Roll of the dice?

[skobrien]

Once again, newbie reloader here and my previous thread about cannelure was most informative. One thing I learned is that the seating depth of a specific bullet type in a specific rifle can only be determined by careful measurement and/or trial and error.

So, what does that mean for factory made ammo? What is the likelihood that any given factory load will produce a near optimal seathing depth? I went to my bench and measured various 270 factory loads and found a surprisingly large variance in OAL, all of them below the SAAMI spec. Does this variance explain why some rifles tend to "like" a specific cartridge?

[WIL TERRY]

Sometimes, but do not bet the ranch on it. IF you make a chamber cast of THAT chamber you will have answered all your questions.
And so it goes...

[Doyle]

1. Factory ammo must go with a "least common denominator" type approach so that it will at least function in all rifles of that chambering.
2. OAL can also be very bullet-specific. The correct measurement for comparison would be to the ogive on all those bullets rather than the tip.

[mikld]

I agree with Doyle. "Lowest common denominator", meaning it's a "generic" measurement and the round can be used in any gun of the appropriate caliber.

Couple of thoughts though; isn't the cartridge dimensions listed in the cartridge drawing in reloading manuals the maximum as per SAAMI specs.? So all factory ammo will be shorter? And for me and a lot of reloaders I know, seating depth, other than "book" specs is close to the last variable to work on for accuracy workup. Powder, powder charges, bullets, primers, bullet shape and weights seem to be tried before OAL...

I have been able to work up some pretty accurate loads using the bullet manufacturer's OAL recommendations for a specific bullet I was using; sub one inch groups using Hornady A-Max bullets in my 308, with Hornady's recommended OAL...

[F. Guffey]

I had two new rifles, a non-Weatherby with a non Weatherby chamber and a Model 70 Winchester with a 300 Win mag chamber. I used the same ammo in both rifles, the non Weatherby shot one hole groups and the Model 70 Winchester shot groups like a shot gun pattern.

Again, both rifles shot the same ammo, both rifles had the same type chamber.

http://bulletin.accurateshooter.com/...record-100-8x/

I purchased a Santa Fe Remington 03 at a gun show from the original owner, he purchased the rifle from Sears with two boxes of Remington 30/06 ammo. The owner threw the ammo in for free. I needed the receiver for an 03A4 barrel that is chambered to 308 Norma Mag. I took the rifle with the old early '60s ammo and test fired it. I could not improve on the accuracy so I applied the 'leaver policy', I lefter the way I founder.

F. Guffey

[bfoosh006]

" Does this variance explain why some rifles tend to "like" a specific cartridge? "

No.... there are MANY more factors at work then meet the eye.

I good example would be Federal Gold Medal Match .308 168gr ammo...

Dang near everyone makes .308 rifles... dang near every .308 uses FGMM 168gr as the standard for what accuracy you can expect from your .308 rifle.

All those .308 Winc. rifles have very little in common ( throat length, actual bore and land sizes, chamber dimensions, leade angles... etc... )

The one thing they do have in common... is the specific ammo... FGMM 168gr.


Another example is Fed. 50gr Tipped Varmint .223.... that ammo routinely shoots just over 1 MOA in every rifle I have seen it fired from ( well over 2 dozen rifles.. bolt action, AR's etc.. )... yet the bullet is NO where near the barrels lands....
Frankly.. that ammo has NO right to be as accurate as it is. Everything about it fly's in the face of reloading wisdom... ( cheap cases, non match grade primers, mass produced powder charges, and the bullet not being fired from a perfect twist rate, the bullet not even close to the barrels lands... )

Where seating towards the lands helps, is with us reloaders... it helps our reloaded ammo be custom fit to our individual rifles.... increasing our chances at good accuracy.

Again... there are a ton of unseen variables at work... no two barrels are ever exactly alike. If you find a factory round that your rifle likes, and likes a lot... consider yourself lucky.

You might find this interesting...http://www.leverguns.com/articles/ballisticians.htm

That article shows some of the dramatic differences barrels can have... Note the identical makes and barrel lengths striking differences... ( velocity wise )

[T. O'Heir]

A "least common denominator" type approach is why there's a SAAMI(Sporting Arms and Ammunition Manufacturers' Institute.). SAAMI specs are about manufacturing, not reloading per se.
Every rifle chamber is slightly different, usually length wise. SAAMI says what the tolerance is by the cartridge. And there's a tolerance. +.015" for the length of a .270 case.

[boondocker385]

I will add that I have noticed that with 30-06 that nearly every rifle I have had liked Remington core locts which is not considered a high end ammo.