Bullet seating testing? has it been done?

[Ervin]

Im keeping 0.002" consistency when it comes to bullet seating. Theyre 175gr SMKs, dont have the ogive comparator to go with the caliper yet.

Ive noticed differences of .20 to a third of a milimeter in supposed factory match ammo.
Which only makes me more confident of my own .002" loads, but whats the real difference on paper?
has anybody tested rounds that were loaded with a bullet seating consistency of .003-.004" +/-?
Im OK with going through all this trouble, but I just want to see some proof.


also, is .002" ok for long range?

 

[zfk55]

Ohhhhh yeah. We can increase velocity by seating the projectile deeper. That's a huge deal for us with our load data development. Its sure easy to run a test yourself as long as you have loads with no variables at all.
That means consistent sizing, trimming, primer pocket uniforming, neck centering with a bushing for neck tension, weighing each case, weighing each projectile, meplat trimming and pointing and finally weighing each loaded cartridge with no more than 1/10th grain difference.
Do all that first and then do a 4 step seat depth indexing on the ogive with 2 thousandths between each step. You'll be amazed at how you can change your velocity with seat depth.

Seat depth will also change POI because the velocity also changes. We expect to see no more than +- 7s/d with our loads.
Your seat depth/accuracy will depend on barrel length, twist, projectile profile and of course load data.

Latigo

 

[Ervin]

I was in a habit of seating deeper with lighter powder charges. Seemed like an economic way to save a few grains per round.
The only problem in my case is, I dont have scoped rifles for a really controlled experiment for this caliber.
So I depend on sniper and benchrest enthusiasts for dependable info.

 

[mc223]

.002 in reference to what? The meplat, the base?

 

[Ervin]

Overall, tip to rim

 

[mc223]

Bullet lengths alone can vary .020 or more depending on type. Soft points tend to vary most in my experience.
If you are controlling the meplat to the base of the case, you are not counting the variation of bullet length. This variation will cause slight differences in pressures. Whether you are skilled enough to recognize it is another matter. It may show up as vertical on the target, but only if you eliminate the weight difference between bullets also. Heavier bullets within the same weight class at the same velocity as a lighter bullet will hit the target lower. Meplat shape has a huge effect on BC. Generally a bullet with a larger diameter meplat will have a lower BC.

If you are loading for long range competition of some kind, there are many other variables to consider.

If you are loading for deer, you're probably Ok

 

[Ervin]

Could you please explain to me what meplat uniforming is? I obviously missed that part. Cant find a simple enough diagram explaining it
Some people are saying its a minor difference and is meant for 600yds+ shooting.

If anyone has time, can you explain the reason behind weighing cases for consistency prior to loading?
I understand the theory behind primer weighing.

Ive used large pistol primers for rifle loads in the past, but is there a trend of them catching on by any chance?

 

[mc223]

Ervin

Could you please explain to me what meplat uniforming is?

Meplat uniforming is trimming the point of the bullet to a uniform length to a datum on the ogive. Uniforming will decrease ballistic coefficient of a bullet because it increases the meplat diameter.
Pointing dies reduce the trimmed meplat diameter to increase the ballistic coefficient.

http://www.bullettipping.com/

Some people are saying its a minor difference and is meant for 600yds+ shooting.

I think it would be most beneficial at longer distances, but it certainly cant hurt even at shorter distances.

If anyone has time, can you explain the reason behind weighing cases for consistency prior to loading?

The theory is that a heavier case will be smaller dimensionally inside therefore reduced volume capacity.

Ive used large pistol primers for rifle loads in the past, but is there a trend of them catching on by any chance?

There is less variation in cup thickness in the large primer families. If you are working your loads and not having piercing or other issues, you should be ok. Some loads tend to perform better with less Uumph from the primer.


Good Luck

 

[warbirdlover]

I did my own seating test years ago and found the standard overall cartridge length worked just as well as getting the bullet close to the lands. And IMHO alot safer pressure wise.

 

[Unclenick]

It varies chamber to chamber and bullet to bullet. This thread on Berger's findings with their VLD's is interesting. Some folks have reported as little as 0.010" difference in seating depth being visible on the target, but IME, a span of .020" to .030" is usually more typical of sweet spot seating depths. 0.002" would not be apparent. Find those sweet spots with mild loads, then tune your best powder charge in, as per description item 3., here.

