP, which is loaded to 1.075"

That is usually determained by the fit and function in the gun I am loading for

Yup, did that too. The barrel will allow seating the bullet so far out that there is hardly any bullet below the case mouth...the magazine was the limiting factor in cartridge length.

Forget internal volume.
Concentrate on the plunk test, and load as long as you can.
Long generally feeds better then short.

Went through that with the RN.

First loads were 1.170" and they fed fine, but there was a lot of variance in velocity working up my IDPA load (1020fps).

Tried seating depths of 1.160", 1.150", 1.140" and 1.130"; had the most consistency (smallest SD) at 1.140". Granted that was with WST powder.

I'm just not sure if I want to press the new bullets down below 1.09"

BTW, what is fprn?

Flat Point Round Nose.

I should correct my inaccurate use of abbreviations here. The FP RN is for the 158gr bullets I ordered to load for .38 Spl, my 9mm bullets are just F(lat) N(ose)

 

[LiveLife]

rcmodel and others covered the process of determining max and working OAL/COL.

9mmepiphany, since you are developing match loads, take this into consideration also.

The barrel will allow seating the bullet so far out that there is hardly any bullet below the case mouth...the magazine was the limiting factor in cartridge length.

As you found out, some barrels have longer leade/free bore and slower start of rifling (like Glocks) that SAAMI max and even longer lengths would work only limited by the magazine.

When I developed my match loads, I figured longer was better as the bearing surface of the bullet would be closer to the start of rifling to reduce high pressure gas leakage. Well, that may be the case if you are loading full power/near max load data rounds but if you are looking at lower 125 power factor loads, initial chamber pressure build up will start to affect peak chamber pressures that will increase muzzle velocity variations (SD number) and decrease accuracy.

So when I load my 9mm 124/125 gr RN loads to 125-130 PF range, I will prefer to use shorter 1.135" OAL even when 1.169" will work (I will use longer OAL if shorter OAL would compress the powder charge - more on this below).

Tried seating depths of 1.160", 1.150", 1.140" and 1.130"; had the most consistency (smallest SD) at 1.140". Granted that was with WST powder.

I'm just not sure if I want to press the new bullets down below 1.09"

There are exceptions. With certain powders, you should calculate the case fill with the powder charge you plan to use and determine the seating depth. Subtract bullet length from OAL to determine the seating depth and see if the powder charge will be higher than seating depth which would compress the powder charge.

With WST and FP bullet that will seat deeper in the case, you are likely going to compress your powder charge to make 125 power factor because powder charge that will make 125 PF with RN will compress the powder charge. When I tested RMR's new 125 gr plated RN and WST for you, even longer 1.160" length would compress 4.2 gr of WST and I stopped my test at 4.0 gr (chances are you would need to use 4.2/4.3 gr of WST to make 125 PF) - http://www.thehighroad.org/showthread.php?p=9655361#post9655361

I don't mind compressing certain powders a bit like fluffy large flake powders but would be nervous about compressing fast burning powders like
WST. Although I tried WST for my match loads, some match shooters commented spikey nature of WST at the top and many actually preferred Titegroup over WST for making 125 PF (and Titegroup burns hot and violent at the top).

Ever wondered why Hodgdon doesn't publish load data for 9mm? This may be one reason.

IMHO, if you are wanting to make PF with WST, I would suggest you stick with RN bullets and load them long. If you want to keep using FP bullet, I would suggest you consider a different powder that would not compress to make 125 PF.

 

[Skinnedknuckles]

I use basically the same calculation to set a minimum (maximum pressure) OAL but I have found that I get better accuracy and function at longer than minimum lengths, particularly in my Ruger SR9. My other guns are less sensitive to OAL.

 

[LiveLife]

This post from Brian Enos forum may help. CocoBolo is using 124 gr FMJ with 4.6 gr WST at 1.145" for 130-135 PF - http://www.brianenos.com/forums/index.php?showtopic=144946&p=1626833

don't push beyond this with this powder. Yes, that is a warning, at a shorter oal less powder!

