# Seating Depth / Neck Tension



## KineKilla (Jan 28, 2011)

Had some time this weekend to get out to the range for some field testing and on the one hand things went fairly well. I have one of my rifles (.270WIN Mod.700 ADL) that is finally starting to group half decent after MANY range sessions, stock work, new scope base/rings and tweaks to my reloading processes.

I've been loading at book values (Nosler) and have narrowed the optimal charge weight to right around 50.1 - 50.3gr of IMR4831, 
trim length of 2.53 (.01 under SAAMI Max), 
and a seating depth of C.O.A.L. 3.32 using Accubond 140gr. (CBTO 2.77)

.270WIN,50.1gr IMR4831 @ 100yds (1.25" max spread)










.270WIN, 50.3gr IMR4831 @ 100yds (1" max spread)










So, my next plan is to begin adjusting seating depth to find that perfect distance from the lands in this rifle. I have the Hornady OAL gauge and the modified .270 case. I have also cut a sized case on the neck and have been collecting measurements with it as well to help confirm the OAL gauge findings.

What I'm seeing is that my lands are right at or near 2.97~.01 when measured with either the OAL gauge or my homemade gauge.










I'm very hesitant to use this measurement because it puts the bullet out 0.20 longer than when loaded to the book measurement...that's darn near a quarter inch! Making my COAL 3.54 and greatly reduces the amount of bullet in the case neck which will undoubtedly affect pressure.










A couple observations:

When using the OAL gauge with modified case, I can feel the bullet "catch" on something then break past, almost like either a burr or rough spot in the chamber..I don't get many significant scratches on the bullet but it is definitely rough sliding the bullet forward until it stops at the lands. I tried it on two other .270 rifles and did not feel the same thing. They measured 2.886 (Mod700 BDL) and 2.92 (Rem Mod 783) to the lands respectively.

So, is it safe to load ammo this long? What could cause the rough feeling in the chamber? With SAAMI Min. Chamber specs listed as 2.88, what would cause the ADL to be so far over? Throat erosion?

...and yes, a cartridge loaded to the long length does fit and cycle through the action so magazine length isn't a factor.

Or...maybe I should just leave well enough alone since this is a hunting rifle and I'm at 1" @ 100yd. groups...?


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## longbow (Mar 31, 2009)

It could be safe to load that long. You just need to inch up on it a little at a time and watch for high pressure signs as you go. 

Sometimes your leade is off a little and your lands don't start in your throat at the same place. You might be hitting the closest land first and as you shove the bullet deeper it "flicks" to the center of your throat and engages the second land. Usually when that's the case it's barely noticeable. Maybe? It's just a guess. It might be as you push past a bit of carbon build up in your throat too. Again, just a guess.

SAAMI specs are overly conservative so they safely fit in all factory chambers. There's just too much variation in manufacturing. If you have an OAL gauge you can match your loads to your own chamber and disregard SAAMI specs, to a point.

You may have throat erosion but unless you've shot that thing a lot I doubt it. .270s aren't known to roast out throats. But since you have a OAL gauge you can chase your throat erosion as it erodes. Or at least you have a baseline to compare it to when you shoot another 500 rounds and want to see how it compares to today's measurement.

I'd use the same charge of IMR4351 and start lengthening your OAL while keeping an eye out for high pressure signs as you search for a little better accuracy.

Nowadays I pick a safe/accurate load out of a manual and adjust my OAL first then try to squeeze my accuracy down by adjusting my powder charge. I've found that my best OAL is the same whether it's a low charge or a high charge.


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## longbow (Mar 31, 2009)

Then again, you have a one MOA hunting rifle.  I'd piss around with it and see if you can squeeze some more accuracy out of it. If not, you already have any excellent load you can fall back on.


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## DallanC (Jan 13, 2009)

I'd set up another target at 200 yards and see if your group tightens up. I really dont understand why people dont discuss bullet yaw and precession, just dont know about it? Some of these sketchy groups at 100 yards might be tight at 200... contrary to what alot of people I've talked to about accuracy believe, groups CAN tighten up over longer distances if you have a yaw issue.

But, back to the OP. My #1 most accurate 22-250 load has its bullets seated less than 1/16" into case necks. I consider these "range only" loads as you can literally pull a bullet out, knock one loose. I do not like bullets loaded so far to the end of the case... BUT... it makes for ragged 1 hole groups and I cant help myself. For hunting, I load'em a little deeper and give up .25MOA.

-DallanC


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## KineKilla (Jan 28, 2011)

DallanC said:


> I'd set up another target at 200 yards and see if your group tightens up. I really dont understand why people dont discuss bullet yaw and precession, just dont know about it? Some of these sketchy groups at 100 yards might be tight at 200... contrary to what alot of people I've talked to about accuracy believe, groups CAN tighten up over longer distances if you have a yaw issue.
> 
> But, back to the OP. My #1 most accurate 22-250 load has its bullets seated less than 1/16" into case necks. I consider these "range only" loads as you can literally pull a bullet out, knock one loose. I do not like bullets loaded so far to the end of the case... BUT... it makes for ragged 1 hole groups and I cant help myself. For hunting, I load'em a little deeper and give up .25MOA.
> 
> -DallanC


Actually, no I don't know about it but I will Google it and do some reading.

As for the rough chamber, it could be the lands as described by longbow because it does kind of "flick" the last bit before stopping at the lands firmly.

I wouldn't rule out erosion either since I have owned this rifle for 20 years and shoot at a minimum 100 rounds a year, 20 per week now that I'm reloading for it and developing a load (it has taken me a long time to find a good load). That and I bought it used so who knows how much it was used prior.

I've decided to increase length in .02 increments while keeping everything else the same. Sure it'll take me 10 groups (50 shots) to get to where my gauge says the lands are but whatever, range time is good time! I may also find a gunsmith to scope the chamber and give it the once over.


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## DallanC (Jan 13, 2009)

If I had to make an educated guess, I'd say i have between 3100 and 3400 rounds through my Ruger #1 22-250... known as a "barrel burner", it still shoots sub .3MOA... after 3k rounds.

I've never burned otu a barrel... even my 7STW is still going strong after 800 rounds (some people had me freaked out it would be toast at 300 rounds... lol.

All I can say is IF you actually do burn out a barrel, you had a heck of a good time!


-DallanC


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## Bo0YaA (Sep 29, 2008)

I like to start at manual seating depths, find a charge that leaves me with more of a horizontal spread than a vertical spread. From there I adjust the seating depths, starting just off the lands and working in from there. Ive got plenty of loads that are way beyond the manual COAL. As long as you aren't seeing pressure signs and they load in the mag, you are good to go.


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## Bob L. (Jan 11, 2015)

You usually can tell if it will make any difference by doing 20,40, 60 thousandths change deeper, and 1 group 20thousands closer to lands and shoot 3 shot groups of those from where it is now. If it makes little difference then leave it alone. Look for pressure as you seat that out.


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