Gunsmithing Loss of accuracy at 1000 yds

[GOING FOR 2000]

Rem 700P-.308

This is the second rifle that has gone bad. The first lost .038 of the throat at 819 rounds. Rem. replaced the rifle. Now the replacement rifle has gone from a 5"-10 shot group to a 50"-10 shot group at 1000 yds after 433 rounds.

When I receive a new rifle, I create a master dummy round to establish the distance from the bolt face to rifling. This master had a (ogive) measurement of 2.231.

To recheck the measurement after this problem occurred, I set the bullet out in the original master dummy round enough that the bolt was just short of locking, then pushed into full lock position to seat the bullet the same way as when I originally created the master (stripped bolt).

The ogive length now measures 2.390., this is an increase of .159. Does anyone have an idea of what would cause this, or have I received two rifles from Remington with bad barrels?

Load:
Lapua Brass trim to 2.005, neck sized, prepped, and matched
175 gn. Sierra MatchKing--ogive seated 2.085
42.8 gn. Reloader-15
CCI- 200 Primer

 

[wbeard]

Re: Loss of accuracy at 1000 yds

Since you suspect a change...what was the jump to the lands you were loading for when you had your best accuracy? If ???something??? changed that changes your chamber depth then maybe just try redialing your load?

In my experience I notice drastic accuracy changes as I change the jump even .05" For example for me i usually don't get best accuracy with zero jump but I test new rifles with 0, .05, .10, .15, .2 and look for the best. I notice .05 and .15 may be crappy but .1 and .2 good. Try to recal your loads??? but no idea on why/how it changed.

 

[Erik Cortina]

Re: Loss of accuracy at 1000 yds

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 1000 YDS. IS FUN</div><div class="ubbcode-body">
Does anyone have an idea of what would cause this, or have I received two rifles from Remington with bad barrels?

</div></div>

Yes, shooting causes it! You need to chase the lands to maintain accuracy. If magazine length restricts you from going longer, then you need to adjust powder/seating depth to compensate for throat wear.

 

[300sniper]

Re: Loss of accuracy at 1000 yds

i think you got extremely lucky to get a factory rifle that would shoot 5"-10 round groups at 1k.

 

[tansinator]

Re: Loss of accuracy at 1000 yds

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body">i think you got extremely lucky to get a factory rifle that would shoot 5"-10 round groups at 1k.</div></div>

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

What he said!

 

[JeffP40]

Re: Loss of accuracy at 1000 yds

You are going to all this trouble to shoot at 1K and you are shooting a factory rifle? You will be a lot happier with a build and it will last longer.

 

[Teggy1]

Re: Loss of accuracy at 1000 yds

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Erik Cortina</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 1000 YDS. IS FUN</div><div class="ubbcode-body">
Does anyone have an idea of what would cause this, or have I received two rifles from Remington with bad barrels?

</div></div>

Yes, shooting causes it! You need to chase the lands to maintain accuracy. If magazine length restricts you from going longer, then you need to adjust powder/seating depth to compensate for throat wear. </div></div>

No, not with round counts that low. A 308 Win. should be a 5-8K round rifle.

 

[Huckleberry75]

Re: Loss of accuracy at 1000 yds

Have you checked your chamber depth? Do you really need to trim all the way back to 2.005"? I know that it is the recommended trim to length, but if your chamber is longer, all that you are doing by trimming shorter is reducing the neck stability and allowing more throat errosion because the chamber is left partially exposed by the shorter neck. My chamber is 2.051", so I work my brass to around 2.040"-ish.

YMMV

 

[LRI]

Re: Loss of accuracy at 1000 yds

When it comes to the 308 the palma rifle typically runs loads about as hot as they come.

46+ grains of Varget will get a 155 bullet somewhere around 3050fps. Barrel life is expected to run around 2500 rounds before you see it open up at 1K.

The heavy charge is where I focus my attention as the OP states he's getting roughly between 1/3rd and 1/2 of that.

So, what the hell is going on?

Assuming you measured the throat correctly with your master dummy round, then all one is left to assume is that the throat/freebore portion of the chamber has indeed gone south. Especially with a round count that low.

I seriously doubt trimming .04-.05 off your case length is going to cut barrel life by 70%. I do think its excessive though. .01-.015 is the max that most use.

If it were me:

I would double check everything one more time. Have a 2nd pair of eyes (experienced/knowledgeable ones) observe your inspection.
If the #'s come out the same I'd be writing a letter to Remington and sending the rifle back to them. (again)

-or-

Send the gun to a smith to have a premium barrel put on it.

Good luck either way.

C.