Advanced Marksmanship Rifling : Projectile weight question :(

[longun83]

I tried my hand at firing beyond 500 metres this passed weekend. I was touching paper at least, I've never shot that far before. I know I wasn't really reading the wind that well and I made the STUPID mistake of taking off my bipod and shooting supported on my bag after 400m. (5 shot groups each at 200, 3, 4, 5, and 600.) I know most of my issues were user related so don't take this as blaming my equipment aside from not having the best rifle out of 9shooters. I did better than 4 other guys at least, all of my rounds were on paper even at 600 metres (656 yards, eh) and the guy who won the little competition is on the base team and the Canadian army team; There were also 2 csor snipers in the mix.

I am running a Remington 700AACsd in 308, most of you know that has a 20" barrel but faster 1:10 rifling. I didn't have the time to do up any hand loads before the shoot (I'm also a new reloader) so I ended up rocking with Norma BTHP 168gr. I have had some guys tell me to go to 150gr, and others to go heavier. To me, heavier makes more sense on account of the rifling and that it would aid in stability of the heavier projectile which I think could give me a smidge more distance.

Thoughts?

A friend of mine who shoots F class told me if he had my rifle he wouldnt be shooting lighter than 178gr.

~ Frank from Canada

 

[thrusty]

At closer ranges (within 600 yrds and even better at 100yrds) I had better luck with the 168gr SMK out of my AAC-SD. But, at extended distances the 175SMK was the clear leader - at around 1000yrds I was becoming sub-sonic and the 175gr bullet remained stable enough to give me hits at around 1097yrds - 175s performed better in the wind for me as well.


Really depends on how far you plan on shooting..... I had TERRIBLE results with 155gr Scenars and 178gr Amax's. YMMV...

And yes....faster twist rates are typically used with heavier projectiles.

 

[gstaylorg]

Although your faster twist rate will enable you to use heavier (longer) projectiles, the fact that you're now reloading will allow you a wider range of projectile choices as long as you're willing to work up a decent load out of your rifle. Obviously, the chamber specs will play an important part in that, particularly if you want to use the longer heavier projectiles. However, IIRC, the Remington 700AACsd has a reasonably long chamber.

The bottom line is that you can choose (within reason) the projectile you want to shoot based on the type shooting you wish to do and work up a load from there. Although you could certainly reach 1000 yd with a decent load, your barrel length and the resultant MV are not going to be optimal for that distance. My recommendation would be to start with Berger 175 gr Tactical bullets, or possibly 185 gr Juggernauts if your chamber is long enough. Both of those projectiles have very good BCs and transition through trans-sonic well. I would estimate you could push the 175s around 2600-2625 fps with no trouble, the 185s somewhat slower. Either one would buy you a LOT more wind resistance out to 500-600 yd than 150s. Alternatively, if you really want to run a lighter projectile, I've had pretty decent results shooting the Applied Ballistics 155.5 gr Fullbore load out of a 23" 10-twist barrel. YMMV.

 

[longun83]

At closer ranges (within 600 yrds and even better at 100yrds) I had better luck with the 168gr SMK out of my AAC-SD. But, at extended distances the 175SMK was the clear leader - at around 1000yrds I was becoming sub-sonic and the 175gr bullet remained stable enough to give me hits at around 1097yrds - 175s performed better in the wind for me as well.


Really depends on how far you plan on shooting..... I had TERRIBLE results with 155gr Scenars and 178gr Amax's. YMMV...

And yes....faster twist rates are typically used with heavier projectiles.

178 Amax were junk for you? I was hitting clay targets at 200-230ish metres with 168 so I assumed it would be somewhat similar aside from flight characteristics. What about 178gr BTHP Match? For now my goal is to shoot sub MOA at 300 metres before pushing it out further. I know that will take some time and lots of development. I had the opportunity over the weekend to shoot 656 yards so I figured what the he77, why not.

 

[longun83]

Although your faster twist rate will enable you to use heavier (longer) projectiles, the fact that you're now reloading will allow you a wider range of projectile choices as long as you're willing to work up a decent load out of your rifle. Obviously, the chamber specs will play an important part in that, particularly if you want to use the longer heavier projectiles. However, IIRC, the Remington 700AACsd has a reasonably long chamber.

The bottom line is that you can choose (within reason) the projectile you want to shoot based on the type shooting you wish to do and work up a load from there. Although you could certainly reach 1000 yd with a decent load, your barrel length and the resultant MV are not going to be optimal for that distance. My recommendation would be to start with Berger 175 gr Tactical bullets, or possibly 185 gr Juggernauts if your chamber is long enough. Both of those projectiles have very good BCs and transition through trans-sonic well. I would estimate you could push the 175s around 2600-2625 fps with no trouble, the 185s somewhat slower. Either one would buy you a LOT more wind resistance out to 500-600 yd than 150s. Alternatively, if you really want to run a lighter projectile, I've had pretty decent results shooting the Applied Ballistics 155.5 gr Fullbore load out of a 23" 10-twist barrel. YMMV.

Up here the only club I've seen Bergers for purchase had them for I think 67-70 bucks per box. Hornady in Canada hovers in the mid to high $30ish range.

My trick for measuring my chamber is to use a piece of brass that has 2 incisions hacksawed down the neck. I slowly chamber a round a few times with projectile which I use to determine the appropriate OAL for a particular recipe. This way I can pull it apart and re do it 4 or 5 times for accuracy. I have "stencil rounds" made up with my measurements written on the side. It cuts down on time for me because at the moment I only have a single stage.

Thanks for your input.

