Inconsistent Seating Depth

P

parsky1

Private
Full Member
Minuteman
Jul 15, 2014
37
1
#1
I'm seeing +/- .002" to .003" difference in my seating depths (base to ogive). Seems like it shouldn't be that much. I'm loading 178gr a-maxbullets in 308 in lapua brass. I use a forster micrometer seating die. I'm not running a compressed load, but do notice that some bullets take much more force than others to seat. I also sometimes see a very small amount of copper shavings around the bullet. I'm using a Lee collet die with a .002" undersize mandrel. Maybe I should reduce my neck tension by .001" and look into taper crimping (loading for semiauto)? I'm wondering if this is contributing to some velocity variation.

Any ideas?
 
#3
Chamfer brass and you may consider reducing your neck tension or adding some sort of dry neck lube to ease the seating operation. Excessive seating force or variable neck tension in your brass can lead to what your seeing.

in a given lot you may find up to .010" variation base to ogive... Not common but it can happen. I wouldn't sweat .006" in seating depth variation. That's pretty good IMHO. If you've properly identified the right powder charge for your load, that small change in seating depth shouldn't make that much difference..
 
#4
Inside chamfer of case mouth.
Anneal brass for more consistent neck tension, required force to seat bullet.
I'd suggest you cull out 10 bullets to get the same base to ogive length and then seat those bullets. Repeat your test on cartridge base to ogive length, pretty sure you'll see your variation drop to near zero.
 
#9
I can think of two possibilities: 1.) your seating die is seating bullets off the tip and not the ogive. I think the AMAX bullets are consistent in length, but there is likely some variation. 2.) What kind of sizing dies are you using? provided you are chamfering properly, I suspect this could be part of the problem if you are getting inconsistent seating pressures. If you are using a bushing die and not neck turning then you will get some variation in neck tension. In my experience, most bullet seating issues and runout are a result of the brass prep process, even the best had dies and press will not produce straight ammo with crooked brass.
- What is the ID of your sized brass, it should be .001-.003 smaller then your loaded rounds, if its more then that then your sizing the necks too much.
 
#10
dauntedfuture said:
I can think of two possibilities: 1.) your seating die is seating bullets off the tip and not the ogive. I think the AMAX bullets are consistent in length, but there is likely some variation. 2.) What kind of sizing dies are you using? provided you are chamfering properly, I suspect this could be part of the problem if you are getting inconsistent seating pressures. If you are using a bushing die and not neck turning then you will get some variation in neck tension. In my experience, most bullet seating issues and runout are a result of the brass prep process, even the best had dies and press will not produce straight ammo with crooked brass.
- What is the ID of your sized brass, it should be .001-.003 smaller then your loaded rounds, if its more then that then your sizing the necks too much.
Click to expand...


Brass is .3045 neck ID measured with calipers after sizing with a Lee collet die with a .002" undersized mandrel. Lee says that the standard mandrel should give you .001" neck tension. I then use a Redding body die to get the shoulder back to within SAAMI spec.

The bullets have some marks on them after seating nowhere near the tip. There are actually multiple marks (very very close together) on the bullet from the Forster micrometer die. Diameter of the bullet at the marks is ~.285".
 
#11
I think you have too much neck tension. for a .308 bullet, you want .306-.307 inside diameter. I think its the LEE underside mandrel that's causing the issue resulting in too much neck tension which is compressing the brass and causing some to "spring back" more then others. .002 in my experience is FINE for semi autos.....003 to be on the safe side. I suspect that your brass is on the thick side. If you have some, measure a sized FC, WIN, LC and LAP case. I think that you will find that your OD and ID neck diameters will very based on brass, LAP is great brass but I think a little thicker then WIN. What rifle are you loading for? Semi auto I think? Are you single shot loading these A MAX bullets? I don't have much experience with them but I think they are quite pointy and I don't know what kind of jump you are getting if you are mag length loading them. If you are loading them single shot, you CAN go to .000-.001 neck tension, realize that you will not get loaded rounds out of the chamber without leaving the bullet in the barrel though, for NRA HP this is OK.

TO FIX: Get a LARGER mandrel which will give you less neck tension, get another sizing die (I like forster or redding bushing dies), get different brass, neck turn your brass. Oh yea, if it shoots well with 25 or less ES then leave it alone and go shoot!
 
