To beat a dead horse, FPS vs group size for distance shooting

[Tipsy Mcstagger]

Ok so regarding the 178 Hornady bthp and 175smk, it should be unaffected by the transition due to the slighter angle of the boat tail. I understand that that transition starts at Mach 1.2. If the 178 bthp (not amax) and the 175 shoot equally well and handle the transition equally well, I should opt for the .530 hpbt bc vs .495 bc of the 175 smk. I also get that Mach is relative to temp, altitude, and humidity so I'm trying to select a 1000 yard bullet that is relatively unaffected by the transition so all I have to worry about is wind and drop, not instability.

[Bart B.]

If your 700's 26" barrel has a 1:10 twist, I would shoot Sierra 190 HPMK's out of a commercial case with 43 to 44 grains of IMR4320 under it. Commercial cases are typically more uniform than LC match cases. That fast a twist shooting bullets just under 180 grains may spin them too fast and those more unbalanced will jump further off the muzzle axis upon exit. When the .308 was popular in high power rifle matches, the 26" long, 1:11 and 1:12 twist barrels shot 190's out at about 2550 to 2600 fps. They remained supersonic through 1000 yards even in cold weather winning a lot of matches and setting records along the way. 7.62 NATO Garands did the same with their 1:12 twist 24" barrels using the above load with 190's.

[Jimro]

Ok so regarding the 178 Hornady bthp and 175smk, it should be unaffected by the transition due to the slighter angle of the boat tail. I understand that that transition starts at Mach 1.2. If the 178 bthp (not amax) and the 175 shoot equally well and handle the transition equally well, I should opt for the .530 hpbt bc vs .495 bc of the 175 smk. I also get that Mach is relative to temp, altitude, and humidity so I'm trying to select a 1000 yard bullet that is relatively unaffected by the transition so all I have to worry about is wind and drop, not instability

Among the 308 match bullets 175 to 190 grains, you don't have to worry about BC. Every one of them is good enough to get you to 1k, and all of them handle the transonic region well.

Since you are starting out, I recommend you buy a couple 250 count boxes of Nosler Custom Compeition 175gr BTHP bullets, or if you want 190s get those. You won't find a better bang for your buck for long range shooting with a 308 than the Nosler CC lineup.

Honestly by the time you can tell the difference in accuracy between brands of match bullets, you'll have shot out a 308 barrel.

Jimro

[Bart B.]

Sierra's 240-gr. HPMK leaving at 2200 fps bucks the wind to 1000 yards better than others. But it takes a 1:8 twist 28" long barrel with a long chamber throat to do it. David Tubb used to shoot Sierra 250-gr HPMK's from such .308 Win barrels leaving 2150 fps using less wind correction on his sight than the rest of us shooting 180's through 220's.

[Jimro]

To put the 240 SMK at 2150 fps verses a 175 SMK at 2650 fps into context, the 10mph wind shift at 1000 yards for the 240 is 9.2 MOA, and for the same conditions for the 175 is 10.1 MOA.

Conversely a Sierra 155 Palma (2156 style) at 3000 fps has 8.9 MOA wind shift in the same conditions, which is a full minute better than the 2155 bullet at the same velocity.

Jimro

[Bart B.]

Good post, Jimro.

You've an insight as to why my best scores at 1000 have been with the original #2155 155's from a 32" barrel leaving at 3075 fps. Aimed with aperture sights. About half MOA accuracy tests as but much less recoil than my 30 caliber magnums.

It's hard to convince most folks about these realities of what works at long range. No wonder why the 6.5x.284 blew most of the belted magnums off the scoreboard in prone long range matches.

[jwrowland77]

When I shoot out my current barrel and put a new one on, I had planned to put at minimum a 30" barrel on it. I have some SMK #2156 still laying around from when I first got started.

[Jimro]

You've an insight as to why my best scores at 1000 have been with the original #2155 155's from a 32" barrel leaving at 3075 fps. Aimed with aperture sights. About half MOA accuracy tests as but much less recoil than my 30 caliber magnums.

KraigWY's noted that his M1A scores at 1k beat out his 300 Win Mag M70 match rifle scores at 1k as well.

