How critical is seating depth?

[pepperbelly]

I shot some BH ammo with 175gr SMKs a couple of weeks ago in my new Savage. At 100 yards it was basically shooting small one hole groups, but I did only shoot at 100 yards. It was basically to be sure I had the scope mounted correctly.
When I started loading for it last night, using 175gr SMKs, I checked some of the BH ammo I didn't shoot to get an idea of an OAL to start with.
The 5 rounds I have left all have different OAL measurements.
1) 2.789"
2) 2.784"
3) 2.781"
4) 2.784"
5) 2.784"

I loaded to 2.800" and still have a jump to the lands. I haven't measured yet but that is still shorter than most loads I have read here.

Is it likely that this BH ammo is good at 100 yards but not so much at longer range, or is bullet seating depth not that critical? This ammo is usually very accurate, but the differing OALs have me puzzled.

Jim

 

[Powder_Burns]

Re: How critical is seating depth?

Its not uncommon at all for bullet lengths to vary...perhaps the bullets are seated to the ogive and the measurement you are taking is the OAL from case head to bullet tip..so the distance from the ogive to the throat may be uniform although the tips are varying in length. Just a thought on the subject, couldn't verify without the comparator tool.

As far as how critical seating depth is, a little variance won't hurt if you are shooting at 100yd. However cases with very small capacities like a .380 or 9x19mm, seating deeper can raise pressures dramatically so there are caveats..

 

[pepperbelly]

Re: How critical is seating depth?

I was measuring to the bullet tip- not the ogive. That may very well be the difference.
I will be buying a gauge very soon.People here have recommended the Stony Point. How is the Dillon gauge? I have one for my .45acp.
BTW this load is a .308.

Jim

 

[pepperbelly]

Re: How critical is seating depth?

I seem to be mistaking a case gauge for an OAL gauge.
I read somewhere that I can take a case, cut a thin slit in the case mouth and put in a bullet by hand. Then gently close the bolt so the bullet is pushed into the case. When I extract the dummy round the bullet should show me the length to the lands- correct?

Jim

 

[Powder_Burns]

Re: How critical is seating depth?

I have the stoney point (now hornady OAL tool) and it works well enough but the threaded portion of the tool is very thin and somewhat delicate...reviews suggest the tool breaks there..need to be gentle with it.

You don't need to cut a case....take the case and run it in a seater die with a crimp groove....just barely start to crimp the case mouth and it will have enough resistance to hold a bullet. Best to take a good sample of your bullets and measure with the shortest and longest bullets and figure the average..or sort them all by length, or buy the comparator tool as well.

You are also going to want to take multiple readings and take an average of those numbers, whether you use the cleaning rod method or an OAL gauge, get statistically relevant data for yourself.

 

[former naval person]

Re: How critical is seating depth?

Read TresMon's stickies at the beginning of this thread. Lots of good info plus an easy and cheap way to find start OAL. JMHO

 

[vman]

Re: How critical is seating depth?

I recomend the Hornady/Stoney Point tool... its pretty good and seems to be accurate if you use the tool carefully.

In regards to seating depth, it all depends on the rifle... some rifles take to jump well, some not so.

The same goes for the projectiles as well... some do some dont.

A good example that I have found is that when i was loading my 155gr Lapua Scenars to AI mag length, my groups at 100 were not bad, sub MOA but then when I moved out further the groups opened up. I was loading these with 46gr of ADI AR2208 (its an Aussie powder same as Varget)

If i tried to shoot out to 500 yards I would find my vertical spread was all over the place.

I have since loaded my Lapua Scenars about 0.015 away from the lands and my oal is well beyond mag length so i have to single feed.

Just last week I went to the range and performed a ladder test at 325 yards and found that I had an accuracy node somewhere between 45.8gr - 46.7gr of AR2208 powder. At this charge range I had two varying but similar loads shooting at almost the same vertical plane.

Now if you think about that for a minute, I was previously shooting 46gr of AR2208 and projectiles loaded to mag length... these would shoot great at 100yards, but at 500 yards the vertical spread was very bad.

With my new loaded, i have a similar powder charge (more testing needed to get an exact amount) but have the Scenars .015 away from the lands. I feel that this change to seating depth has made the most significant improvement for my rifle and I feel confident that I will get at least 2MOA at 500 yards with this load.

I have heard people say that .308s tend to shoot well even with lots of jump... and I have also heard that Lapua Scenars arent too difficult to get shooting nicely, or at least much easier than a VLD projectile. I have found almost the opposite. My rifle did take well to changes in seating depth, almost like how you would treat VLD's

 

[BCP]

Re: How critical is seating depth?

Mine vary from a little under 2.8 to 2.81. I haven't noticed any aberrations at least to 300 yards. Bullets aren't all exactly the same length, and they probably have to jump a bit before they hit the rifling anyways. I think run-out matters more.