308 PA-10 Heat vs Accuracy problem

[survivalshop]

1-10 seems to be  the go to twist rate for 30 cal Barrels( 308/30'06 )& most shoot 150 gr. ammo out of them , so it must be more to it then just twist rate, Bullet configuration may be why some shoot better then others . All Firearms will see some degradation of accuracy when Barrels is heated or over heated .

You have not said how bad accuracy does get , so if your groups are only opening up a little , it's normal . Having a  Match HB will show less deviation in group size .

Edited July 6, 2019 by survivalshop

[PA-10]

4 hours ago, survivalshop said:

1-10 seems to be  the go to twist rate for 30 cal Barrels( 308/30'06 )& most shoot 150 gr. ammo out of them , so it must be more to it then just twist rate, Bullet configuration may be why some shoot better then others . All Firearms will see some degradation of accuracy when Barrels is heated or over heated .

You have not said how bad accuracy does get , so if your groups are only opening up a little , it's normal . Having a  Match HB will show less deviation in group size .

Thank you for the information on this, as far as groups opening up once the barrel is hot can’t say because I’m only trying to hit a 18x30 target at ranges of 200-600 yards. At 400-600 I can say I miss the target due to heat. 

[98Z5V]

4 hours ago, PA-10 said:

400-600 I can say I miss the target due to heat. 

That's like shooting a 55gr 5.56 projectile at 500 yards - it's beyond it's intended range.  400?  No problem.  When I shoot a 450-yard target with 55gr, I have to hold for a tick over 500 yards on a good BDC scope - because the bullet drops so much at that distance.

Get some good ammo, heavier projectiles, and go re-visit the 400~600 that is giving you fits.  Start with the ammo first.  Don't change anything else on the gun.

What kind of experience to you have with 400~600 yards with this cartridge?  .308 Winchester?

[Armed Eye Doc]

Here is a great price on some FGMM 168gr. $15.94

Shipping was $13 (flat rate) when I checked on 5 boxes.  I have not bought from them before so I can't say good or bad.

https://globalordnance.com/federal-gold-medal-match-308-winchester-168-grain-boat-tail-hollow-point-20-round-box-gm308m-upc-029465089337/

Edited July 6, 2019 by Armed Eye Doc

[PA-10]

12 hours ago, 98Z5V said:

That's like shooting a 55gr 5.56 projectile at 500 yards - it's beyond it's intended range.  400?  No problem.  When I shoot a 450-yard target with 55gr, I have to hold for a tick over 500 yards on a good BDC scope - because the bullet drops so much at that distance.

Get some good ammo, heavier projectiles, and go re-visit the 400~600 that is giving you fits.  Start with the ammo first.  Don't change anything else on the gun.

What kind of experience to you have with 400~600 yards with this cartridge?  .308 Winchester?

I will be trying some heavier grain Ammo such as SK Match soon. As far as my experience with the .308 not a lot I started last fall when I got my new primary arms scope. Up until then i was shooting 5.56 and 7.62x39 along with multiple military surplus calibers, but not past 200 yards. When I was in the Marine Corps long ago we shot 500 meters prone iron sights on a pretty large draw target at the farthest. Like I said long ago, so eyesight is also a factor by the end of the day.

[Magwa]

just going to throw this out there but what are you basing your come ups on at 400 and 600 yards do you have solid info for those ranges based on chronographed speed on your loads BC.coefficient etc the 308 will be dropping like a rock at 600 it does not take much to miss solid dope from 400 out is a must

[Sisco]

With ammo, you get what you pay for. My cheap 149 gr ammo now collects dust. Get some decent match ammo or start reloading.

[survivalshop]

59 minutes ago, Sisco said:

With ammo, you get what you pay for. My cheap 149 gr ammo now collects dust. Get some decent match ammo or start reloading.

That sums it up . 

Magwa  has a good idea also , what are you dope changes for shooting at those distances ? Did you shoot at 100 yard intervals to see where the Bullets grouped or hit/missed on the Target. Your  Sight/Scope adj. dope for those ranges may be off . 

[PA-10]

1 hour ago, survivalshop said:

That sums it up . 

Magwa  has a good idea also , what are you dope changes for shooting at those distances ? Did you shoot at 100 yard intervals to see where the Bullets grouped or hit/missed on the Target. Your  Sight/Scope adj. dope for those ranges may be off . 

I am using a acss reticle which was sighted in at 100 yards and was hitting about a 1 Moa on a 18x30 target. Once it is sighted in at 100 yards I use the acss which has  bullet drops out to 800 yards for a 5.56/308. I’ve been hitting at 600 about 70 % until our temperature getting really hot. I’m getting better Ammo to try soon. 

[Magwa]

without knowing the speed your ammo of choice ,in your rifle is going then you are shooting blind no reticle can just shoot you your dope in both 5.56 and 308 two different animals it is all about speed of bullet out of your gun.....weight of bullet ,twist of barrel,altitude, temperature,and a few other factors when you start going beyond 400 yards as a example  federal gold match 168 HPBT ammo drops 35 inches at 400 yards and 105 inches at 600 yards and 315 inches at 900 so you see many of your misses may be to bad dope it is critical to have good dope and consistent ammo if you hope to have any luck beyond 400 also you have to figure wind which is another conversation...

[98Z5V]

5 hours ago, PA-10 said:

I am using a acss reticle which was sighted in at 100 yards and was hitting about a 1 Moa on a 18x30 target. Once it is sighted in at 100 yards I use the acss which has  bullet drops out to 800 yards for a 5.56/308. I’ve been hitting at 600 about 70 % until our temperature getting really hot. I’m getting better Ammo to try soon. 

That particular scope (ACSS HUD DMR) is calibrated for heavier ammo, 175gr and 168gr.  For a true 100 yard zero, the BDC marks will be more "on" at the distances indicated in the scope.  On the lighter ammo, the bullet impact is going to come up short at the greater distances indicated, starting after 400 yards.  The longer the distance, the more they're gonna be off, because the lighter bullet is dropping like a rock the further it goes.

[PA-10]

2 hours ago, 98Z5V said:

That particular scope (ACSS HUD DMR) is calibrated for heavier ammo, 175gr and 168gr.  For a true 100 yard zero, the BDC marks will be more "on" at the distances indicated in the scope.  On the lighter ammo, the bullet impact is going to come up short at the greater distances indicated, starting after 400 yards.  The longer the distance, the more they're gonna be off, because the lighter bullet is dropping like a rock the further it goes.

That makes perfect sense so I will try a heavier round. My scope is a primary arms 1x6 Raptor First focal plane and I also have there second focal plane, both are very accurate and hold zero I’ve had no problems. 

[Cliff R]

+ 2 or three on sight dope.

When the problems are at their worst have you tried dropping back to 100 yards to see if you are still holding 1MOA?

That's a pretty big deal too and not much has been mentioned about wind drift and shooter error.  The smallest things done to the weapon before the bullet exits the barrel are greatly multiplied at long distances.

Shooter error is multiplied by frustration, especially on hot days.  We tend to push harder to get the rounds off sooner without repeating everything required for best accuracy.  Have seen that deal play out many times locked into a sling on the 1000 yard line getting baked in the sun and the damned wind is shifting around a bit........Cliff