I will shoot 168 & 175 gr. SMK at 600 & 1000 yards. Are heavier/longer bullets better for these yardages? What about the Sierra TMK bullets ? The Sierra web site is beating the drums for the TMK, but I know nothing about them.
600 & 1000 yard bullets for Aero Precision AR10 .308?
- Thread starter Roy Allain
- Start date
I’m still relatively new so I might be wrong but I think the Palma match guys shoot 155gr out to 1000. They tend to have longer barrels though. I use 175gr SMK almost exclusively for my .308 reloads and shoot out to 1000 with my LMT MWS. And that’s out of a 16” barrel so I doubt you’ll have any trouble provided your fundamentals are sound.
I don’t have any experience with 168gr SMKs but I’ve read they tend to destabilize at the transonic range which is usually around 800 yards. This is a problem with the shape of the SMK bulled and this is not seen with hornady ELD-m 168gr bullets as a comparison. I haven’t looked into the TMK bullets and don’t plan to. They’re a fair bit more expensive than the SMKs which work just fine for me.
I don’t have any experience with 168gr SMKs but I’ve read they tend to destabilize at the transonic range which is usually around 800 yards. This is a problem with the shape of the SMK bulled and this is not seen with hornady ELD-m 168gr bullets as a comparison. I haven’t looked into the TMK bullets and don’t plan to. They’re a fair bit more expensive than the SMKs which work just fine for me.
I think there are a couple things you want to review. What speed are you pushing the current 168 and 175gr SMKs? What twist is your barrel and how long is it? Can your set up take a lot of pressure and can you adjust the gas pressure to account for larger bullets flying faster? At a sufficient speed, the 175s may be fine. Hornady makes a 178gr ELDX and Berger makes a 168gr Hybrid that is good too. If you want to push it reloading, then Berger makes a 185gr Juggernaut. I think it was made for maG length 308 applications. Hopefully you can get enough push to make it worth it.
I am building my aero Precision AR10 .308 and haven't yet received the barrel. It is a 1:10 twist and I will mount on it a Superlative Arms adjustable Gas Block. As for gas pressure we shall see. Finally I will change out the stock trigger with a 1/2 to 2 pound trigger. That will help.
I do have a custom .308 blueprinted rem 700 bolt gun with a 1:8 twist Kreiger barrel for 600 yards shooting 168 gr. SMK.
I do have a custom .308 blueprinted rem 700 bolt gun with a 1:8 twist Kreiger barrel for 600 yards shooting 168 gr. SMK.
Most AR-10 pattern rifles will have a rifling twist of 1:10, and magazine length restrictions that limit OAL to a practical 2.810"-2.815".
The 155gr Palma bullets get their effectiveness from (much) longer barrels that are wildly inappropriate for AR's (28"-32"); so I'd suggest they're not a best choice.
I used to handload for 1000yd at near sea level altitudes (NJ), and could manage to get rounds supersonic at target with 175SMK's in a 22" M1a; so I would consider that to be a practical combination of barrel length (22'), twist (1:10"), chambering (.308/7.62x51 NATO), and altitude (1000ft ASL and lower).
So 20" or more, 1:10" twist is OK, 175SMK at or around sea level, 168's up around my way at 4000ft-5000ft ASL, is a good generic/ballpark bullet weight choice.
My current situation is rather different, living and shooting at around 4000ft-4500ft ASL (SE AZ), and this allows more flexibility. I shoot a 20" PA-10, and can achieve the same performance goal (supersonic at 1000yd), with the 168gr range of bullets.
This altitude range also allows for the 155 to be somewhat more practical out of shorter (than 28"-32") barrels, but I can't speak from experience. I think that you'd still need a pretty long barrel (24" or so) to get acceptable 1000yd performance out of the 155 at the higher than sea level altitudes.
In a bolt gun, you might get away with hot loads, but with the AR's, not so much.
The matter of dwell time becomes critical (the period after the bullet passes the gas port, and on until it exits) as it gets longer and longer with barrel length, and this can wreak hell on brass and extractors because it drives the bolt carrier too hard, too soon. It can get to the point where the bolt is unlocking and attempting to drag a still (at least) partially pressurized case out of the chamber, imposing impossible stresses on the extractor (and brass). In other words, bad things can happen. I have the broken extractor to prove it; in my case because I tried to hotload an AR, never do that.
Accuracy also begins to suck, often confirmed by cartridge necks and shoulders getting a pretty big bunch of carbon soot. Hot loads can cause and/or intensify this issue.
That magazine/cartridge length restriction also puts a premium on cartridge length. The longer bullets get seated deeper to stay within that 2.815" overall cartridge max length, and that's another pressure issue. I don't use the longer bullets in a semi, and I single feed them in my bolt gun.
In essence, these limits are at the basis of why so many LR shooters have abandoned the .308 for the 6.5mm chamberings. It's doable, but it takes practice, experience, and finesse. Getting the load to 1000yd supersonic is the easier part, getting it there accurate as well is the harder part.
I shoot both the 308 and the 260 Rem at the 1000yd distance, made easier by the higher altitude at which I live and shoot. The .260 has the better reach, being (on paper) capable of several hundred more yards of supersonic performance. I don't load heavier than 168gr in my 308, counting on the added altitude to allow my rounds to retain better velocities at the extreme distances. I wouldn't shoot my 308 PA-10 168 loads at all down at sea level.
