Seating Depth / Lands Measurement Way Off?

[_Thor_]

Reloading novice here - I've got an RCBS Matchermaster FL die set that I've been using for a while but never explicitly tested anything with seating depth. This is for a 6.4 CM Tikka that was recently rebarreled with a Proof Match Contour 26" steel, machined from a blank by a gunsmith. I've picked up the Hornady OAL tool and Hornady bullet comparator set, and I'm going through the process of trying to find the lands on my setup using the same 140gr ELDMs I've been loading for this rifle for a while (with mediocre results due to my inexperience). The way I initially set up my seating die was just to match the COAL of the factory 140 ELDMs I shoot regularly. However, consistenly I find that with the OAL gauge I'm seeing a much shorter length for the lands vs the length I already load my reloads to (or to what box ammo is at).

In the comparator, I'm seeing this:

• OAL Gauge: 2.1075
• Reloaded 140gr ELDM seated with "4.30" on the die mic: 2.1915
• Factory 140 gr ELDM: Also 2.1915
• Dummy round loaded with 140 ELDM, die at "3.45": 2.1040

I've checked the OAL measurement several times and even tried pushing "hard" on it to see if it wasn't actually into the lands, but I get the same measurement plus or minus maybe 1 thou. The difference is COAL is very obvious between box ammo vs what is supposedly "at the lands".

In the picture, the top is the OAL gauge's modified case at the lands, supposedly, and the others are as labeled. The last picture shows more clearly that there's scuffing on the ogive for basically all of them, but especially the longer ones. Those that measured 2.1915 are very difficult to cycle, and oddly that includes the factory/box ammo. I tried a couple, and one I had to smack the bolt back to get it out, while the other factory round cycled more or less normal. I do recall from a recent match shooting box ammo that I had some difficult cycling at times, but I thought at the time it was maybe heat-related or not to do with my ammo at least. Note also that when I loaded a dummy at the lands measurement, it cycled with no resistance.

1. Why would factory ammo be so tight in this rebarrel? Is that an indication that my gunsmith spun the barrel incorrectly, or maybe they were to tight on the chamber? Should that be considered defective?
2. Am I missing anything in my process measuring the lands, or would it be logical to find the lands and then just back off .020-.060?
3. Is it even safe to send something like the shorter rounds pictured? How can I tell the minimum overall length that's safe?

 

[Maurygold]

step 1: stop using OAL (base to tip) this is a useless measurement and you do not need it for anything ever unless you need to measure if a bullet will fit a magazine
Step 2: only use ogive measurements - this is where your bullet will contact the lands and you have the guages in the hornady kit

There may be something wrong with your chambering if your factory rounds need to be forced in. Factory rounds are intentionally very short, so they can universally fit into different chambers.

I would never attempt to use a barrel where factory rounds wouldn't fit in it. The first thing I would do is rent a go/no-go gauge (https://4drentals.com/) to see if it's spec'd right before I asked gunsmith to look at it.

 

[jetjock07]

If factory ammo is being jammed into the lands then I would definitely be looking at the chamber job by the gunsmith.

COAL will vary bullet by bullet. The best measurement is Base to Ogive (BTO). That is more consistent from bullet to bullet and may vary by only a couple of thousandths.

Best way I’ve found is to find lands is to seat bullet longer, then take marker and color entire bullet, i sweet into chamber by hand, then close the bolt. The lands will take the marker off. Take dummy round out and seat deeper. Keeps doing this till either you can barely see a mark or no mark at all. If when doing this if the mark is heavy you can seat say .005 at a time but as the mark becomes lighter you want to go slower by .001-.002 at a time. Hope that helps. There are several videos on the tube that show various ways to finds lands.

 

[LR1845]

@_Thor_ First thing you need to do is talk to the smith that chambered that barrel and find out what free bore his reamer has as there are several different reamers, Alpha lists 4 choices(I think)for free bore....I believe the sami reamer has a .199 free bore.

How many rounds through this barrel? Have you cleaned it? I ask because, and I am no expert and may be wrong, but where the marks are hitting the bullet look more like carbon or a carbon ring than the bullet going into the lands...unless you opened and closed the bolt several times.

 

[_Thor_]

step 1: stop using OAL (base to tip) this is a useless measurement and you do not need it for anything ever unless you need to measure if a bullet will fit a magazine
Step 2: only use ogive measurements - this is where your bullet will contact the lands and you have the guages in the hornady kit

There may be something wrong with your chambering if your factory rounds need to be forced in. Factory rounds are intentionally very short, so they can universally fit into different chambers.

I would never attempt to use a barrel where factory rounds wouldn't fit in it. The first thing I would do is rent a go/no-go gauge (https://4drentals.com/) to see if it's spec'd right before I asked gunsmith to look at it.

I don't see any go/no-go gauges on that site, am I searching it wrong?

If factory ammo is being jammed into the lands then I would definitely be looking at the chamber job by the gunsmith.

COAL will vary bullet by bullet. The best measurement is Base to Ogive (BTO). That is more consistent from bullet to bullet and may vary by only a couple of thousandths.