Last edited:
#12
Inconsistent OAL of the cartridge can sometimes be traced to inconsistent OAL of the projectile.
Here is an extreme example where the ogive to base is different from the same box of ammo. (And why I don’t use Berger bullets anymore.) I understand that they have improved their quality control since I took this photo about 15 years ago.
Changing the seating depth of a bullet .003 can easily change the group size on target. As a matter of fact, I experiment with changing the seating depth to tighten up my groups after the charge weight is established.
802140Berger.jpg
 
#13
I called forster today and they said that the seater stem shouldn't be leaving marks and that I should send in some bullets and they can polish the plug up and make it fit the bullet shape better. He said the multiple rings is likely because it is slipping as it is seated. I have a .001" undersized mandrel so I will play around with that as well.
 
#14
dauntedfuture said:
< snip > TO FIX: Get a smaller mandrel which will give you less neck tension, get another sizing die (I like forster or redding bushing dies), get different brass, neck turn your brass. Oh yea, if it shoots well with 25 or less ES then leave it alone and go shoot!
Click to expand...

A smaller mandrel in a Lee collet die lets the neck get squeezed down smaller, which increases neck tension. To reduce neck tension, I believe you would need a slightly larger mandrel.
 
#15
dauntedfuture said:
< snip > TO FIX: Get a smaller mandrel which will give you less neck tension, get another sizing die (I like forster or redding bushing dies), get different brass, neck turn your brass. Oh yea, if it shoots well with 25 or less ES then leave it alone and go shoot!
Click to expand...

A smaller mandrel in a Lee collet die lets the neck get squeezed down smaller, which increases neck tension. To reduce neck tension, I believe you would need a slightly larger mandrel.
 
#17
parsky1 said:
I called forster today and they said that the seater stem shouldn't be leaving marks and that I should send in some bullets and they can polish the plug up and make it fit the bullet shape better. He said the multiple rings is likely because it is slipping as it is seated. I have a .001" undersized mandrel so I will play around with that as well.
Click to expand...

Wonder if them fitting the plug to the sample will make it worse with other bullets?

Interested to see what you end up with. I have the forster comp/mic seater too and I've been surprised to see what appear to be major inconsistencies in seating depth. I've run a batch of 20 with my cheapo lee seater and I'll see coal variances of 2 thou or less. Same test with forster and variances are up to ten thou. That's coal, of course, because I use an rcbs mic to measure ogive and I'm usually late for the range so I don't have time to measure each one...calipers are fast and I just noticed the spread while doing final checks. Inclusive data but enough to make me question my purchase of the expensive die. 178 amax by the way so less tip length variance bullet to bullet for those of you that were getting ready to blame it on that. Maybe I need to do an experiment and check ogives for two samples of ten. There's also the issue of runout, which I can't presently check...could be the forster has a clear advantage over the Lee there.

Plus the marks are never 1 thou so if I'm doing seating depth workups I end up with some warm-up rounds because I can't confidently dial out to my next depth (sometimes off by 30-40%).

Not quite sure about the die. I still use it but I look at it sideways
 
Last edited:
#19
Ok, so a quick update...

I ordered a custom seating stem from Forster. Appears to make better contact with the bullet, still varying base to ogive measurements after seating. Still makes a mark on the bullet, but at least the mark is large and much more consistent so it is likely the stem is contacting more surface area. Next I went from the .002" undersized from the .001" undersized mandrel (less neck tension) for neck sizing. After all that, I still get seating depth variances of .005" base to ogive. What I have been doing is setting my die to not seat so deep initially and go one full stroke. Then measure and adjust the die to set the final depth and run the ram down one more time. I can definitely tell when I seat a bullet that it is either loose or tight by how much force it takes from my arm on the ram. I measured quite a few bullets and they are all very consistent from the tail to ogive.
 
#20
Are your loads compressed?

how many firings on the brass?

I'm guessing variation in neck tension or load compression. If you have bullets that seat with varying pressure that can change your seating depths.
 
#21
Make sure that the tips of the bullets are not bottoming out in the seating stem, even with the new one. If you seat another bullet and the other bullet is consistent, that's the issue. This should not be a problem but you never know. My redding comp seater was seating Berger 80's off the tips for a year until I started corrected the problem. Seating bullets should be relatively easy and consistent. If you pull a bullet there should be very little to no damage to the base.
 
