throwing a stick in the seating depth chicken yard

[fguffey]

I am the fan of all the bullet hold I can get.

F. Guffey

 

[Jim Watson]

Well, they didn't blow up the gun and the bullets hit the targets, so it can't be horrible. But I don't consider it good practice.
Some guy named Tubb loads ammo "soft seated" with just enough neck tension to hold the bullet way out of the case such that chambering the round seats the bullet all the way with the nose against the lands. I wonder how rough a ride he gets on the way to a match.

I have seen BPCR shooters finger seating bullets in unsized brass at the range, but they have the compressed powder charge to keep them from falling into the case.

 

[murf]

taliv,

you have just invented a new tool called the "inertia bullet pusher". way to go. if the ammo box hit a hard enough surface for that many repetitions over that much time, it is no wonder you have bullet bases sitting on top of your powder. your neck tension was probably fine. obviously, some rounds had more neck tension than others. maybe if you go over bigger bumps in the road the other rounds will recede as well.

since the case neck is already expanded when you pulled the bullets back up into position in the case neck, col was probably "close enough" to the original length. that is probably why they shot normal. the 243 win case is overbore and has a ton of room to mitigate the affects of col changes on pressure. do that in a straight wall pistol case (big bullet, small case volume) and you would see a much larger affect on pressure.

no worries,

murf

 

[berettaprofessor]

I believe when the primer detonates, it shoves the bullet forward into the lands before the powder burns enough to build pressure. i could be wrong of course, but seems like as far as powder burning is concerned, the volume is determined by the size of the bullet and case, and how far the lands are from the bolt head. i don't see how seating depth could change it.

If that is true, then it would also be true that all those competitive match reloaders are wasting their time messing with finding the best cartridge OAL. They'd be getting the same results if they loaded every bullet to minimum OAL or .020 from the lands, wouldn't they?

 

[243winxb]

How bullet seating depth may affect accuracy

i don't see how seating depth could change it.

When the bullet jumps to the rifling, there is a pressure spike when the bullet makes contact. The pressure spike changes the burn rate of the powder for a millisecond . Different seating depths change when the spike happens. If neck turned brass is compared to unturned brass with very different neck wall thickness, bullet pull is changed. The variation in bullet pull/tensions allows the bullet to start moving at different times. The results is, the pressure spike also happens at different times in the powder burn rate cycle. If the bullet is jammed into the rifling, there is no pressure spike. The problem with the bullet jammed and very light neck tension comes when a chambered round has to be extracted without firing. The bullet stays in the chamber and you now have powder in the chamber and the area of the locking lugs. With IMR4350, your done shooting till its cleaned up. Sorry, no proof or links. Just my 2 cents.

 

[tcoz]

I don't think that taliv is trying to start a discussion about loading practices and neck tension but rather a discussion of whether and how much bullet seating depth will affect accuracy.

 

[Ifishsum]

As far as accuracy is concerned, I have not personally found much change with varied seatiing depths, except when working with a secant ogive or VLD style bullet. I'm imagine it also depends on exactly how the chamber/leade are cut in the individual rifle too. But I no longer spend a lot of time messing with seating depth with most of the bullets I load unless my results are unsatisfactory to start with.

 

[X-Rap]

I think taliv has ample credentials to use his ammo as he sees fit. I wouldn't think of using that ammo hunting but so far as I know he didn't. I would have, however done the experiment that he did rather than pull all the bullets and start over if for no other reason than to see if there was a difference in accuracy so long as there was no powder that had shaken out into the container.
Commercial ammo is transported cross country every day and it stays in its loaded configuration so what he loaded was not what you'd call the norm but it certainly must suit his needs as a competitor.
Personally I seat my bullets to fit my shortest magazine length unless for some reason the bullet sticks in the lands and pulls out (which I've never encountered).
I too have to agree that pistol ammo using full case diameter bullets would seem to be much more susceptible to dangerous pressure spikes than the typical bottle necked case.

 

[Walkalong]

I have seen this happen in a Benchrest match. The guys bullets just dropped through. He didn't have the time to do anything with them, so he went to the line and shot a group. He said he couldn't tell a difference. He used a smaller bushing to load for the next group.

 

[Gtscotty]

I don't have much experience with high dollar, heavy barrel precision rifles shooting match bullets, as most of the rifles I have loaded for were light barrel production guns shooting hunting bullets. Maybe that's the difference, but I always use seating depth to refine my loads, and almost always see the OAL changes reflected on the target.

One of the posters further up stated that he thought that changes in OAL had the same effect as small changes in charge weight. I could see that being the case as I usually refine my charge to the best half grain increment and use seating depth to finish the load.

 

[murf]

and then there are the commercial match loads that use fully sized cases and cols short enough to fit every rifle. those loads are more accurate than most handloads.

go figure.

murf

 

[Gtscotty]

and then there are the commercial match loads that use fully sized cases and cols short enough to fit every rifle. those loads are more accurate than most handloads.

go figure.

murf

True, FGMM usually turns in respectable results, but not always, again though, that's a match bullet/load. I can't really think of a similarly universally accurate hunting load. Maybe it has something to do with the ogive design of hunting vs match bullets, or perhaps the fact that I'm usually trying to tune for a combination of top velocity and accuracy. Or maybe it's thin fly weight barrels vs heavy custom jobs, or some combination of the above. I don't know, but I do know I'm not going to stop playing with seating depth when developing loads, I've seen it make a useful difference too often.

