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danf_fl 07-28-2014 05:13 PM

Interesting problem yesterday
I have a Bushmaster ORC in .308 with 1:10 twist.

I tried to sight in using mil issue 7.62, 175 gr boat tail, and it seemed like the scope was losing center. Some high, some left, some right.

After a little rest, I tried some 146gr ball, and the thing grouped around 1" at 100 yards (but I was getting sweat running down into my glasses).

I have seen where some ammo will do different things, but this is something that has me baffled.

Any ideas?

jjfuller1 07-28-2014 05:20 PM

i doubt its the scope. more likely it was the ammo. even though we use twist as a guideline sometimes rifles break the rules. my bet is the heavy bullets were just not as stable as the lighter bullets. that or maybe you have a barrel that shoots better dirty than clean.

JonM 07-28-2014 06:06 PM

After you settled down did you try the 175 again??

Most likely it was your trigger finger.

Although im not a fan of anything bigger than 165-169 grain in a 308. Thats about as big a bullet as you can use and still stuff enough powder behind without a kaboom to be useful. Kinda why im not a fan of 1-10 twist in 308. You really cant get enough speed to stabilize a 175 well except in very very few special blends of powder or select powders that are hard to get when it was easy to get powder

Sniper03 07-28-2014 06:31 PM


I guess one other question we might have is what Brand and Model of scope is it. Regarding any Parallax? Did you torque the screws and mount and use a little Blue Loctite? With that being OK then I would have to agree with the thought of poor ammunition. Bullet concentricity may be very poor! What ammunition is it as far as manufacture.
Other than that not being critical, but trigger pull and breathing is important. Also muscling the gun can cause this. Natural point of aim for the rifle is important. When you get ready to pull the trigger close your eye or eyes and then open it or them and see if the gun is still pointing at the target center. If not you are muscling the rifle and it will respond when it recoils causing the left to right and or elevation variances. The elevation variances can also be caused by breathing when the shot is fired. A lot of shooters try to muscle the gun when in position or do not stop breathing! I know I am talking to the choir with you but just sharing some thoughts!


danf_fl 07-28-2014 06:33 PM

If there was only one shooter, then the shooter could be blamed. But this was with me and another shooter.
He had been shooting at 800 yard targets the day before, so I eliminated myself in the equation.

But, no, we did not try to go back to the 175 gr. I'm keeping that for another session.

c3shooter 07-28-2014 07:28 PM

Personal opinion- 1-10 is a bit fast for a 175. There are some 175 VLDs that are quite a bit longer than usual- and while we USE bullet weights, it is the length that really affects stability.

USUALLY weight drives the length, but if a bullet goes outside the usual profile, that does not work. Myself, would go for 1-12 for a 175- but again, just my opinion.

danf_fl 07-28-2014 07:36 PM

One possibility that was brought up yesterday.

The weight of the rifle and the forearm being tapered.

The light weight of the rifle did not absorb the recoil that well of the heavier bullets, and the movement of the rifle on the sand bag. With the lighter bullet, the movement was less.

Just for the record, I did not get any bruising from the shoot, and even as hot as it was yesterday, I still had fun.

jjfuller1 07-28-2014 08:44 PM

well operator error was eliminated. my bet is as stands. ammunition and barrel. one of yours does not like the other... :D

danf_fl 07-28-2014 09:34 PM

We were using a brown box 7.62X51 175 gr M118LR ammo.

JonM 07-30-2014 03:10 AM


Originally Posted by danf_fl (Post 1610938)
We were using a brown box 7.62X51 175 gr M118LR ammo.

if its actual 118 thats your issue. that is junk. ive got a bunch of it i use for the wife to get trigger time at 100. bought a bunch of airpulls cheap a bit back for her. you can hold ten, points down and see the the out of round on the jackets by naked eye. what i mean is the cores arent center of the jacket with some jackets much thinner on one side

weighed a bunch deviation is +-5grains

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