Have you ever or have you considered doing an article on bullet seating depth? This is one part of my reloading that still remains a bit of a mystery to me and I was wondering if there were any detailed articles on it.

Would be interesting read.

Good suggestion.

I think it would be a difficult article to do because of all the variables. Some bullets prefer a jump. Some guns are more accurate with a jump. Others prefer being right up against the lands. Ultimately the article would probably tell us we simply have to experiment.

centershot,

Actually I'm working on an article primarily about that very subject for November's issue of RIFLE LOONY NEWS.

Great what I would like to know is can you determine anything about group shape and bullet seating? Some people claim they can and it seems to work for them but for me it's like trying to read tea leaves. Is there any other way other than trial and error to figure out optimal seating depth? I start out at maximum magazine length and work backwards usually if three to five increment depths don't work I figure it is the load.

Looking forward to it MD. I remain mystified about the best approach.

I look forward to that article too JB.

Currently working with a 7x57, economy A&B 21" bbl ( I was gifted several vz-24 recievers, A&B bbls in various chamberings, reamers, go/nogo gages, Timney triggers, sporter stocks, & so forth). Dyna coated the bore due to the A&B bore is very prone to copper foul.

Anyhow, worked w/ Hornady 139 IL & Nosler 150 BT. Goal is to get some background w/ Nosler BT, then work with 150 Nosler Accubonds for the final load.

Seated the Hornady to 3" oal, per Hornady book. I did the slit case neck, start bullet, push case in chamber until case shoulder butts chamber shoulder. OAL =3.080". Hornady 139IL jump is ~0.080". 2700 fps per crono, makes 1 3/4" @ 100.

Nosler 150 BT seated to 3.070" (SAMII max is 3.065" per Nosler book). I did the slit case neck, start bullet, push case in chamber until case shoulder butts chamber shoulder. OAL =3.150".

I conclude that the Nosler 150 BT is jumping ~0.080". This shoots ~1.00-1.25" @ 100 yard. W/49gr IMR 4350 makes 2815 fps per crono.

Intuition tells me to jump the Nosler BT a bit less, say 0.050" using same powder weight. Given I'm working with an A&B barrel, could be that 1" 3-5 shot groups could be all I can expect.

I've always approached seating depth (bullet jump) as trial & error. I'll say it again, looking forward to that article JB.

Pat

Ya know......the 'fire seems to have such good timing for you. Are you sure this isn't a set-up?........

If anybody wants to keep it really simple (which is the primary reason any shooter looks for simple solutions on the Internet), start with the bullet seated as far out as possible, whether limited by the magazine or chamber throat. Then if the accuracy isn't all you expect, seat 'em deeper and see what happens. Unless rifle bullets are seated REALLY deeply (which isn't what occurs most of the time), then pressures are lower with deeper seating.

The article will go into a little more, uh, depth.

I had an A&B barrel that would consistently average 3/4" at 100 yds with its favorite load. It was also on a Vz-24 ,but was a .458 winchester . I liked the barrel and it only fouled about like most factory barrels. A 150 gr Accubond at 2800 and grouping an inch would be fine killing medicine in my book........

Is there a rule of thumb that is close but ensures that variances in the bullets does not create an issue? .020, .030, .040 or so just to be safe but still typically gives good results?

Looking forward to article.

Aha! I see what you did there JB!

Centershot,

I haven't found any rule-of-thumb to work consistently, probably because bullet construction and shape varies too much these days. Chamber throats are another factor, whether custom or factory.

Centershot,

Perhaps you are asking, "How far out (how close to the lands), when not limited by magazine length, can one seat the bullet so as not to create an issue (pressure issue), considering variances from bullet to bullet?

If that is your question, then you realize that touching or jamming into the lands causes a significant rise in pressure as opposed to being somewhat short of the lands, and you are concerned with bullet variance. You wouldn't want one bullet out of ten to hit firm against the lands and have a higher pressure and velocity than the other nine rounds.

Today's bullets don't vary a whole bunch. I remember some old manuals suggesting as much as .030" for hunting loads. With today's bullets I am comfortable with .010" to .015" off the lands to start with, then work shorter (more jump) from there looking for best accuracy. That should keep all bullets in a batch from actually hitting the lands. And just as important, preclude having a random bullet stick in the lands and stay there when you extract a loaded round.

