With all the talk about case shoulder bumping and slamming into the chamber shoulder, has anyone ideas on how full length sized and neck only sized fired rimless bottleneck cases will center any different at the case-chamber shoulder junction when the firing pin drives them there?
Chambered Round Alignment to Bore; Neck Sized vs Full Length Sized
- Thread starter Bart B
- Start date
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I had to post up a CROW EATING picture. I have been working on some new loads for my hunting rifle to shoot at 1000 or more yards. What do you know I shot this group with new brass. Thought it was a fluke...so I loaded up three more and shot the second group the following day. Impact location has nothing to do with the load, as I had made a adjustment for checking my scope/bore alignment.
This is a hunting rifle with a standard contour barrel burning a lot of powder. Yes I had overall better groups across the testing with once fired neck sized cases...but this was the best load.
100yds.
R-P Case Neck Sized in a standard RCBS die. Not trimmed only neck chamfered. (sp)
104.0 H50BMG
200 Accubond at 3240.
Fed 215M primer.
#1 = .480
#2 = .410
I guess this is why we try all options...just never know what is going to work for your rifle with a particular load. So I will shut my mouth over what is better...and simply try different things and go with what works.
This is a hunting rifle with a standard contour barrel burning a lot of powder. Yes I had overall better groups across the testing with once fired neck sized cases...but this was the best load.
100yds.
R-P Case Neck Sized in a standard RCBS die. Not trimmed only neck chamfered. (sp)
104.0 H50BMG
200 Accubond at 3240.
Fed 215M primer.
#1 = .480
#2 = .410
I guess this is why we try all options...just never know what is going to work for your rifle with a particular load. So I will shut my mouth over what is better...and simply try different things and go with what works.
Mikecr
Well-Known Member
Has anyone tested for this crushing headspacing on primer fired cartridges with ~35deg or more shoulders? And body tapers at or below 10thou/inch?
Were those exhibiting HS datum changes actually headspacing differently -as re-chambered, or just measuring with a new datum?
Is there evidence that the cartridges were held at new chambered position(like cases stretching on actual firing), or simply springing back to another or normal position?
Were those exhibiting HS datum changes actually headspacing differently -as re-chambered, or just measuring with a new datum?
Is there evidence that the cartridges were held at new chambered position(like cases stretching on actual firing), or simply springing back to another or normal position?
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Yes, if a .30-.338 belted case qualifies. I didn't see any belt headspace get measureably shorter with the few new cases I used. Their shoulders didn't touch the chamber shoulder from firing pin impact.
In my opinion, the following conditions result in different amounts of shoulder setback based on the tests I've made:
* firing pin spring strength.
* case brass hardness and/or thickness.
* firing pin protrusion from bolt face.
* shoulder area.
* shoulder angle.
* friction at the case-chamber shoulder.
.308 Win. and .30-.338 cases have a .012" taper per inch. These are the ones I used the most in my tests. To see the effects of very little body taper, I think the case body would have to have much less than .001" clearance to the chamber walls.
Measuring rechambered cases' head clearance with a dial indicator on a rod in the barrel resting on the bottom of the case and measured at the muzzle showed the same headspace change as my RCBS Precision Mic.
My test cases may not have been indexed the same but with squared up bolt faces but I've not seen any significant difference indexing the same case at different times on a clock face.
Note that my .30-.338 and .308 Win. cases all got a few thousandths shorter from head to case mouth and their head to shoulder headspace got longer when fired with powder and bullet. They lengthened head to mouth a few thousandths and had their shoulders set back and body diameters reduced a couple thousandths when full length sized.
Trickymissfit
Well-Known Member
Just doing some thinking about it, and also picturing the round being chambered at the sametime.
1. a chamber that is a simple factory style will have as much as .006" clearence at the neck, and may be on the high end of the nominal on the O.D.'s (this make sense?) There are some exceptions to this thought (Savage and Coopers seem to be on the lower side of the nominal deminsions)
**these are kind of a "fits all" chamber, and thus are a little on the big size for a reason. When you chamber a round it can be offset as much as four or five thousandths of an inch even though the taper will help guide it to center.
2. a good varmit chamber cut on a national match reamer will still be right in the center of this window and have about .003" neck clearence (give or take .001") These for sure are not typical factory chambers.
