Bullet seating depth

JockStalk

Well-Known Member
My reloading journey continues.

I write this to gain further knowledge, probably draw some fire and generally throw myself prone before the wisdom of the SD loading gurus.....

Having changed my 243 last year and with the longer evenings here giving me the chance for range work, I'm now working up loads.

Being unhappy with the accuracy of the first batch I tested in this rifle, I've gone back to first principles.

One of the issues was bullet choice - long VLD's in a ten twist (not for live quarry) so I'll leave them alone for the moment. (but if you read my tagline below, you'll see I may well come back at them. Possibly several times.)

I've got a couple of short 100gr bullets and a 95gr bullet that will theoretically be stable in a ten twist at expected velocities. THese gave me groups of 2" at 100m which I know the rifle can do better than.

One variable I wanted to check next was seating depth as I'd continued using the same bullet seating depth from my previous 243 in my 'new' 243. (yes, I know)

I took a fired case, eased the neck open very slightly, lubed the inside neck surface a tiny bit and just inserted a bullet so it was central and holding under very slight neck tension. then I gently chambered the round and then gently extracetd it. Making sure it did not (like the first one did) land with a clatter on the floor.

The bullet was pushed back into the case each time, none jammed in the bore. Repeated this ten times and then, using a hex nut type Sinclair bullet comparator and micrometer, measured the cartridge base to ogive length. (remembering to deduct the 1.0005" from the comparator!) There was hardly any marking on the bullet from rifling and 1 thou variation in the ten chambered and measured, so I'm happy (or under a delusion?) that the bullet is being seated with little or no perceivable jam at that depth.

What I believe I now have is one measure of my rifles distance from bolt face to lands that I can at least use in load development as a consistent reference point.

Comparing that with the loaded rounds I'd been using, there was .195" or 195 thou of jump to my above measure of bolt face to lands.

I'm not saying this DOES cause some of the inaccuracy I've seen, but I'm acting on the basis that it MAY do.

Next step will be to load up stepped charge weights with bullet seated to 20 thou less than my CBTO, measured using the same kit.

Why 20 thou less? Because its the 'magic' number I have heard spoke of in hushed voices and I'm following the herd. (but I will experiment from that point if I still don't get what is to me an acceptable degree of accuracy.)

The charge weights I previously used SHOULD develop a slightly lower pressure due to less reduction in case volume from the bullet seated further out, but I'll start working up loads again from scratch.

Any howling errors or mistaken assumptions you can see?
 

Muir

Well-Known Member
Your "return to basics" seems to have you in the weeds. Try this: Full length Size your brass, trim to uniform length, prime, charge, and seat to the recommended OAL of the data provider. This is a return to basics. It is also a return to how the data was developed and was intended (even as a guide) to be utilized. I seldom measure the distances to the lands. These days i load to recommended OAL. I shoot out to 1100 yards pretty frequently.~Muir
 

Heym SR20

Well-Known Member
Keep to the shorter flat based 243 bullets. Get the velocity up. And crimp the bullet in place. I find that a crimp makes a big difference. I think it allows the pressure to build before bullet moves out of the case giving a more uniform burn. You would get the same effect if bullet was seated on the lands - but that gives the chance of bullet getting stuck when cartridge is unloaded. An embuggerance in a hunting rifle and happened to a friend when we were on the the top of a hill after a long stalk.
 

long_range_rob

Well-Known Member
The .243WIN was designed around the 70gn bullet (A FMJ actually for coyote pelt hunting) and staying around this ball park makes it easier to get good accuracy.

My Sako 75 hates 95/100gn bullets but puts 70-80 grainers through a ragged hole. I also find optimum accuracy (at short range, 200-300) is obtained with flat base bullets and a VLD chamfer on the neck.

I'm just testing out some 70 Varmaggedons for Charlie now and hope for excellent results
 

JockStalk

Well-Known Member
Yep 70-80 grainers shoot well, but don't really help me on hinds where I need 100gr up here.......

Will be on the range over next few days and will see how we go. Planning to compare manufacturers COAL against 20 thou off lands and see how they shoot.

Keeps me off the streets!
 

levigsp

Well-Known Member
I must say I have never had a problem with any 100 gn bullets of any type in my 243s only when I went up to 107 and 110 gn I had problems stabilising them.
 

hybridfiat

Well-Known Member
I lost accuracy in my .222 for no apparent reason years ago and I played with a number of factors till my friend told me to neck turn my cases for concentricity.
No more than a whisker off so the necks were all in line and the same thickness. There was more brass on one side than the other on every case.
The next batch shot just as they had before it went wonky.
 
Last edited:

Top