neck tension and seating depth

D

docsleepy

Guest
New 6PPC learner here. Trying to find best bullet seating for groups. I have a wilson micrometer seater and hornady OAL, but I'm discovering that without a fair amount of neck tension, I don't always KEEP what I seated.

Where is the tradeoff between neck tension and jam seating? I've seen quite a few urging "jammed .010" seating, but doesn't that take a lot of neck tension?

If I try to jam it more than .010, after neck sizing on a collet with .240 mandrel, the berger bullet just ends up getting pushed back to what I calculate (based on Hornady OAL) to be about .005 jammed (at best).


Others say minimal tension makes for more consistency. I've seen some recommmend relatively little space between the turned neck dia. and the barrel neck, so that the brass cannot expand (or work!) and then simply seat bullets without any sizing at all. With my current batch of firefomed cases [turned to .268 for a .270 chamber on a .240 mandrel in a K&M turner] that works out to relatively little neck tension -- certainly not enough to jam much if any. (I could certainly work up a new batch aiming for a thicker neck and more tension, if that is the answer).

Before I fire a zillion shots trying to prove which is best, I'd appreciate advice on whether to aim for light neck tension with zero or <.005 jam; or whether to collet neck size and tightly grip and try .010 jammed. Is there any consistency between barrels or must I simply try several groups lots of different ways? Does ANYONE end up with best results jumping in 6PPC?

thanks
 
oh well, guess everyone thinks I'll just have to experiment....
 
I'm listening...

docsleepy said:
oh well, guess everyone thinks I'll just have to experiment....
Click to expand...

You're doing a precision process that is going to be unique to your equipment and system. And I think (if I have followed you correctly) that your question is multi-dimensional. Are you talking about case OAL/w to chamber? Or total AOL/w.?
 
Hi Doc.
Here's a book to read. Everything about Short range BR.
http://www.sinclairintl.com/product/5819/Books-Magazines
Next.
Jam: is when you seat a bullet long, and run cartridge into chamber. NO PRIMER or POWDER. Do this 2-3 times. Get a good measure.
Off of jam: is where you shorten that cartridge. Move bullet into case.

I have a .262 barrels. So my measuring is a little different.
But, The number is a reference only.
On the bullet. You will see marks left by the rifling.
In Jam. These marks are long.
Move bullet back till the marks are square. And measure OAL. This is a real good starting point. For a cut rifle barrel. IE. Kreiger.....
I have read stories/articles going back 30-40 yrs. Always the same. Make the marks a square.
.262 neck. I use a .258" bushing.
 
zippy06 -- thanks!
I've observed "square" marks but wondered if that was TOO much jammed. It happened when I seated quite long and found the bullet was pushed by during chambering to what now appears to be about .010 beyond first touch of the lands. With your suggestion, I'll work from that seating and do some experiments. That kind of starting point is extremely helpful.

I'll get that book, too!

Yes, I'm probably asking a multidimensional question -- not sure whether to go with tighter neck (allowing somewhat to more jammed seating) or very light neck (which doesn't allow jammed)....zippy06 argues for somewhat jammed.

Thanks!
gordon
 
I studied a far-jammed seating that I've used with good results and found the marks were .070 long and .030 wide. Contrary to my assumption, the bullet did actually hold its seating! I decided to focus today on a seating somewhat short of that, which would give marks more square than rectangular and had performed well in some previous tests.

Before the rain started, I shot groups with different loads, spaced .3 or .6 grains apart, re-using the same shells over each time, loading at the range. I did see signs of "in-tune" and "out of tune" in the vertical. There was (for me) very little horizontal. I was able to get the chonometer to work in heavily overcast skies for the last half of the session, got some good data. I had time to shoot one group, where I simply seated a bullet back in the neck, without neck-colleting. There was more velocity variation in that group than in the ones that were neck sized, and more vertical variation... so I think I'll stick with the slight-jam, neck-colleted settings and focus next on more uniform primer pockets/seating etc.

THANKS for the suggestions! I keep learning and chipping away at my inaccuracies.
 
Are you using a Lee Collet die? What is the difference in neck diameter between sized and over the pressure ring of a seated bullet?

Different powders "like" different load specifications. 133 seems to like more starting pressure. Higher neck tension is one way to increase this pressure (I believe).

How the marks on a bullet looks is a function of the shape of the ogive, the shape of the leade, and how those shapes interface. Holding the leade angle constant, a lower ogive number, tangent ogive bullet will tend to engage more abruptly. It takes more push to make a given length mark on a bullet. Bullets that have shapes that are closer to parallel to the leade angle, tend to get to a given mark length with less push (neck friction) I have also observed that different ogive shapes have different seating depth "preferences" in the same barrel. If I am shooting something like a Berger 68, I find that marks that are well short of square seem to work the best for me. On the other hand, My Tucker #3s seem to like marks that are quite a bit longer than square. I believe that the Tuckers have a larger ogive number at the point where the rifling first touches. This is by no means a complete essay on the subject, just some discussion points...hopefully helpful. Opinions?
 
