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Interesting discovery when loading a tight necked chamber

 
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  #1  
Old 02-12-2014, 06:45 AM
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Join Date: Dec 2005
Location: Tucson Az
Posts: 1,195
Interesting discovery when loading a tight necked chamber

I chambered a 30 cal heavy varmint barrel a few years back in a 308 win variant. I had a 30 BR reamer and decided to head space it as a 308. Asked Dave Kiff if it would work. He said yes and you would have less body taper and steeper shoulder angle, an improved 308 win but you will have to turn the necks to fit the chamber.

Why? I wanted a 308 but didn't want to buy the reamer.

I copied the neck thickness of the 30BR I had used in another barrel. Neck would be .0105" which would allow a bullet release of .001" per side.

The sizing was accomplished with a 30 BR RCBS FL die without the sizer ball. I thought that was pretty cool as all I had to do with the 308 is run it up into the die to wack the necks down for a .001" neck tension. If necessary the same die can be used to bump the body enough for easy bolt closure.

Now for the interesting part. I remember reading a wonderful article called the Secrets of the Houston Warehouse.

Secrets of the Houston Warehouse

In this article the shooter, Virgil, didn't size his fired brass! "With about .00035" clearance on all sides between the loaded round and chamber neck, the natural spring-back of the brass, in combination with his neck preparation, correctly gripped the bullets. Some other warehouse shooters, including T.J. Jackson, followed the same practice."

I noticed that my fired brass had a tiny bit of tension, enough that I couldn't push a 168 SMK back into the neck without some effort. I decided to deprime and load with NO case sizing. I single load so I didn't think .0005" neck tension would be an issue. The bullet also makes contact with the lands. I figure with this configuration I am soft seating and the bullet will move as bolt is closed to maintain consistent rifling engagement.

Bottom line? It shoots tight ragged holes at 100 yds just like it did with the previously neck sized brass with .001" neck tension.

I thought this would be an interesting find worth sharing. Imagine no case sizing! The lapua brass is on its 5th firing and the bolt still closes easily with no body bump.

Just had to share. Hope a few of you find this interesting.

Ross
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  #2  
Old 02-12-2014, 07:26 AM
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Join Date: Mar 2008
Location: Helena, AR
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Re: Interesting discovery when loading a tight necked chamber

Very interesting results. Thanks for sharing. Are you getting more velocity with the improved 308?

Last edited by canderson; 02-12-2014 at 07:56 AM. Reason: Spelling
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  #3  
Old 02-12-2014, 07:51 AM
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Join Date: Nov 2005
Location: Shreveport, LA
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Re: Interesting discovery when loading a tight necked chamber

I remember that article. Pretty cool stuff
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  #4  
Old 02-12-2014, 08:22 AM
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Location: Tucson Az
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Re: Interesting discovery when loading a tight necked chamber

The barrel is 22". Using 43 gr of IMR 8208 XBR with 168 SMK for velocity of 2765 or so. Think I could get more velocity but I don't need it.

I don't hunt with it as it weighs 11 lbs. It is used it for all sorts of range activities. It shoots very consistent bugholes, perfect for testing suspect scopes. It has a picatinny rail so I can switch out scopes quickly.

Also use it for practice shooting with a bi-pod. Have evaluated several approaches with rear bags and bi-pod buddy at 100 and 200 yd ranges.

I have friends shoot it to determine if their shooting methods are working.
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Old 02-12-2014, 09:33 AM
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Location: Houston, Texas
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Re: Interesting discovery when loading a tight necked chamber

Thats pretty awesome. Ive read about guys seating with the lands but doing it without sizing is really cool.
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Old 02-12-2014, 10:22 AM
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Re: Interesting discovery when loading a tight necked chamber

Some BR shooters will use a specific sized expand iron to open up a fired case neck just enough for mild tension for the method called soft seating. They don't size anything else. The idea of soft seating is to seat the bullet out more than kissing the lands. When the bolt is closed the bullet is forced into the cartridge till it stops against the lands. A shooter can chase the lands as they wear.
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  #7  
Old 02-12-2014, 10:34 AM
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Location: Houston, Texas
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Re: Interesting discovery when loading a tight necked chamber

It sounds like a viable way to maintain accuracy throughout a barrels life. I dont think that im good enough at controling neck tension to pull it off though. It also seems you wouldnt want to remove a loaded cartridge from a rifle you were soft seating with.

AZ shooter, right after you anneal, are you still able to load your rounds this way?
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