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inconsistent OAL in 9 major


pewpewpew03

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i have a mark7 650 pro

Lee seating and crimp die

125gr gallant coated lead bullet

mixed cleaned range brass

 

my target is 1.165 and most come in a 1.163-1.165 but then I get some that are 1.171 and its absolutely driving me nuts..... 29 round test batch 5 were too long at the 1.17 mark....

 

ive checked shell plate, cleaned the die, readjusted the die, measured a handful of projectiles and they all are within .003

 

Any suggestions?

 

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21 minutes ago, pewpewpew03 said:

i have a mark7 650 pro

Lee seating and crimp die

125gr gallant coated lead bullet

mixed cleaned range brass

 

my target is 1.165 and most come in a 1.163-1.165 but then I get some that are 1.171 and its absolutely driving me nuts..... 29 round test batch 5 were too long at the 1.17 mark....

 

ive checked shell plate, cleaned the die, readjusted the die, measured a handful of projectiles and they all are within .003

 

Any suggestions?

 

What powder? Compressed load? Compressed loads will lengthen on there own.

 Lubing cases? Lubing cases decreases variations significantly.

 

Sort brass by headstamp. Oal is more consistent within same headstamp.

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You know there are multiple threads on this subject. All progressive 

presses do this. There are tangs you can do to minimize this.

End result get over it. Adjust your seating die so that the long round

are not to long and short ones are not to short. Some of the veneration is in your brass

some in your bullets.

 

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3 hours ago, pewpewpew03 said:

 

If i shorten them, they will be below 1.160 and I dont want excessive pressure spikes

 

I've loaded 9mm Major down to 1.145", but not with 9.5 gr AA7 - if you can seat the bullet, it's okay.

 

But, as you said, if the long ones pass The Plunk Test, you are good to go.     :) 

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I recommend that you determine what the max OAL is for this bullet in your chamber.

Make a dummy round that is extra long - say 1.200 as a start. Plunk test it and gradually reduce the OAL of your test round until it just passes.

Then you know what your OAL needs to be under 100% of the time in your gun. You might find out your chamber is throated longer than you thought and your 'long' loads aren't even close to being a problem.

 

AA7 is a very slow powder and forgiving powder (slowest powder widely used for 9 major). Shortening your OAL from 1.165 to 1.145 is not extreme at all. You may need to drop .1 grain to maintain the exact same PF. Chrono to be sure and look at your primers for increased pressure signs.

 

I normally load at 1.165 as well, but recently experimented with 1.145 OAL loads and MG115JHP's. Dropped my charge from 10.8 to 10.7 AA7 for the same PF. Primers looked the fine - same as longer loads. Accuracy of shorter loads was definitely not as good in my gun. If you play with shorter OAL's in a gun throated for long loads, you need to shoot some groups off a bag to ensure you accuracy is still what you want.

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