In general, I'd answer your question "yes", with the caveat that I'd want at least a 20" barrel for the task. All my LR bolt guns have 24" or longer (260/28") barrels. If you find you have something shorter, this is my Upper, still in stock at the time of this posting.
TMK's, a qualified "yes". Hornady has addressed a real problem where fast, high BC bullets with plastic tips encounter enough aerodynamic heating at the distant extremes that their dimensional integrity become compromised. In other words they get hot and go smoosh. Hornady addresses this with the ELD line and now the A-Tip line of projectiles. These are longer bullets and may not be suitable for loading at AR-10 magazine feedable cartridge lengths.
With a semi, with lighter triggers; I'd prefer a 2 stage, to minimize the potential for doubling. My Garand and M1a can/could both be made to double at will with the standard 4-5lb single stage trigger (the M1a has been gone for some time, I will never let my Garand go). All of my six AR's have 2 stage triggers. For your applications go with a good one. I'm a cheapskate; and four of my six are PSA Nickel-Boron 2-Stage Triggers, currently temporarily o/o stock. I paid $70-$80 apiece for mine over several months.
My guess; prices everywhere will be going up now.
Greg
The 155gr Palma bullets get their effectiveness from (much) longer barrels that are wildly inappropriate for AR's (28"-32"); so I'd suggest they're not a best choice.
I used to handload for 1000yd at near sea level altitudes (NJ), and could manage to get rounds supersonic at target with 175SMK's in a 22" M1a; so I would consider that to be a practical combination of barrel length (22'), twist (1:10"), chambering (.308/7.62x51 NATO), and altitude (1000ft ASL and lower).
So 20" or more, 1:10" twist is OK, 175SMK at or around sea level, 168's up around my way at 4000ft-5000ft ASL, is a good generic/ballpark bullet weight choice.
My current situation is rather different, living and shooting at around 4000ft-4500ft ASL (SE AZ), and this allows more flexibility. I shoot a 20" PA-10, and can achieve the same performance goal (supersonic at 1000yd), with the 168gr range of bullets.
This altitude range also allows for the 155 to be somewhat more practical out of shorter (than 28"-32") barrels, but I can't speak from experience. I think that you'd still need a pretty long barrel (24" or so) to get acceptable 1000yd performance out of the 155 at the higher than sea level altitudes.
In a bolt gun, you might get away with hot loads, but with the AR's, not so much.
The matter of dwell time becomes critical (the period after the bullet passes the gas port, and on until it exits) as it gets longer and longer with barrel length, and this can wreak hell on brass and extractors because it drives the bolt carrier too hard, too soon. It can get to the point where the bolt is unlocking and attempting to drag a still (at least) partially pressurized case out of the chamber, imposing impossible stresses on the extractor (and brass). In other words, bad things can happen. I have the broken extractor to prove it; in my case because I tried to hotload an AR, never do that.
Accuracy also begins to suck, often confirmed by cartridge necks and shoulders getting a pretty big bunch of carbon soot. Hot loads can cause and/or intensify this issue.
That magazine/cartridge length restriction also puts a premium on cartridge length. The longer bullets get seated deeper to stay within that 2.815" overall cartridge max length, and that's another pressure issue. I don't use the longer bullets in a semi, and I single feed them in my bolt gun.
In essence, these limits are at the basis of why so many LR shooters have abandoned the .308 for the 6.5mm chamberings. It's doable, but it takes practice, experience, and finesse. Getting the load to 1000yd supersonic is the easier part, getting it there accurate as well is the harder part.
I shoot both the 308 and the 260 Rem at the 1000yd distance, made easier by the higher altitude at which I live and shoot. The .260 has the better reach, being (on paper) capable of several hundred more yards of supersonic performance. I don't load heavier than 168gr in my 308, counting on the added altitude to allow my rounds to retain better velocities at the extreme distances. I wouldn't shoot my 308 PA-10 168 loads at all down at sea level.
In general, I'd answer your question "yes", with the caveat that I'd want at least a 20" barrel for the task. All my LR bolt guns have 24" or longer (260/28") barrels. If you find you have something shorter, this is my Upper, still in stock at the time of this posting.
TMK's, a qualified "yes". Hornady has addressed a real problem where fast, high BC bullets with plastic tips encounter enough aerodynamic heating at the distant extremes that their dimensional integrity become compromised. In other words they get hot and go smoosh. Hornady addresses this with the ELD line and now the A-Tip line of projectiles. These are longer bullets and may not be suitable for loading at AR-10 magazine feedable cartridge lengths.
With a semi, with lighter triggers; I'd prefer a 2 stage, to minimize the potential for doubling. My Garand and M1a can/could both be made to double at will with the standard 4-5lb single stage trigger (the M1a has been gone for some time, I will never let my Garand go). All of my six AR's have 2 stage triggers. For your applications go with a good one. I'm a cheapskate; and four of my six are PSA Nickel-Boron 2-Stage Triggers, currently temporarily o/o stock. I paid $70-$80 apiece for mine over several months.
My guess; prices everywhere will be going up now.
Greg
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