How hard can I push a 308?

[light rain]

I am looking for the node on my new 308. It's a surgeon rsr action and broughton 22 inch 1-12 twist barrel. Using lapua brass, fgmm 210 primers, varget and 175 smk. I am getting a standard deviation of 7 and median speed 2667 with 44.1 grains 5000ths off the lands. I am doing 5 shot groups every 3/10 grain. Can I push to 46 grains?

 

[XTR]

Not but once per casing.

The short answer is no.


You are pretty close to max that you can shoot and not lose your primer pockets very quickly. You may be over max depending on your throat; if you are seating at mag length you are probably over max now.

 

[gilmillan1]

I have been down that road. You simply cannot hot rod a case that is not capable of your speed expectations. My advise is to find the best accuracy node you can without crazy pressures. You can only do so much with a 308. Find the accuracy of the gun and maximize your shooting skills with it. Even if you can push the bullet to the speeds that you want, it will not make a noticeable difference at 600 yards.

 

[jlow]

One can always try to go higher, but for safety sake, I would suggest going 1/10 grain increments and look for pressure signs. Also remember that unless you are absolutely sure that your powder is not affected by temperature, you need to be careful if the testing and shooting temperatures are significantly different.

 

[light rain]

Ok, did I shoot through my node?
43.2 es 21 ms 2612 sd 9
43.5 21 2651 8
43.8 25 2651 12
44.1 18 2667 7

Should start over and do 1/10 grains ? This is my first 308 so I am not to savvy. But I shoot off the low end of my node in my 6.5x47 lapua and have the standard deviation to 3 fps I would think I should get that with a 308.

 

[jsthntn247]

Don't go higher and smoke your primer pockets within 3 firings, it's not worth it.

 

[chkunz]

The Sierra manual list 41.7 grains of Varget as a max load for the 175 SMK. Why did you start out over the max load looking for a node?

 

[light rain]

I didn't I started at 39 grains and went up 3/10 from there. The last numbers I gave we're the best and looking like the node or at least where it should be.

 

[XTR]

Ok, did I shoot through my node?
43.2 es 21 ms 2612 sd 9
43.5 21 2651 8
43.8 25 2651 12
44.1 18 2667 7

Should start over and do 1/10 grains ? This is my first 308 so I am not to savvy. But I shoot off the low end of my node in my 6.5x47 lapua and have the standard deviation to 3 fps I would think I should get that with a 308.

You are using a different system than I do to find your node. Most chrono's are not that repeatable, all kinds of things effect the quality of the results from most chronos. Look at what the target it telling you. There is a node that most people hit between 43.0 and 43.5.

Danger sign, you poured in 0.3 grains of powder and got an increase of 39FPS, then added another 0.6 grains of powder and only got an increase of 16FPS. You are about to blow the pockets on your brass.

I would suggest that you look into the OCW test process from 42.0 to 43.5 and find a node, then take your chrony and figure out how fast you are shooting in the node. I'm going to guess you will find it in the vicinity of 43.2, you have a 22" barrel, you are not going to be able to get the velocities that you see guys (like me) who shoot F-TR with 30" tubes. (that is unless you read what is posted on Snipers Hide). You're at about all you can wring from that short tube. You are not going to get to 2700 safely with a 22" barrel.

I'd suggest that you look into shooting 155s (I'd even suggest the Sierra 2156). That rifle is not built for long range. 155s will give you better velocity and shoot much flatter out to 600 yards.

 

[jlow]

The Sierra manual list 41.7 grains of Varget as a max load for the 175 SMK. Why did you start out over the max load looking for a node?

The Sierra manual data is incredibly conservative - that is well known.

If you look at the other manual i.e. Hodgdon's you will find that it list a starting load of 42 grain of Vaget for the 175s with a max load of 45 grain.

 

[XTR]

The Sierra manual list 41.7 grains of Varget as a max load for the 175 SMK. Why did you start out over the max load looking for a node?

