New #2231 200gr SMK for F/TR

[Jdne5b]

In theory, what velocity does node 4 work out to?

 

[Bart B.]

In the 308 Win's heyday in NRA XTC matches as well in Palma events, a common load winning and setting records was a Sierra 200 HPMK over 48 grains of IMR4350. 2450 to 2550 fps from 26 inch barrels twisted 1:11. The 200-19X 600 yard record was set with that load in Remington BR cases with Rem 7.5 primers.

I've no doubt this new 200 won't do as well.

 

[Dos XX]

In theory, what velocity does node 4 work out to?

For a 200g Hybrid, 2700 to 2720ish. Depends on some variables.

Quickload doesn't know the Sierra bullet, but it is likely in that same vicinity.

 

[Ned Ludd]

^^^ What Russel said. Regardless of the powder you use, it's a hot load. However, a few days ago I inadvertently loaded up some test rounds of something quite different that was as hot, possibly even slightly hotter than a predicted Node 4 load with 200s. I would never do that knowingly, and only on one other occasion have I ever even done it unintentionally. Regardless, much to my surprise, there were no hard bolt lifts, no ejector marks, and the primers weren't even noticeably flattened. Although I don't intend to run anything like what I was testing again, I am once more impressed with how much more pressure the Palma brass can take relative to standard .308 Win brass without apparent issue. So for those willing to run the 200s fast enough to hit Node 4 (I personally am not), it may not be any problem at all as far as [Palma] brass life is concerned, although you'll still have to effectively manage the recoil.

 

[Bart B.]

What is "node 4" regarding load details, velocity, accuracy or anything?

How many nodes are there and what conditions cause them?

Ignorance is bliss. Please enlighten me.

 

[swadiver]

^^^ What Russel said. Regardless of the powder you use, it's a hot load. However, a few days ago I inadvertently loaded up some test rounds of something quite different that was as hot, possibly even slightly hotter than a predicted Node 4 load with 200s. I would never do that knowingly, and only on one other occasion have I ever even done it unintentionally. Regardless, much to my surprise, there were no hard bolt lifts, no ejector marks, and the primers weren't even noticeably flattened. Although I don't intend to run anything like what I was testing again, I am once more impressed with how much more pressure the Palma brass can take relative to standard .308 Win brass without apparent issue. So for those willing to run the 200s fast enough to hit Node 4 (I personally am not), it may not be any problem at all as far as [Palma] brass life is concerned, although you'll still have to effectively manage the recoil.

200gr Berger Hybrids, 44.6 Varget, Lapua Palma brass, 30" Bartlein 5R barrel, 1 in 10 twist, .180" original throat length (a bit longer now ). base to ogive currently 2.337", which is approx. .010" off the lands

this is yielding an average of 2700 fps, sea level, standard day. chronographed with a LabRadar a number of times

 

[Laurie]

I also wonder just how finicky a secant ogive really is to tune. I know the conventional wisdom says that they're responsible for all manner of difficulty but how and why?

Is it not just as likely that it's because nobody makes short secant ogive bullets, and the real culprit is that long bullets are just not as accurate as short bullets? (Or put another way, longer bullets require higher quality than shorter bullets to shoot as well - they have to be straight and concentric, or they'll be penalized by mother nature more than short bullets with the same flaws.)

I dug up some words of wisdom from Bryan Litz on the seated in/out ... amounts of jump ... issue that were written some years back and saying that he knew no reason(s) to explain the widely observed phenomena on this subject. And, he asked for suggestions / hypotheses from shooters as to what mechanisms might be in play here. Result: silence! I started a thread in the ELR, Ballistics and Bullets section some weeks ago asking if we're any the wiser today..........

http://forum.accurateshooter.com/threads/bullet-nose-profile-and-seating-depth-sensitivity.3948062/

......... and the answer judging by the lack of response is apparently not.

 

[dcali]

I dug up some words of wisdom from Bryan Litz on the seated in/out ... amounts of jump ... issue that were written some years back and saying that he knew no reason(s) to explain the widely observed phenomena on this subject. And, he asked for suggestions / hypotheses from shooters as to what mechanisms might be in play here. Result: silence! I started a thread in the ELR, Ballistics and Bullets section some weeks ago asking if we're any the wiser today..........

http://forum.accurateshooter.com/threads/bullet-nose-profile-and-seating-depth-sensitivity.3948062/

......... and the answer judging by the lack of response is apparently not.

I can't think of a single reason. I've never rigorously tested anything like this, but I've seen too many tiny groups shot by secant ogives (and aggressive ones at that - like the Berger 90) to believe there's much disadvantage to using them. I might even begin to wonder if this isn't just urban legend, or perhaps something related to a special case rather than generally true. Maybe even just a matter of perspective blown out of proportion.

