Projectile too close to lands ?

[Martin52]

One round in a batch of reloads would not chamber. All others were OK. Followed my usual reloading procedure, no changes there, just curious as to the likely cause - irregular projectile ?? I have not yet disassembled the round until I first eliminate queries that need to refer to the loaded round.

308 Lapua case (first firing unturned,)
Once fired, FLS, then neck turned and neck sized (arbor press, Wilson die 334 bushing)
Dyer HBC 155 gr projectile seated 30 'thou off the lands. Projectile measures .3075.
Loaded round measures 0.3355 at the case neck.
Case trim length 2.005.

Just below the red arrow you will see marks on the projectile that go all the way around, this indicates to me it touches the lands, but this does not reconcile with my measurements..and no other rounds were problematic.

Martin.

 

[Martin52]

Here's another image.

 

[Terry]

Are you shooting a compressed load?

 

[Martin52]

No Terry, I am using 46.0gr AR 2208/Varget.

 

[Terry]

How does it measure base to ogive?
Is it longer than the others?

 

[cjmac]

Well it might be hard to chamber or not.chamber at all . Its kinda a old trick but i know some people. That seat there bullets long so thay are in the lands ,thay say it gives them a uniform start pressure. I just use a very lite crimp. It helped my groups shrink. And i have a very long jump to lands

 

[Martin52]

I think that's OK if soft seating, in my case the neck tension in the loaded round is greater than when soft seating and so prevents the projectile from being pushed back, (if it touches the lands). This particular round does not chamber, tried twice and left it at that, did not want a loaded round stuck on the chamber with no bolt close.

 

[Martin52]

How does it measure base to ogive?
Is it longer than the others?

Terry - I will check that when I disassemble the round, just holding off doing that until I eliminate queries that require the loaded round. i sort my projectiles using Bob Green's comparator - no guarantees of course, but this one might have slipped through.

 

[Terry]

Martin

Don't take it apart. Measure it and one that fits. Maybe it's longer.
If it is, the next question is why? If the base to oglive is the same, the base to case shoulder is next to check.

 

[lrgoodger]

How does the runout on that round compare to the others? The marks are not from the lands. They are from the mouth of the freebore. I've had tight chambers make these marks on a bullet that would not chamber if the bullet was crooked by as little as 6 or 7 thousandths on runout. I then took the round apart, full length sized the case and put it back together with the same bullet and it would chamber fine once it was straight enough.

 

[Martin52]

Martin

Don't take it apart. Measure it and one that fits. Maybe it's longer.
If it is, the next question is why? If the base to oglive is the same, the base to case shoulder is next to check.

OAL on the round is 2.808 and that's generally consistent with the rounds that do chamber.

Will check base to ogive length when I take it apart.

 

[Martin52]

How does the runout on that round compare to the others? The marks are not from the lands. They are from the mouth of the freebore.

Run out is not bad - less than 2 thou, just checked this on my Sinclair gauge.

I am beginning to think this round may have been left seated long (when I can, I seat long and do the final seating the night before a match). Neck tension, though not excessive, did not allow the projectile to soft seat but 2 attempts at bolt closure did push it back somewhat, but still not enough to chamber.

 

[Shynloco]

Martin,
Have you checked the casing itself for sizing in your chamber? Not being able to chamber a finished cartridge can involve several issues and MAY not be your bullet seating depth at all. I use RCBS Precision Mics to check every casing I reload for to see if there is a shoulder bump issue before ever getting to working on the necks and neck tension issues. Also check the bullet for sizing as every once in while there's an oddball bullet in the pack. Just a thought.

 

[Martin52]

The marks are not from the lands. They are from the mouth of the freebore.

Thinking further about your comment - I have about 1800 rounds through this barrel without a problem, is it possible there's now a carbon ring building up around the mouth of the freebore?

 

[Martin52]

Martin,
Have you checked the casing itself for sizing in your chamber?

Shynloco, the case checks out OK, it was full length sized in my Forster die (custom 0.3345 neck) along with all the others and its shoulder was set back similar to the other cases. I have just verified this with my comparator. When I take the loaded round apart I should be able to examine/measure it more closely and can then chamber the empty case to test "fit".

Even checked that the projectile had not got swapped over from another batch (I use HBC's, 2156's and the Berger FB's).

 

[tclaunch]

If this was a new chamber, I`d suspect the reamer print had a tighter than norm freebore diameter, since it has 1800 rounds I feel it is carbon buildup. Get some Iosso and a 338 diameter nylon brush installed on a pistol rod with no bearing in the handle. apply the Iosso to the front 1/3 of the brush, push it in till it tightens up and start turning clockwise. It will clean up with a little time.

 

[243winxb]

irregular projectile

 

[Martin52]

Have disassembled the round and removed the primer. The empty case chambers easily so no problems there.

The projectile measures 0.575 base to ogive, most of the others are around 0.565-0.570 so this is one factor.

I then rechecked the chamber length using a Sinclair gauge. Past records indicate 2.023, but at present it measures 2.015 after repeated measurements. Suggests a carbon build up I think.

Will get to work on the chamber and give it a good clean, using Iosso and BT Eliminator.

I think that probably resolves this one, the round would not chamber because of the 2 factors combined - projectile irregularity and carbon ring build up.

Thanks all for comments and suggestions.

Martin

 

[lrgoodger]

The carbon ring typically referred to is not in the mouth of the freebore (it is at the tip of the chamber neck just ahead of the freebore mouth where the brush does not hit it because the bristles are being swept back when entering the freebore). That is not to say that you can't get a carbon buildup there, but it is doubtful since the freebore area is normally well cleaned right along with the bore.

The irregular bullet suggestion should be checked. measure the bullet to see if it is perhaps .0005 larger than the others in the scratched area. If you were indeed seated long that may have been the problem, too.

 

[dkhunt14]

If you don't clean good enough and don't work on the neck and throat area you can get carbon back of where the neck is cut in the chamber. Trimming cases too short can also really build up there. I let my guns soak between matches by keeping them wet with a patch ran through every day or so. It seems to keep the carbon out of there. You really should borescope to see. Matt