Pressure

[Ruskin]

I am trying to work on a paroblem I have with a 6.5x55 round.  I initially had a swede.  I had a 110 DL made into a 6.5.  It has a shllen barrel. 

I have looked at the primer and it is not flattened.  However, around the primer on one side it looks like there is rubbing of bolt face.

I have some brass that I neck sized after shooting in Swede which will not chamber in the made rifle.  I have concluded the new chamber is closer to specs than the older swede.

If pressure is building up? Why?  If I download powder and pressure is lowered so as not to cause the spent cartridge to rub on the bolt should speed still be up there?

[wncchester]

"I have looked at the primer and it is not flattened.  However, around the primer on one side it looks like there is rubbing of bolt face."

Actually, it requires a LOT of over pressure to make much difference to already flat primers.  If the bolt face marks are too small for you to be sure that's actually what they are, you are probably fine.  If the pressure was truly excessive I doubt you would have any question of what it is, and it would almost certainly be over the full face of the cap and not just on one side.

"I have some brass that I neck sized after shooting in Swede which will not chamber in the made rifle.  I have concluded the new chamber is closer to specs than the older swede."

Maybe.  But specs have a  tolerance, minimum and maximum.  All you can see now is the your new chamber is indeed smaller than the original.  But, you would encounter the same variables between any two new factory rifles as well.

"If I download powder and pressure is lowered so as not to cause the spent cartridge to rub on the bolt should speed still be up there?"

Decreasing chamber pressure will decrease velocity, every time.

[Lone Star]

...If the bolt face marks are too small for you to be sure that's actually what they are, you are probably fine.  If the pressure was truly excessive I doubt you would have any question of what it is, and it would almost certainly be over the full face of the cap and not just on one side...

This is absolutelty not true.  What the OP is probably seeing is the shiny spot left when high pressure has extruded the case head into the ejector hole - opening the bolt polishes the case in a round area the size of the ejector.  This is a common indication of very excessive pressure.    He is WAY overpressured and needs to back off on his load right now!

The pressure is high because he has used too much powder, or the wrong type.   The velocity does not matter if the pressure is too high.   It would be helpful if the OP tells us the exact load he used. 


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[wncchester]

"What the OP is probably seeing is the shiny spot left when high pressure has extruded the case head into the ejector hole - opening the bolt polishes the case in a round area the size of the ejector."

Read the OP again, and perhaps what I said also.  What HE SAID was he has a SMALL "rubbing" around the PRIMER, not the case head adjacent to the primer, nor did he mention any "extrusion" into the ejector hole, which not all rifles have anyway, and that is not located very close to the primer and that would be a second observation.  So, by it's absence, I assume it's not there.

In other words, I answered the man's question based on his own observation, not your intrepretation of what he may have, or "probably", meant but you assume he failed to mention.  I'm simply trusting his intelligence and figure he said what he meant well enough, was that not good enough?

It does indeed take some exceptionally high pressure to extrude brass into an ejectory hole/slot but the signs are generally obvious, it's not "Gee, is that really a brass extrusion or not?" sort of thing.  In the total absence of any other pressure sign (highly flattened cap, swollen head or enlarged pocket, sticly extraction, etc.) I think you are reading far too much into a small rub on a primer.

Reading an occasional magazine article is nice but we do need to correctly interpret and then apply what we read.

But, it's all free here anyway. 

[Ruskin]

I have thought about chrono test.  What puzzles me is why the chamber would make a difference in pressure.  Is it because the bullet when exiting is retard or restrcit more than the older rifle?  if pressure is too high then dropping pressure should drop velocity; however, the velocity should drop into specs of the 6.5.

[Lone Star]

There must be a reason you are concerned about high pressures or you would not have mentioned it.  Does it take some effort to open the bolt?  It certainly appears that you are experiencing excessive pressures (bright spots on the case head can be a pretty clear indication), and the cure is to use less powder, or a different powder.  High pressures usually mean higher velocities, but the relationship is not always linear.  Once again, it would help if you told us the load you are using. 

The throat of the chamber can make a dramatic difference in chamber pressures.  Loads developed in a rifle with a long throat will show high pressure signs - like yours does - if fired in a rifle with a short throat.

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[Graybeard]

I HATE these kinda questions. Yes I do understand why folks ask them and it would be nice if someone could really give you a proper and correct answer but quite honestly no one can unless they have the rifle in hand and are able to experiment with it. Even then unless they have proper pressure measuring equipment they can at best give you a WAG not even a SWAG.

There are NO RELIABLE pressure indicator signs  you can look at and go by to tell you pressures are OK. When REAL signs of pressure develop and display the pressure is usually so far in excess of what SAAMI pressures are there is no really reliable way to know how far to back off.

It might be you have no problem at all. It might be your pressures are such that if you continue your rifle will come apart on you. The problem is there is no real reliable way to know which. If you've studied several reliable reloading manuals and your load is within normally accepted safety limits the chances are all is OK. If you are above those levels then chances are all is NOT OK. To be brutally honest that really is all any of us can tell you or tell with our own rifles even tho many of us still think we're experts and can tell everything just by looking at a case. HINT: They can't.

Is pressure building up? Yes most definitely and without it the bullet won't exit the barrel. How much is it building up? That can ONLY be told by use of pressure measuring equipment.

If you back off the powder will velocity reduce? You better betcha that's the way it works.

[stimpylu32]

I am trying to work on a paroblem I have with a 6.5x55 round.  I initially had a swede.  I had a 110 DL made into a 6.5.  It has a shllen barrel. 

I have looked at the primer and it is not flattened.  However, around the primer on one side it looks like there is rubbing of bolt face.

I have some brass that I neck sized after shooting in Swede which will not chamber in the made rifle.  I have concluded the new chamber is closer to specs than the older swede.

If pressure is building up? Why?  If I download powder and pressure is lowered so as not to cause the spent cartridge to rub on the bolt should speed still be up there?

Lets see if this helps , first off the old Swede would have a larger chamber as do most Mil. rifles just to make chambering a round in battle easier , so your sporting rifle will have a tighter chamber as you will not be shooting 100s of rounds in a hurry between cleaning .

As for the shiny spot it could be just a case of the bolt face not being perfectly aligned with the chamber , it does happen , and for the powder drop reducing pressure , sure it will , also the speed will drop , unfortunately there is no direct correlation between 1 grain of powder = 100 fps , it just doesn't work that way .

As Bill has said , if your with in the listed data for the round that your shooting and the bullet comes out of the rifle you may be looking for a problem that just isn't there .

stimpy