But to even start to answer that question, we need to know who seating depth impacts group size to begin with. I'd argue we don't really know. My own speculation is that when the bullet is released into the bore, it happens with imperfect balance, which starts the bullet to yaw in a cyclic manner, which gets straightened out by the freebore. The seating depth, therefore, determines the point on that cycle that the freebore takes hold. If the bullet is already pointing relatively straight, you have success. If not, there's some deformation or tipping that adversely impacts precision. Jamming into the lands, of course, allows for no oscillation, and tends to help by ensuring that the bullet is straight - if the lands are not worn asymmetrically.

Unfortunately, this doesn't do anything to explain why a secant ogive might be more sensitive.

Obviously, that's all made up and I have no idea how you'd even try to verify it as true. But I can't think of much else that would cause such a dramatic impact from such small changes. If people can reliably document a cyclic pattern in seating depth, that might be a start. If not, back to the drawing board. I've never really tried.

 

[Laurie]

I've just had one of my F-rifles rebuilt in 300 SAUM with a GB Barrels 9.5 twist barrel, the primary reason being to use up the 2,000 + Berger and JLK VLDs I have in the 185-190gn range as well as trying the new 195 Sierra TMK (another aggressive form VLD). The objective isn't the usual short magnum one of superior ballistics at 1,000 - my 284 will retain that role - rather to have a 308 Win plus (or 30-06 ballistics if you will) for 500-800 yard matches. As well as using up these now superseded bullets, all of the tin of this and couple of tins of the other powders sitting in my powder cabinet will be used up too - Viht N550/560, Re19/22, and more.

I also plan to try the recommended Berger seating depth test for VLDs too - one of these things I've long been aware of, but never tried and I don't think I know anyone who has done the whole 'shooting match' (if you pardon the pun) as described in this US Palma / US Rifle Teams' Long-Range forum thread started by the late, great Jerry Tierney.

http://www.usrifleteams.com/lrforum/index.php?/topic/10924-jumping-berger-vlds/&

It'll be interesting to see what it throws up in terms of effects not just on group size and shape, but also MVs and SDs. (I also have a fair number of 6.5 and 7mm VLDs that will also be retried in due course having been put back on the shelf when initial results were disappointing.)

 

[dcali]

It'll be interesting to see what it throws up in terms of effects not just on group size and shape, but also MVs and SDs. (I also have a fair number of 6.5 and 7mm VLDs that will also be retried in due course having been put back on the shelf when initial results were disappointing.)

I would be very interested in tracking group size, MC, and MV SD for a *wide* range of seating depths - say every .010 over a range from touching to -.200. Some have hinted/implied before that long jumps can be as good as short, but I've never seen anyone test it rigorously. I certainly haven't. The question is what do you do about powder charge? It might be interesting to keep weight constant, or to keep pressure (via QuickLOAD) constant.

I know, I could do it myself... but it's much easier when someone else does it!

 

[Laurie]

Phil Hoham of Berger Bullets (barefooter56) mentioned this recently on another live thread saying use the bottom load level, play with the COALs, then when you find an apparently acceptable one, work up the loads from there as normal.

I'd always thought of it being the other way round, of starting with a likely COAL (which with a VLD would be in the lands especially as that will increase pressures) and working loads up with that, then playing with COALs to refine the groups. The problem as you say though, would be do you then need to refine loads again? ............. after which exercise you need a new barrel!

So, as I'm looking for ~58,000 psi type loads with the SAUM, I'd apparently need to start with something that is a bit under that, say in the low 50s, do an initial pressure / velocity run with a range of charges to choose one, then go into the COAL variations. ......... or I might start with two initial pressure / velocity test lots with one 'in'; the other maybe 20 thou' 'out' and see where that takes me.

 

[Boatschool02]

I tried tabling a discussion like this a couple weeks ago and it died on the vine. I'm sure I worded it poorly.
It seems more than suspicious (downright unlikely) to me that my entering seating depth assumptions during charge testing for vertical dispersion can commonly end up being the same ones that test best when going back through detailed seating testing. In one case particularly, I went with a mild jump on some 105VLDs (which many jam) just to be safe & prudent during initial work-ups. I settled on a safe load with hardly any vertical in or between groups and then worked back from jam in 0.003" increments and my best group was right where I did the charge testing... jumping a secant ogive bullet. I have no way to prove any potential causality, but I too would be interested to see initial work ups done significantly in and out. It would be interesting to see how far apart the loads are on charge and or velocity (if at all) and then step through a full seating depth test with each to see if any depth actually works better for each load than the initial charge tuning depth. I say all of this conceding that I've read Eric Cortina's method and his general experience of finding two points from 0.010 to 0.040 off jam that shoot well. Maybe my total system noise is just too high to accurately discern the right signals.

