pressure problems

W

woodbutcher

Guest
I am loading for 300 WSM . I had a bolt click so I decided to stick the barrel in the lathe and polish the rear of the chamber with 400 grit paper. The reamer had tight dimensions which I now know was not a good thing. I put the rifle back together today and shot a load into a bank. The extraction was ok but the case had a pronounced ejector mark and the primer pocket was stretched; no way to reload. This was a minimum recommended load and the very same load that had been shot before with no bad signs except the bolt click. Any recommendations?
 
Two Things

By "polishing" the chamber, you might have made it so slick that the case no longer grips the chamber, slamming back against the bolt face. Second, there might not have been anything wrong in the first place, and by polishing the chamber, you actually now have made it too big.

There is always the possibility that the 'click" in the beginning was telling you that the load was too hot, regardless of what a loading manual says. The barrel might be a little on the tight side, or whatever.

Remember, every barrel is different. Loose primer pockets can be caused by two things, a chamber that is way too big, and too much pressure........jackie
 
I did a limited amount of polishing; virgin brass is still slightly tight in the chamber. The chamber is certainly slicker than it was at the head forward about 1/2 inch. The headspace is the same,almost zero headspace, bolt will not close on a go gauge.
 
Last edited by a moderator:
woodbutcher said:
I did a limited amount of polishing; virgin brass is still slightly tight in the chamber. The chamber is certainly slicker than it was at the head forward about 1/2 inch. The headspace is the same,almost zero headspace, bolt will not close on a go gauge.
Click to expand...

My experience...

The bolt should close on a go gauge. If it does not you will usually have problems sizing your fired brass.

Bolt 'click'... you should not have bolt 'click' on lifting the handle on unfired rounds... if you do the chamber is too tight in diameter on the rear of the brass. If you do not have bolt click on the unfired round but when fired the 'click' occurs, the load is too hot.
 
No bolt click on unfired rounds. When I reamed the chamber I checked it with several pieces of virgin brass. After the brass is fired I check it with a stoney point gauge to make sure I do not push the shoulders back. This is a high pressure chambering I probably should have never messed with it; shooting 125 grainers out of slow twist barrel. Supposed to get around 4000 fps. I did throttle back on the load to try and save wear and tear on my norma brass and action, but there must be something about the bore diameter of this barrel that is not going to allow it to work.
 
alinwa said:
Jackie, in making this statement...... have you ever tried it? What's your evidence that a large chamber can cause primer pockets to expand?

al
Click to expand...

Al

Jackie doesn't need me to back up his statements but they are true under the right conditions. Back when guys first started messing with the 284 Winchester as the basis for long-range and HBR wildcats, they cut their chambers to .500+" because that was the nominal base diameter of the Winchester case. Well, it turned out that much of the new brass actually measured about .495" or less and when they started developing their high-pressure, high velocity wildcats, primer pockets started loosening. Barrels were re-chambered to more closely match the actual brass dimensions and everything was hunky-dory.

This all came back to bite them in the a$$ when the new 6.5-284 brass came out in the late 1990s. That brass actually did measure .500" and couldn't be used to make the better quality cases that we'd been waiting for. Some shooters persevered and rechambered once again but most, like me, said to heck with the whole idea and turned to different cartridges.

Ray
 
Cheechako said:
Al

Jackie doesn't need me to back up his statements but they are true under the right conditions. Back when guys first started messing with the 284 Winchester as the basis for long-range and HBR wildcats, they cut their chambers to .500+" because that was the nominal base diameter of the Winchester case. Well, it turned out that much of the new brass actually measured about .495" or less and when they started developing their high-pressure, high velocity wildcats, primer pockets started loosening. Barrels were re-chambered to more closely match the actual brass dimensions and everything was hunky-dory.

This all came back to bite them in the a$$ when the new 6.5-284 brass came out in the late 1990s. That brass actually did measure .500" and couldn't be used to make the better quality cases that we'd been waiting for. Some shooters persevered and rechambered once again but most, like me, said to heck with the whole idea and turned to different cartridges.

Ray
Click to expand...



OK Ray, so clue me in here.... you're saying that "cutting the chambers closer" somehow contains the casehead when it expands, which then springs back?

I've got series' of reamer cut progressively larger from only .002 over virgin brass to .009 over...... in two chamberings.....