Best way I’ve found is to find lands is to seat bullet longer, then take marker and color entire bullet, i sweet into chamber by hand, then close the bolt. The lands will take the marker off. Take dummy round out and seat deeper. Keeps doing this till either you can barely see a mark or no mark at all. If when doing this if the mark is heavy you can seat say .005 at a time but as the mark becomes lighter you want to go slower by .001-.002 at a time. Hope that helps. There are several videos on the tube that show various ways to finds lands.

I'm using the Hornady comparator and zeroing it out with the base on the micrometer, then measuring with the cartridge inserted. Is that the correct way to measure BTO?

I'll give the other method a try as well for finding the lands. This sounds like the Erik Cortina method, if I remember correctly?

@_Thor_ First thing you need to do is talk to the smith that chambered that barrel and find out what free bore his reamer has as there are several different reamers, Alpha lists 4 choices(I think)for free bore....I believe the sami reamer has a .199 free bore.

How many rounds through this barrel? Have you cleaned it? I ask because, and I am no expert and may be wrong, but where the marks are hitting the bullet look more like carbon or a carbon ring than the bullet going into the lands...unless you opened and closed the bolt several times.

About 400 rounds through this barrel. It was cleaned about 100 rounds ago. I don't think the marks are carbon because they're shiny scuffs.

As for asking the smith about the reamer, I can do that, but what do I do with that information after?

 

[Maurygold]

I don't see any go/no-go gauges on that site, am I searching it wrong?



I'm using the Hornady comparator and zeroing it out with the base on the micrometer, then measuring with the cartridge inserted. Is that the correct way to measure BTO?

I'll give the other method a try as well for finding the lands. This sounds like the Erik Cortina method, if I remember correctly?



About 400 rounds through this barrel. It was cleaned about 100 rounds ago. I don't think the marks are carbon because they're shiny scuffs.

As for asking the smith about the reamer, I can do that, but what do I do with that information after?

has it always been hard to close on factory or is this new? I assumed it was a new barrel.

I guess 4d stopped renting them, but you can buy a no-go gauge from them if you're concerned.

 

[LR1845]

I don't see any go/no-go gauges on that site, am I searching it wrong?



I'm using the Hornady comparator and zeroing it out with the base on the micrometer, then measuring with the cartridge inserted. Is that the correct way to measure BTO?

I'll give the other method a try as well for finding the lands. This sounds like the Erik Cortina method, if I remember correctly?



About 400 rounds through this barrel. It was cleaned about 100 rounds ago. I don't think the marks are carbon because they're shiny scuffs.

As for asking the smith about the reamer, I can do that, but what do I do with that information after?

You'll know if your free bore is short and why factory ammo is jammed into the lands.

 

[_Thor_]

has it always been hard to close on factory or is this new? I assumed it was a new barrel.

I guess 4d stopped renting them, but you can buy a no-go gauge from them if you're concerned.

No, it hasn't been hard to close before the rebarrel. Also, I just ran another ~8 rounds from the same box through the mag and in fact the only one it really binds on is the one I picked originally and sharpied. The others run fine. Like I said, it was an occasional thing during the match too, but it seems somewhat infrequent. Just now I thought maybe that one round was different in terms of BTO (assuming I'm measuring that right), so I put that in my comparator vs the other rounds that cycled fine but actually found either no difference or that the "good" rounds were slightly longer BTO (2.1915 vs 2.1935). So I'm not sure what to make of that. Also, cycling all those rounds through did put a scuff on most of them near the ogive, which makes me think this chamber is just tighter. Given that, wouldn't a no-go gauge certainly "work", but the risk would instead be that the "go" gauge wouldn't close?

The main question in my mind is, if my measurements of the lands say to seat them .070 - .090 shorter, is that 1) safe and 2) likely to lead to better results?

 

[Maurygold]

No, it hasn't been hard to close before the rebarrel. Also, I just ran another ~8 rounds from the same box through the mag and in fact the only one it really binds on is the one I picked originally and sharpied. The others run fine. Like I said, it was an occasional thing during the match too, but it seems somewhat infrequent. Just now I thought maybe that one round was different in terms of BTO (assuming I'm measuring that right), so I put that in my comparator vs the other rounds that cycled fine but actually found either no difference or that the "good" rounds were slightly longer BTO (2.1915 vs 2.1935). So I'm not sure what to make of that. Also, cycling all those rounds through did put a scuff on most of them near the ogive, which makes me think this chamber is just tighter. Given that, wouldn't a no-go gauge certainly "work", but the risk would instead be that the "go" gauge wouldn't close?

The main question in my mind is, if my measurements of the lands say to seat them .070 - .090 shorter, is that 1) safe and 2) likely to lead to better results?

if the scuff is on one side thats just feed ramp as you push from magazine. It is very unuusal to see a factory round near the lands in my expereince but you have quite a few things happening at once here to try to diagnose anything

 

[_Thor_]

if the scuff is on one side thats just feed ramp as you push from magazine. It is very unuusal to see a factory round near the lands in my expereince but you have quite a few things happening at once here to try to diagnose anything

I just checked, and the scuffs are all the way around on all of them