 

[jsthntn247]

I think several people will be trying these out in the Missouri regional this weekend. Maybe some of them will report back how they shot.

 

[Ned Ludd]

I can't think of a single reason. I've never rigorously tested anything like this, but I've seen too many tiny groups shot by secant ogives (and aggressive ones at that - like the Berger 90) to believe there's much disadvantage to using them. I might even begin to wonder if this isn't just urban legend, or perhaps something related to a special case rather than generally true. Maybe even just a matter of perspective blown out of proportion.

But to even start to answer that question, we need to know who seating depth impacts group size to begin with. I'd argue we don't really know. My own speculation is that when the bullet is released into the bore, it happens with imperfect balance, which starts the bullet to yaw in a cyclic manner, which gets straightened out by the freebore. The seating depth, therefore, determines the point on that cycle that the freebore takes hold. If the bullet is already pointing relatively straight, you have success. If not, there's some deformation or tipping that adversely impacts precision. Jamming into the lands, of course, allows for no oscillation, and tends to help by ensuring that the bullet is straight - if the lands are not worn asymmetrically.

Unfortunately, this doesn't do anything to explain why a secant ogive might be more sensitive.

Obviously, that's all made up and I have no idea how you'd even try to verify it as true. But I can't think of much else that would cause such a dramatic impact from such small changes. If people can reliably document a cyclic pattern in seating depth, that might be a start. If not, back to the drawing board. I've never really tried.

The one clear fact we can all agree to is that seating depth can, in fact, have a huge impact on precision/grouping. Even very small changes can show this effect. In my hands, groups will generally go from mediocre/poor to good, or even outstanding within a single .003" increment once you are "in the optimal seating depth window".

My gut feeling tells me seating depth is about barrel timing, but I cannot currently prove that to be true. The argument against it being a barrel timing effect is that such a small length increment relative to overall barrel and/or cartridge length is insignificant. However, it is important to remember that during the time the bullet is traversing the rifle's freebore, it is not moving with anywhere near the velocity it will have when it exits the bore. So even a very small distance increment could have a significant impact on barrel timing. If this is the case, one would expect seating depth to follow a cyclic pattern over a large enough window; i.e. tune in and tune out with a repeating pattern. I agree with Damon and Laurie's thoughts above that it would be interesting to test a very wide seating depth window in very small increments. The problem with this idea is that such a seating depth window is large enough that dramatic changes in pressure and velocity would be encountered. So it would be critical to actually adjust charge weight in order to maintain relatively constant velocity/pressure over the entire seating depth test window. Basically, you're talking about a huge amount of time, effort, and components to carry out such a test, which is probably why it isn't commonly done, even though it's possible if one was sufficiently motivated.

Another potential effect of seating depth is with respect to how the bullet engages the lands as it enters the bore. I can easily imagine how differences in the relatively smooth transition between ogive and bearing surface found in tangent ogive bullets versus the rather abrupt transition found in secant ogive bullets might have a significant affect on precision with regard to how the bullet is positioned relative to the bore axis when it enters the rifling. In the case of the 90 VLDs as Damon referred to above, a large number of folks are currently using the PTG 223 Rem ISSF reamer that cuts 0.169" freebore. In my hands, 90 VLDs in two different chambers cut with this reamer always seem to tune in at either ~.004-.007" into the lands, which is a fairly narrow optimal seating depth window, or starting at ~.018" to .021" off the lands, which seems to be a much wider optimal window. It is important to note that the freebore cut with this reamer is only about .0002" over bullet diameter. For some time I have heard common [anecdotal] wisdom regarding VLD bullets to the effect that they like to be started into the lands and may not shoot well when jumped. Although there are many examples suggesting otherwise, such wisdom stills seems fairly commonplace. One possible explanation why the 90 VLDs can be tuned both into and out of the lands could be that the very tight freebore cut with the 223 Rem ISSF reamer simply doesn't allow the bullet to do anything but go straight into the bore/rifling along the freebore and bore axis (i.e. with minimal yaw/pitch). However, I am currently also testing a new (to me) 30 cal VLD bullet in a rifle that does not have such a tight freebore. This bullet seems to shoot optimally at .006" to .009" off the lands, so clearly there are examples where VLDs don't have to be seated into the lands.

