Seating depth looks too small

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I am loading 150gr .311 dia SPFT into new 7.62x54R brass from Tradeex.

When I chamber an empty case with a round held loosely in the neck I get a base-to-tip length of 3.000" on the nose repeatably for the same bullet.

Backing that off by 0.02" for a bit of clearance I only have about .120" of the base actually being grabbed by the neck.

I compare that to some good-old Soviet Army Surplus rounds (my reference standard) and they have roughly the same amount of interface, although the boat tail back means that there is about another .16" of non-bearing length, and that is of course in a steel casing.

Does .120" of bearing area sound right? For the thin/soft neck brass that seems too little somehow.

Last time I just winged the length, but looking at what I did I probably had about 0.2" of bearing area, meaning the rounds were .1" off the lands. That being said, they grouped well enough to make me happy.

How does that compare to other folks doing this? How much neck/bullet interface are you getting when you seat to an acceptable off-the-lands spacing?

Ulrich
 
I wouldn't use ammo where the bullet is only held by about .120" of the neck. Rule of thumb is a very minimum of 1/2 the bullet diameter, and that is really minimum. Many people, or books, will say to seat the bullet in the neck to the diameter of the bullet.
Just seat them deeper. It may increase the pressure, or it may decrease the pressure a very small amount and you will have no way to know whether it did, or didn't.
It may or may not, affect the absolute accuracy, but if you are an ordinary shooter with an ordinary rifle, you will never be able to tell whether it made it more accurate, or less accurate. Oh, you may make some groups better, or worse, and think you affected accuracy, but tomorrow the exact opposite may occur!
 
OAL max for this cartridge is 3.038. A quick check of my Hodgdon manual shows 2.875 OAL with 150GR so you can seat deeper. Check web site for powder your using and see what OAL they spec.
Check out Terminal Ballistics Research site you'll find full info on the cartridge.
 
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Thank you for the link. There is some good data there.

I put together 20 rounds with the same 0.2" neck interface I previously used. They are noticeably a bit shorter than the Soviet Surplus, but the neck interface feels more secure.

Tonight I'll make up a few no primer/no powder ones and check how that geometry feeds.
 
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