can a tight chambered neck cause high pressure

C

crout

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It seems most loads i've been firing from my 6.5x55 shilen barrel have some good pressure signs on the primers. can a tight necked chamber cause this?

i'm guessing it's a tight neck becasue when i fire a round i can pretty much seat another bullet without having to neck size it. I cannot force a bullet into the neck with my fingers. every other rifle i have owned and reloaded for the bullet could be easily pushed into the neck with no effort.
 
Yes. You should have 2-3 thou of clearance - sounds like you don't.

You need to do a chamber cast and probably either neck ream your brass or open up the chamber neck.
 
Just a suggestion, why don't you use an outside neck turner or a reamer to remove a few thou off of some of your cases and try them. If the problem goes away then you know what your up against.
 
Tight Necks

I use fitted necks on a 6PPC bench gun, and on two 6.5x55 F-Class. There is about 1.5 thou clearance and fired cases will not accept a bullet inserted by hand. All my cases are neck-turned. A reamer is used to remove the "doughnut" that sometimes occurs.

A person has to watch this, because any neck thickening will upset things and cause high pressure.
 
Crout:

Please see a gunsmith before you blow yourslf up. Tight necks can cause catastrofic failure. We can help if the chamber diameter is known and it sounds as if neck-turning is required.

Regards,

Peter
 
i've got an outside neck turner coming in the mail. so we'll see how that works. but for now the gun will sit. it kind of sucks because i'll probably have to redo all my load development.
 
If the Shilen barrel was chambered by the maker, it seems very strange that it would be delivered with a tight neck.
I don't think it is unussual not to be able to push a bullet into the fired neck of the case, with just your fingers.
It sounds like you are guessing at pressure, by the look of the primers, only. Of all the signs a shooter looks at to judge pressure, the primers are the iffiest way of all. If there is no sign of bolt stickage, whatsoever, I wouldn't be too concerned about overly high pressure.
I would take out the bolt, stand the rifle on its barrel, then drop a loaded round into the chamber. If the cartridge dropped full in, by its own weight, I would think the neck would not be too tight.
I think a quick trip to the gunsmith would set your mind at ease.
 
Since I wrote the above post, I tried pushing bullets into the fired cases, with just my fingers.
The 30-06 cases I tried would all accept the bullet by hand.
About one in three random 270 fired cases would not accept the bullet.
Of the 243 cases I tried, fired in a 77 Ruger, none would accept the bullet by hand.
 
I believe most gunsmiths would(should) stamp on the barrel neck dimensions if other than SAAMI. Tight necks are used for accuracy gains requiring neck turning of the case.
 
I had this issue with my new 6.5-08 barrel. I had necked down Lapua .308 brass and did not turn the necks enough.

The result was 2 blown primer pockets and the extractor groove that should measure .403 (I believe) now measures .416

The reamer was made based on Winchester brass that already has a .013 neck wall thickness, the Lapua brass necked down measured about .016 thick so I now have it turned to .0135

Have a gunsmith look at your chamber and he should be able to tell you what your loaded round should measure at the neck. Give yourself .003 clearance. For example, if your chamber is .293 your loaded round should measure .290 which gives you .0015 clearance on either side.
 
The Shilen reamer for the 6.5 should be saami. I just got another barrel and new Lapua brass headspaces perfectly - drops into the chamber and stops just above the extractor groove perfectly.

Measure the diameter of your case with a bullet seated. This will tell you how thick your necks are. They don't need to be more then 15 thou.

I always outside neck turn my brass and this also ensures I have enough clearance.

Many BR setups have it tight enough that the bullet will not go into a fired case by hand. As long as there is clearance for the bullet to release properly ( 1 to 2 thou per side), how much it springs back is really up to the end user.

How is the velocity of your loads? That is a decent indicator of pressure. Flattened CCI primers are also very good.

Jerry
 
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