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bomadera

O.A.L.

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What is the ideal o.a.l. for a 9mm 124 JHP (Hornady XTP)?
I have been loading this per Hornady's recommendation (most accurate load tested) of 1.060 with excellent results.  Yet Federal, Speer, and Sig all load longer 1.100-1.130
What have all of you found to be the ideal o.a.l?

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You have to use what runs best in your barrel, not theirs.  If you have excellent results with your load,  then you have an excellent load, including OAL.

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50 minutes ago, bomadera said:


I have been loading this per Hornady's recommendation (most accurate load tested) of 1.060 with excellent results. 

 

If you're happy, that's the Perfect OAL.     :)

 

To explore alternatives, I'd try to run The Plunk Test - see if you

can lengthen that OAL and still get excellent results.

 

Are you shooting 9mm Minor, or 9mm Major ?

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Posted (edited)
12 minutes ago, Hi-Power Jack said:

 

If you're happy, that's the Perfect OAL.     :)

 

To explore alternatives, I'd try to run The Plunk Test - see if you

can lengthen that OAL and still get excellent results.

 

Are you shooting 9mm Minor, or 9mm Major ?

I've tried the plunk test but I keep going back to the short 1.060 because of the accuracy. BTW my load is 5.4 of

Power Pistol @ 1.060 gets me over 1100fps

Edited by bomadera

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1.140 OAL on a 124 works perfect for me. It's long yet not too long that it wont get stuck in Glock mags or similar gun magazines.

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power pistol is a some what slow burning powder.  You will get better results with a faster burning powder.  N320, WST, sport pistol, clean shot, HP38 ,231

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I think this is a barrel specific issue. If it works for you then keep doing it. I wouldn't put much stock into what functions in other barrels. 

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OAL is subjective to magazine dimensions, gun reliability preference, chamber depth, bullet profile, and effect on chamber pressure. Generally speaking the faster the powder the more sensative the OAL plays on chamber pressures. With minor loads in a 9mm running a shorter OAL with middle of the road powders (231 on up to WSF or HS6 or slower) is usually not a concern for pressure spikes and you can afford to run on the short side. Faster powders like Bullseye, Titegroup, and especially Clays will spike pressure pretty quick when you shorten OAL. Most chambers are cut deep enough to allow for longer OAL but depending on the bullet profile you may have no choice but to run shorter than published OAL. I had a Tanfo with a short chamber and it ran 1.070 OAL with any TC or RNHP to chamber and it had feeding hangups. I switched to plain RN and was able to get a longer OAL and it ran reliably. All the 9mm's Ive ever owned had better function with OAL at the longer end of the spectrum. But if you are getting 100% reliability with your shorter OAL and you have no over pressure signs than go with it! 

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On 1/9/2019 at 9:54 AM, bomadera said:

What is the ideal o.a.l. for a 9mm 124 JHP (Hornady XTP)?
I have been loading this per Hornady's recommendation (most accurate load tested) of 1.060 with excellent results.  Yet Federal, Speer, and Sig all load longer 1.100-1.130
What have all of you found to be the ideal o.a.l?

My factory Hornady 124 JHP's are loaded to 1.065, I shoot Precision Delta 124 JHP's that I found are most accurate for my guns and loads at 1.080-1.085. Which has a similar profile of Hornady XTP's and only .004" difference in length.

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Posted (edited)

Apart from an OAL that affects feeds with your mag and barrel, OAL is all about "barrel time".

 

Barrel time is the time that it takes a bullet to exit the crown of the barrel once the round is fired.  The reason this is important is because when a round is fired, the barrel rings like a bell due to the concussion.  The concussion travels like a wave from the chamber to the crown where it is reflected back and this repeats.  When the concussion is at the crown, it is the worst time for the bullet to leave the barrel because as one can imagine, the concussion can distort the crown and cause uneven gas leaks and the concussion can impart a slight uneven lateral force on the bullet in an unexpected direction.

 

What is ideal is to have the concussion as far away from the crown when the bullet leaves the barrel i.e. during the quiet time.  One can do this a number of ways.  A crude way is to adjust powder weight which of course change the speed of the bullet, making it arrive at the crown at a different time.  A finer way to do this is to change OAL.  The reason is changing OAL changes the volume of the case which in turn affect pressure.  Pressure of course affect again the speed of the bullet which of course allows you to time when the bullet arrives at the crown.

This is well known for centerfire rifle reloading and a handgun is no different.

Edited by jlow
correction

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