Seating depth issues

[Bob3700]

I noticed quite a variation in bullet seating depth. Cases have been FL sized, necks chamfered n brushed, inside of necks are dusted with dry graphite powder. Cases are run over a mandrel that is .005” below bullet dia. Bullets moly coated. Seating dies are Redding Comp. And Forrester BR. Cases are annealed after 3 firings.

Am working with Berger 6mm 105 Hybrids in a 6 BR case. I am seeing seating depth variations of .010“ to .020” measured from the base of the case to the bullet ogive. I have a bbl. Chamber gauge the gunsmith made for me. This amount of variation seems excessive.

How do u maintain consistent seating depths.

 

[DaveTooley]

Do have a VLD seating stem in the die? You may be seating on the meplat instead of the ogive.

 

[AlNyhus]

It starts with the bullet.

You can measure the bullet base-to-ogive but a better way is to measure the forward section to the ogive.

For example, bullets made on the same point die can show different bullet base-to-ogive. But when they're seated, the case head-to-ogive will be virtually identical.

I'd suggest sorting your bullets until you get a group of identical ones, then seat them and use that to try and find if there's something else going on. Don't forget to check that the bullet tip isn't bottomed out in the seater stem. -Al

 

[Daddycaddie67]

Is the .005” dimension you mention neck tension? seems excessive. Could be ur problem. E

 

[CharlieNC]

If you also notice associated differences in bullet seating force, then you may need to anneal.

 

[Coyotefurharvester]

So you are using a stub barrel chamber gage cut with the same reamer? Can you measure the length of the brass with the stub? If you can measure the brass after sizing, do you get identical length measurement with/without the stub?

 

[marchx]

It's difficult to get exactly the same neck tension and subsequesntly exactly the same seating depth with 3x fired brass even if it's annealed. There will be variance in neck tensions, so you have to play with micrometer seater die. if you want to have consistency in seating depth.

 

[Bob3700]

My misprint on the mandrel diameter. It is .0005" smaller than bullet diameter. So, Technically, I have a 1/2 thou. neck tension (bullets are soft seated).
Al, I believe it has to be the bullet. I sort the bullets for bearing surface length and all are within .002" of each other. There is a ring on the bullets, in the ogive section from the seating stem. To my knowledge, I don't have a special seating stem, just the one from the factory. With the low neck tension, the ring on the bullets (visible on the moly coating) cannot be from neck seating pressure. The weight of the press handle seats the bullets.
In my 308, it could be a combination of low neck tension, and full cases of powder that the bullets are pushing on. I use a 6 inch drop tube on my funnel and try to get the powder to compact in the case as much as possible. The powder could be pushing the bullets back up with the low neck tension.
To get the same base of the case to the ogive of the bullet, I am working the seating stem on my die to hit the target OAL. It gets there and the target reflects good scores, but it is a lot of extra work to make them all OAL brothers.

 

[gunsandgunsmithing]

My misprint on the mandrel diameter. It is .0005" smaller than bullet diameter. So, Technically, I have a 1/2 thou. neck tension (bullets are soft seated).
Al, I believe it has to be the bullet. I sort the bullets for bearing surface length and all are within .002" of each other. There is a ring on the bullets, in the ogive section from the seating stem. To my knowledge, I don't have a special seating stem, just the one from the factory. With the low neck tension, the ring on the bullets (visible on the moly coating) cannot be from neck seating pressure. The weight of the press handle seats the bullets.
In my 308, it could be a combination of low neck tension, and full cases of powder that the bullets are pushing on. I use a 6 inch drop tube on my funnel and try to get the powder to compact in the case as much as possible. The powder could be pushing the bullets back up with the low neck tension.
To get the same base of the case to the ogive of the bullet, I am working the seating stem on my die to hit the target OAL. It gets there and the target reflects good scores, but it is a lot of extra work to make them all OAL brothers.

Inspect the seater stem for a very fine crack. If it's ok....use it for a gauge to measure where the actual stem being used contacts the bullet.

