Excessive seating depth with a twist

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barnfrog

barnfrog

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I have read a number of threads on the subject of potential hazards of seating bullets too deeply. They mostly focus on the effect of seating depth on load density and thus on pressure. I am wondering if there is another concern.

I loaded some .243 Win cartridges with Barnes 80 gr TTSX bullets on top of 43.0 grains of Hybrid 100V, varying the seating depth to do a test this weekend. Going on the advice I found on the Barnes website, I seated these bullets fairly deeply. The deepest is 0.225" off the lands. On these cartridges the bullets are so deep into the case that there is a gap between the bullet and the case mouth. In other words, the beginning of the ogive is past the case mouth. The pic below shows a 0.125" jump cartridge on the left and a 0.225" cartridge on the right, showing the gap.

upload_2021-2-24_21-25-22.png

Does this create any sort of hazard? I think there's still plenty of bullet bearing surface meeting the inside of the case neck. Will this gap allow pressure to release from the cartridge early? The powder charge is a full grain below the load at which I began to see very slight primer cratering and light ejector swipe, so I don't think the decrease in load density would create a huge pressure spike, but if I'm wrong on that score I'd love to hear it before I fire these rounds.

Thanks for any thoughts you all might have.
 
I've attached the SAAMI specs for .243. If you're not familiar, that's Small Arms and Ammunition Manufacturer's Institute. The diagram will hopefully help you understand a bit about the cartridge.

I'm not going to attempt to take you much farther on basic reloading here. I highly suggest that you buy a couple of reloading manuals like Barnes, Hornady, Speer, Sierra, or the like. I don't have a copy of Barnes, however, I would guess that it will tell you max and min cartridge length for that particular bullet.

Search this forum for basic reloading techniques, but remember that manufacturers have a big stake in your safety and want to avoid liability whereas us common folk don't have that same degree of accountability. That said, there are some very good reloaders on here.

We all were new to reloading and made oodles of mistakes. I for one am glad you dropped by with your question. Welcome.
 

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My question is why you seated them that deep to begin with?

Buddy did that back in the eighties and his excuse was he was using a lee loader that you used a hammer to rezise and seat. At least he did.

Three of those rounds out of his savage 110 7mm Rem Mag landed in less than a half inch much to our surprise.
 
NMexJim said:
I would advise that you not shoot any of these just yet.

Internal Ballistics - Hornady Manufacturing, Inc

Read this carefully. I, and I'm sure others will be posting more in just a bit.
Click to expand...

Thanks, Jim. I am familiar with SAAMI and their specifications, although I did not consult them this time around. I have the Lyman 50th edition in hard copy, which I refer to every time I load any cartridges to make sure I don't screw up the process. I also have half a dozen older manuals in electronic format, all of which I have read thoroughly and I don't recall seeing any specific reference to this issue, although I wasn't looking for it at the time so I may have forgotten about it. Mostly I recall them cautioning against cartridges being too long, not too short.

I read the entire page you linked, and I didn't see anything that appeared to address the gap I'm seeing, at least not explicitly.

The one SAAMI spec that I do see these shorter rounds do not meet is the minimum COAL of 2.540". The Barnes data I looked up only lists one COAL, which I figured was probably maximum, not minimum. So, since SAAMI does have a minimum COAL spec, it would seem prudent not to fire those rounds that do not conform with it.

fxvr5 said:
This looks like a question for Barnes.

https://www.barnesbullets.com/contact/
Click to expand...

Good idea. I'll drop them a line.
 
swg1 said:
My question is why you seated them that deep to begin with?

Buddy did that back in the eighties and his excuse was he was using a lee loader that you used a hammer to rezise and seat. At least he did.

Three of those rounds out of his savage 110 7mm Rem Mag landed in less than a half inch much to our surprise.
Click to expand...

Barnes's website indicates the TTSX tends to shoot well with larger than normal jump. They suggest starting at 0.050 off the lands and increasing in minimum increments of 0.025", and say that best accuracy may be achieved with bullet jumps of up to 0.250". I have seen numerous threads that seem to bear this out, suggesting that the Barnes monolithics like to be seated well off the lands.
 
I'm not an expert by any means, but lookig at this question, I'd be thinking about the lenght of the case that is actually holding the bullet - and considert that the effective case, and then wonder if my spec for case lenght is not too short. The intent of the minimum case lenght spec, from my understanding is to have enough tension to correctly hold the bullet, so - changing the hold the case has on the bullet - effectively IMHO may be shortening the case lenght below spec.
 
film495 said:
I'm not an expert by any means, but lookig at this question, I'd be thinking about the lenght of the case that is actually holding the bullet - and considert that the effective case, and then wonder if my spec for case lenght is not too short. The intent of the minimum case lenght spec, from my understanding is to have enough tension to correctly hold the bullet, so - changing the hold the case has on the bullet - effectively IMHO may be shortening the case lenght below spec.
Click to expand...