I've also had boltfaces fitted based on this sort of information...... I listened, I spent the money, I lost the money.....

I cannot duplicate these results using Norma, Win nor Lapua brass in any of the common cases (.243/308, 30-06, 6PPC/BR, 22-250) so I can't see what's so special about the .284 case? IMO the .284 case went away for entirely different reasons.

All I've EVER gotten from tight fitting is frozen or tight cases.... at best the dreaded click.

I now purposely chamber .007 to .009 over my chosen cases.

Ain't the first time I've disagreed with perty much everybody on the BRC board.... :)

al
 
al

Yes, you first determine what brass you are going to use, buy a barrel's worth, measure it, and then chamber to fit. It's called a tight butt. If you switch brands of brass you may, or may not, get away without problems. Most Benchrest chambers, both point blank and long range, are cut with both a tight neck and a tight butt. Or, maybe better terms are fitted necks and fitted butts, but tight butt sounds better.;)

Some brands of brass that are notoriously soft, such as Norma, require special attention while hard brass such as Lapua is more forgiving.

The 284 case hasn't gone away quite yet. The Winchester made 284 cases are still around but few, if any, Benchrest shooters use them. The 6.5-284 is what's used.

Ray
 
I am puzzled how a tight chamber diameter would cause the primer pocket not to expand while a looser chamber diameter would cause the primer pocket to expand.

The pressures should run slightly higher in the tight diameter chamber. The primer pocket is equally unsupported in either chamber.

Explain the theory please.
 
It's not a theory, it's a fact.:rolleyes:

Dig out the old issue of PS and find the article where Bill Shehane was developing his 6/284 with the old W brass. Read all about it there. Then call Bill and tell HIM it was all his imagination or an optical illusion.

If you don't believe that it happens, then don't.:cool:

Ray
 
Last edited by a moderator:
Cheechako said:
It's not a theory, it's a fact.:rolleyes:

Dig out the old issue of PS and find the article where Bill Shehane was developing his 6/284 with the old W brass. Read all about it there. Then call Bill and tell HIM it was all his imagination or an optical illusion.

If you don't believe that it happens, then don't.:cool:

Ray
Click to expand...

I don't have any old issues to find the article in...

so I guess I need the facts explained.

I am puzzled how a tight chamber diameter would cause the primer pocket not to expand while a looser chamber diameter would cause the primer pocket to expand.

The pressures should run slightly higher in the tight diameter chamber. The primer pocket is equally unsupported in either chamber.

And does this happen with brass other than old Winchester .284 brass necked to 6mm?
 
I just got off the phone with Bill Shehane.........


We do agree on this, fireform first with an "80% load" and then a "90% load" and then proceed with your work-hardened brass to keep your primer pockets solid.

Also that chambers may be "too tight".......

I guess all y'all's out there looking to spec reamers had best just read between the lines. I'm not going to argue with Ray Meketa. (I've had the argument before with many others....)

good luck all

al
 
I am not trying to argue with anyone either... I am trying to understand the reasoning behind what is being said.

I don't understand the relationship the diameter of the chamber has on the unsupported primer pocket if pressures are equal. I understand how excessive pressure distorts the pocket.
 
I can tell you I got some major pressure problems after polishing the chamber. I probably did not go much more than a .001. I did use some oil on the sandpaper; I wonder if some of the oil burnished in the metal.
 
woodbutcher said:
I can tell you I got some major pressure problems after polishing the chamber. I probably did not go much more than a .001. I did use some oil on the sandpaper; I wonder if some of the oil burnished in the metal.
Click to expand...

That would not have changed the actual pressure... any oil in a chamber is not a good thing though.
 
Clean the chamber with lighter fluid.

Start your load workup from scratch USING A CHRONOGRAPH and weighing your charges and I'm quite certain you'll find your maximum achievable velocity to be unchanged.

The question of whether or not a polished chamber holds the brass from sliding MORE or LESS than say a 240 grit finish is not easy to answer, there has been much long and convoluted discussion on the subject.

It is currently my belief that the most slippery surface (lowest slippage coefficient) between brass and steel occurs with the steel polished to around 320grit.

As always, others' opinions will vary.

As always, these opinions will be based on various experiences.

facts are hard

al
 
You must log in or register to reply here.
Back
Top