The Sierra manual data is incredibly conservative - that is well known.

If you look at the other manual i.e. Hodgdon's you will find that it list a starting load of 42 grain of Vaget for the 175s with a max load of 45 grain.

Just a little note about "conservative" loading tables. They have to account for all manner of conditions. The loading table doesn't come with a list of conditions that must be met for the load to be safe. Just load and go.

Three yrs ago at the state F class championship I had my bullets in my truck while I was pulling targets in the middle relays. First time at the range and it didn't occur to me that the truck would be in the sun for a couple of hours. (4 relays, so 4x33 min plus changes).

When I went back to the line my 185 Berger load blew three primers in the course of the match. At the time I was loading in a chamber that was shorter than what most use in F class and my loads were mag length. I was loading 43.3 grains of Varget in WW brass with BR2 primers jumping 0.010. That is a pretty mild load in most F-class circles, but under those conditions, with the ammo heated to however hot it got in the sun in the seat of my pickup it was way beyond where it should have been. Lost every piece of brass I shot in that match.

So, yea, under normal conditions the Sierra numbers may seem conservative, but leave your bullets in the seat in the Tennessee sunshine for two hours and you get a different answer.

 

[jlow]

When I said conservative, I of course as stated meant relative to what else is out there i.e. the Hodgdon data. Really no one should load without understanding what you stated, but still 41.7 grain as max is incredibly conservative and there is no way around that.

As for your comment about effect of temperature, I for one do not completely believe and ascribed to the extreme temperature i.e. not temperature sensitive claim as you can see in my own comments on care and testing in different temperature in my above “Reply #3” post.

Frankly leaving ammo in the sun is nothing compared to letting it cook in your chamber after firing a long string. As usual, "shooters beware".

 

[chkunz]

OK, you do not like the max load in the Sierra Manual but could it just be that your are shooting over the node? Most folks find the accuracy load for the 308 around 2550 fps (military 308 match ammo is loaded to 2550 fps). You do not normally get max accuracy at max velocity. Take a look at the original Ladder test by Cheighton Audette, he did it with a 308, 168 SMK and 4895 which is similar to Varget in burn rate and the node was around 2550 fps and 41.8 grains of powder.

 

[jlow]

Do you know what was Audette's barrel length?

 

[Wjesswheel]

Node.? Newbie hear can you please explain. Also any advice on what to purchase as far as presses, dies,scales maybe a bullet pointer.. Powder and if my 200 federal match cases are at least adequate

 

[chkunz]

Do you know what was Audette's barrel length?

I will research but probably the standard for the NMC shooter of the day.

 

[chkunz]

Node.? Newbie hear can you please explain. Also any advice on what to purchase as far as presses, dies,scales maybe a bullet pointer.. Powder and if my 200 federal match cases are at least adequate

I would recommend you start a post(s) with your specific question(s), one at a time and be as specific with as many details as possible. All good questions but will not get proper response buried in a thread on another subject.

 

[fdshuster]

"my node in my 6.5x47L and have the standard deviation to 3 fps I would think I should get that with a 308".

I don't know where you got the idea that the 308 should have the same chronograph results as your 6.5x47L. Two completely different cartridges: different case design, capacity, shoulder angle, primer size (unless you are using the Palma brass in the 308), etc. etc.

 

[light rain]

My idea on the results isn't the speed but the standard deviation, shouldn't I be able to expect it to be in the 3-5 fps range ?

 

[fdshuster]

No. Again, two completely different cartridges, and I have not even mentioned the differences in barrels, bore diameters, barrel length's, powders, primers, bullet diameters, hardness or softness of different copper jacket material, cut versus button rifled rifling, and the list goes on and on.

I have numerous chamberings in 6BR, my favorite for varmint score match's, and even though the chambers may have been cut with the same reamer (mine), matching barrels (Kriegers), same basic components, etc. SD and ES numbers will be different, using my Magnetospeed chronograph, which I find to be very accurate.

Think of each rifle as having its' own personality.