Range Report .308 SMK 168 gr at 2820 + fps.... ???

[A5M]

Friends,
I have been reloading my .308 for a short amount of time. I'm not an experienced reloader. Your thoughts will be greatly appreciated.

I have been reloading as follows:

SMK 168 gr
43.7 gr of IMR 4064
CCI #200
OAL 2.780"
Federal case

According to my Lyman book, the minimum load for IMR4064 is 40.0 for a velocity of 2415 fops and Maximum load of 45.0 for 2717 fps. As I stated above, I have been loading 43.7 grains of IMR4064 which, according to the book, should be in the safe side...more or less in the middle. My primers don't show pressure marks. My groups at 100 yards are consistently between .25" and .50"...depending on whether I have been shooting often or not. Today I fired groups at 500 yards in the neighborhood of 3". So, I'm pretty happy with the way things are.... However:

This week I bought a Chronograph. I know, I should have bought it a long time ago...Mia culpa.

Today I fire 10 rounds and measured their velocities. My average was 2820.... Which obviously implies that a few rounds were hotter than that.

My first thought was that I should bring my velocity down a little bit...and keep it in the 2650-2700 fps range. I have noticed a little bit of a sticky bolt from time to time. Could this be attributed to the loads being too hot or my poor reloading technique? I only neck size since I only shoot those rounds from the same rifle. 99 per cent of time, I have no problems ejecting the empties.

On the other hand, I don't see any signs of pressure, unless the sometimes sticky bolt is one, and since the load works well for me, as far as accuracy goes, I am also inclined to just leave it alone. I have fired over 500 rounds with this load out of an FN SPR rifle.

What do you think? Slow them down a bit....???? Leave them alone????

Any thoughts, suggestions would be greatly appreciated.

Thanks in advance.

 

[Dshooter]

What brand chrono do you have? Magnetospeed seem to be very accurate as is Oehler 35p. I have heard others complain about the cheaper chronos such as the shooting chrony and such. Maybe your getting generally high readings. How long of a barrel are you running also? That load is fairly common to others and seems like you are about 100fps faster almost

 

[A5M]

DS
I bought a Chrony Alpha.... And I'm shooting out of a suppressed 24" barrel. Could the suppressor be "adding" any velocity to the rounds?

Today was my first day using it.... If this is a common load, and within limits, and yet I'm running at least 100 fops faster, I wonder if the problem was with the way how I set up the Chrony itself. If it wasn't perfectly straight, It would probably read faster, huh? Since the photocells would be closer to each other than they are calibrated for? However, I'm pretty sure it was straight facing the target.

Now I realize that I should have taken a couple of factory GMM 168 gr rounds and measured their velocities to get an idea of whether I was getting velocities that made sense or not....

 

[Tx_Flyboy]

A5M,

Your load is ok as long as it's safe in your rifle. You don't need to download your powders for a certain velocities unless you find the recoil at the higher velocity accuracy node objectionable.

Regarding your velocity, you are likely getting bogus chrono readings given the brand of chrono you are using. The best way to confirm your velocity is to shoot your load at longer distances, 300yards, 600yards, and farther, then see if the dope corresponds to velocity.

 

[A5M]

Thanks Tx

When I compare my dope out to 500 yards (only had access to 500 yard range) it matches the velocity for each distance. I used Strelok to run the dope. According to Strelok the velocity is 2800 fps which is about the average (2820) I got from the Chrony.

I guess the sometimes sticky bolt is not connected to this load being too hot??
I really like this recipe, and it works for me. So if I don't need to change it, I'd rather leave it alone.

 

[Tx_Flyboy]

A5M,

I missed the part about the sticky bolt...that's normally a sign of excess pressure.

What does your brass look like?

 

[Dshooter]

A5m, you could try another chrono, a friends maybe, to verify or as Tx said shoot at farther distances, measure drop and use a ballistic app to verify results of velocity. As far as sticky bolt, yes it can be attributed to a hot load, improper headspace..... Are you bumping your shoulders? If not could be the issue, and if you are and you bump them to far that would also do it. Check your trim length and make sure it is within tolerance.

 

[artee]

Wow, so many ways to go on this....
From my experience of about 25 years with an original Chrony and more than that with your exact load:

This load should give about 2640 fps. It's a great match for Fed GoldMedal Match (at least, as the factory loaded in mid 90's.). In a factory Remington Varmint with 26 inch Lawyer designed chamber and throat both GMM and handload do 2640 fps. This barrel matches several 24 in custom barrels with match chambers with many loads. Your load far exceeds what the "book" tested values yield. Your Lyman data shows 60.4 fps /grain of powder velocity change and therefore an interpolation of 2638.5 fps for the load. Beating this by 180 fps better give you pause. And the "sticky" bolt lift IS an important consideration/sign of high pressure. (Notice, my results with your load, in about 7 different barrels, closely match the interpolated data)

Yes, a spot check against a Good standard is a great idea (ie, Fed GMM across YOUR A-Chorny). This one act will tell you that your Chrony is in the ballpark of it's design specs and your installation (rifle setup verses the Chrony for position and alignment of the shot through the screens) is 'good'.

