308 win OAL

[spudgun]

Just got a new 308 bolt gun and was checking chamber depth OAL.

Ok, first off I know the OAL for 308 win is 2.81.

I have 2 different bullets with different oglive.
1. Hornady 168 AMAX
2. Hornady 168 MAX.

So I took my modified 308 case and placed a A-MAX bullet into the neck. Placed it in my chamber and closed the bolt. Removed the bullet and measured OAL (I can see the rifling marks on the bullet). This bullet came out at 2.83 OAL. So that told me I had .02" to play around with.

Took the 168 MAX bullet and did the same thing, it came out at 2.87 OAL.

I have used these same bullets on my 6.5 CM and the MAX bullet comes out longer every time.

Anyway my question is if I wanted to say be .01 off the lands then I would seat the MAX bullet to 2.86 OAL.

The other issues is I must single feed as they will not load into the mag (too long). Not a big issue since I will be bench shooting.

Thinking in the right direction?

 

[dbaird]

For my .308 I load Sierra 168 BTHP @ 2.840 behind 43.5 Varget-Fed210M primers for 2570 FPS (20” bbl). Outstanding accuracy.

 

[spudgun]

For my .308 I load Sierra 168 BTHP @ 2.840 behind 43.5 Varget-Fed210M primers for 2570 FPS (20” bbl). Outstanding accuracy.

Thanks for the info.

Right now I am running Varget 42.5, CCI primers. Avg 2725 FPS.

Will see how it works.

 

[Howland]

Just got a new 308 bolt gun and was checking chamber depth OAL.

Ok, first off I know the OAL for 308 win is 2.81.

I have 2 different bullets with different oglive.
1. Hornady 168 AMAX
2. Hornady 168 MAX.

So I took my modified 308 case and placed a A-MAX bullet into the neck. Placed it in my chamber and closed the bolt. Removed the bullet and measured OAL (I can see the rifling marks on the bullet). This bullet came out at 2.83 OAL. So that told me I had .02" to play around with.

Took the 168 MAX bullet and did the same thing, it came out at 2.87 OAL.

I have used these same bullets on my 6.5 CM and the MAX bullet comes out longer every time.

Anyway my question is if I wanted to say be .01 off the lands then I would seat the MAX bullet to 2.86 OAL.

The other issues is I must single feed as they will not load into the mag (too long). Not a big issue since I will be bench shooting.

Thinking in the right direction?

You'll be more precise if you measure catridge base to ogive with your modified case and your loaded rounds, and use a VLD type seating stem, but you're on the right track and it's your only option if you don't have a comparator.

Before I was turned on to comparators, I got excellent results smoking a bullet in a case with a loose neck then measuring base to tip. My .30-06 happens to like the Nosler Ballistic Tips at 0.010" off the lands. Don't be afraid to try seating deeper. Some VLD types can be very forgiving of jump.

 

[Texas10]

By your description it sounds like you measured hard jam, not touching lands. The difference could be quite large, as large as .1 inch. Are you using the Hornaday modified case and are you neck sizing it?

 

[spudgun]

By your description it sounds like you measured hard jam, not touching lands. The difference could be quite large, as large as .1 inch. Are you using the Hornaday modified case and are you neck sizing it?

It is a hard jam (well not really hard), just enough to push the bullet back into the modified neck in the case.

You can see the rifling marks on the ogive of the bullet.

I know there is a better way to do it, but this is my cheap way.

 

[Texas10]

The method I use costs exactly ONE fire formed case and will measure to touch within .001. I'll PM you the details if you like.

 

[Texas10]

PM sent

 

[Bart B.]

308's erode the throat further down the barrel about .001" every 30 to 40 shots.

Can you see accuracy degrade if you don't "chase the lands" seating bullets to keep up?

 

[Howland]

The method I use costs exactly ONE fire formed case and will measure to touch within .001. I'll PM you the details if you like.

Could you post that method? Inquiring minds want to know. Thanks.

 

[Bart B.]

You'll be more precise if you measure catridge base to ogive with your modified case and your loaded rounds, and use a VLD type seating stem, but you're on the right track and it's your only option if you don't have a comparator.

Is the case base (head) against the bolt face when fired?

 

[Texas10]

Could you post that method? Inquiring minds want to know. Thanks.

I start with a fire formed and properly sized case just as you would prior to loading. Drill and tap the flash hole 6-32 (in my case) because I use a portion of a 3 piece, "el cheapo" cleaning rod you can buy anywhere. That requires a 5/64 drill and 6-32 tap. Quick and easy, don't worry if it's not perfectly straight.