The bottom line is that it is probably possible at this time to determine experimentally what the effect(s) of seating depth are with respect to precision. However, such tests are probably not easy and not cheap in terms of time, effort, and components. So even though I'd really love to have more definitive answers on the topic of how seating depth affects precision, I'm personally just going to continue doing straightforward seating depth testing, which I know from experience will give me sufficient information for load development, even if it doesn't reveal any deeper insight into the "how" and "why" of seating depth versus precision.

 

[Laurie]

My gut feeling tells me seating depth is about barrel timing, but I cannot currently prove that to be true. The argument against it being a barrel timing effect is that such a small length increment relative to overall barrel and/or cartridge length is insignificant. However, it is important to remember that during the time the bullet is traversing the rifle's freebore, it is not moving with anywhere near the velocity it will have when it exits the bore. So even a very small distance increment could have a significant impact on barrel timing. If this is the case, one would expect seating depth to follow a cyclic pattern over a large enough window; i.e. tune in and tune out with a repeating pattern.

I've heard this view expressed by some and it has to be a possibility. The other main one is bullet alignment in the bore as it enters the rifling. If misaligned, it is said that it won't be corrected as it travels down the barrel, so-called 'in bore yaw'. That seems to be the way that Bryan Litz leans, ie it being an alignment issue. (As a bullet designer, you'd expect him to think in these terms though?)

There is one powerful argument though that this (alignment) is the primary factor - if it were entirely or even mainly due to barrel timing variations, then changing the seating position of tangent ogive bullets would also have a major effect on precision, while we know that some designs are if not completely unaffected by this factor, are at the very least, little so.

 

[Ned Ludd]

In my hands tangent ogive bullets like the Juggernaut most definitely do show obvious seating depth preferences in pretty much the same manner as do secant ogive bullets, albeit the "optimal" windows may be a bit wider and don't necessarily always show the same distance to lands relationship as with Hybrids or secant ogive bullets.

The reason I surmise that barrel timing is at least a part of what we're tuning with seating depth is a similar corollary to the argument you detailed against barrel timing above. Why would seating depth affect bullet entry into the lands? The bullet won't be spinning, so you ought to be able to change seating depth and freebore length at will without specifically altering the orientation of the bullet axis with respect to the bore axis, as it enters the lands. The caveat to this is that the freebore dimension itself cannot be so loose as to allow much bullet wobble as it traverses the relatively short distance prior to rifling engagement. It would also require that the leading edge of each land be perfectly perpendicular to the bore axis and their angles be absolutely uniform, which anyone that owns a borescope knows isn't always the case.

In a rifle barrel with ideal land geometry, it could be argued that if optimizing bullet orientation with respect to the bore axis and land geometry were the primary effect of seating depth, one could render seating depth non-essential simply by using a long and very tight freebore. A bullet in such a freebore would essentially be self-aligning with respect to the bore and land engagement and in theory, seating depth optimization should no longer have much of an effect on precision. I have a couple rifles that satisfy these requirements reasonably well, yet both show very obvious effects of seating depth on precision. So I would reason that the effect of seating depth on precision likely involves both timing and bullet orientation, and perhaps some other factors as well.

 

[dcali]

I don’t have time to flesh this out right now but I had a thought. Does gravity have something to do with it?

 

[Ned Ludd]

I don’t have time to flesh this out right now but I had a thought. Does gravity have something to do with it?

Damon...you're killing me! Aren't barrel timing and bullet entry into the rifling enough to think about LOL?

 

[dcali]

Damon...you're killing me! Aren't barrel timing and bullet entry into the rifling enough to think about LOL?

I'm just wondering if the fact that the body of the case is sitting in the bottom of the chamber doesn't automatically start things out a little off. But now that I think about it, that would cause sideways dispersion (or at an angle, but not random). Carry on.

 

[AA1200x]

Has anyone done any jump tests yet?

I tried them this weekend in my Match Rifle at 1000, 1100 and 1200 yards.

Average velocity was 2855 fps (50.5 grains of RS 60 and a moly'd bullet) in new Lapua SP cases and CCI primers.

Fired in a 1-9T 34" Krieger.

I gave them 5 thou jump and ended up with what appeared to be 3 or 4 groups, each of c.0.25 MOA, spread over 1.5 MOA. It wasn't
Velocity as I chrono'd them all so assume it has to be the jump as I got the patterns over 60 shots. I tried both supported and rested shooting positions to eliminate those variables and it still performed the same, bullets going consistently into one of the groups.

Photo below

I am planning on trying them with 10, 20 and 30 thou jump next weekend, I think my chamber is too long to actually jam them.