Barnes has always suggested seating their all-copper bullets at .050" off the lands for accuracy and pressure reasons. This was more important with their older non-grooved bullets, I believe, but many people find good results at that seating depth with their bullets.

Others may have their own thoughts on this. If I correctly interpreted your question, I hope this helped. Good luck.

nifty, that is exactly what I'm asking/concerned about. I like to get all the accuracy I can but am not interested in blowing up my rifle for 1/8" better groups.

One other question I have - Is a bullet comparator the way to go or is measuring OAL with a good un-marred bullet good enough?

I like a comparator. The Sinclair "nut" is a good way to go, and relatively inexpensive.

https://www.sinclairintl.com/reload...-style-bullet-comparators-prod83792.aspx

Another fan of the Sinclair nut. I've been using one for thirty years.

A bullet comparator. I use the Stoney Point/Hornady comparator but the Sinclair nut MM mentions is less expensive.

I used the Stoney Pt comparator for several years, but only with cartridges for competition rifles. For military surplus and hunting rifles, I never noticed any difference, so I quit using it.

With improvements to both bullet mfging and rifles, I don't see a need. Load. Shoot. Smile.

A bullet comparator is the best way to go, and you will find that most good bullets measure within a couple of thousandths.

Without a comparator, just use two or three or four bullets to compare with each other to determine exactly where the lands are, and to determine the average OAL to the bullet tip. Ensure that they reasonably agree and that you didn't just happen to pick the shortest or longest bullet in the box.

As Steve says, as long as you know you aren't unintentionally hitting the lands, and you aren't exceeding reasonable pressures, just load, shoot and smile.

I have both the comparator and case length gauge, each with a dedicated Mitutoyo caliper for the bodies. For me, they are as important for accurate ammo as a concentricity gauge.

For your hunting rifles or competition built rifles?

I use the rolling round on a mirror technique, and I quite clearly distinguish those with no apparent wobble from less concentric rounds. On the best, apparently straight rounds, how far off straight might this still be?

Wrapids,

I use the Sinclair concentricity gauge, and I had never played with rolling rounds on a mirror before. So I got out a mirror and some ammo and played with them a bit.

I found it difficult, with my old eyes, to really see any wobble until the gauge said the bullet was showing about .010" out of round (+/- .005").

That is about three times more out of round than I hold most of my ammo to. And I am no benchrest shooter, either.

What do others say? I don't think I would be happy just using a mirror.

Can you explain this a bit? It would seem the opposite happens given that the volume in the 'powder room' is actually decreased by seating the bullets deeper.

Using the ideal gas law: pv = nrt where n and r are basically constants, p is pressure, v is volume, t is temp. If v (volume) decreases due to deeper bullet seating, pressure must rise to keep the system in equilibrium.

What am I missing? .

You're missing a couple of things. While pressure starts to build as soon as the primer ignites, it doesn't rise nearly as rapidly until the bullet hits the rifling, due to the force required to engrave the bullet. Seating bullets deeper essentially results in a longer throat, giving the bullet more room to accelerate before engraving on the rifling.

This is exactly why custom chambers for Weatherby cartridges that eliminate the longer "freebore" result in much higher pressures: The bullet hits the rifling much sooner, and pressures skyrocket. The freebore results in a flatter pressure curve.

The same effect is created by seating bullets deeper, which essentially increases case volume, rather than decreasing it as you suggest. The "pressure vessel" is essentially the entire chamber, to the beginning of the rifling, rather than the space occupied by the powder to the base of the bullet.

Second, modern rifle powders are progressive-burning: After ignition they burn slowly, due to either granule size (large granules have less surface area for their volume) or burn-deterrent coatings, or both. As they continue to burn, they burn faster--but by then the volume has increased considerably, due to the bullet being further down the bore. Like a longer throat, this flattens the pressure curve.