Starting with a clean chamber and throat, screw the tapped case on the rod and slide it up into the chamber with a firm push. Now retract and feel for any resistance. Rotate it 1/4 turn and slide in and out. You're checking fit of your sizing methods to the chamber and determining if the neck is off axis with the case. Any drag must be investigated and corrected as it will give false indications later on.

Now seat a bullet long into the case, and again slide it into the chamber with a firm push. Now retract it noting any tendency to stick in the lands. Any tendency to stick indicates the bullet is jamming into the lands. Gradually seat the bullet further into the case (shorten the OAL) until you find the point where the tendency to stick ends. You should be able to repeatedly check and get same results to within .001-.002 with your CBTO tools.

You can also use the Hornaday tool and modified case for this check by FL or Neck sizing it beforehand. The shortcoming to this is that the modified case is not formed to your chamber and the CBTO distance will be slightly different.

Save this dummy bullet (tool), labeling it accordingly for future checks. I use a new one for each new bullet or lot. If you buy your bullets by the thousands, you can use this tool to check throat erosion knowing you've eliminated all variables in your measurement and are getting a true assessment of erosion.

In the end, this is just a starting point for loading. As long as your method is consistent and repeatable it is adequate for the job. But because I want to know exactly how much my barrels throat erodes, I chose this method for its accuracy. Those with custom actions use a different approach however, I see no reason that this method will not work as well in custom actions.

I hope this helps.

 

[Zero333]

This video will show you how to find the lands exactly with out any special tools.
(thanks Alex Wheeler for making this video a few years ago)

If you have a Savage Action with a floating bolt head, it's best to tape the sides of the bolt head cross pin (that holds the head to the body), so the pin doesn't wiggle out. That's because once you take the firing pin out of the Savage bolt, the cross pin can freely wiggle out.

 

[Howland]

Is the case base (head) against the bolt face when fired?

The head is only truly flush against the bolt face at ignition with a fully expanded case, otherwise the ejector will push the case forward until the case shoulder is in contact with the chamber shoulder, leaving any gap between bolt face and head.

 

[CharlieNC]

Those and many bullets like .020 or more jump, so you should not have any problem getting an accurate load that fits the mag.

 

[Bart B.]

The head is only truly flush against the bolt face at ignition with a fully expanded case, otherwise the ejector will push the case forward until the case shoulder is in contact with the chamber shoulder, leaving any gap between bolt face and head.

What about bolts that don't have those ejectors? Or if it's removed and not used?

 

[Howland]

What about bolts that don't have those ejectors? Or if it's removed and not used?

If there is no ejector pushing the case forward (all my rifles have them and I have no reason to remove them), then your head may be flush against the bolt face. My thinking is, unless you're neck sizing only and using a crush fit, whether you're bumping back 0.002" or 0.004" or whatever your pleasure, that gap is either at the shoulder or the bolt face. If you've got an ejector pushing, well, that kind of narrows it down.

 

[Bart B.]

If there is no ejector pushing the case forward (all my rifles have them and I have no reason to remove them), then your head may be flush against the bolt face. My thinking is, unless you're neck sizing only and using a crush fit, whether you're bumping back 0.002" or 0.004" or whatever your pleasure, that gap is either at the shoulder or the bolt face. If you've got an ejector pushing, well, that kind of narrows it down.

With a rimless bottleneck case with its shoulder bumped back a couple thousandths....... or with less headspace than chamber...

Doesn't a 2.5 ounce firing pin pushed 9 fps by a 26 pound spring drive the case shoulder hard into and against the chamber shoulder on those headspacing on their shoulders? Then dent the primer and fire the round so positioned?

 

[Medic505]

308's erode the throat further down the barrel about .001" every 30 to 40 shots.

What brand of barrels do you shoot? They must be made of something other than I shoot. I've never experienced erosion of that magnitude. The barrel I'm currently shooting has 2200 rounds and has only eroded 0.010. Bartlein 5r, heavy varmint, Berger 200 hybrids@ 2650 + or - a few...

 

[Texas10]

This video will show you how to find the lands exactly with out any special tools.
(thanks Alex Wheeler for making this video a few years ago)

If you have a Savage Action with a floating bolt head, it's best to tape the sides of the bolt head cross pin (that holds the head to the body), so the pin doesn't wiggle out. That's because once you take the firing pin out of the Savage bolt, the cross pin can freely wiggle out.

I found this doesn't work with a Savage action, even taped. The Savage bolt just isn't as smooth as a custom. Besides, I can ascertain CBTO to lands on a half dozen bullets in the time it takes to tear down and reassemble the bolt for the Wheeler method. After you've mastered the method, it goes pretty quickly.