Measure your 7mm 180 Bergers!!

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I was chatting with Mick McPhee regarding the F-Class Team bullet choice, and he was in the process of chambering a 284 Shehane for someone, who had also provided him with some 180 Berger VLD's.

He was measuring them and found that they were .2845!

This much difference affects the reamer needed for these bullets. An email from Berger revealed that Berger allows their bullets to go as large as .2848!!

Considering Sierra allows 2/10,000 tolerance, i found this a bit shocking. I am finding it harder and harder to love Berger these days.
 
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The problem is not accuracy but rather fit. The throat dimension of most if not all 7mm reamers is .2845. If the bullet is that big or bigger it's not going to fit into the throat of the gun. That will lead to problems with pressure, rounds not chambering or being squashed into the chamber, all sorts of bad ju-ju.
 
I have fielded a few emails on this topic and wonder if the variation at the 10 thou level has any affect on pressure at all.

how much variations in throat and bore dimensions does fouling cause from shot to shot?

How much does the expansion of the barrel steel have on pressures? Maybe the perfect set up is to get ever increasing bullet diameters using the "big ones" later in a relay?

What if you shoot faster then normal? What if you have a slow puller and have to shoot slower?

You know that you should have kept case 6 in the fire a bit longer.....

Loaded ammo on a rainy day....Bad?

Did I leave too much time between sizing and seating the bullet?

Should have lubed the seater spring one more time.

Are the primers in this new box really the same as the last one?

I look for holes in paper. If the groups are small, and consistent, focusing on doping will have a much larger affect then a whole host of stuff.

Shooting is a very mental game. cloud it with all manner of things to worry about and your results are likely to slip.

As long as all the bullets in the same lot are the same size, you will adjust your load accordingly to account for whatever the variations are in the components.

Remember start low and work up when changing ANY component????

I am not saying Bergers range of tolerance is good or bad. I simply have never measured and tested. But I know that their overall consistency continues to exceed my expectations so I continue to shoot them.

And I have access to just about anything.

Jerry
 
Great. I have two boxes of Berger 180 VLD for my 7mm WSSM. :(
I really hope it doesn't make any difference.
 
PG is right. Palma shooters use barrel 2-3.5/1000" under-sized as a matter of routine, in fact it makes some bullets work better. It isnt the fit in the barrel per se, it is the throat. Many people do order minimum clearance throats (3 of us from KTSA were using .264 throated 6.5's) but this would be pretty much impossible with 180 Bergers, at least without measuring bullets and making sure your batch fits.
 
A few ten thou at the base of the bullet makes no difference, other than perhaps the selection of the bushing in use. Any decent match bullet has this pressure ring. Some mfgs will run the bullet through a final sizing die to remove the pressure ring, but why bother other than cosmetics? As Jerry notes, the heat of your hand, or a warm day will swell the bullet a few ten though anyway. The heat of the chamber for sure will cause the bullet to swell.

There is one problem I would be more concerned with, that is the problem of having the pressure ring drop below the neck when seated, in which case you may end up with a looser grip on the bullet than you planned for. Usually the elasticity in the neck will cover you for adequate grip, but not always. Especially if you are using a compressed load.

If you are running tolerances so close that 5 ten thou (.0005") becomes an issue, you are into the realm of the "fitted neck", which all but the most dedicated BR experimenters gave up long ago. Basically too much work to set up, and minimal if any results on paper. There is a trend back to looser necks, in the .003" range now.

I gave up measuring pressure rings on BR bullets, but when I did measure 6mm's they ran .2433" to .2436" on the pressure ring. It is actually very difficult to measure to the tenth of a thou' using commonly available instruments. You really need a controlled environment and lab grade equipment. I consider my efforts highly suspect as you could measure the same bullet over and over and get different results.
 
prairieguy said:
The problem is not accuracy but rather fit. The throat dimension of most if not all 7mm reamers is .2845. If the bullet is that big or bigger it's not going to fit into the throat of the gun. That will lead to problems with pressure, rounds not chambering or being squashed into the chamber, all sorts of bad ju-ju.
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I am afraid I disagree here. There is no way a copper and lead projectile with a 50,000+ psi sledgehammer behind it will not be swaged down an extra .0005" if required. I am sure the pressure rise caused by the rifling engraving the jacket far exceeds what we are talking about here.

The only concern I would have is failure to chamber. Has this become an issue recently with 7mm's? If so I haven't heard about it.

The bullet itself will begin to slump (obturate) on acceleration and any measurements to the ten thou' will be tossed out the window.
 
prairieguy said:
The problem is not accuracy but rather fit. The throat dimension of most if not all 7mm reamers is .2845. If the bullet is that big or bigger it's not going to fit into the throat of the gun. That will lead to problems with pressure, rounds not chambering or being squashed into the chamber, all sorts of bad ju-ju.
Click to expand...

I had word the other day from the owner of the .284 Shehane that it is shooting 3/4" at 100 with zero load development and still fire forming the .284 brass. Chambering does not seem to be a problem and it was his lot of bullets that measured .2845 (Same dimension as the reamer throat) and caused the emails to Berger.

I have 2 boxes of an older batch that I measured at .2842 at the pressure ring.

I am chambering my 7mm in the same configuration with the same reamer so we will see what happens with the 180's when I get my hands on some newer lots.
 
rpollock said:
I am afraid I disagree here. There is no way a copper and lead projectile with a 50,000+ psi sledgehammer behind it will not be swaged down an extra .0005" if required. I am sure the pressure rise caused by the rifling engraving the jacket far exceeds what we are talking about here.

The only concern I would have is failure to chamber. Has this become an issue recently with 7mm's? If so I haven't heard about it.

The bullet itself will begin to slump (obturate) on acceleration and any measurements to the ten thou' will be tossed out the window.
Click to expand...

The issue is if the bullet is bigger than the throat this may prevent you from reaching the lands and the throat could push the bullet back into the case causing accuracy issues and not a safety/pressure issue.

I personally am not too terribly worried about this latest "issue"....if I was I would be looking to a different bullet manufacturer.
 
Jim Bullock, who may add to this, had lab-pressure tests conducted which showed that tight throats effect pressure more than other factors. Dr. Kolbe, Border Barrels, did work on this and there may be info on their site.

Regards,

Peter
 
Are we talking about the pressure ring or are we talking about the bullet body? Ian's e-mail at the top included an e-mail from Berger, referencing the pressure ring. Looks like this quote has been removed now. This should be cleared up, otherwise the discussion makes no sense. The pressure ring resides in the cartridge, not the throat.
 
rpollock said:
Are we talking about the pressure ring or are we talking about the bullet body? Ian's e-mail at the top included an e-mail from Berger, referencing the pressure ring. Looks like this quote has been removed now. This should be cleared up, otherwise the discussion makes no sense. The pressure ring resides in the cartridge, not the throat.
Click to expand...

The email from Eric mentions the dimension at the pressure ring.

"I reviewed the paperwork for the most recent lot and the diameter at the pressure ring (where the BT meets the bearing surface) is consistent with your findings at .2845."
Click to expand...
 
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