This post quotes 1997 Hornady HandBook Of Cartridge Reloading (page 174) showing much higher charges of WST and shorter OAL than I have ever seen used (I would definitely verify the data before using higher/shorter OAL) but I usually find CocoBolo's posts spot on so I would highly recommend following his advice - http://www.brianenos.com/forums/index.php?showtopic=144946&p=1928938

 

[murf]

Using one headstamp and sufficient bullet tension are important, too. case wall thickness varies a lot in this cartridge. Col won't matter much if the bullet is pulled out of, or pushed into, the case.

murf

 

[RAT807]

I started with load data from the powder company of the powder I was using (N350). It listed OAL at 1.142 so I worked up my first set of groups at 1.142. Using Sierra 125gr FMJ, they plunked at 1.165. I Loaded several groups at 1.165 to compare. The accuracy was better at 1.165 with the same powder charge I used at 1.142. I added another .2 grains to match the speed of the most accurate load at 1.142, and the group shot even tighter. I saw the same when I loaded with Power Pistol as well.

I do load at shorter OALs as the Sierra 125gr JHP likes 1.090 in my G34. I use less powder than the 1.165 FMJ load but the speed is very close. Accuracy is awesome at 25 yards, clover leaf groups. The Sierra 125gr JHP has a long bearing surface so keeping the same case volume as the FMJ load is not possible. Use the plunk test with each bullet and work up loads to find what your gun likes. I have several different bullets with similar profiles that I load at 1.122. I have loaded these as short as 1.060, (Berry's recommend OAL) but my gun likes them about .005 off the lands.

 

[Walkalong]

I generally load RN 9MM bullets at 1.130 to 1.135 OAL. Naturally a FP or HP will be loaded shorter.

As posted, function is the most important so I usually find that OAL and go from there.

I always log the length of the bullet I am loading, so between the bullet lengths and the OALs I can determine if the new to me bullet is seated to the same depth, deeper, or less deep in the case. That gives me a good idea if I need to tweak the powder charge to get a similar burn and velocity.

Then we need to see if it shoots well at that velocity.

 

[9mmepiphany]

IMHO, if you are wanting to make PF with WST, I would suggest you stick with RN bullets and load them long. If you want to keep using FP bullet, I would suggest you consider a different powder that would not compress to make 125 PF.

Yup, only shot WST for part of the season...until I pickup up 8lbs of Titegroup.

Titegroup burns hot and violent at the top

That's what I found when using the common .40 grains at 1.140"...also I found it dirtier than I wanted.

Got lucky that the 8lb jug of BE-86 came in...so I sold off the Titegroup

Started at 5.2 - 5.4grs of BE-86 and found them too hot. Moving down to 4.8 and seating to 1.10" looking for consistency and twenty more at 1.09"

Using one headstamp and sufficient bullet tension are important, too.

I sort by head stamp when developing a load. I'm doing this group in GFL cases

 

[gamestalker]

Post #5 nailed it. Your over thinking things slightly, there is really no need to approach it like that.

Plunk them, make sure they feed / cycle, and fit the magazine.

Use start charges when using a new component.

There is more to pressures than just case capacity, though that is pertinent, bearing surface also plays a part in this respect. But these are aspects of published data, that have already been accounted for by the publishers.

Perform a proper work up and oal approach (plunk).

GS

 

[LiveLife]

8 lb jug of BE-86 came in ... Started at 5.2 - 5.4 grs of BE-86 and found them too hot. Moving down to 4.8 and seating to 1.10" looking for consistency and twenty more at 1.09"

5.2 gr of BE-86 I used for 124 gr RN was loaded longer at 1.160" OAL/COL. For your FP bullet, shorter OAL and lower powder charge would make sense as long as it made 125+ PF.

My range test with BE-86 and 124 gr RN showed promise as it produced sub 2" shot group at 25 yards and sub 1" 4 shot cluster. Let us know how your range test goes.

 

[vaalpens]

I have been collecting data on bullet lengths (OAL) for a while, just so I can have another data point when deciding on the starting COL/load. I basically use the same calculation to determine what the COL could be, and then based on what will cycle in my gun and the length of the body of the bullet, adjust it up or down, and then adjust the powder down if needed. For similar type bullets where the base is shaped the same it has worked for me, but the hollow base bullets (Berry) I think has to be treated differently. It seems it generates a bit more pressure so I will adjust the powder down a bit.

I normally just use this calculation to get to a starting load. Once I have decided on the COL and starting load, then the bullet/powder combination will be evaluated with its own ladder.