Be aware that if your gun needs recrowning, lug lapping, bedding, has severe chamber eccentricity, or has a ten pound trigger with a lot of over-travel, the best ammo in the world likely won't group great for you and you won't see any big difference from taking a lot of trouble with your loads. On the other hand, with a gun in really good shape, it's not uncommon to be able to get down to around 1/2 moa at 100 yards without doing anything but tuning the powder charge, though you do need a good bullet that the chamber likes.

Dan Hackett wrote in the Precision Shooting Reloading Guide how he had a 220 Swift he could only get about 3/8" groups with at 100 yards (not good enough for a benchrest kind of guy) no matter what he did to powder charges. Then one day he accidentally turned his seater micrometer the wrong way and wound up seating twenty Nosler BT's .050" off the lands instead of his intended .020" that he'd always used. Rather than pull the bullets and start over, he decided just to shoot them in practice. To his amazement he got two 1/4" groups and two bughole groups in the 1's. So, seating depth can make a difference, particularly to fine tuning, but it's unpredictable what any particular bullet and throat combination will actually want until you find it by testing, and it's not usually a hugely sensitive adjustment.

Below is a chart derived from data in the 1965 U of M Lloyd Brownell study. It shows how pressure changes with seating depth. This is why it's a good idea to establish seating depth with a light load, then adjust the load, as the maximum will change with bullet position.

 

[Rimfire5]

In my experiments with overall depth variations related to seating closer and further from the rifling, with any particular bullet and rifle there seems to be a relationship between relative velocity and depth with respect to accuracy.

In three diffenent riflles in .223, .22-250 and .308, if I was using a load that the rifle shot accurately, I could get slightly better results if I increased depth or reduced depth from the recommended norm from the loading manual if I also slightly reduced the velocity nominally by 10fps for longer COAL seating by 0.005 or increased the velocity nominally by 10 fps for shorter COAL seating by 0.005.

The depth changes didn't always show the same effect, partly I believe because of the characteristics of the bullets.

I found the most predictable results with Sierra Match Kings, expecially in .308, although the results for Sierra .223 Varmenter bullets also showed similar but not as predictable results. Perhaps that is because it is harder to make a minor velocity adjustment in a smaller powder charge.

The .22-250 was a slightly different case, it prefers faster bullets and seems not to follow the same relationship between velocity and depth.
Varying depth does often make a difference but it seems to be more of a crap shoot than perdictable.

 

[zeke]

Maybe try measuring to a set diam on the bullet, instead of bullet tip for judging seating consistentcy in relation to how far you are of the lands. using a comparator makes this easier.

Course COL may matter if too long to go through action, and seating can affect pressure.

Alot of bullets are not as consistent as sierra match bullets, and very inconsistent in length. It may help is knowing the distance from a set diam to the lands, especially when trying other bullets.

 

[Unclenick]

Even the Sierra match bullets can vary in length due to slight angles across the edges of the hollow points, so that ogive measurement is more consistent.


Rimfire5,

Interesting results, but not entirely unexpected. It's because you established a good load first. If you look at that graph I put up, you'll see you are varying peak pressure as you change seating depth. Higher peak pressure makes the whole charge burn faster, which increases the portion of the bullet's acceleration that occurs early in its travel down the bore. That shortens the bullet's barrel time even if the MV stays about the same. Reducing the charge brings the peak down a little, putting the barrel time back into phase with the sweet spot in the barrel harmonics, but also losing a little velocity. It's good that you were shooting well enough to tell, because it makes such an excellent example of the principle that you can change barrel time with either powder or seating depth.

That also creates a kind of chicken or egg problem. You have to change the bullet a little, tweak the load, then repeat that for a whole range of seating depths to find the one combination that is ultimately the best. That's slow work.

Next time you play with the idea, try finding the seating depth sweet spot with a really mild load that doesn't recoil enough to deflect the barrel much. The idea is that because different loads tend to produce about the same start pressure, regardless of the powder or charge used, how the starting dynamics affect bullet alignment in the throat before pressure builds seriously will tend to be the same for all (except loads below 10,000 psi, the pressure at which HP White tests a number of years ago showed the bullet could be clearly discerned to have begun moving). The smallest group from that test may not be terrific, but should be better than the rest. Once you find the best seating depth with that mild load, clean the bore spotless, then start working up with the actual powder you want to tune in, beginning with fouling shots. See if that doesn't land you on your ultimate combination. Dan Newberry's system for finding that is good. I modify it to find the seating depth and look for the smallest groups with it rather than group center location for seating depth.

