I think it's the barrel warming up

[Keithjohn]

Well I went out with my 7rem mag Sako 75 HB a couple weeks ago and nailed the 300 yd 10 shot challenge 1st try and I thought this is easy I'll try my other rifles . First I tried my ctr in 308 last week which does 3 and 5 shot groups consistently under 3/4 moa at 100 yds and failed , I had 8 within the 1 moa and 2 outside . The group is slowly stringing to the left with the first two one inch right of the moa group of 8 with a proven load .

So I have a ctr in 260 rem that I tried for the first time today and found a load quickly that's awesome so off I go to my back 40 range to try the challenge with this gun . This time I gave it two warm up shots and established my 300 yd zero and started with confidence . Failed again , didn't miss by as much but again 8 in the one moa and 2 just outside . Again my group was slowly going down and to the left .

I'm thinking the barrel needs more warm up shots to give me the 10 inside the one moa limit I'm after .
Am I wrong -maybe the ctr barrel is still to light ? Maybe I need to try more loads at 300 with different powders !?

My 308 load is in IWI brass shoulder bumped with 44 gr varget and 155 vld wlr primers
Mr 260 rem load is in lapua brass neck sized ,44.5 gr.H4831 with 140 hunting vld and fed 210 primers

I'm shooting off a bench with bipod and monopod with an awesome meopta scope , could be my shooting form too maybe . I have never tried 10 shot groups at 300 before
Any comments ?

 

[Evil_Dark]

Try to shoot 4-5 rounds, and let it cool down, then refire. You will see if your barrel have a tendencie to shift when it heat up. I have a Browning that does that. More it is hot, higher the POI is. It does'nt have a bull barrel tho.

Dark

 

[Ron AKA]

Does it have a hammer forged barrel? If so, they can have significant residual stresses which show up under heat. Could be wind, but a right to left wind should have raised POI not lowered it.

 

[Mystic Precision]

Back to a distance where wind is no a problem for you.. say 150yds.

Put up targets with multiple aiming points and in a horizontal line. Send 4rds at each plotting where each shot goes. Shoot at a slow but steady pace say 10 to 15secs per bang. Focus on making good breaks. By the 3rd target (12 rds), you will have an answer to your question.

Repeat as necessary to prove the point.

Jerry