#22
Ogive to base variations do not equate to seating depth variations. The datum line for each measurement is the same, a contact point on the ogive by either the ogive to base gage or the seater stem. The seating stem has no relationship with the base of the bullet. The ogive only changes shape in one of two ways. Wear from use or a different point up die. A set of carbide bullet dies make millions of bullets before they are replaced so the chances of a mixed lot with bullets from a new set of dies and the same set at the end of their life is rare if not impossible . A die replacement would call for a new lot number and wouldn't be mixed with a previous lot. Point up dies wear at the meplat/ejector pin hole and it becomes a problem getting them out of the die before the shape changes significantly. When they do change it's in millionths of an inch not thousands.
Variations are caused by neck tension and the operator on the handle. The fit of the seating die stem on the ogive which translates to deformation of the ogive during the seating process, has a lot to do with it. In some HP bullets the lead line does not extend forward to where the stem makes contact leaving the jacket unsupported. Even then pure lead and heavy neck tension can cause the ogive to deform slightly and then there's the flexing of the case during seating. Oh and all presses have some spring in them so we're back to neck tension again.
 
#23
Slide1_zps89df7dca.jpg


1) Bullet length variation between the base and the bearing surface/ogive transition where the caliper comparator insert seats will have very little effect on seating depth or CBTO measurements. It can, however, affect your internal case volume and can affect pressure if the length variance is large enough.

2) Bullet length variation between between the bearing surface/ogive transition and the point on the nose out toward the meplat where the seating die stem seats will have an effect on seating depth proportional to the variation in length between these two contact points.

3) Bullet length variation between where the seating die stem seats and the meplat will not affect seating depth unless the nose of the bullet is actually "bottoming out" in the seater stem, in which case the actual seater stem contact point is the meplat itself. If that is the case, a VLD-tyoe seater stem might help solve the issue.

Chances are good that there will be some amount of length variance in all three sections of a typical lot of bullets. By carefully measuring the base to ogive and OAL from a given lot of bullets, you can pretty easily determine whether one segment has much more variation than another. If necessary, bullets can usually be sorted to minimize any potential effect on seating depth, either by length using calipers and a comparator insert, or by ogive measurements using something like Bob Green's bullet comparator (Bob Green New Products).

I personally do not worry much about length variance between the base and bearing surface/ogive transition. The amount it takes to significantly change internal volume and pressure is much more than I have ever observed in the various Berger .223 and .308 bullets I load. From 0.002"-0.003" seating depth variation isn't really all that bad, particularly if you have not "optimized" your seating depth using less than 0.005" increments. My guess would be that you issue has more to do with neck tension and/or chamfering than it does with bullet length variation. If you can actually feel a difference in the force required to seat bullets, then your neck tension is not consistent.
 
#24
I just loaded up 178amax bullets in 1xfired FGMM FC brass FL resized in my Forster FL die then followed OCW load development to load them up with 4064. I use the Forster Ultra BR Micrometer seating die. All bullets seated almost exactly the same up until 43.6gr. above 43.6gr my bullets were not seating all the way to 2.800. They were .006-.007 off above 43.6gr. I believe my situation was because of the amount of powder in the case stopping the bullet from seating deaper. I just didn't load anymore loads above 43.6. My brass was also fully prepped, chamfered, deburred and ss tumbled and had no issues seating the bullets.
 
#25
Brass is new lapua brass. I ran a Lee Collet die with a .001" undersize mandrel to make sure the necks were round. Trimmed all to 2.005" and then ran them through the RCBS case prep center. The seater stem contacts the bullet where the bullet diameter is .285", this appears to be normal since no die actually seats at the ogive transition start. I'm putting in 43.0g of Varget and quickload estimates the fill to be 99.5%. I've messed around quite a bit with the Lee collet die and have yet to see the neck tension be consistent. When I chamfer the mouth I hold it on the RCBS trim mate for about 10seconds. Most if the pressure difference I see is when the bullet is first getting starting. Less variation at the end of the seating stroke. I'm wondering if it isn't the Lee collet die. I've tried a little pressure all the way to bust the aluminum cap out of the top. Doesn't seem to matter. It is resizing because it takes my once fired brass neck ID down to .306"
 
