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Old January 28, 2012, 09:27 PM   #1
Join Date: January 27, 2012
Posts: 49
AOL Help for Nervous Newbie

how critical if any to the saftey and ballastics is the AOL?

My situation: 9mm luger loads
Just loaded the following per the Lymann Manual-
124gr plated/rn- 3.5gr bullseye- cci500- and AOL is at 1.18 and it will not feed in my test pistol. can I tighten the aol uo to 1.045 as it shows in the manual under lead rn and not effect the c.u.p .. I guess what im asking is what effect will this have on the round doing so?
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Old January 28, 2012, 09:38 PM   #2
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You do not need to use the OAL listed on published load data as testing barrel fixtures (not real pistols) are used to measure chamber pressures and using published OALs WILL NOT ensure reliable feeding/chambering of finished rounds in your pistols.

Determining OAL should not be a guessing game and I use the following process for semi-auto loads whenever I use a new bullet:

1. Make sure resized cases drop freely into the barrel chamber. If not, adjust the resizing die to ensure the cases are resized full-length (bottom of resizing die almost "kisses" the shell holder/plate) and fall in freely into the chamber.

2. Determine Max OAL - Make a dummy round (no powder/primer) and perform the barrel drop test with the barrel out of the pistol starting with the SAAMI max OAL until the dummy round falls into the chamber freely with a "plonk" and spin without hitting the start of rifling. To determine the amount of taper crimp to return the flare back to flat, I usually add .020" to the diameter of the bullet (So for 9mm .355" diameter bullet, .375" taper crimp and for .356" bullet, .376" taper crimp).

3. Next determine Ideal OAL - Load the Max OAL dummy round in the magazine and manually release the slide without riding the slide with hand. Incrementally decrease the OAL until dummy round reliably feed/chamber. Depending on the pistol/barrel used, Ideal OAL that will work reliably will vary. If you are reloading for multiple pistols, use the Ideal OAL that will work reliably in all the pistols. FYI, most jacketed/plated RN bullets have worked well for me at 1.125"-1.135" OAL in various pistols.

4. Then conduct powder work up using Ideal OAL and published start-to-max load data. Regardless of the scale used, I highly recommend the use of check weights to verify the accuracy of powder charges to 1/10 of grain -

Not all factory/aftermarket pistol barrels have the same groove diameter, leade length, rifling type as used in the test barrels to develop load data that result in different high pressure gas leakage and may require different powder charges to produce same chamber pressures. If you do not have a chrono (or can't use one because you are shooting at indoor ranges), I typically use consistent shot group sizes as indicator of consistent chamber pressures without exceeding published load data (when shorter OALs are used, I often use a slight buffer headroom near the max load data - maybe .2-.3 gr less).

Variations in the published load data are often due to variations in reloading/testing components (i.e. type/nose profile of bullet nose and how deep the bullet base is seated inside the case neck, etc.).

Starting with the published start charge (or 10% below max), load 10 rounds of each increment of .1-.2 gr in powder charge. If using shorter OAL than published/typical for bullet type, I will decrease my start charge by .2-.3 gr. For initial range trip, 3 rounds are shot at 7-10-15 yards and shot groups are compared to identify charge range that reliably cycled the slide/extracted cases while looking for accuracy trends (usually 2-3 powder charges will stand out). On range trip #2 and subsequent trips, I will verify most accurate powder charges with 5 round shot groups at 7-10-15 yards (Typically, I will use 3 consecutive range tests to verify the accuracy of particularly accurate loads).

Conducting full work up allows you to identify the most accurate powder charge for the particular bullet/OAL combination and lighter target/plinking loads that still produce accurate shot groups while reliably cycling the slide/extracting the spent cases.

Some large flake powders like Unique, Promo, etc. may not dispense to .1 gr consistency when using powder measures. Do not get discouraged by this as I still get accuracy from these powders even with .2-.3 gr variations. Go by the shot group sizes.

Last edited by BDS-THR; January 28, 2012 at 09:43 PM. Reason: corrected link for check weights
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Old January 28, 2012, 09:44 PM   #3
Join Date: January 27, 2012
Posts: 49
awesome info.. this place rocks.. thanks man
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Old January 28, 2012, 11:28 PM   #4
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124gr plated/rn- 3.5gr bullseye- cci500- and AOL is at 1.18 and it will not feed in my test pistol. can I tighten the aol uo to 1.045 as it shows in the manual under lead rn and not effect the c.u.p
The short answer is no. Using a powder as fast as Bullseye and reducing the COL from the book load of 1.18" to 1.045" will increase pressure and could so dramatically or catastrophically. Are you sure about that book load of 1.18"? The SAAMI max for 9mm is 1.169"

With fast powders in the 9mm as little as 0.020" reducing in COL can result in huge pressure increases. That is why setback can be a big problem. But what determines peak pressure is seating depth. The amount of bullet in the case. So even if you have the same COL but are using a bullet with a different length the seating depth will be different. Follow the directions by BDS-THR and you will be fine.
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