Temp Stable Version of Ramshot TAC?

[MarkCO]

Originally Posted by Shadow9mm

1/2 moa truing bars? What are they, how are they used?

{Edit: Sorry, but hotlinking images is against board rules. You need to ask the OP for permission to post it and to give an attribution to him here. Also best to hold image sizes down to 1024 wide for those with lower screen resolutions.}

Basically, a long bar, that is not very tall. 12 to 24 inches wide, 2 to 4 inches tall. The theory is to put the bar at a distance where the height is the accuracy potential of the rifle, but at least out past 400 yards. Wide enough so that a bit of a miss on wind call will still get a hit.

Shoot at the truing bar. If you go low, figure out why. MV slower than you thought, BC worse than published. Then "true" your data to get hits. Of course, if too high, BC is too low or MV is too high. Use of a truing bar, as opposed to paper measuring groups or just a horizontal line on a steel target is the ability to immediately tune without conditions changing. I have one of my own, and my range has just recently added one. I've shot with others as well. Very useful and helpful tool. Most of the top precision rifle shooters use them. A truing bar at 600 and 1000 makes quick work to verify data from a rifle zerod at 100.

BTW, Austin at AA Targets makes them. Great target maker and a super great guy.

[jackstrawIII]

Hey, quick update. Based on all your comments encouraging me to stick with the TAC load, I went to the range today to verify exact FPS and check for pressure signs again. This load is well within Barnes published load data for comparable bullets.

308 Win with Lapua brass
125 Tipped MKZ from Cavity Back Bullets
50.0 Grains of TAC
3180 fps 5 shot average (with very low SD)
CCI standard primer
COAL 2.67"

Even though this load is within published limits, I will admit that the load "feels" high pressure. The sound of the shot "smacks" different, if that makes sense. The only pressure signs I can see are cratered primers, as in the pic.

Two questions:
1. What do you think of the pic? Is that type of cratering something I should be worried about?
2. Does anyone have Quickload to tell me what pressures I'm at, approx?

Thanks!

[MarkCO]

Too hot IMHO. CCI LRPs should not look like that unless you are over max in a .308 bolt gun. That load specifies Lapua brass? The COAL seems really short too. Even my 110 varmint bullets are over 2.7" OAL in .308. You are not shooting "Barnes" bullets, so their data is not what you should be using!

I assume you have a typo and that your MV is 3180, not "2180"?

Based on your post, I'm a little concerned. Check your data source, back off the load and work it up consistent with best practices.

[tangolima]

Too hot. It is close to have a pierced primer. It needs to go down by at least 3%, I think. I can take barely visible cratering but not like this.

I assume good fit between the firing pin and bolt in your rifle. There is no chambering around the firing pin hole on the bolt face either.

-TL

Sent from my SM-N960U using Tapatalk

[jackstrawIII]

Too hot IMHO. CCI LRPs should not look like that unless you are over max in a .308 bolt gun. That load specifies Lapua brass? The COAL seems really short too. Even my 110 varmint bullets are over 2.7" OAL in .308. You are not shooting "Barnes" bullets, so their data is not what you should be using!

I assume you have a typo and that your MV is 3180, not "2180"?

Based on your post, I'm a little concerned. Check your data source, back off the load and work it up consistent with best practices.

Mark, thanks for the feedback. Here are my responses:

- I measured the COAL when I was using the non-tipped, hollow point version of this bullet. Recently switched to the tipped version, which is what started me on the quest to "improve" this load. Now, with the tips in the bullets, they barely fit in the Win 70 magazine box. Can't go much longer, at all.

2. You are correct, thanks! The actual MV is 3180, and that's from a 21" barrel.

3. And yeah, Barnes lists book max for TAC with 130 grain copper bullet at 51.5 grains. So I'm well under that threshold, especially considering this is a 125 grain. I wonder if the form factor is different enough, however, that this is causing problems. The two bullets look very similar to the eye, but I'm sure that's a very rough way to look at it.

4. I developed this load using ladder testing, but I guess I went too high up the ladder. The SD on this load is wicked small. Like less than 10fps spread over 5 shots. It's such a promising load, but if it's too hot, I'd rather cool it off a bit.

Thank you.

[MarkCO]

On response #3...

I've spent a bit of time in ballistics labs, professionally and avocationally. Even the type of copper of the jacket on a cup and core bullet can result in pretty large changes in pressure in rifle cartridge's. I'd not assume, same size and shape, that the pressures would be the same...unless verified by the manufacturer or a ballistician. The composition of the copper, and it's ability to engrave is a component of pressure.

[jackstrawIII]

I'd not assume, same size and shape, that the pressures would be the same...

Mark, it would appear that you are correct. My 50.0 grain load should be way under max, but apparently not.

Going to start a new ladder test starting at 47 grains and see if I can find a nice node at lower pressure.

[Unclenick]

My reaction to the image is that it does not appear to include mushrooming, which is good, though you'd have to confirm it by looking at the decapped primer. The cratering around the firing pin imprint is bad, but if you have a Remington or other gun with a chamfered firing pin tunnel or if you just have an oversized firing pin tunnel, you'll get that even with reasonable pressure.

That said, and assuming you don't have the firing pin tunnel problems, it is a good reminder to remember powder lot burn rates vary several percent, so you can't count on book maximums always to be good with your lots of components. That is why we always work up from the lowest listed load in the data.