New Load

[SavageF/TR308]

Just tried out a new load for my .308 yesterday... I used 45 grains of Varget behind a 168 grain sierra matchking, using a CCI 200 Large Rifle primer. The crono showed it going an average of 2835fps. Hodgdon's load data on the Varget container said 46 grains with this same bullet but a Federal 210M primer would net just over 2700fps. Does the M on the end of the federal primer stand for magnum? If so, this even further confuses me. I loaded up some 150 grain Hornady SST bullets a while back with H380(cant remember the charge, but it was almost a compressed load) and they only showed about 2700 on the crono. Maybe the Varget likes a long barrel better? My rifle has a 30 inch barrel. Just seemed wierd that by changing powders and going with a heavier bullet that they would go faster.

[44 AMP]

And finding out that the published velocity figures are at best, only a guideline.

Guns with longer or shorter barreals will give you a different number. Shoot at 0 degrees temp and get a different number than the same gun and ammo at 70 degrees. Shoot a gun with the same barrel length as the test gun, and still get a different number, due to variations in the interaction between all components. Usually less than 100fps, but greater differences are by no means uncommon.

Each powder/bullet/case/primer combination will deliver a certain speed, in your gun. It can be a different speed in my gun, even if my gun appears identical to yours. This is a simple, but not well known fact of life. Before personal chronographs became common (affordable), few people recognised this. Today, more are learning.

What is in the loading data, or on the ammo boxes or in the catalogues is what they got with their ammo, in their test gun. What velocity you get, and whaty is a safe maximum working pressure, in your gun, can only be determined by firing and testing in your gun!

I have seen guns that safely handle loads well above the maximums listed in the manuals. I have also seen guns that gave signs of dangerous pressures from the recommended "starting loads". Every gun is an individual in that regard. While most fall into the same general groups, there are exceptions, and the exceptions can be drastically different than the general group performance. There is no way to tell from a visual inspection. Only shooting, and careful tracking of all the performance indicators will show what, and how much is different from the "average".

I would expect a rifle with a 30 inch barrel to chronograph higher velocities that "standard" piblished data, as most of that is taken using a 22" or 24" inch barrel (in suitable calibers).

Yes, Federal 210M are magnum primers, intended to reliably ignite large volumes of slow burning powders. Their performance with faster burning powders may not be what you expect. Sometimes magnum primers deliver a significant velocity increase with medium burning rate powders (along with an increase in pressure). Sometimes they do not, and only increase the pressures, especially in smaller than magnum size cases.

This belongs in the handloading forum, I think.

[SavageF/TR308]

I guess I have a lot yet to learn about this reloading lol. I knew every gun was different but didn't know they could be THAT much different. Yes, I saw the handloading forum after I had submitted this topic. Sorry about that.

[Scorch]

With the longer barrel, it does not surprise me that you are getting another 200 fps over the Hodgdon manual stated velocities. The old "rule of thumb" says you will gain about 50 fps per inch of barrel length, about 300 fps of velocity with a 30" barrel over what a similarly loaded rifle would give you with a 24" barrel (it actually works out to a bit less than this with long barrels, but you get the idea). My Lyman manual shows a bout 60 fps gain per grain of Varget with that bullet weight. So you are showing about 200 fps velocity gain with less powder and a hotter primer through a longer barrel. Makes sense!

kraigwy, a regular poster on this forum, recently did an experiment where he cut a 308 barrel back by 1" at a time and charted the velocity changes for that barrel. You can search for it. Interesting stuff!

[Unclenick]

the "M" in 210M is for MATCH, not magnum. That's why it is part of their Gold Medal target shooting line. The Federal magnum large rifle primer numbers are 215 and 215M.

The SAAMI specification for the .308 gives a test barrel as being a 24" barrel with minimum chamber dimensions. Published velocities are always for the test barrel unless stated otherwise.

How much velocity you get from a longer barrel depends on the pressure the load produces near the muzzle. For a given peak pressure, slower powders will produce higher pressures near the muzzle, and thus accelerate the bullet more per inch of barrel at the end.

QuickLOAD shows 46 grains of Varget getting 2726 fps from a 24" barrel with a Winchester case. Winchester cases hold a couple grains more powder than most, so they need a little more to hit a given pressure. If I only change the barrel length to 30", it gives me 2841 fps from the same load. If I drop the charge to 45 grains it gives 2787 fps in the Winchester case in a 30" barrel. If I drop the case capacity on that 45 grain load to that of a Lapua or a Hornady/Frontier case, the pressure rises and I get 2828 fps. Pretty good agreement to what you actually have.

That same case and load at 24" gives 2712 fps, so you are gaining an average of 19.33 fps/inch with your extra barrel length. Shortening the barrel to 18" from 24" would make a bigger velocity change per inch of barrel because that is in a higher pressure portion of the powder burn pressure curve.