Finding "JAM" with seating depth

[savageshooter86]

Looking for anyone that can show me a good picture of what the marks on a bullet should be when you find initial"jam" on seating depth test.

Trying to understand this method that Tony B mentions in his book. Friend is trying this and we can not see any rifling marks on the bullet where they should be. It is a 95 Palma chamber and using 155 Berger bullets.

 

[BoydAllen]

Jam is the longest length that you can seat a bullet to, using the neck tension of a regular loaded round, without the bullet being seated deeper into the case, when the round is chambered. The best way to see marks is to wrap 0000 steel wool around the bullet of a loaded (or dummy) round, applying pressure with your thumb and bent index finger, and rotating the round so that fine marks are made on the bullet by the steel wool. (This will not hurt the bullet or its accuracy.) If you measure the loaded, or dummy round (Don't chamber loaded rounds unless the striker has been removed from the bolt, or you are at the range, with the rifle pointed down range, at the back stop.) before it is chambered, and it is shorter after being chambered and removed, you are at jam length, and if you did the 0000 trick, you should have no problems seeing the marks.

 

[Duster_360]

I shoot high power, but what I've done is to simply 'paint' a seated bullet with a black magic marker in a dummy round. Carefully load so you don't disturb the marker and then chamber the round. Likewise, slowly eject the round and grab it as soon as you can as it is removed from the action. The lands leave very clear marks on the 'painted' bullet. You will see the jacket where the marker has been removed by the lands and the contrast is pronounced.

You can apply fresh magic marker and continue if needed. When finished measuring, I use naphtha and remove the marker and then use the bullet in a fouling shot or sighter.

 

[Shynloco]

The lands leave very clear marks on the 'painted' bullet.

Try using a magnifying glass if you see nothing with the bare eye. If there are no marks, you haven't touched the lands or you have throat deterioration and it may be time for a new barrel.

Alex

 

[savageshooter86]

Thanks for the replys. We know what jam is but we were having difficulty seeing the rifling marks on the bullet. There is a perfect ring around the bullet that is very thin that looks like scratches and the rifling marks were blended in and difficult to detect.

Is that ring there from the small diameter of the freebore in chamber? I can try to post pics if it will help describe what we were seeing

 

[BoydAllen]

You probably have a carbon ring in the throat. Do you know anyone with a bore scope? With a clean barrel, start a tight patch about a foot down the barrel, and grasping the handle gently, with fingertips, slowly and carefully pull it back. If it hesitates at the throat, with a slight increase in the pull, that can be another indication. With a barrel that does not have a ring, you will not get the circle unless your freebore diameter is smaller than the bullet shank.

 

[AlNyhus]

Thanks for the replys. We know what jam is but we were having difficulty seeing the rifling marks on the bullet. There is a perfect ring around the bullet that is very thin that looks like scratches and the rifling marks were blended in and difficult to detect. Is that ring there from the small diameter of the freebore in chamber? I can try to post pics if it will help describe what we were seeing.

There are a couple of things that can cause the 'ring' you're speaking about.

-This is often seen in what's called a 'zero freebore' chamber...you see this quite a bit on 30BR's with theoretically 'zero freebore' chambers. In your application, I doubt if that how the 155's are throated, though.
- You can also see this if you're checking with a fired case that is sized a bit excessively, esp. at the shoulder. Or if you're using a new unfired case.
- It can also be from the throat not being perfect relative to the lands. On a perfectly aligned throat, you'll see the groove metal perfectly 'scalloped' between the lands...on every land. You'll need a bore scope to check this out.

If it's a new chamber, there can be some machining 'metal fuzz' where the freebore ends and the leade angle begins. This will go away in a few rounds. If the freebore diameter is too small, you'll see a scuff mark for as long as the freebore length is. Boyd's carbon ring is another thing to check, if it's a used barrel that hasn't been JB'd in a whle.

Just some things to check. -Al

 

[savageshooter86]

maybe Jeff will see this and respond. His barrel is "new" less than 200 rounds fired down it and brass is older brass. Bullets are the 155 Bergers so should be near perfect match to the 95 Palma reamer that was used

 

[A j shooter]

95 Palma chamber I believe it has .066 free bore . It's a 12 twist Kreiger.
Chambered by John Whidden . It is chambered for 150gr up to 168gr bullets.
Just having trouble find land marks on bullets if that makes any sense.
There is a bright ring around the bullet which I think is part of the freebore
I've never had any trouble finding jam in my other rifles . Laying all this aside the rifle shoots really good at the so call jam I found. It's really coming together .

 

[savageshooter86]

Can someone please help Jeff and I on this one. On dave Kiff's reamer which letter is the freebore length? A or B