Boyd. The Berger 68 and the marks. I am seeing the similar results.
A SMK 70. Appears to have more ogive. or larger. Longer marks worked better. For a starting point.
 
docsleepy.
Are you using a Lee collet Die?
I didn't know Lee was making 22 PPC and 6 PPC.
Most people use a Harrell's die.
http://www.harrellsprec.com/
Give them a call. You will usually get Lynwood or ??? forgot his name.
Anyway. You send them 4 fired cases. Fired 3 or 4 times. They send these back with your order. For $70 they send you a Full Length die. And a small Shoulder tool. For measuring the length of the brass, from the shoulder to the head.
You will need a bushing for your particular neck. This is for the neck tension.
Redding has them with the Tin coating. No lube. Call Sinclair for these.
You will have a custom die for that barrel.
 
In my opinion

if one wants to be precise with their loading and know for sure where their bullets are seated they must start at a point that is more precise than "Square Marks". We worry about our chambers being "Dead Nuts" yet some are absolutely cavalier about how they seat bullets.

My recommendation is to use what I call "Kiss" as one's starting point, that way there is no guessing how big the square marks are or where in the barrel they are caused. One can then reliably measure their OAl's so that they know for sure how far they are in or out. (Sometimes being off the lands is the best place to be and it sure is easier to know how far they are off the lands if one works from "Kiss").

To find "kiss": take an empty case and re-size the neck with light or only a small section of it sized. Start a bullet, insert the case with the started bullet into the chamber and close the bolt. Visually observe the mark on the bullet. If it is anything more than a faint marks of the lands then push the bullet back into the case by .003 to .005. Polish the bullet with fine steel wool or anything abrasive enough to polish the land marks off. Keep chambering the round, continually pushing the bullet back with the seater until you can just see faint marks caused by the lands. STOP HERE.

Next, measure the round using a comparitor and a vernire calipper. I recommend the type of comparitor that clamps to the jaw of the vernier but the Sinclair nut works I am told. The Nut I have is old and does not have a chamfer in the holes so I find it useless for my purposes.

Record the length of that round and set it aside. I keep mine in one of the boxes with a the lot of the bullets I just used to make that dummy. I record the length in case the dummy gets lost or is dropped, etc, etc.

One must do this process for each bullet type and/or lot and chamber they are using. Get a good notebook. Use it religously.
 
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Wow! A treasure trove of additional information from you guys! I works nights at the hospital, teach science during day...so just found these replies.

[I'm sorry this is so long]

1. Yes, I use the Lee collet dies; they make 6PPC (and probably 22PPC). I'm at work and don't have the exact measurements both both with and without bullet, but I think they differ by about .001. Once loaded, the O.D. is running .267-.269 for a .270 chamber, as I am still learning and do bettter on some batches than others. The mandrel in the K&M neck turner measures .242 and they slide over that and get turned, and the mandrel against which they are colleted is .240, but there is some kickback when they come out of the collet and I don't have an accurate way to measure the ID (get different answers depending on how I hold the calipers).

2. Seating 60 or 68 gr Bergers with the Lee collet and a lee press, you FEEL almost no pressure...but when I used a K&M arbor press with a dinky 3" moment arm on a Wilson die and the same cases, it felt horrible to me....10 lbs or more. I have never used arborpress/wilson before. That is what precipitated the questions; I had read that maximum accuracy is achieved with light neck pressure, but if you use light neck pressure, you can't "hold" seating to accomplish a jam! How much force should one expect to use with a Wilson seater????

3. The Harrell die idea (especially the test jig!!) sounds like a good idea.....but I thought lee colleting would be better than full length type dies? My action is not trued, but I expand the cases so that they fit SNUG and I hand place them every time with the same mark "up" so I think that is about the best I can do to take care of non-true irregularities.... Comments??

4. OAL measurement: Don't want to bore you; I've done the loose bullet, also test seatings to feel the bolt, and also the Hornady OAL. Hornady case fit my chamber with .008 shim behind it, so I correct those measurements appropriately. (Havent had a special case made yet.) Hornady measurement of land position comes out .005 shorter than my previous "shining the bullet" measurements. Currently I'm trying jams of .010 - .020 past the measured lands. Perhaps I should back off and try a KISS setting as well?


Groups:
5. Groups shot 2 days ago were almost pure vertical strings. Horizontal (with my much-more-carefully-prepped cases) was much better than my usual: only anbout half a bullet width on 3 out of 4 groups. Vertical was another story: 3-4 bullet widths (6mm) for 4-shot groups during what I thought would be charge weight testing...reloading same 4 cases repeatedly to eliminate case variation. That suggested to me that my case-prep techniques were improving, but that my bag/trigger technique might be quite faulty and overshadowing any effect of charge weight. My trigger is about 1.5 lbs (spring scale measurement).

But I have on other days been able to get groups with far less vertical! Must have been doing something better than? If the gun can now reduce horizontal to (for me) tiny amounts, shouldn't I be able to reduce vertical with better technique on the trigger or better trigger?