That's an interesting way to look at it. It's sort of what I was referring to when I mentioned the amount of bullet bearing surface making contact with the inside of the case neck. Oddly enough, because of the grooves around the TTSX there may be more contact between the bullet and the neck at this deepest seating depth than there is in the longest rounds I've loaded, in which the case mouth is at the mid-point of the top groove, as you can see in the pic below.

upload_2021-2-24_23-44-8.png
 
I won’t opine on if they’re safe or not. I usually load just off the lands, even with Barnes.

but I made a mistake and let my seating die get loose recently. I believe they are the 65 grain Barnes, maybe 80s, .243. I saw my mistake and purchased my first bullet puller.

These were test loads. Going up .2 grains every 5 rounds. But after reading this, I’ll measure them and if they are longer than min, I may shoot them. Probably won’t be until the weather warms a little.

Mine aren’t as far in the case as yours appear to be.
 
barnfrog said:
Barnes's website indicates the TTSX tends to shoot well with larger than normal jump. They suggest starting at 0.050 off the lands and increasing in minimum increments of 0.025", and say that best accuracy may be achieved with bullet jumps of up to 0.250". I have seen numerous threads that seem to bear this out, suggesting that the Barnes monolithics like to be seated well off the lands.
Click to expand...

Interesting. Thanks for the follow up.
 
barnfrog said:
I loaded some .243 Win cartridges with Barnes 80 gr TTSX bullets on top of 43.0 grains of Hybrid 100V, varying the seating depth to do a test this weekend.
Click to expand...
If I were you, I’d start with the longer of them, see how they shoot and if they met your expectation pull the really short ones. I’m presuming you did some load workup to find the optimum charge? I haven’t loaded Barnes, but have done plenty of lands tests and never found that much of jump would help precision. But then again, I’ve never gone that short, however, I would have expected ammo manufacturers in an attempt to have precise ammo would have employed that by now if it did work. Good luck.
 
barnfrog said:
I have read a number of threads on the subject of potential hazards of seating bullets too deeply. They mostly focus on the effect of seating depth on load density and thus on pressure. I am wondering if there is another concern.

I loaded some .243 Win cartridges with Barnes 80 gr TTSX bullets on top of 43.0 grains of Hybrid 100V, varying the seating depth to do a test this weekend. Going on the advice I found on the Barnes website, I seated these bullets fairly deeply. The deepest is 0.225" off the lands. On these cartridges the bullets are so deep into the case that there is a gap between the bullet and the case mouth. In other words, the beginning of the ogive is past the case mouth. The pic below shows a 0.125" jump cartridge on the left and a 0.225" cartridge on the right, showing the gap.

View attachment 980444

Does this create any sort of hazard? I think there's still plenty of bullet bearing surface meeting the inside of the case neck. Will this gap allow pressure to release from the cartridge early? The powder charge is a full grain below the load at which I began to see very slight primer cratering and light ejector swipe, so I don't think the decrease in load density would create a huge pressure spike, but if I'm wrong on that score I'd love to hear it before I fire these rounds.

Thanks for any thoughts you all might have.
Click to expand...
Shorten the neck to get a proper crimp at the point of the crimp groove - but not past minimum case length per spec’. Too much neck like that will shorten case life. I don’t know of any other real hazards so long as you’re keeping charge weight proportional to setback. Shortening case life is bad enough to do a proper trim and only takes a few seconds per case.
 
As someone new to reloading metalica, still reading and getting up to speed myself. But am beginning to notice a couple things. One is a disconnect between what reloaders are doing and what the bullet makers recommend as far as seating depth, and even SAMMI specs.

What I"m beginning to realize is SAMMI specs are by and large a standard for factory ammo. Guardrails to keep everyone out of the ditch. Will feed and chamber in almost all firearms chambered for the round. Not ideal for any single gun......probably far from it, but will chamber and fire in all of them, and would be accurate enough to kill a deer inside 100 yards, which probably covers 90% of the shooting world in this category.