Also note, it's not uncommon to find more than one such sweet spot. They may not be equally good, but sometimes, especially for magazine feed, a pretty good one that's deeper than the very best one (if it's too far out), may be desirable. For tangent ogive pointed shapes, like the MatchKings, one such spot often occurs somewhere between 0.000"—0.050" from having the ogive touch the lands, but another is not uncommon back in the general vicinity of the bullet bearing surface being one caliber into the case mouth.

 

[Sweet Shooter]

OAL

I have a Howa that shoots .3's and .2's sometimes and ~.7's always with my hand loads. I mention it because being essentially a Wetherby it has a long throat. It's a 1x12 .223 and I have failed to reach the lands with sensible seating. I shoot 40gr Nosler B-Tips and there is no way seating makes a jot of difference in this rifle. Except for safety checks, I almost don't bother measuring OAL anymore. I just seat it so it looks about right and the neck of the case is full (of bullet). Maybe longer VLD projectiles are more sensitive perhaps in bigger calibers, but this is one more case that leads me to believe there is too much emphasis put on the issue.

Also, I know a guy who makes beautiful custom bench rifles. I started talking to him one day because he was shooting single hole tiny groups every time I see him at the range. 100 yards, 200 yards— it didn't appear to matter. I wanted to know what he was doing to achieve it. The point is I respect his opinion and he says hogwash to chasing lands, and to my surprise he also says powder charge—within reason—is also unimportant. He says with a powder that suits the caliber (pressure-wise) and fills about 90 percent of the case there's not much more to worry about with hand loading.
Justsayin'
-SS-

 

[Unclenick]

It's easy to extrapolate from one set of anecdotal experiences to a generalization that doesn't always hold true. Every gun and shooting system seems to be a law unto itself, and that's why Berger customers sometimes got good groups touching the lands, as Berger originally recommended, but many could not. It's why Dan Hackett saw groups cut in half by a simple 0.030" change in seating depth in his rifle, where you can't get it in yours. It's why an old 8mm Mauser with a shot out throat could be turned into the most accurate rifle Somchem had ever developed a load for, just by adjusting seating depth.

So, "too much emphasis" is relative to the particular gun and components. If it doesn't affect your gun, don't mess with it. But it's still worth finding out if it will first.

The same is true of powder charge sensitivity. I've had, at the extremes, a load in my M1A with 168 grain MK's and 748 that even .2 grains either side of center would open up. I also had a load with the 155 grain SMK with Brigadier 3032 (a top .308 powder for lighter bullets that is no longer available) that ran a full 2.5 grain span from 41.5 to 44 grains without the groups opening up at all (though they weren't quite as tight as the 168's were when dialed in). I don't like charge-sensitive loads because they are likely to be touchy with change in temperature.

Hatcher has a good story about this in Hatcher's Notebook. In developing National Match ammunition one year he worked up loads with two powders that he said were similar in burn characteristics to modern IMR 4320. One had a short grain and the other a large grain. The arsenal loading equipment could meter the short grain to within a 0.6 grain span. The coarse grain it could only meter within a 1.7 grain span, a number modern handloaders laugh at. Despite that, ammo off that equipment using the coarse grain powder were consistently more accurate in their test regimen, and wound up being used for that year's National Match load. He says several records were set with it.

I can only conclude from my experience and Hatcher's that powder ignition and burn characteristics have a lot to do with how sensitive they will be to charge weight. The expansion ratio of the gun and chambering as well as the bullet weight will affect these characteristics, so it's not surprising some guns see more of it than others.

Dan Newberry's site is dedicated to finding powder charge insensitive loads. It's worth a read-through.

 

[Sweet Shooter]

Sure I get that. I'm not saying every rifle will/can be made to shoot great with little to no attention to these kinds of details. I guess what I'm saying is when you've tried and failed to see a marked change/difference, it's probably time to look elsewhere for the fine tuning. It was upward fore-end pressure on a 700 that cut my groups in half with that gun for example. It's not the end-all.
-SS-

 

[Unclenick]

Actually it isn't always easy to tell when to look elsewhere. See my post #24 here. The Lyman #46 has a good chapter on statistics for shooting that shows how to use the T-test to tell if your improvements are statistically significant or not, so I recommend that for more in depth study.

Also, it you have a tight match chamber and a heavy barrel relative to caliber a lot of these issue get harder to detect because the gun corrects some of them by imposing better alignment with its tighter tolerances. The reason Creighton Audette fired his ladders out at 200 and Randolf Constantine recommended 300 is that with a good gun, you often don't discern the effects clearly at 100. Especially not velocity variation.