The opposite effect is usually seen in handgun rounds, where seating bullets deeper increases pressure. First, many if not most handgun powders are degressive-burning: They start off burning very fast, then slow as the burn progresses. Seating bullets deeper encourages this initial fast burn, increasing peak pressure. Handgun chambers also have very short throats, especially in semiautos.

Ahhh that makes sense. I didn't consider the chamber and was only thinking of the case itself as the 'volume' under consideration.

Thank you!

Glad to see this here John. ^^^




Throughout my years of hand loading, I have always put more emphasis on the internal ballistics aspect. I guess I got that from the early loading manuals from way back when. Some manuals used cartoons to explain. Made it easy for me.


18 hours of chemistry and physics in college help a little. Not a lot.

I find determining seating depth for best accuracy a lot easier with cup and core bullets.

Monos, any brand, can be really pissy about seating depth in specific rifles. The best I have been able to work out is that you have to not only account for seating depth by itself, but also the effects of fouling, specifically copper fouling. I have solved more than fifty, maybe more than 75 rifles now for monos. I always use the Hornady (Stoney Point) gauge and comparator.The only "shortcut" I have found with them is start at ~.050 off and work up to best accuracy/max load. Sometimes that's all it takes. Usually to get MOA/sub MOA, I need to adjust depth. I have learned that I cannot begin to predict What a rifle will like. What I do is to bump them out to .010 or .005 off and start working back in .010 incements. I do not recall having found any that were out past .150 off. I have fount a couple that were close though.

One thing that I have also learned is that the "classic" 2 and one pattern doesn't mean much if anything. Normally that pattern is a signal to adjust seating depth. Monos are extremely consistent bullets. The don't have voids in the core, they do not have wrinkles in the jacket. They are vastly less susceptible to damage. I find that if I get down to less than 3 inches and just cannot shrink the groups any further it is best to go looking for a node. I have a 26 inch Sendero 25-06 that should produce 3400or a little better with 100 grain monos. It will do almost 3500with carefully selected loads, but so far I just cannot get to MOA at those velocities. By accident I discovered the barrel is flat out accurate. I bought a few boxes of Black Hills Gold ammo really cheap for the bullets and cases. On a whim I shot a few. Well under and inch! So, I immediately started with the measuring. It showed me that the difference was solely velocity. The Seating depth is identical, Case length identical to what I had worked up. I backed down the loads to a very pedestrian (for this rifle) 3225 and there it is, sub MOA. Normally, I will not chase velocity. This rifle was bought for one purpose, to move a 100 grain bullet fast and deliver all the velocity possible out at 500 + yards. The project now has been reduced to finding a powder that produces 3400+ and allows that barrel to produce a node there. I even went so far as to try a donut on the barrel to see if it would help. Problems like this are where Quickload can help.

Miles,
Most of what you said is what I have learned through trial and error too.
Late this summer I backed off the charge of slow burning powder in a 243 and went from 1" + groups to 1/2" groups.

Yeah, your case volume starts to increase the moment the bullet starts to move forward. This is why MD's suggestion is the most simplified, boiled-down way to approach seating depth- start at the depth that produces the highest pressure, work up your powder charge to wherever you want it, and if accuracy isn't there, work seating depth backwards, going deeper and deeper, until you find the accuracy you're looking for, since pressures will only get lower and lower (until you've got the powder column packed with a fair bit of compression) as you go. Seems I've heard this before..."kiss, find pressure, and rock on"

You need to realize that once you start working with custom throats rather than SAAMI-spec throats, all those max COAL suggestions go out the window. They give you those max COAL numbers to guarantee that your ammo will fit in any SAAMI chamber. If you're loading for a particular rifle, you can determine your own max COAL by finding where the bullet contacts the rifling, and then the max COAL that I've commonly seen and used, is 0.030" into the lands, and that's typically only used for BR-type shooting. That would be the max, but reliability may suffer with that deep of a jam, so you may want to consider 0.010" into the rifling (or until the rifling makes a square engraving mark on the bullet when the cartridge is chambered) as max COAL for reliable hunting and field ammunition. Then work backward until you find optimal accuracy.

Of course, this hinges on you having enough magazine box length to accommodate these max OAL's, and if not, then your mag box max length, minus about 0.010-0.020", becomes your max COAL for a repeater. If you don't mind feeding the rifle as a single shot, then mag box constraints are irrelevant.