Reloaders wanting far better than that willing to test the guardrails in favor of performance and accuracy. One of those guardrails is seating depth to gain accuracy. It seems most go longer than specs while chasing the lands. Seems there was a study about that, and everyone has assumed that is gospel, so many do it. What is that magic spec........ .002 off the lands to start? Except if Barnes is saying something different, then they are in good company. I've seen stuff from a Nosler ballistic engineer who said bullets need a bit of jump.......way more than .002 for sure. He mentioned as much as 0.200. And I'm finding multiple other sources suggesting best accuracy is not to the lands, but somewhere between the lands and minimum OACL to be found by trial and error, which backs up Barnes and Nosler and probably others.

All very confusing to someone trying to sort it all out. But one thing I would believe, at no time would I want to seat a bullet so deep there is unsupported case neck sticking out proud of the bullet. That don't seem right.
 
barnfrog said:
Barnes's website indicates the TTSX tends to shoot well with larger than normal jump. They suggest starting at 0.050 off the lands and increasing in minimum increments of 0.025", and say that best accuracy may be achieved with bullet jumps of up to 0.250". I have seen numerous threads that seem to bear this out, suggesting that the Barnes monolithics like to be seated well off the lands.
Click to expand...
Barnes Farms'''' What does your rifle indicate for optimum seating depth?
BTW: when someone says jump xxxx amount im pretty sure they are not suggesting a measurement deducted from SAMMI min or max rather from their representation of the point to where the projectile is contacting the lands.
 
Last edited:
Walkalong said:
That's not good, and I can't imagine any proper chamber that needs the bullet seated that deeply.
Click to expand...

Exactly what I was thinking, which is I why I asked. I just don't know if it's actually hazardous to shoot them. From a curiosity perspective I want to fire them, but I have no desire to risk injury to myself in the interest of science.

lordpaxman said:
I’m presuming you did some load workup to find the optimum charge?
Click to expand...

Yes. The factory Barnes ammo shoots well out of my rifle, so I started by matching their seating depth and tested loads to find maximum powder charge. My best groups were at 42.0 and 43.0 grains. Slight pressure signs started appearing at 44.2 grains, a couple tenths below Barnes's listed max of 44.4, which they show as a compressed load. So I backed off to 43.0 and loaded these up to see if adjusting the seating depth would improve accuracy.

lordpaxman said:
If I were you, I’d start with the longer of them, see how they shoot and if they met your expectation pull the really short ones.
Click to expand...

That's my plan at this point.

GeoDudeFlorida said:
Shorten the neck to get a proper crimp at the point of the crimp groove - but not past minimum case length per spec’.
Click to expand...

I don't believe the grooves on the TTSX bullets are intended for crimping. From the Barnes website FAQ: "We usually don’t recommend crimping our smaller-caliber bullets. However, if you choose to do so, a light crimp is best." Monolithic bullets build higher pressures, and the grooves are actually intended to compensate for that, as evidenced by the phrase "Grooved for lower pressures" on the website.

South Prairie Jim said:
What does your rifle indicate for optimum seating depth?
Click to expand...

Not quite sure what you mean. This rifle does seem to prefer more bullet jump, based on other loads I've worked up. For instance, the last load I worked up was for 75 gr HPBT bullets with IMR 4350. The groups tightened up considerably as I went from 0.010" to 0.050" in 0.010" increments. These were just practice rounds and I was getting 0.6 MOA accuracy, so I didn't bother to go any deeper.

South Prairie Jim said:
BTW: when someone says jump xxxx amount im pretty sure they are not suggesting a measurement deducted from SAMMI min or max rather from their representation of the point to where the projectile is contacting the lands.
Click to expand...

Yes, I understand that. I have measured the CBTO for the Barnes 80 gr TTSX in my rifle necessary to just touch the lands, and subtracted from that to get the seating depth to achieve the bullet jumps I had intended to test.

Thank you for the link, AJC1. The Barnes load data page for .243 bullets has been among my bookmarks for quite some time.
 
I always understood the overall length spec on rifle ammo as the best case for accuracy using that particular set of components in the firearm or test barrel they used that day. I set my length as the longest length that will feed from the MAG and reliably chamber. There should be at least one caliber of bullet in contact with the case neck to assure good neck tension as well.

For handgun ammo it is the minimum COAL to keep you from going overpressure by reducing internal case volume at the published max load.
 
Howa 9700 said:
As someone new to reloading metalica, still reading and getting up to speed myself. But am beginning to notice a couple things. One is a disconnect between what reloaders are doing and what the bullet makers recommend as far as seating depth, and even SAMMI specs.

What I"m beginning to realize is SAMMI specs are by and large a standard for factory ammo. Guardrails to keep everyone out of the ditch. Will feed and chamber in almost all firearms chambered for the round. Not ideal for any single gun......probably far from it, but will chamber and fire in all of them, and would be accurate enough to kill a deer inside 100 yards, which probably covers 90% of the shooting world in this category.

