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Discussion Starter #1
Do you guys trim your brass to the nominal trim length of 2.028, or do you find better results/case life using a different trim length?
 

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I just use the Lee trimmers in the RCBS case prep unit to trim to standard length.

Tim

 

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I just use the Lee case trimmer too. Quick and easy.
 

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Speer #14:
max. case length of 2.0395", trim to length of 2.030".

Nosler #7:
max. case length of 2.040" (implied from photo), trim to length not stated.

Hornady 9th:
max. case length of 2.039", trim to length of 2.029".

SAAMI:
max. case length of 2.0395", min. length of 2.0195".
That's 0.020" (20 thousandths of a inch) to work with.



All say max. cart. OAL of 2.550". There is no reason to mill your cases to the minimum length. How wide is a cannelure? If all of your cases crimp into the cannelure of your bullet and meet the max. cart. OAL, you'll be "OK" with minute case to case differences as your rounds will fit your rifle and every other 30-30 rifle.

Trimming all cases to the same length is one way to get to max. cart. OAL. Some variable length in cases is permissible (thus min. and max. lengths). Whether case length variability (+/-0.010" plus or minus ten thousandths of an inch) affects target accuracy (variable compression of crimp on bullet) is for testing and Food For Though and discussion.
 

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Discussion Starter #6
Seeing those maximum case length figures, it appears to me that staying towards the long-end on case length could assist in seating some bullet designs at least a caliber of depth in the case (not counting the boat tail).....which seems to be a challenge with bullets like the 125grain Ballistic Tip. I have gathered that any ogive in the case is to be avoided if at all possible.......seems hard to do with the 125 BT. At this point, I presume that many folks don't seat the bullet an entire caliber of depth into the case.
 

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Here's the S.A.A.M.I. derived "math" as a "word problem" (followed closely by the math):

Min. "Trim To" Case Length plus Bullet Length equals Unseated Component Length minus Max. Case Length equals S.A.A.M.I. Bullet Seated Depth (embed) in Case.

Take for example my 270 ('cause the data is easy for me to find):

2.530" Min. "Trim To" Case Length
+1.250" Nosler Partition 150 gr. bullet length (+/-)
3.780" Total unseated component length
-3.340" Max. Case Length
0.440" S.A.A.M.I. Bullet Seated Depth (embed) in Case (> 0.277" [one caliber])


You should measure the chamber (face of receiver to lands) by hack sawing a fire formed, neck sized, deburred, chamfered, and unprimed case longitudinally (~1/2"), insert your bullet choice in the chamber - by hand - ahead of this sawn case, and slowly close the rifle on the two. Then carefully extract this "dummy round". DO NOT disturb the two components, now together as one. Measure the COL of this "dummy round" and write that down for posterity. This is your chamber's Specific Max. Cartridge Overall Length (SMCOL and it could be pretty long).

You can't load rounds in your chamber that are longer than your SMCOL. Trying to do so will cause the the bullet to be jammed backward into the case as you close the receiver - making the receiver "difficult" to close and if fired, potentially increasing chamber pressure to an unanticipated extreme.

The bullet is the only component that can move longitudinally between the receiver face, chambered case, and the lands. You don't want to jamb a round in the chamber. That's not advised. You should and most likely will make rounds shorter than SMCOL by seating bullets deeper.

If you substitute your SMCOL in place of Max. Case Length, you will derive the specific minimum bullet seated depth (embed) such that your SMCOL round will touch the lands when chambered. This is your rifle's ZERO JUMP to lands for that specific bullet in your chamber (this may vary for different bullets).

Your minimum bullet seated depth should be "close to" one caliber of embedment. For the (0.308") 30-30 (say not more than minus 10% or 0.030" thirty thousandth) and this is my opinion, a MIMIMUM of 0.278" calculated embedment.

For the single shot rifle shooter trying to find the barrel's "Sweet Spot", after accurizing with a suitable powder (you know the drill), consider modifying the bullet's jump to lands (by increasing bullet embedment) to improve barrel harmonics. Increase bullet embedment increments similar to powder trial increments (say 0.003" at first, then tighten up when a relative minimum is noted) until accuracy is satisfactory.
 

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Discussion Starter #9
I found that carefully extracting the dummy round from my ejector-fitted handi chamber was easier said than done, and produced less than consistent results for me.

However, I found GunBlue490's "scotch tape method" of determining COAL to work with repeatable precision.

150 Ballistic Tips=2.818 COAL
150 Hornady RN SP=2.503 COAL (!!)

Looks like those Hornady RN SP's are gonna be a no-go in my gun for now. I like the book data in the Lyman manual for that specific bullet, but I would have to load it deeper in the case than the prescribed maximum OAL, and then figure things out from there on my own. Nope........I'm to green for that.
Here's the S.A.A.M.I. derived "math" as a "word problem" (followed closely by the math):

Min. "Trim To" Case Length plus Bullet Length equals Unseated Component Length minus Max. Case Length equals S.A.A.M.I. Bullet Seated Depth (embed) in Case.

Take for example my 270 ('cause the data is easy for me to find):

2.530" Min. "Trim To" Case Length
+1.250" Nosler Partition 150 gr. bullet length (+/-)
3.780" Total unseated component length
-3.340" Max. Case Length
0.440" S.A.A.M.I. Bullet Seated Depth (embed) in Case (> 0.277" [one caliber])


You should measure the chamber (face of receiver to lands) by hack sawing a fire formed, neck sized, deburred, chamfered, and unprimed case longitudinally (~1/2"), insert your bullet choice in the chamber - by hand - ahead of this sawn case, and slowly close the rifle on the two. Then carefully extract this "dummy round". DO NOT disturb the two components, now together as one. Measure the COL of this "dummy round" and write that down for posterity. This is your chamber's Specific Max. Cartridge Overall Length (SMCOL and it could be pretty long).

You can't load rounds in your chamber that are longer than your SMCOL. Trying to do so will cause the the bullet to be jammed backward into the case as you close the receiver - making the receiver "difficult" to close and if fired, potentially increasing chamber pressure to an unanticipated extreme.

The bullet is the only component that can move longitudinally between the receiver face, chambered case, and the lands. You don't want to jamb a round in the chamber. That's not advised. You should and most likely will make rounds shorter than SMCOL by seating bullets deeper.

If you substitute your SMCOL in place of Max. Case Length, you will derive the specific minimum bullet seated depth (embed) such that your SMCOL round will touch the lands when chambered. This is your rifle's ZERO JUMP to lands for that specific bullet in your chamber (this may vary for different bullets).

Your minimum bullet seated depth should be "close to" one caliber of embedment. For the (0.308") 30-30 (say not more than minus 10% or 0.030" thirty thousandth) and this is my opinion, a MIMIMUM of 0.278" calculated embedment.

For the single shot rifle shooter trying to find the barrel's "Sweet Spot", after accurizing with a suitable powder (you know the drill), consider modifying the bullet's jump to lands (by increasing bullet embedment) to improve barrel harmonics. Increase bullet embedment increments similar to powder trial increments (say 0.003" at first, then tighten up when a relative minimum is noted) until accuracy is satisfactory.
 
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