Velocity issue.

K

knowledge_is_power

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First off let me say that I'm fairly new to the precision shooting world. I have a Rem 700 .308 with a 20" 1:10 twist. I JUST started reloading and am experimenting with it still. The other day I took 30 rnds out to test fire with my rifle and chronograph. I loaded them with once shot casing I had, 40g of Rx-15 and Sierra 168 grn BTHP. It was a hotter humid day and I started off shooting upwards of 3200 fps. After about half way through, my velocity dropped to around 2300 fps. I snaked my barrel two times five times each with no change. What gives?
 
The chronograph might have been too close to the muzzle, so the blast triggered it.
The chronograph might need new batteries.
The 2300 reading might be right.
 
2300 does sound right for a 20" barrel. I agree that the higher velocity probably came from the muzzle blast which will give erratic readings.

For the record, 40g reads as 40 grams, 40 grains would be 40gr.
 
15 feet should be about right for a 308. That's an approximate industry standard, used for factory ammo. It works for almost all guns, except those with truly excessive muzzle blast.
 
I'd say the 2300 fps would be better than 3200 fps. 3200 fps sounds like there would be some serious pressure going on in a .308. I don't shoot a .308 and don't have my manuals handy but that speed sounds excessive on all counts.
 
Technically, he's right about the powder. The real abbreviation is RX15 but people still write it as RL-15 most times. It's all over the manuals with the X.

308 has quite a bi t of muzzle blast. Just keep moving back until readings stabilize.
 
The real abbreviation is RX15 but people still write it as RL-15 most times. It's all over the manuals with the X.
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Not in any of mine, but I prefer to get my load info from the powder manufacturers website. Alliant http://www.alliantpowder.com/reload...?gtypeid=2&weight=168&shellid=80&bulletid=140 shows 45 gr as a max load @ 2710 fps. Getting 2300 with 40 gr is reasonable. There are a few 130 gr loads that will do near 3200 fps, but not 168. That is hot 300 mag speeds and has to be a chronograph error.

As you work up you should be able to get good accuracy and better speeds. Reloader 15 is a good 308 powder that I used for a while. Don't worry about the 20" length costing you much velocity. I'm using 46 gr of Varget with 168's and getting 2730-2740 fps from my 22" guns and 2700 with my 20" 308's
 
It's abbreviated as RX in my Lyman manual. Though RL makes more sense its called Reloader and I don't see an "X" anywhere in it! But whatever, minor technicalities. But sense we are somewhat on the subject, what are some other good powders out there to try? As well as perhaps other bullets to look into. Like I said, I just started reloading. And for everyones entertainment, I just got my first (and hopefully last) stuck casing. And the worst part is I saw it coming and still preceded...
 
Give 4064 and 3031 a try, they are tried and true standby powders. Sierra Matchkings are always a good place to start.
My best loads in 308 come from 3031 and 150 gr Nosler Ballistic Tips in WW cases.
 
Not sure when they changed it, but the Reloader series of powders was RL for decades.

20" barrel is on the shortish side, and normally will not deliver the velocities a 22" or 24" barrel will.

3200fps with ANY .308 Win bullet is an error, other than the 55gr Rem Accelerator!

Chrono 10ft from the muzzle for handguns and 15 ft for rifles is general standard. But, if muzzle blast is giving you erratic readings at those distances, move it back some.
 
But sense we are somewhat on the subject, what are some other good powders out there to try? As well as perhaps other bullets to look into. Like I said, I just started reloading.
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Try 42.5 grains (42.0 grains is the starting load) of Hodgdon Varget powder with 168 gr HPBT Sierra Match King bullets.

I used .308 Win. Winchester cases, and Federal Large Rifle Match Primers (GM210M).

Make a dummy cartridge. Seat the bullet till it just touches the lands (makes marks on the bullet). Then reseat the bullet in just a touch (no visible markings on the bullet).

In my Savage 12 BVSS .308 I managed to get just under .5" groups at 200 meters. Recoil to me is non-existent. Very pleasant to shoot. Around 2,680 fps from a 26" barrel.

It's a very accurate load. I haven't tried Sierra Match King 175 grain HPBT bullets yet. Hopefully soon. I may also try CCI Large Rifle Bench Rest Primers.
 
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I like Reloder 15 in the .308, but I doubt you were getting 3200 fps. My standard load in that caliber is 43.0 grains of RL15 and the 168 Sierra Matchking. That gives me a very consistent 2600 fps that is very accurate in every rifle we've tried it in. It's averaging just under 1 MOA for three rifles. Great load.

Other folks like Varget in that load, and I have no experience with the powder. I started using RL15 in the caliber and haven't found a reason to switch.
 
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