Bit of .260 trouble (pics added)

[HSNARC]

Went out on Saturday for some more load development in my .260. Im using once fired necked down 7mm-08 win brass 140gr A-MAX's over 41.5g of H4350 and a fed 210 primer. stuck my target out at 300 yards (wind was directly at my back) I found that 41.5g of H4350 and the bullet seated to mag length was the most accurate load at 100 yards but I thought I could do better than .75 moa. I made up some rounds all the same powder charge (41.5) but varied the seating depths .005 from mag length to slightly jammed, 3 rounds a piece. here is where it got weird, i would shoot and 2 rounds would be touching or an 1/8th inch apart, and the other round would be 1.5-2 inches away horizontally. WTH? i would understand if the rounds were all equally spaced but to have 2 touching and one way the hell off confuses the shit out of me. and yes everything is tight and intact
What does this sound like to you, im sure i forgot something important so ask.

First group is seated to about mag length 2.850 and the increase by .005 until touching the lands

group measured 1.575

group measured 3.015

group measured 2.835

group measured 1.600

group measured 1.840

group measured 2.585

group measured 2.100

group measured 2.410

group measured 1.985

 

[bohem]

Re: Bit of .260 trouble

I think that it's your seating depth that is FUBAR'd. The 140 Amax (and the 123 Amax for that matter) seem to REALLY like about 0.015-0.025" jump to the lands.

If I load them at mag length in my LR-260 (2.800") they are jumping about 0.045" and 0.062" at this point in my barrel wear. Both will shoot around 0.6-0.7" from the magazine.

When I single feed them they will tighten up at 2.830" and 2.840" to overlapping holes.

 

[HSNARC]

Re: Bit of .260 trouble

hmmmm....that sounds reasonable

ill work with some shorter seating depths if anyone ever gets the 140's back in stock

Btw Bohem what load are you running in yours?

 

[42769vette]

Re: Bit of .260 trouble

here is a pic of your load threw my rifle @ 110 yds. this is a 3 shot group.

i load mine threw a ai mag so my col is 2.88ish. that is about a .02 jump to my lands

 

[bohem]

Re: Bit of .260 trouble

DPMS LR-260 24" 8.5tw upper

All cases are:
Win 243 Brass, sized, prepped
CCI 200 primer


140 Amax @ 2.800" OAL
42.5gr H4350
~2775-2800fps MV (based from dope, not chrono data)

123 Amax @ 2.800" OAL
45.0gr H4350
AVG 2940 fps avg

123 Amax @ 2.800" OAL
45.0gr IMR4350
2925 fps avg

 

[HSNARC]

Re: Bit of .260 trouble

Thanks guys. Good info

I got to looking at these targets and it seems like the majority of them string from 10o'clock to 4o'clock .......I would assume this pattern is tell tale of some problem in my technique?

 

[427Cobra]

Re: Bit of .260 trouble

Try CCI primers

 

[bowslngr]

Re: Bit of .260 trouble

Scope parallax?

 

[HSNARC]

Re: Bit of .260 trouble

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">Scope parallax? </div></div>

Elaborate please

 

[260shtr]

Re: Bit of .260 trouble

Straight behind the rifle, pull rifle straight into shoulder, pull trigger straight to the rear, load the bipod.

Or it could be a wind call at 300. several groups had very little vertical, at 300 that is more a indicator of a good load than the horizontal spread. What do chrono # look like?

 

[HSNARC]

Re: Bit of .260 trouble

What do chrono # look like? [/quote]
the sun was going down and it was about 30 degrees
#1 2732,2754,2737
#2 2743,2743,2760
#3 2743,2737,2760
#4 2749,2749,2760
#5 2743,2749,2749
#6 2749,2749,2754
#7 2772,2760,2749
#8 2776,2772,2754
#9 2754,2754,2783

 

[bowslngr]

Re: Bit of .260 trouble

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: HSNARC</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">Scope parallax? </div></div>

Elaborate please </div></div>

If I understand your original post correctly, you went from 100 yards to 300 yards. Where is the parallax set for your scope? Is it adjustable?

 

[Clark]

Re: Bit of .260 trouble

sub moa @300y in wind?
That would be a good day for me.

 

[HSNARC]

Re: Bit of .260 trouble

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: HSNARC</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">Scope parallax? </div></div>

Elaborate please </div></div>

If I understand your original post correctly, you went from 100 yards to 300 yards. Where is the parallax set for your scope? Is it adjustable? </div></div>

Sorry its poorly written, i only shot at 300 that day. Yes my scope is adjustable, and yes i had adjusted correctly at the time.

 

[260shtr]

Re: Bit of .260 trouble (pics added)

By looking at the targets and chrono numbers I would retest loads #4 and #5 with five rounds each on a calm day. The E/S for those loads look very good (for 3 rounds). In general a 20 fps E/S will yield 1 MOA vertical dispersion at 1000.

 

[HSNARC]

Re: Bit of .260 trouble (pics added)

sounds like a plan. ill work on that as soon as 140 A-Max's come back into stock

 

[deadly0311]

Re: Bit of .260 trouble (pics added)

If you can get your hands on some H4831SC, try 47 grains over a 140 AMAX lit by a CCI BR2, seated .015 from the lands. It netted me these results at 725 yards.

 

[tdow]

Re: Bit of .260 trouble (pics added)

What was the wind speed like? If it was at your back it was probably also fishtailing.

 

[HSNARC]

Re: Bit of .260 trouble (pics added)

probably between 13-15mph