Various methods for determining seating depth?

[Coloradocop]

I need a little guidance on how to best determine the maximum cartridge length in my new gun. I was planning to use one of the Hornady tools with a modified case, but I simply can't find the .260 Rem modified case in stock ANYWHERE, which kind of eliminates that option. As such, I'm looking for alternative methods to figure out how long I can seat the bullet before it touches the lands.

I actually don't have a lot of experience with this particular process, since my last rifle had a maximum magazine length that was right at SAAMI spec for the bullets I was using... I never experimented with longer seating depths on that rifle, simply because it would have turned the gun into a single-shot rifle. My new AI has a bit more magazine clearance, but I don't want to load long without knowing when I'm hitting the lands.

I tried coloring the tip of a bullet with a marker and seating at various depths (including some that were barely in the case mouth), but I didn't notice any discernible marks on the bullet like I was hoping for (so, that method sort of fell short of expectations).

Any thoughts?

 

[AZ.noob]

If the sharpie method isn't showing any rifling contact, then the throat of your barrel is pretty deep. If your mock-ups were jamming into the lands, they'd probably be sticking in the bore

No worries, just pick a bullet that likes a jump. SMKs don't seem to mind jumping, whereas Bergers don't seem to be as happy doing that.

If you send a fired case (or two) to Hornaday, they can modify it for you to work with the gauge.

 

[1J04]

http://www.snipershide.com/shooting...d-loading-long-range-3-finding-start-oal.html

Good spot to start. But I just strip my bolt, load a dummy round long and begin seating the bullet deeper and deeper with the die, not the bolt, till the bolt "just" closes on it without resistance. If ya do this a few times you'll feel and definately see where the ogive makes contact.

Like this:

Bullet Seating Depth Method - YouTube

By the way, this is a great way also to check and see what setting your shoulders back only .001 - .003 feels like when closing your bolt with a slight crush or not on your resized brass, without a bullet in it of course.

 

[mdmp5]

I use the Sinclair gauge

 

[Coloradocop]

http://www.snipershide.com/shooting...d-loading-long-range-3-finding-start-oal.html

Good spot to start. But I just strip my bolt, load a dummy round long and begin seating the bullet deeper and deeper with the die, not the bolt, till the bolt "just" closes on it without resistance. If ya do this a few times you'll feel and definately see where the ogive makes contact.

Like this:

Bullet Seating Depth Method - YouTube

By the way, this is a great way also to check and see what setting your shoulders back only .001 - .003 feels like when closing your bolt with a slight crush or not on your resized brass, without a bullet in it of course.

Hmmm... may have to try this. The idea of removing the firing pin seems like a brilliantly simple way to avoid influencing this measurement with the bolt.

 

[1J04]

It's a sweet deal. Just strip your bolt and it will just bounce around nice and easy till either your case and/or your ogive begin to make contact. You'll feel it and know right off the bat. I'd recommend not using a fire formed case to check your seating depth cuz you don't want to feel any resistance of the case when the shoulder/datum makes contact.

On checking your fire formed cases that your setting the shoulder back a bit on you'll really enjoy the feedback you get on bolt tension also. Give them both a try, you're gonna like it.

Hmmm... may have to try this. The idea of removing the firing pin seems like a brilliantly simple way to avoid influencing this measurement with the bolt.

 

[mdmp5]

http://www.snipershide.com/shooting...d-loading-long-range-3-finding-start-oal.html

Good spot to start. But I just strip my bolt, load a dummy round long and begin seating the bullet deeper and deeper with the die, not the bolt, till the bolt "just" closes on it without resistance. If ya do this a few times you'll feel and definately see where the ogive makes contact.

Like this:

Bullet Seating Depth Method - YouTube

By the way, this is a great way also to check and see what setting your shoulders back only .001 - .003 feels like when closing your bolt with a slight crush or not on your resized brass, without a bullet in it of course.

If you are using sinclair comparator inserts, like this guy says he is, the measurement you get is not an actual measurement. It is a relative one. This is because the opening of the insert is the diameter of the bullet, and tapers down to an ogive measurement. For example, the 30 cal insert measures .308 at the opening, and tapers down to ogive contact at .300.

 

[Ultraman550]

I did this method mentioned above but I also took a fired round from my chamber, put it in my Redding Neck Sizing die with bushing and just lightly and I mean lightly as hell tapped on the press handle to give it a little bit of tension on the neck so the bullet I was using (175 smk) didn't fall into the case or get stuck to the lands. I placed the bullet in the case, pushed it in a very little but so it wouldn't fall out. I then loaded it into the chamber, slowly closed the bolt and waited about 5 seconds. When pulling the bolt back I press on the case with my finger to keep the bullet from sliding across the inside of the chamber. When the bolt is all the way back the extractor will hold onto it and actually point it out of the chamber making it easy for you grab by the case body or neck. I measured the bullet ogive to case base. I did this a total of 10 times and took the average. The variance between all 10 tries was like .002 so I took the average. When I want to jam I load .0015 off the lands, maybe .0020.

 

[phxfa]

tag for later

 

[mdmp5]

I did this a total of 10 times and took the average. The variance between all 10 tries was like .002 so I took the average. When I want to jam I load .0015 off the lands, maybe .0020.

Ultraman, you can take the mean, as you have done. But for a measurement like this, the ideal method is to use the MODE. I would measure until you get one measurement 3 times and use that.

 

[SWThomas]

When I want to jam I load .0015 off the lands, maybe .0020.

How are you jamming if you're loading off the lands?

 

[Jethro80]

I also bought the sinclair seating depth gauge and after watching their instructional video it makes perfect sense

 

[Squid284]

Thanks for posting this. I will have to try to compare this against my current method using the Hornady tool and a self modified case.

 

[1J04]

Ya, there's obviously many ways to skin this cat. I use the Hornady Comparator as I do this. I also make sure my gun is squeaky clean. You can also do the cleaning rod down the tube to the bolt face, put tape or a dot with a sharpy on the rod, remove bolt and put a bullet into the lands and use a pencil to hold it there, place rod back into the barrel and work the pencil and rod back and forth as you feel the ogive make contact, mark the rod again and it's a fairly good starting point measurement. So many ways, some more simple than others. I guess this is part of the excitement of reloading eh?

Thanks for posting this. I will have to try to compare this against my current method using the Hornady tool and a self modified case.

 

[bruddah]

I use the Hornady gauge. As mentioned, Hornady will modify one of your cases for you for a small amount of change. Or you can find a local machinist to chuck up the spent case and drill and tap the end to fit the threads on the Hornady tool.