It's hard to convince most folks about these realities of what works at long range. No wonder why the 6.5x.284 blew most of the belted magnums off the scoreboard in prone long range matches.

Yes it is, the belted magnums don't do so well from the sling as lower recoiling rounds for the same reason that the 308 does better at 1k, and the 223 does better at 600, ease of use on the operator. Even when bipods and scopes are allowed in F Open class, not too many people are reaching for belted magnums any more. Most are shooting hot 6 or 6.5 mm pills.

I've wanted to build a wildcate 6.5 on the WSSM case for a while, but the lack of quality brass options keeps me on the sane side. That and it would only duplicate the 6.5x55 Swede ballistics, although from a shorter fatter case so the accuracy potential would be increased.

Jimro

[Tipsy Mcstagger]

Let me ask another question. If it doesn't get much traction I may post a separate thread or maybe you can point me to one but it has to do with jumping and powder. Say I find a decent book coal and a good consistent charge to go with it but want a little more accuracy so then I jump it. Now, that leaves less space for powder, and if I'm not touching the lands I should also see a reduction in pressure/fps. Is there a rule of thumb for upping a charge to match the previous charge since now I have less pressure and maintain accuracy? I'm lead to believe that a certain charge or node is best but wouldn't that be negated by then jumping? Do you stick with your previous accuracy charge when you start jumping till you find accuracy then start upping the charge again if it's too slow for you?

[Jimro]

As you decrease COAL pressure will decrease until it starts increasing again.

Unclenick has a graphic of pressure to COAL jump from the lands that shows this.

I take it you are trying Berger's COAL jump testing method?

Jimro

[Tipsy Mcstagger]

Yes I found the sweet spot for accuracy using the old accuracy charge. I don't know if there's a correlation between jumping and charge. I'm wondering if I jump and use the old charge, Is it the distance to lands that makes it accuracte or a change in volume or both? So I guess what I'm getting at, could I find the potential sweet spot by jumping and miss it due to an incorrect charge? I'm trying to get out of jumping a bullet, working up a load with it, jump it another .02, .04, .06 etc without working up a charge of weights every time I jump it.

[Jimro]

Well, that's a can of worms.

Unclenick has a method for using Trail Boss (I think, brain's getting fuzzier recalling memories) and testing for optimal jump before you ever move to your full power powder.

But, if you keep the charge the same and adjust the distance to lands, you will see the optimal distance to lands for that charge weight. You might see a tighter group with a different charge weight at a different jump, but you can't know for sure until you measure.

But, most people don't adjust charge after they've found one that works, they fine tune the distance to lands to wring the max accuracy out of that charge. That way they can increase COAL as the lands wear and they can keep good accuracy over the life of the barrel.

Jimro

[Tipsy Mcstagger]

Fair enough. I'm going to build my 1k range tomorrow and see how far I can track my groups solo. I don't expect to group at 1000 yards, but I expect to learn some stuff.

[Tipsy Mcstagger]

I learned that I don't have enough internal adjustment with my scope, and shot out to 800 yards, had plenty of hits on a torso with 168 Fgmm. Thank goodness it's a bdc reticle. I'll have to get an moa rail. I'm shooting the grendel tomorrow and will test my reloads.

[Jimro]

You don't need a new rail, unless you can get one cheaper than a set of Burris Extreme Z rings with offset inserts.

Jimro

[Tipsy Mcstagger]

Do you trust them and are they sturdy? Thanks for all so far.

[Jimro]

Yes, they work.

However, I'm not sure if they are cheaper than an EGW 20 MOA rail. Midway has them on sale for 44.99 for Savage, Remington, Tikka, Winchester, Browning, and Mauser.

I've used EGW rails, and they are a quality part.

Jimro

[jwrowland77]

Originally Posted by Jimro

Yes, they work.



However, I'm not sure if they are cheaper than an EGW 20 MOA rail. Midway has them on sale for 44.99 for Savage, Remington, Tikka, Winchester, Browning, and Mauser.



I've used EGW rails, and they are a quality part.



Jimro

+1 on the EGW 20 MOA bases. I bought to start out competition shooting based on reviews and plus they cheaper than other bases. I have not been dissatisfied. I've been several more since then and love them. They are a quality product.