Thanks for all the education, you guys are great!
gordon
 
again I want to thank all of you for every bit of education and insight!
gordon
 
Gordon,
If you want to stick with your collet die, you might consider a body die, and a two step sizing process. The reason that FL sizing has become just about universal in Benchrest is that the pressures that work the best, with the powders that are common require it. You will need a way to measure shoulder bump. Also, you can try different amounts of neck tension by using different diameters of mandrels in the collet die. Two other things that you need to do. Get set up to load at the range, and make yourself some way to look at what the wind is doing. BTW the Harrell's die is a pretty standard piece of equipment at matches, and an excellent value.
 
Marks on the bullet

If you are having trouble seeing the marks on the bullet I've found that if you coat it with a black texter pen, the land marks are very easy to see. Just re-coat it when you use it again.
Cheers Mick:D
 
Boyd Allen said:
Gordon,
If you want to stick with your collet die, you might consider a body die, and a two step sizing process. The reason that FL sizing has become just about universal in Benchrest is that the pressures that work the best, with the powders that are common require it. You will need a way to measure shoulder bump. Also, you can try different amounts of neck tension by using different diameters of mandrels in the collet die. Two other things that you need to do. Get set up to load at the range, and make yourself some way to look at what the wind is doing. BTW the Harrell's die is a pretty standard piece of equipment at matches, and an excellent value.
Click to expand...

Boyd and Torana - thanks for even more info! You are selling me bigtime on the Harrel die.

I do need a way to measure shoulder bump. I am probably using too low a pressure (kinda scared of lots of powder; I've had an occasional pierced primer; will set the firing pin protrusion back a tiny bit next). I did bump my shoulders back once using rcbs FL die with expander taken out.....so I have a way to do it, but the Harrel die set would help with measurement if I understand you.

I had thought o the different mandrels, will call Lee.

I actually have been loading at the range recently. No one else does (I look strange), and some of them have incredibly expensive guns and produce amazingly tiny groups. (.144, .125, .185 on some of their targets I find after a club competition) Also, none of them use wind flags; I made one and use it when I am practicing. Again I look strange; there are bushes on both sides and I'm learning to watch the bushes as well as my homemade flag.)

Question: Does the Harrell die size the neck from the OUTSIDE with a fixed bushing that squishes the neck inward? The Lee squishes the neck from a serrated bushing against a fixed round mandrel. Is there a theoretical advantage to one over the other?

Thanks again for all the teaching!
Gordon
 
I had promised to get some real numbers. Here they are:
Representative multiply-used case:

OD prior to bullet seating: .266 or .2665 on multiple measurements
Neck thickness (one side) .013 (agrees with what my indicator gage showed when I turned them)
Suggests ID of 0.240 (collet mandrel is .240 by the way)
attempts at measureing ID give inaccurate numbers; all I have is a digital caliper, nothing fancier to use.

Measured OD of base of Berger 60gr .243 bullet: .243 (duh! but provides check on calipers)

Measured OD of neck after seating bullet: .268 (about .002 larger than prior to seating)

Neck carefully chamfered on inside, and smoothed with fine steel wool.
Feeling on seating with Wilson seater, using K&M arbor press, about a 3" moment arm: horrible! Feels like I'm pulling down with >10 lbs force.

I think the numbers above suggest I am using .003 neck tension based on ID calculation, or .002 based on OD measurements, if I'm thinking right? Is that a lot? Or reasonable? Perhaps Lee could make me a .241 and .242 mandrel?

Your comments/education invited!
gordon
 
also: I grasp the advantage of the fitted Harrell die: it would size to MY chamber, a real advantage over my off-the-shelf RCBS FL die. With the shoulder device you say they will also send, do I just use a set of calipers to measure headspace on prepp'd cases? Or would I need some other measurement instrument?
 
You can make a "thingy". A couple thousands bigger then the neck OD. Sloppy.
And a 60 degree counter sink. there is a drawing around here somewhere.
Yes. You would use calipers. And spin the case to get the smallest number.
Bump shoulder .0005". Very little. Keep notes.
Another thing. Maybe more important. How the case fits after fire form.
On the 3-4 th reload. The case should be stretched out.
Remove firing pin from bolt. Insert case into chamber. Close bolt very easy. The bolt should fall to 1/2 way closed. And light finger pressure to close.
If hard to close. The die needs to go down more.
If too easy or falls on it's own. Die needs to go up. You moved the shoulder too much.
Sinclair has a a shim kit to adjust this.
If hard to open after shot. you are not sizing the "web". Time to call the Harrell brothers. This usually happens around 15-20 loads.
If you have a custom barrel and chamber. Don't worry about too much powder. I have seen guys use an 8" drop tube and pour/dump real slow. And get 30.8 gn ????? of N133. The powder is on top of the rim in a pile and they put a bullet on top. And squish the powder down. :eek:
But, they also use new cases at each tournament.
A 2 gun tournament is 20 targets.
 
zippy06: wow! Shims! Never thought of that! I found the shim kit on sinclair. Obviously a better idea than trying to adjust the die each time. Thanks a zillion for the tip, and for the experienced insights into how to know what I'm working toward. I've been using such low charges (24-26 grains H322) that the cases haven't been giving me much trouble YET. But that will change of course. Thanks again.
gordon
 
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