 

[liljoe]

If the neck tension is that light, can you push the bullet into the case with your fingers?
Or if the tension is that light, is the bullet sticking in the seater stem and pulling the bullet out from the case as you lower the handle?
Joe

 

[Bob3700]

If the neck tension is that light, can you push the bullet into the case with your fingers?
Or if the tension is that light, is the bullet sticking in the seater stem and pulling the bullet out from the case as you lower the handle?
Joe

Joe,
The seating tension is just enough that you cannot move the bullet with your fingers. I test each seated bullet to make sure they are held securely. Don't want them moving as I transport them to the range.
All bullets are seated +.035" so the bolt final sets the bullets.

I did take the time this afternoon to clean all of my seating dies as I was concerned that there might be a moly buildup that was an issue. We will see if that was an factor.
Bob

 

[JFrank]

That seems pretty light for a 6 br, what distance are you shooting ?

 

[ronemus]

Lapping the stem using a bullet to carry the lapping compound may help - the contact area will widen which should help uniformity. I use moly-coated bullets exclusively and use an expander (Hornady FL die) that is bullet diameter; there is plenty of bullet retention, even in my spacegun (no change in BTO after loading by letting the bolt fly freely).

 

[Bob3700]

That seems pretty light for a 6 br, what distance are you shooting ?

I am shooting a 308 Palma Gun and my 6mm BRX is used for mid-range to 1K. All sling shooting with iron sights.
ronemus - I will give lapping the seating stem a try. smoothing it up a bit cannot hurt.

 

[JFrank]

How can you maintain a pressure curve with that light of neck tension ?

 

[Bob3700]

How can you maintain a pressure curve with that light of neck tension ?

Bullets are seated into the lands. OAL is .035” long. Works just fine.

 

[JFrank]

Bullets are seated into the lands. OAL is .035” long. Works just fine.

Interesting and Yes you mentioned jamming +.035 , I’ve jammed as much as .025 but had to use enough hold to maintain that depth otherwise the groups become erratic. Evident at 500 and will ruin your day at 1K
Thx
J

 

[PracticalTactical]

First point... Having a mandrel that is 0.0005" smaller than the bullet does not necessarily mean you have 0.0005" neck tension.

The amount of spring back after sizing has to be taken into consideration, and spring back depends on multiple factors but key points are brass hardness and the inside diameter before sizing. The amount of mandrel sizing you do affects the amount of spring back you will get.

I would suggest that you also pay close attention to your inside neck chamfer. The quality of that chamfer is critical to the forces needed to seat the bullet. I prefer to use a 1/4" shank cone shaped carbide burr for this critical step. No other inside neck deburr tool can compare.

The next thing to consider is the donut. If you are seating your bullets into the corner of the neck to shoulder, that swelling on the inside can affect the resistance you will encounter when seating into it. You can test for this by seating bullets long enough that they are ahead of the donut and see if your seating depth becomes more consistent. If it is, then you might consider pushing your throat further out to get forward of the donut.

If pushing your throat out is not an option then consider inside neck reaming.

 

[RGRobinett]

I noticed quite a variation in bullet seating depth. Cases have been FL sized, necks chamfered n brushed, inside of necks are dusted with dry graphite powder. Cases are run over a mandrel that is .005” below bullet dia. Bullets moly coated. Seating dies are Redding Comp. And Forrester BR. Cases are annealed after 3 firings.

Am working with Berger 6mm 105 Hybrids in a 6 BR case. I am seeing seating depth variations of .010“ to .020” measured from the base of the case to the bullet ogive. I have a bbl. Chamber gauge the gunsmith made for me. This amount of variation seems excessive.

How do u maintain consistent seating depths.

If you have made certain that the me'plats are not bottoming in the stem (Dave Tooley #3 above), then the following may help.
Using these dies, in order to obtain consistent seating depth, you may need to establish solid contact between the die-base and the shell-holder, thus eliminating/minimizing play/slop in the press parts. Doing this eliminates relying on the [internal] die-spring tension to establish/influence the "stop". Good shootin'! RG

 

[AlNyhus]

If you have made certain that the me'plats are not bottoming in the stem (Dave Tooley #3 above), then the following may help.
Using these dies, in order to obtain consistent seating depth, you may need to establish solid contact between the die-base and the shell-holder, thus eliminating/minimizing play/slop in the press parts, which
results in not relying on the [internal] die-spring tension to establish/influence the "stop". Good shootin'! RG

This^^^^^^ -Al