The 20fps difference from Chrony velocity average and Strelok (computer prediction) is insignificant. Your Chrony is advertised as 99% accurate. That means, if the actual TRUE velocity between the screens was 2800 fps, and the chrony figured and displayed ANY NUMBER from 2772 to 2828, it was "accurate" for that shot. Also, if the real world results are matching the computer predicted trajectory, and the backed out computer velocity is only 20 fps from the Chrono velocity, we have good indication that the chrono is within design specs. Bottom line, your TRUE velocity average does look like it's smoking along almost 200 fps faster than it ought to be.

The biggest reason for an unexpected velocity from a chronograph is the start screen is too close to the muzzle. The muzzle gasses cause false triggering. Have no less than 10 feet, and 12 to 15 feet is safer, distance from the muzzle to the face of the A Chrony. I don't think your data is bad if real world results and Strelok agree. Having said that, it would be EASY to drive Stelok to incorrect answers. Garbage in IS garbage out with ballistic programs.

I could write an easy 5 pages on ballistic problem solving. I won't. Jumping to the next likely area. New reloader. At least two indications of high pressure observed (Higher than expected velocity and sticky bolt). Check that you are measuring your charge correctly. Is it really 43.7 grains? Have you checked your scale against another scale? Have you checked the scales against a verified 'check weight'? If the scale is moved from when it WAS verified, it needs to be REVERIFIED. Absolutely you must treat reloading like a chemistry lab procedure. A scale must be leveled. It should be checked every time you use it. A normally accurate scale that is out of level WILL give readings that no longer match true weights. A scale must move freely if a 'mechanical beam' scale. If you trickle powder on KERNAL by KERNAL and don't see a slight change in the index lines for EVERY kernel; if you get jumps of the pointer/index suddenly every X kernals, than your scale is hanging up and you will get 'measured weights' that are greater than true. Not being level or worn knife edge/bearings are the normal culprits. Electronic load cells (ie, electronic scales) have similar (and more numerous) problems. Finally, IMR 4046 is a long thin stick powder. It throws for volume measurement terribly. Weigh the charges on an accurate, leveled, verified scale. (At least till you resolved this issue, and you DO have a problem).

 

[MontanaMarine]

Load data seems very safe, per quickload calc around 2680 fps, 55K lbs-psi.

Your stiff bolt lift could have something to do with neck-sized only ammo, after a while the cases can get a little snug and need a shoulder bump.

I'd verify erector calibration, then take it out to 1000 yards to cross-check actual come-ups with your trajectory calcs at 2820 fps.

 

[MontanaMarine]

Your velocity/charge corresponds to a QL calc of 43.7gr IMR 3031, at 62K psi. There's always an outside chance the wrong powder got put in the can.

 

[A5M]

Tx,
The brass looks good. I have found no deformities or scratches, and the primers don't show signs of pressure. When I pass my finger on top of the primers, they are level with the bottom of the case, and don't feel or look swollen.

For what it's worth, I also showed it to a couple of others shooters/reloaders at the range and they didn't think it looked weird....

 

[A5M]

Thanks D,
No, I haven't bumped the shoulder and it's probably about time to do it. I have fired out of these cases 5 times. The length of the cases is 2.015" as it should be, according to the book.

 

[A5M]

Thanks Montana,
I don't think it's the powder because I have been firing this load since this past summer and have gone through several cans of IMR 4064. I have had the same dope all along. I believe that if I had the wrong powder in the bottle this time, my dope would have changed. It was still on the money.... (At least something is consistent, huh?).

Probably in two weeks I will go a 1000 yard range and check the dope out to that distance.....

 

[A5M]

Thanks Artee.

Yes, it seems to me too that this load is a little bit too hot. The real world trajectory (at least out to 500 yards) is pretty much on the spot, and the real world trajectory matches Strilok when I calculate the dope with a velocity of 2800. Because of this, I think the Chrony is giving me good results since the Chrony and Streloks velocities match. Btw, I placed the Chony at about 10-12 feet from the muzzle.

Regarding the scale....it's a Hornady electronic scale. It's on a flat surface. I calibrate it, religiously, every time I turn it on. I have also rechecked the weight of the powder with a second, cheaper, electronic scale. Both match. I have also checked the weight of known items, such as a 168 grain bullet, and the both agree with the weight within reason. Bullets are not perfect....but they are consistently close within a few tenths of a grain.

I think I will check the velocity of a GGM round to verify that the Chony is working properly.
I will also check on whether I get a sticky bolt or not after firing the factory GMM.
If the Chrony is working properly, and I believe it will be, I will work up a slower load that will give me the same accuracy. Back to the drawing board. I think 42.5 grains of IMR4064 will be a good starting point... Will adjust it to get a good match between velocity and accuracy.

My mistake was not to have bought a chronograph at the very beginning....

 

[A5M]

I really appreciate you guys having taken the time to read my post and think of reasons to explain my problem. Thanks for running this load through some of your better software, and coming up with ideas based on your experience. Like I said earlier, I'm relatively new to reloading, but enjoying it a lot. This really is fun stuff...

I will take your suggestions and give it another try.... I will post my results!

Big thanks!!