#26
Measure the OD of the neck before and after bullet seating. The difference is your neck tension. 0.0015"-0.0020" is about where you want to be. Virgin Lapua brass out of the box can have a wide range in terms of neck dimensions. Depends on the Lot # as to how severe it is. I've had Lots of Lapua .308 brass where a .307" expander mandrel wouldn't touch even the inside of the necks on about 1 out of every 5 cases. Ultimately, I felt compelled to FL resize those cases with a .337" bushing/die in order to get the neck tension even remotely consistent. On a Lot# where all the case necks show very similar resistance to being opened up with the expander mandrel, I will treat them exactly the same way as you did, prime them, load them up, and shoot them. However, it is worth noting that even on those cases, the neck tension is still somewhat inconsistent (although much less than the extreme example I mentioned above). You can definitely feel that some bullets seat easier than others. After fire forming and the first full brass prep, it becomes much more consistent.

You mentioned the diameter of the bullet at the "ring" is ~0.285. Is it really that far down the nose? I looked at a diagram of a Forster seating die that appears to seat on the bullet much farther down than the Redding seater die I'm accustomed to using, which seats out closer to the meplat (link below). Based on the design, I can see where that might be advantageous in terms of minimizing the effect of bullet length variance, because it appears to seat much closer to where the comparator insert will seat when measuring. In any event, hope you get the issue solved. Good luck.

http://www.forsterproducts.com/client_images/catalog19938/pages/images/Seater_Die_Chamber.jpg
 
#27
Yep it is really that far down the nose. Stem is definitely deep enough for the long bullets. My brass neck OD before seating the bullet is .334"-.3345". After is is .337". I did have a few that were .3375" and one .338". I noted which ones seated easy and they don't really measure any appreciable amount different from the harder to seat ones in OD after seating the bullet. In fact some measurements would suggest the opposite.
 
#28
Ok, so I got frustrated tonight and started over from scratch. I reset my Lee Collet die and decide to not let the press cam over anymore. The two turns past when the shell holder makes contact instructions did not work and caused the die to do nothing. I then started over and just started screwing it in and trying a piece of brass until it did not cam over and sized it. I tried to apply about the same amount of pressure each time and did it twice to each case rotating the case 1/2 turn for the 2nd. A 5 gallon bucket 3/5 full hanging off the handle gets you really close to 25lbs. Primed, dumped charges, and seated. My Base to Ogive measurements after the initial seating were 2.172, 2.174, 2.173, 2.172. I noticed more consistent seating pressure as well. I feel a bit better about these results. I'll need to try it out on more brass to confirm that this isn't a fluke.
 
#29
parsky1 said:
Ok, so I got frustrated tonight and started over from scratch. I reset my Lee Collet die and decide to not let the press cam over anymore. The two turns past when the shell holder makes contact instructions did not work and caused the die to do nothing. I then started over and just started screwing it in and trying a piece of brass until it did not cam over and sized it. I tried to apply about the same amount of pressure each time and did it twice to each case rotating the case 1/2 turn for the 2nd. A 5 gallon bucket 3/5 full hanging off the handle gets you really close to 25lbs. Primed, dumped charges, and seated. My Base to Ogive measurements after the initial seating were 2.172, 2.174, 2.173, 2.172. I noticed more consistent seating pressure as well. I feel a bit better about these results. I'll need to try it out on more brass to confirm that this isn't a fluke.
Click to expand...

Had the same problem with the Lee collet die. Solved it by installing the equivalent of a torque wrench on my reloading press to limit the amount of force exerted on the case neck. Tool is adjustable in small increments. Made neck tension consistency quite a bit better. A little expensive though, but you will never have a stuck case if you listen for the click.

https://www.titanreloading.com/consistent-crimp

There are probably other companies making a similar product, so shop around. Works well with collet dies and crimp dies. I don’t allow the handle to cam over.

Michael
 
Last edited:
You must log in or register to reply here.

Similar threads

N
Seating depth, what’s acceptable variation?
Replies
27
Views
1K
CK1.0
CK1.0
Cardboard Assassin
9mm Micrometer Die Options - Automated Progressive Compatible
Replies
6
Views
235
Cascade Hemi
C
U
Different neck tension and seating depth from round to round
Replies
18
Views
694
ma smith
ma smith
U
Bushing die sizing problems
Replies
7
Views
291
Edsel
Edsel
M
Die Setup
Replies
3
Views
254
Conaso
C
Top Bottom
Back
Home
Forums
Merch
Alerts