If someone doesn't think seating depth is worth tweaking in their rifle, more power to them, that's one less step.

 

[ATLDave]

There was an interesting article in Handloader magazine earlier this year about reloading myths. One of them, IIRC, was that deeper seating in rifle brass caused pressure increases in the same way that deeper seating in straight-walled pistol brass does.

I came away from the article with the conclusion that I do not understand rifle internal ballistics nearly as well as I think I understand pistol internal ballistics!

 

[PJSprog]

I think it's a valid question, especially since he now has first-hand experience that counters the conventional wisdom. One factor that definitely plays into his experience is the (obviously) incredibly weak neck tension of those loads. However, I fail to see how that affects the burn pressure, as noted before the bullet is pushed to the lands by the primer whether there's powder or not.

I don't know that I'd go so far as to call it defective, but it's certainly not a practice I'd be comfortable with in my own loading.

 

[Gtscotty]

I don't have the equipment (e.g. strain gauges, etc.) to measure actual peak pressures, but while playing with seating depths I have seen measured velocities climb when I got to some of the deepest seating depths. Velocity is usually regarded as indicative of pressure (perhaps average more so than peak), so I would suspect higher average pressures driving the higher velocities, but you'd have to actually take pressure measurements to conclusively prove anything. Even then you wouldn't have the data to support an assertion that all other loads will necessarily behave like the one you sampled.

 

[Archie]

What 'this' shows is...

"This" being the original episode, is that some rifles are not as sensitive to 'bullet-land' distance as others. Which, for that particular rifle and the owner, is a good thing. In my experience, it is not universal.

However, 'accuracy' is a flexible concept. For a bench rest competitor the measure is smaller than for a casual hunter - even with the same caliber rifle. As example, a British SMLE in .303 British has shown itself very well suited to puncturing enemies of the Empire for a good long while, yet no one (knowledgable and with alternatives) would make such a rifle first choice for a varmint shooting expedition.

Decide for yourselves.

How do 'deep seated' bullets increase pressure? By decreasing the volume of the initial burning chamber.

How do 'long seated' bullets increase pressure? By jamming the bullet into the leade of the rifle, movement of the bullet is momentarily stopped (at least retarded) and the burning powder gets to higher pressure before the normal physics of the moving bullet and increase in internal volume come into play.

One notes the charts showing 'pressure versus seating depth' only deal with what one would normal think of as 'normal seating depths' out to contact with the leade. I don't see any of them showing 'seating depth' as being abnormally seated into the interior of the cartridge case.

Also note the (first) chart, attributed to Dr. Brownell, the pressure drops from the bullet seated against the leade, then at a certain point begins rising. That rise in pressure is due to the reduction of the chamber volume due to a 'deep seated' bullet. If continued - as in accidentally jamming a bullet very deep into the case - the pressure would increase further.

Another factor to consider in this discussion. "Pressure" in the common usage, is NOT absolute. "Excess pressure" isn't always the same. There are overpressure - meaning in excess of the SAAMI average standards - which will merely make extraction 'a bit stiff'. Then an increase in that pressure level can damage cases (primer pockets seem to suffer early on). Another increase will begin to damage the locking lugs of the rifle; not shearing, but 'set back', which is actually cold forging the lugs or recesses eventually causing excessive head space. At some point, one suffers damage to the mechanism itself, concluding with catastrophic failure, where metal is stretched beyond elastic limits and breaks. (Ka-bloowie!)

The original poster did not report any damage. (Good, by the way.) But I would wager if those loads were tested by adequate measurement, one would find the resulting pressures were more than expected. Obviously not enough to cause damage to the shooter or arm, but more than expected. May I suggest Taliv report findings from de-priming the fired brass - how much pressure compared to 'normal' required to de-cap - and another other observations of the fired brass.

I have never blown up a rifle. I have fired a few loads that caused leaks about the primer pocket and loosening of the primer pocket. (Primers didn't fall out, but they de-capped alarmingly easy.)

Some of this information comes from own experience and some 'war stories' by older - now gone - shooters and reloaders. Much of the technical information comes from Firearms Pressure Factors, by Lloyd Brownell, PhD.

Short version:
1. There is always more than ONE factor at work.
2. Just because 'nothing happened' that time, doesn't mean there won't be complications later.

If I may lecture like an old man for a moment, those two observations apply to more in life than reloading.

 

[jmorris]

Bullet set back can increase pressures as can seating them long can also increase pressure.

There are other variables involved and if your load and rifle are forgiving that is a good thing.


If you have been playing with annealing, you can over do it and loose neck tension, permanently.

 

[homatok]

As long as the rest of the case has not been compromised by over annealing, an over annealed case neck can be reclaimed by expanding up one caliber and resizing the case once or twice (as needed).