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338 lapua pressure? HELP PLEASE

 
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  #8  
Old 06-10-2011, 07:44 AM
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Re: 338 lapua pressure? HELP PLEASE

Im no expert either, but one step I have tried in the past is to try factory ammo and see if it replicates the problem with reloaded ammo. It would be my opinion that, if a factory round gives the same ejector mark, then you may not have a problem. If I had to pick a source of the problem, I would think that the chamber could be too polished causing the brass to be forced back into the bolt face too hard.

Hope this helps

Joel
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Old 06-10-2011, 08:22 AM
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Re: 338 lapua pressure? HELP PLEASE

Quote:
Originally Posted by aroshtr View Post
Im no expert either, but one step I have tried in the past is to try factory ammo and see if it replicates the problem with reloaded ammo. It would be my opinion that, if a factory round gives the same ejector mark, then you may not have a problem. If I had to pick a source of the problem, I would think that the chamber could be too polished causing the brass to be forced back into the bolt face too hard.

Hope this helps

Joel
I tend to agree except that if factory ammo does the same thing, you may still have a problem. Rather it's just not necessarily the ammo's fault.
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Old 06-10-2011, 09:42 AM
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Re: 338 lapua pressure? HELP PLEASE

After all of the comments I would check out the ejector. It sounds like it is to long or the retaining
slot is not long enough to let it move out of the way when the case comes backward.

In order to head space a cartrige correctly you "must" remove the ejector first to prevent false
readings with the head space gauge.

If this is not done you could end up with excessive head space and high impact velocities with the
case head striking the bolt face.

I would have trouble believing that this is normal. The ejector hole is drilled deep enough to allow
the ejector to recede just below the bolt face but not far enough to allow it to much travel creating
a crater for the brass to flow into.

When re facing the bolt face you must check the plunger length to make sure it will retract enough.

So if you are getting a ejector mark that is bright(The case is shaved while extracting) there is
pressure from some problem because the brass should not extrude into the ejector hole with normal
pressures.

If there is a dimple in the case head then there is a good chance that the head space is to much or
the ejector is not set up correctly as long as pressure is not excessive. and shooting factory ammo
tells me that pressure is not the problem as long as everything else is correct.

Don't give up looking, because something is just not right. and just because it is a custom action
does not automatically rule out any possibility that there is not something wrong with it.

It is hard to trouble shoot a problem without actually looking at it (Kind of like when your wife
tells you the car is making a funny noise).

I hope some of this gives you some ideas.

J E CUSTOM
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  #11  
Old 06-11-2011, 03:22 PM
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Re: 338 lapua pressure? HELP PLEASE

Quote:
Originally Posted by Edd View Post
I'd be interested in seeing some data showing that the tension from a .015" inch ring of brass gripping the bullet can dramatically raise the pressure.
Reload some ammo two different ways using a full length sizing die with an expander ball. Pay particular attention to the force needed to seat bullets in each method.

Load two rounds the way you normally do.

Load two more rounds the same way, but don't use an expander ball on the decapping stem. If you have to use one, use one a couple calibers smaller so it won't expand the sized down case neck. You might want to use an Easy Out turned clockwise to debur the case mouth so bullets will seat without too much trouble.

Shoot both rounds of each type noting pressure signs on each. Chronograph them to see the difference.
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Old 06-11-2011, 05:05 PM
Edd Edd is online now
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Re: 338 lapua pressure? HELP PLEASE

Quote:
Originally Posted by Bart B View Post
Reload some ammo two different ways using a full length sizing die with an expander ball. Pay particular attention to the force needed to seat bullets in each method.

Load two rounds the way you normally do.

Load two more rounds the same way, but don't use an expander ball on the decapping stem. If you have to use one, use one a couple calibers smaller so it won't expand the sized down case neck. You might want to use an Easy Out turned clockwise to debur the case mouth so bullets will seat without too much trouble.

Shoot both rounds of each type noting pressure signs on each. Chronograph them to see the difference.
I said I would be interested in seeing some data. I'm not interested in an R&D project. I already have more projects than I have time.
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  #13  
Old 06-11-2011, 10:59 PM
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Re: 338 lapua pressure? HELP PLEASE

Quote:
Originally Posted by Edd View Post
I said I would be interested in seeing some data.
Here's some facts; you may consider it data. Or heresay. Doesn't matter to me.

I suggested to two people years ago they should lap the necks out of their .308 Win. full length sizing dies to a few thousandths less than a loaded round neck diameter so expander balls were not needed. They instead just removed the decapping pin, full length sized some cases then loaded them normally. Both noted bullets seated harder. When fired, case head brass had extruded back into ejector holes in the bolt face. Their normal reloads didn't. Pressure was noticably higher.

I and others who seated Lake City match ammo bullets a couple thousandths deeper to crack the asphultum seal to get more uniform release force noted they needed another minute or two up on the sights for zeroing at 600 yards. While the cracked rounds had less elevation spread from more uniform muzzle velocity and therefore were more accurate, it was low enough below normal ammo zeros to make a difference. Pressure ring diameters from new case to fired dimensions was greater by a few ten thousandths with regular ammo; rounds with their bullets reseated just enough to break the seal had less pressure.

Someone mentioned that few thousandths extra jump made up the difference. So we pulled some "seal cracked" round's bullets back out a bit then reseated them to standard length. They shot the same as those seated a few thousandths deeper.

While not laboratory-grade testing and measurement, the difference was noticable to folks holding the highest NRA classifications for competition.
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