Reloaders wanting far better than that willing to test the guardrails in favor of performance and accuracy. One of those guardrails is seating depth to gain accuracy. It seems most go longer than specs while chasing the lands. Seems there was a study about that, and everyone has assumed that is gospel, so many do it. What is that magic spec........ .002 off the lands to start? Except if Barnes is saying something different, then they are in good company. I've seen stuff from a Nosler ballistic engineer who said bullets need a bit of jump.......way more than .002 for sure. He mentioned as much as 0.200. And I'm finding multiple other sources suggesting best accuracy is not to the lands, but somewhere between the lands and minimum OACL to be found by trial and error, which backs up Barnes and Nosler and probably others.

All very confusing to someone trying to sort it all out. But one thing I would believe, at no time would I want to seat a bullet so deep there is unsupported case neck sticking out proud of the bullet. That don't seem right.
Click to expand...

SAAMI also set the min/max cutting standards for chambers.

The best way to get started is with a good reloading manual. There's lots of reloading general info as well as specific loading for a caliber. I would suggest that you start by following one of the given loading screen exactly - bullet, powder, primer and seating depth. Then, keep studying.
 
GeoDudeFlorida said:
Shorten the neck to get a proper crimp at the point of the crimp groove - but not past minimum case length per spec’. Too much neck like that will shorten case life. I don’t know of any other real hazards so long as you’re keeping charge weight proportional to setback. Shortening case life is bad enough to do a proper trim and only takes a few seconds per case.
Click to expand...

I wanted to follow up on this a bit. Regarding the case trim length, SAAMI spec is 2.045 minus 0.020 according to the diagram NMexJim provided. If I understand that correctly, the acceptable case length range is 2.025 to 2.045. The Lee case trimming tool I use trims cases to 2.0375. If I were to trim down to the very minimum of 2.025, there might not be that gap between the neck and the bullet. The cartridges would still look quite short, but I guess the real question is whether or not there is any practical effect to trimming them shorter. Can you elaborate on how the neck material being proud of the bullet shortens case life? Does it somehow get hardened faster?

Also, can you give any specifics on "keeping the charge weight proportional to setback?" I think you're referring to the fact that at some point seating the bullet deeper reduces case capacity enough and thus increases load density enough to create a pressure spike. As I alluded to in my original post, I've read a bunch of threads on that topic, but most of them caution against the pressure spikes that are generated by seating bullets too close to or touching the lands. IIRC they all generally agree that initially moving back from there will decrease pressure, until you reach some unspecified point at which pressure will start to rise again. So in the case of these rounds, firing the longest first and working towards the shortest is also a pressure test of sorts. Or are you referring to something else?

Thanks to everyone who has offered thoughts. Also a public apology to NMexJim if I seemed snotty in our PM exchange. I certainly meant no disrespect and truly do appreciate your time and effort.
 
barnfrog said:
I wanted to follow up on this a bit. Regarding the case trim length, SAAMI spec is 2.045 minus 0.020 according to the diagram NMexJim provided. If I understand that correctly, the acceptable case length range is 2.025 to 2.045. The Lee case trimming tool I use trims cases to 2.0375. If I were to trim down to the very minimum of 2.025, there might not be that gap between the neck and the bullet. The cartridges would still look quite short, but I guess the real question is whether or not there is any practical effect to trimming them shorter. Can you elaborate on how the neck material being proud of the bullet shortens case life? Does it somehow get hardened faster?
Click to expand...
I have seen cracking with bullets set back behind grooves like that, mostly with 7.62x54R and .303 Mk.VII British service rounds where the groove is a true crimping groove and kind of "aggressive." That's my only experience with trying this kind of thing. In both of those rifle rounds with surplus rifles where the rifling is a bit worn from corrosive ammo use, leading the chamber helps improve accuracy but at the cost of case life. The neck expands with pressure to seal the chamber. Having it "scraped" and potentially scorched can be bad. It's not an absolute, just something to watch for. If you see signs of cracking along the edge of the neck, cut them back a bit.

barnfrog said:
Or are you referring to something else?
Click to expand...
Nope, that. I think its always smart to decrease charge a little as you decrease volume. Maybe not necessary but I still have all of my fingers and no blowed up guns in all the time I've been making custom loads - starting around 1977 - so maybe its over-caution or maybe maybe its playing safe. Either way, I still got all my fingers and no blowed up guns so, "works for me." :)
 
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