** these chambers are much smaller than the factory chambers are. The necks here will help to guide the loaded roud towards being concentric with the centerline of the bore. Still about the best you could hope for is .003" in alignment. The one advantage here is that a typical die set will size the case back .003" to .004", and should fit the chamber a little better. A custom reamed die may help this chamber greatly, and thus make it a border line (upper end) bench chamber
3. a benchrest chamber for something like a 6PPC or a 6BR will be right on the minimum side of the spec, if not slightly undersize. The neck will usually have less than .002" clearence
** These chambers are custom made to the shooter's spec with a die set that made to fit that individual chamber. Rounds go in with minimal clearence, and thus align themselves much better. You could well align the cartride with less than .0015 TIR
Over the years I came to the conclusion that it is pretty much a waste of energy to neck size a case going into a factory chamber, and here's why. The chambers are cut on a prodution line and are not always perfectly centered with the bore. The neck O.D.'s are rather loose so they can't help in aligning the case in the chamber. But if you do, and the chamber is fairly centered up with the bore it might help a bit. I saw no advantage doing this in Remingtons, Winchesters, and rounds that were most intended for big game use (.308 being an exception before all you climb on me). I did see it help in Savages and a few of the high end Remingtons and Coopers
But with a N.M. chamber I saw the groups tighten up a little bit (usually about 20%). Yet to differ here, I saw little help with my Remington that has a very tight .223 chamber. Neck sizing did shrink the groups alittle (maybe .075"). I have two N.M. barrels for Savages, and I can see the 20% thought come into effect. (I can't say why positively). What I have found with neck sizing here is that I seem to have much greater controll on the bullet grip, and this seems to reduce the spread in velocity somewhat (in one case quite a bit)
Bench rest chambers are obvious, and no need to respond much.
What I have found with neck sizing is that the dreaded doughnut seems to appear quicker (anybody else notice this?). I see zero difference in case life, as most cases split at the neck for me anyway or the primer pocket enlarges.
gary
rscott5028
Well-Known Member
It seems to me that bushings or custom dies is what gives you control over bullet grip (neck tension) rather than FL vs NK sizing per se.
I think partial neck sizing may be a contributor to the doughnut. ...which can be a function of either neck only sizing, or FL sizing with bushings set to do a partial neck size. I wonder how dreaded it really is when you're not seating the bullet to or past the doughnut anyways?
-- richard
Trickymissfit
Well-Known Member
That's what I ment to say in my post about bullet grip and neck tension. You just seem to have better controll of what's going on in the neck area. But all that great work can be negated by alot of clearence in the chamber neck. This causes the neck to open up a little more than we'd like, and thus over working the brass again. I once saw a Ron Pence 6BR barrel that ran just slightly under .002" total clearence in the neck. You almost didn't have to resize the necks because it worked so good.
I would like to see somebody figure out a way to make an adjustable sleeve to size the body only. Then you could make that body of the case fit the chamber exactly. I know exactly how to do it, but the cost is way over the top for 99% of shooters (use a female hydra-lock arbor), and wouldn't fit in any press on todays market. The shoulders are easy to bump back, and of course we all know how to neck size.
gary
David Tubb makes dies for his 6XC cartridge that has an adjustable body sizing part. With this die, you can set your fired case shoulder back and reduce the body diameters so some degree. He's been using this die for years full length sizing his fired cases to win matches and set records.
Note that all fired cases fit the chamber body area with a thousandth or so clearance. Full length sized ones have a bit more clearance depending on how much their diameters are reduced. Sizing fired case body diameters down a few thousandths as well as setting the shoulder back the same has been done for decades. As the front of the case centers perfectly (from firing pin impact) due to both the case and chamber shoulder angles being the same, there's no accuracy-robbing misalignment of the bullet to the bore. The most accurate 30 caliber rifles I know of shoot that way with full length sized cases that do not fit the chambers shooting them tight; there's a few thousandths slop between the out of round cases in that out of round chamber.
The back end of the case at its pressure ring typicaly rests against the chamber wall at that point from extractors pushing them that way or jumping off center from the firing pin striking the primer off center and moving the case head sideways due to the shape and position of the anvil in the primer cup. So even perfectly round cases don't center perfectly at their back end in perfectdly round chambers; they're still at a slight angle. Even with 4 or 5 thousandths clearance around the case neck to the chamber neck, such reloaded ammo's shot as accurate as any neck only sized stuff. And there' never an issue of slightly out of round cases' shoulders interfering with a slightly out of round chamber; neither are perfectly round anyway.