 

[thrusty]

178 Amax were junk for you? I was hitting clay targets at 200-230ish metres with 168 so I assumed it would be somewhat similar aside from flight characteristics. What about 178gr BTHP Match? For now my goal is to shoot sub MOA at 300 metres before pushing it out further. I know that will take some time and lots of development. I had the opportunity over the weekend to shoot 656 yards so I figured what the he77, why not.

I wouldn't say the 178Amax was junk - I was getting around 1-1.5" groups consistently using Varget. I tried just about every charge and COL that I could, but wouldn't tighten up. The 178 BTHP were junk though...for MY rifle. I really wanted both to shoot good because of the excellent BC on them...but, didn't happen.

NOW....the 155 scenars shot terrible bad for my gun. I'd contribute it to the 1:10 twist.

Didn't try any of the Bergers, but the 168Amax (46gr varget), 168SMK(45.5gr Varget) and 175SMK(44.7gr Varget) shoot great.

 

[longun83]

I wouldn't say the 178Amax was junk - I was getting around 1-1.5" groups consistently using Varget. I tried just about every charge and COL that I could, but wouldn't tighten up. The 178 BTHP were junk though...for MY rifle. I really wanted both to shoot good because of the excellent BC on them...but, didn't happen.

NOW....the 155 scenars shot terrible bad for my gun. I'd contribute it to the 1:10 twist.

Didn't try any of the Bergers, but the 168Amax (46gr varget), 168SMK(45.5gr Varget) and 175SMK(44.7gr Varget) shoot great.

I'm up to 44gr of Varget for mine at the moment. I always thought 46 would be too much. I was getting small stress signs with my primers (cratering, but I deleted the picture) mind you this was with Federal brass which I have heard has primer pocket issues. I have a fair bit of Winchester brass and I managed to snag a pile of Norma ammunition for the shoot I started this thread in reference to.

 

[thrusty]

For some reason my rifle likes the powder charges close to max. 46gr of Varget behind a 168Amax is max charge (per Hogdon), I occasionally saw ejector swipes but that's about it as far as pressure signs. This was in Hornady brass...

 

[Strykervet]

Twist rate formula doesn't require a weight variable. It's mostly geometric with a velocity "variable" (typically just used as a constant based on just how fast --I'm guessing the error isn't significant at rifle velocity, but I didn't work it out). The weight comes into factor when you determine trajectory and drift, as it's acted on by other forces like gravity and wind. The formula is very simple, just look up "twist rate formula" on Wikipedia (it'll explain it more than I care to here).

Of course, in practice, it doesn't always work out that way. I have a 6.5G that has a twist mathematically optimized for around 120-130gr. It'll shoot Nosler BT 120's at .33MOA. It'll also shoot 100gr. AMAX to the same group --but that bullet SHOULD require about a 13:1 or thereabouts! FWIW, it shoots 120gr. SMK's to about 1MOA (SMK's shine in most of my other rifles). So sometimes it really comes down to the load and the barrel. But optimizing the barrel for the bullet you intend on firing most isn't a bad idea.

The bullet should also be designed for the speed it's intended on traveling, so I suspect the SMK's don't work as well as they should, because perhaps, they were designed to work at higher velocity in Creedmores and such. On the other hand, the 123 AMAX was designed specifically for the Grendel but I have other loads much more accurate than those. Again, load and barrel...

I usually start with the math and then go from there.

Forgive me for my ignorance, but wasn't that rifle designed for subsonic loads? If it is for subs, then yeah, it'll likely prefer heavier bullets. I forget the optimum twists for 7.62, I just don't fire it much anymore. But run that formula for different weights and you'll figure it out --try the ones closest to the figure.

Also, too much twist on lighter bullets tends to open the groups from my best experience (M193 vs. M855 with 20-30 shooters all keeping excellent dope class to class shot from NIB issue Colt M4's).

 

[longun83]

Twist rate formula doesn't require a weight variable. It's mostly geometric with a velocity "variable" (typically just used as a constant based on just how fast --I'm guessing the error isn't significant at rifle velocity, but I didn't work it out). The weight comes into factor when you determine trajectory and drift, as it's acted on by other forces like gravity and wind. The formula is very simple, just look up "twist rate formula" on Wikipedia (it'll explain it more than I care to here).

Of course, in practice, it doesn't always work out that way. I have a 6.5G that has a twist mathematically optimized for around 120-130gr. It'll shoot Nosler BT 120's at .33MOA. It'll also shoot 100gr. AMAX to the same group --but that bullet SHOULD require about a 13:1 or thereabouts! FWIW, it shoots 120gr. SMK's to about 1MOA (SMK's shine in most of my other rifles). So sometimes it really comes down to the load and the barrel. But optimizing the barrel for the bullet you intend on firing most isn't a bad idea.

The bullet should also be designed for the speed it's intended on traveling, so I suspect the SMK's don't work as well as they should, because perhaps, they were designed to work at higher velocity in Creedmores and such. On the other hand, the 123 AMAX was designed specifically for the Grendel but I have other loads much more accurate than those. Again, load and barrel...

I usually start with the math and then go from there.

Forgive me for my ignorance, but wasn't that rifle designed for subsonic loads? If it is for subs, then yeah, it'll likely prefer heavier bullets. I forget the optimum twists for 7.62, I just don't fire it much anymore. But run that formula for different weights and you'll figure it out --try the ones closest to the figure.

Also, too much twist on lighter bullets tends to open the groups from my best experience (M193 vs. M855 with 20-30 shooters all keeping excellent dope class to class shot from NIB issue Colt M4's).

So what I asked then should only be used as a guideline when developing the right recipe then? Good to know.

I will have to look that up and do the math later on when I have some spare time.

You sound more than well versed in long distance ballistics.... are you a sniper by trade? Or just hobby?