Bullet Seating Depth ID Issues

[mbeavers1]

Hi all:

I am new to the forum (and reloading!) and have some questions regarding determining the case head to ogive length in my Cooper m92 6.5x284 Norma.

The rifle is about 5 months old and have run 3.5 boxes of HSM Trophy Gold 140gr Berger VLDs through it with no apparent issues. Groups were ok, but not spectacular (est 1-1.5 MOA). I decided to improve accuracy and stop spending so much $$$ on factory ammo, that I would put together a reloading kit.

Everything is in place and in preparation for loading my first batch of ammo, I have run into an issue determining the correct seating depth for the Bergers. I have a Hornady OAL gauge with the appropriate bushings to measure my CH to Ogive length. I selected the correct modified case and inserted a new 140gr Berger Hunting VLD then proceeded to locate the lands. I was quickly able to locate the first point of contact so I started measuring. I took about 5 measurements to make sure everything was pretty consistent and came up with a CH to Ogive length of 2.272" but I could visually see that the bullet was seated FAR deeper in the modified case than the factory loaded HSM ammo. I measured the HSM ammo using the same set of bushings and came up with 2.388", a difference of 0.116"!!

At first, I had a hard time believing this would be true because factory ammo "should" be loaded short with a longer jump to ensure that it would fit into any firearm, so I began experimenting. First, I tried to visually locate the lands by coloring the bullet with a permanent marker and looking for scratches. I set my depth gauge to provide the same CH to Ogive length as the factory HSM ammo and loaded it. The bullet got stuck and had to be removed with a cleaning rod. The bullet showed very slight scratches that were ~0.125" long (hard to measure!!).

I proceeded to increase the seating depth (shorten the OAL) until the bullet stuck occasionally in the lands. To me, this is pretty darned close. The measurement came out at 2.278", which happens to be 0.005" different from my original measurement.

I am now pretty confident that my original measurement is good and the factory HSM ammo is way too long for my chamber. I realize this has the potential to be bad so I am concerned that I have run ~80 rounds through my gun. Luckily, no pressure signs have been observed but I am not going to shoot until I figure out what the issue is.

Has anyone ran into any issues with factory ammo being jammed this far? Does anyone see any other potential issues/errors that a Newb, such as myself, is not aware of?

 

[midnightmalloy]

It sounds like you are doing the right things. It's odd that the factory ammo is not sticking in the lands but the ammo you load to the same coal is sticking. Is the 140 berger in the HSM ammo loaded with the 140 vld or the 140 hybrid? Is the factory ammo leaving marks from the lands when you chamber it or just your reloads?

 

[mbeavers1]

It sounds like you are doing the right things. It's odd that the factory ammo is not sticking in the lands but the ammo you load to the same coal is sticking. Is the 140 berger in the HSM ammo loaded with the 140 vld or the 140 hybrid? Is the factory ammo leaving marks from the lands when you chamber it or just your reloads?

The factory ammo DOES stick when using the same CH to Ogive length in the modified case. The length I measured appears to be right on the edge (lightly sticks one time, then not the next). I am pretty sure they are all 140gr Hunting VLDs, but will double check. I do not remember buying anything else, but good point.

I didn't color a loaded, factory round and chambered it, but definitely will tonight.

 

[Mikecr]

What's the twist rate of this gun?
Maybe it was chambered for lighter/shorter bullets.

 

[mbeavers1]

What's the twist rate of this gun?
Maybe it was chambered for lighter/shorter bullets.

It is 1-8". The qualification rounds fired by Cooper were 142gr SMKs. I called Cooper today and they informed me that the CH to Ogive length of their handloaded rounds was 2.410"...which is a lot closer to the HSM factory ammo that what I measured in my chamber.

 

[Mikecr]

Ok, when you chamber HSM ammo and extract it, has it shortened in CBTO (soft seated)?

 

[Trnelson]

The factory HSM sticks into your lands when you try to eject a loaded factory round? That seems to raise a flag to me. The 142 SMK has a different shape than either of the Berger bullets. Do not base anything off of that CBTO measurement. Only believe your actual measurement of the actual bullet you are using in your chamber. It is what it is and it maybe too short and need professional work or a factory exchange.
Purposely seat a bullet long in a piece of your sized and prepared brass, color it with a sharpie and chamber it in your rifle. Get the bullet out of your chamber throat with a cleaning rod and carefully seat it to where the sharpie is scratched off by the case neck. Measure that bullet, that represents the exact CBTO length of your chamber. Nothing else is more than conjecture and comparison.

 

[mbeavers1]

The factory HSM sticks into your lands when you try to eject a loaded factory round? That seems to raise a flag to me. The 142 SMK has a different shape than either of the Berger bullets. Do not base anything off of that CBTO measurement. Only believe your actual measurement of the actual bullet you are using in your chamber. It is what it is and it maybe too short and need professional work or a factory exchange.
Purposely seat a bullet long in a piece of your sized and prepared brass, color it with a sharpie and chamber it in your rifle. Get the bullet out of your chamber throat with a cleaning rod and carefully seat it to where the sharpie is scratched off by the case neck. Measure that bullet, that represents the exact CBTO length of your chamber. Nothing else is more than conjecture and comparison.

The factory loads dont stick in the chamber if I load a live round and cycle the bolt. The bullets stick when using the Hornady Modified Case and a loose bullet. I was originally using only the Berger bullets when I noticed the issue. The seating depth was so different I could see it VISUALLY.

I colored the rounds just like you suggested and ended up with approximately the same distance I measured with the OAL gauge. I called Cooper and asked for the CBTO for the handloads they used to test fire my gun. They use 142gr SMKs so I went and bought a box of 142gr SMKs so that I could make a comparison to what they used. Coopers bullets measured 2.410" and I found the lands at 2.305". Cooper has requested that I send the rifle back. They are going to cast the chamber, measure it, and fix it as needed under warranty.

 

[Trnelson]

The factory loads dont stick in the chamber if I load a live round and cycle the bolt. The bullets stick when using the Hornady Modified Case and a loose bullet. I was originally using only the Berger bullets when I noticed the issue. The seating depth was so different I could see it VISUALLY.

I colored the rounds just like you suggested and ended up with approximately the same distance I measured with the OAL gauge. I called Cooper and asked for the CBTO for the handloads they used to test fire my gun. They use 142gr SMKs so I went and bought a box of 142gr SMKs so that I could make a comparison to what they used. Coopers bullets measured 2.410" and I found the lands at 2.305". Cooper has requested that I send the rifle back. They are going to cast the chamber, measure it, and fix it as needed under warranty.

Sounds like you are on the right path! Something is certainly not 'right' when you hit the lands at 2.305" and they fired it at 2.410" with the SMK. Keep us posted as to how things progress. Merry Christmas!

 

[Howland]

Purposely seat a bullet long in a piece of your sized and prepared brass, color it with a sharpie and chamber it in your rifle.

And I've been smoking them with soot from a candle.

Thanks for the tip.