I had a tech at Western powders tell me that the pressure will increase by seating the bullet deeper in small amounts. I didn't think that was correct because I had read Mule Deer's material on this subject before. I couldn't believe i was hearing that misinformation directly from a powder company.

Good point!

You might want to look into 4451. The last .243 I solved for Barnes TSXs really liked it and when my scale messed up and I got a substantial overload, the L-R was right with the group but the vertical for that shot was an inch or so up. If I remember right the chrono was showing me over 3400 before the overload and I was still under Max load for paper that was showing 3/4 inch.

One thing I'll not be doing is jamming, or even touching the rifling lands with bullets, for hunting rifles. When I remove an unfired cartridge from a chamber I want the bullet to remain in the case.

I'll not do that for my F-Class rifle as well. Seen others who jam bullet, have to remove cartridge from chamber for whatever reason, then have to grab a rod to remove jammed bullet.

Kills any sort of cadence they had when shooting timed fire.

Agreed on the hard jam. If you have 0.002-0.0025" of neck tension or more, a light kiss won't cause problems, and often results in great accuracy.

Mule Deer I appreciate your explanation on the seating vs pressure but at what point does deep seating increase pressure in rifle cartridges?
Also does crimping increase pressure or make it more uniform as some claim like Lee? Other than jamming the bullets is the pressure difference due to seating enough to need to drop down in charge weight and work back up? Currently I don't only when switching from standard to magnum primers or other component changes will I work up again.

This thread is a wealth of knowledge. Wow. Thanks all.

Miles, what did you mean by "classic 2 and 1 pattern"?

Tejano,

The pressure results I've seen indicate pressures start rising when rifle bullets are seated pretty deeply, close to 1/2" deeper than out to the lands, or maximum magazine length. Probably that's when powder compression starts to play a role, but also probably varies with the type of powder, primer, etc. I can't even remember ever seating rifle bullets as much as 1/4" shorter than normal, so I've never found any need to reduce the powder charge.

Quite often velocities drop measureably as bullets are seated farther off the lands, though not always, especially when bullets are seated only a little deeper. This also depends on the particular bullet, powder, primer etc.

Crimping may have some effect, but I've never seen enough difference in velocity to assume it does. But I don't crimp rifle bullets very often, even in some cartridges where many handloaders assume it's necessary. Consistent neck tension on the bullet normally has more effect on both accuracy and pressure than crimping.

MD,
Excellent point about crimping.
I have gone through stages where I have tossed dies that did not size cases enough to those that over sized in order to obtain a consistent hold on the bullet to the point that I have never crimped a .460 Weatherby load, even when using up to 550gn and 600gn bullet at full velocity in generating 8000FPE.

By contrast, I have however, crimped "some" .458 Winchester and .45/70 loads, but it was for assumed assurance, rather than need.

John

Seating depth experiments using new, unfired Remington case. Seating depth test where 0.050", 0.035", 0.020" cartridges assembled.

Determined the 150 BT is best with 0.020" bullet jump. Makes ~0.63" groups @ 100 yards.

Tried the Hornady 139 IL with 0.040" jump. Groups opened to ~2.50" at 100 yards (was 1.75" w/0.080" jump). Could be a powder thing with the 139, using IMR 4064. Need to work with IMR 4350 with this boolit. Maybe the Hornady likes to jump that 0.080", and that's why Hornady book suggests an OAL of 3.00".

Using once fired cases where shoulder is bumped back from chamber shoulder to allow 0.0015 headspace will tighten groups more.

Been my experience oversized cases ( where shoulder is bumped back excessively), or where successive neck size only results in case shoulder bumping chamber shoulder opens groups. My experience with what I described was from experimenting with a 95 Palma chambered f-class 308 rifle. This has translated to other rifles I work with.

That's very helpful. Seating depth has always seemed like voodoo to me. I usually load to SAAMI specs and call it good. However, I've always known that I was "leaving something on the table" so to speak, by not learning more about the theory and practice of varying seating depth for optimal accuracy.
Looking forward to seeing your article.