The top benchresters have been moving away from neck only sized fired cases as well as tight neck chambers. They're getting smaller groups more consistantly full length sizing their cases headspace and body diameters only a couple thousandths; that's all that's needed.
This is news to me; not moving the rifle from closing the bolt. Is there some movement of the round in the chamber that hurts accuracy if the rifle's moved when the bolt closes?
The only unwanted movement I can think of is with cases that don't have enough headspace clearance, closing the bolt may make its face bind up a tiny bit on the case head. And that may minutely reposition the rifle. It's always been a big no-no (if accuracy's important) for the bolt to bind up, even the slightest, when closing it on a chambered round.
My comment was about something Walt Berger wrote about BR rifles 6ppc and bag technique and adjust FL die.
Has nothing to do with what your posting about and not really sure what your talking about as usually.
Fine. I thought I explained it pretty good with:
Mikecr
Well-Known Member
I wouldn't buy into Tubbs merchandising hype on a regular basis..
There is nothing special about his dies, especially when they don't match your 6xc chamber(mine didn't -and with a stock Tubb2000!).
Also, I think discussions in reloading about 'what is' and 'what ifs' should steer clear of anecdotal niches.
Competitive Point blank BR shooters have no choice but to FL cases they intend to reload. This, because their winning loads run at extreme pressures way beyond viable for hunting/other cartridges. These high pressure systems represent a major work-around for many reloading flaws. They are more forgiving.
They can get away with it only in tiny cartridges like 6PPCs(223AI capacity) and close to it in 30br(extreme under capacity), and less so still for mid-ranges in 6.5x47(again undercapacity). Beyond these, NONE of it applies.
You could never run a loading scheme like this with something like a 243, 270, 308 or 30-06, no matter the sizing, without a big ol 'bolt hammer' on the bench.
Nor could anyone skip body sizing with a well punished 6PPC, and then be able to machinegun conditions.
So any discussion about it from them could be considered rationalizing of what they must do anyway, and as more niche than basis across the board.
Now someone could decide on a carry varmint gun in 6PPC,, run normal loads with hunting bullets, and probably achieve 3/8moa out to 400-500yds from it(with efforts). In this case there could be little need for FL sizing, if setup for other sizing schemes.
It's a reloading choice. I don't see anything wrong with it, and it's more interesting than turn-key PB BR examples as implied best.
There is nothing special about his dies, especially when they don't match your 6xc chamber(mine didn't -and with a stock Tubb2000!).
Also, I think discussions in reloading about 'what is' and 'what ifs' should steer clear of anecdotal niches.
Competitive Point blank BR shooters have no choice but to FL cases they intend to reload. This, because their winning loads run at extreme pressures way beyond viable for hunting/other cartridges. These high pressure systems represent a major work-around for many reloading flaws. They are more forgiving.
They can get away with it only in tiny cartridges like 6PPCs(223AI capacity) and close to it in 30br(extreme under capacity), and less so still for mid-ranges in 6.5x47(again undercapacity). Beyond these, NONE of it applies.
You could never run a loading scheme like this with something like a 243, 270, 308 or 30-06, no matter the sizing, without a big ol 'bolt hammer' on the bench.
Nor could anyone skip body sizing with a well punished 6PPC, and then be able to machinegun conditions.
So any discussion about it from them could be considered rationalizing of what they must do anyway, and as more niche than basis across the board.
Now someone could decide on a carry varmint gun in 6PPC,, run normal loads with hunting bullets, and probably achieve 3/8moa out to 400-500yds from it(with efforts). In this case there could be little need for FL sizing, if setup for other sizing schemes.
It's a reloading choice. I don't see anything wrong with it, and it's more interesting than turn-key PB BR examples as implied best.
While anything's possible in the shooting sports, I'll check this out. Seems a bit too far fetched for me to believe, but for now I'll admit ignorance regarding it. I'll be more knowledgable later.
To me, this comment's the most interesting:
I've a pretty good idea of the pressures such on-goings will produce in these cartridges. I'll check this out a bit more.
