I think I dodged a bullet??? (or a bolt)

T

tiny68

Member
I purchased a used PacNor pre-fit 30BR barrel for a Savage a couple of weeks back. The barrel is clearly marked 30BR, 1:18, 0.333. I was told it was a 0.333 neck and never thought twice about it. My other 30BR is a 0.332 neck and I have my rounds turned to 0.3305 -0.3310". I took a few brass from my older 30BR and chambered them. They were pretty tight and snug to close the bolt. I thought I just had the headspace set a little tight. I loaded up about 20 rounds with a H4198 latter. A few rounds were considerably tighter than others. I thought it was just seating the bullet deep in the lands. I didn't blow any primers. I remember thinking these babies are cruising. I was getting +3100 fps with 34.0 gr H4198 with 118 BIBs. Accuracy was ok, but usually two in one hole with a flyer and one 0.077" group (3 shots at 100 yd). I took the barrel off and was working up the brass.

I just purchased a new 0.330 neck 30BR pre-fit Shilen at the swap meet on Saturday and after mounted it, I decided to confirm the headspace with some of the brass I fired in the PacNor with the 0.333 neck. I expected considerable resistance due to the oversized neck. There was none. I put in another case. Same thing. I checked the brass from the 0.333 PacNor. All exactly 0.330. My brass from my 0.332 neck 30BR comes out at 0.332 after firing.

I think I got very lucky. Not sure why I didn't blow a primer. I know PacNor's 30BR reamer is a 0.330 neck. I have a print of it. I guess I figured this was openned up to a 0.333 as a no-turn 30BR. Now I don't know. If the brass comes out at 0.330 after firing, is it a 0.330 neck? Should I make a chamber cast to be sure?

Tiny
 
more confused

OK. I went and dug out the PacNor reamer print. It is a 0.333 neck. Now I am even more confused.......:(:(:(

tiny
 
I think what you are seeing is variations in brass springback.
It blows out upon firing to the chamber neck then springs back to 330 .
Soft cases dont spring back as much.
 
If the chamber is indeed .333 I see no problem shooting a .3305 case in it. The hard bolt closing you refer to is more than likely a difference in case head to shoulder length between the (2) barrels possibly as a result of how the barrel is set in the action. That being said, I would find the diameter of the neck in the chamber. It should be marked on the barrel. You can use Cerrosafe to cast the chamber or use gage pins. If you take the barrel off the action you can use a gage pin to reach the neck area of the chamber. If a .333(-.0002) pin goes I'd guess it's a .333 neck. Get the chamber squeaky clean and try it. If a .332(-.0002) pin goes the .3305 case should be good to go as well. Recheck how the barrel is set it may just be short.

Mike Swartz
 
I hope not to sound petty but I feel that YOU MUST find out where you're binding....

I agree that near to zero neck clearance isn't dangerous, I've run necks as tight as "scuff fit" or minimal interference with no danger, but necks too long which crimp onto the bullet ARE dangerous. And it's just important to KNOW this stuff :) Find out if it's the neck? The shoulder? The base? The OAL? The NS Junction?

I shoot several chamberings such that the necks just stay the same after firing..... The way I establish fit is old fashioned trial and error, I just keep shaving the neck down on a try-case until it fits, then MARK IT by wrapping masking tape around it with pertinent info written down and put it in a drawer..furthermore write down a detailed explanation of what the case is. I put this whole mess into a small ziplok bag and file it away.


Now make another one, play with the fine tuning to find out exactly where scuff-fit is. You can get them close enough that they won't close on Dykem ;) ..... MARK IT and put it away with copious notes.

Now you KNOW where you are re neck diameter.


BTW......... don't forget to leave a bullet in the case when you put it away. This ain't about neck THICKNESS, it's about keeping a reference of just exactly what your neck diameter is.


hth


opinionsby



al
 
tiny68 said:
I just purchased a new 0.330 neck 30BR pre-fit Shilen at the swap meet on Saturday and after mounted it, I decided to confirm the headspace with some of the brass I fired in the PacNor with the 0.333 neck. I expected considerable resistance due to the oversized neck. There was none. I put in another case. Same thing. I checked the brass from the 0.333 PacNor. All exactly 0.330. My brass from my 0.332 neck 30BR comes out at 0.332 after firing.

I think I got very lucky. Not sure why I didn't blow a primer. I know PacNor's 30BR reamer is a 0.330 neck. I have a print of it. I guess I figured this was openned up to a 0.333 as a no-turn 30BR. Now I don't know. If the brass comes out at 0.330 after firing, is it a 0.330 neck? Should I make a chamber cast to be sure?

Tiny
Click to expand...
If you are purchasing "prefit" barrels and using benchrest fit brass (as opposed to SAAMI tolerances) I would definitely want to know the headspace and the chamber neck diameter.

As to headspace you should own or have access to headspace gages for that cartridge.

As to neck diameter, making a gage pin as Mike Swartz suggests, or taking the barrels to your local gunsmith or machine shop and let them use a small hole gage and micrometer to determine neck diameter would be safe.
 
tiny68 said:
As indicated in the first thread, I have a go-gauge.

I think I will buy some CerroSafe or what ever it is called and make a cast. I want to make sure.

tiny
Click to expand...

That's an excellent idea!!!

You really need to know the neck dimension if you're gonna cut it close.
 
Good folks at Shilen

Wade at Shilen is going to make a chamber cast for me for free. That is good people.

tiny
 
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