X7 HV HB accuracy problems

[P52]

Hello to all
this is my first post , i'm writing from Italy sorry for my incorrect language.
My son have bought about four month ago a rifle model X7 HV HB caliber .308W. From the start we are discontented of the result on shoot field; my son shoot at the distance of 200 m. (about 220 yd) with recharge ammunition Geco and S&B brass trimmed 1,99" , sierra MK HPBT 168 gr. powder 44,5 gr. BL-C(2), AOL 2,815" (freebore 2,875") primer Federal GM210. The scope is a Konus Pro M30 6,5-24x40 with ring mount Leupold iron billet milled (100 € = 130 $) and Harris bipod. I think that these are one of the best solutions. But the target aren't good and are very incostant, we have made a float barrel with removal of matter from the gun stock under the barrel but the improvement have been very modest. the shoot have pause of 1-2 minuts from one and other, the barrel go max to about 45-50°C (113-122°F).
Something could say what there is for a better results? Thanks Paolo

Rovereto 200m 20120310.jpg

Incredibily, at the same distance, with an old and cheapest Mosin Nagant 91/30 (PU scope 3,5x22) with hot barrel after many shoot consecutively it obtain better results; the shooter i think that there is!

Mosin91_30_PU_Rovereto_200m_20120310.jpg

[OLBIKER]

Group No.4 looks good.What did he do differentYou have vertical stringing which indicates a bedding problem.I would skim bed the action and go from there.Good luck,OB

[P52]

Olbiker thanks for the answer, do you think that the problem could to solve with a bedding with epoxy under the action?

[OLBIKER]

I use Marine Tex.Here is a good Tutorial.
Rifle Bedding Technique

[Darkker]

A few things strike me.

First off, what is the ambient temp? 122 F seem like a pretty warm barrel to me.
Also, you are seating the bullets .06" off the lands. For match bullets, try less jump. .03125" is more in the realm of standard.
Marlins have(IME) a very rough bore from the factory. They tend to grab a lot of jacket material when brand new. Have you given it a good scrubbing with some copper solvent?
It is also not uncommon for barrels to have twist rates that vary by about a half a twist. IF your barrel has a actual slower twist(12.5") with 44.5gr of BL-C(2) you are at a very light load. It is possible that they aren't stabilizing properly, or you have a barrel duration issue confusing you.

[P52]

A few things strike me.....
....

Hello Darkker
The ambient temperature was about 60°F the barrel has warming regularly as could to do after 20 shoot in 60', you could touch the barrel with the hand without problem.
I don't think that reduce the measure between AOL and freebore could to do great difference; the problem is the incostant accuracy trougth a session and other.
After read yours answers i think that the problem is the bad quality of the standard stock too flexible. The confirm of it is the petition for the request of a laminate stock for these rifles that there is at the top page of this forum.
Next time we will test without bipod with the rifle layed on a sand bag just front the action and increase the clearance between barrel and stock. If the accuracy will be better after we could make a glass bedding

[luvalever]

scrub the barrel and shoot more. the barrels are rough and shooting them smoothes them out. group number 4 has potential but its still strung, you will need a bedding job and stoot that gun alot. tweak that load like darkker said and you should see definate improvement. i think darkker is right saying your load is light and for the record the seating depth of bullets matters and especially with long ogive match bullets seating depth can help or hurt more than you think. the stringing is definatly the stock. the large groupings probably could be worked in with load development and stock bedding.

[dmsbandit]

I'd get the gun off the bi-pod and get it on a good solid benchrest. Put the stock [just forward of the action] on the front bag and get the heel of the gun on another bag.

Have you tried another powder? Sometimes that alone will make a HUGE difference. I've seen it myself in more than one gun. Some guns have almost an alergic reaction to some powders. I've had the best luck with IMR4895, IMR3031, IMR4320, and win748 in my Marlin 308s.

These targets are shot at 100yds, but they have been consistant out to 200yds also.

[P52]

thanks for yours answers

I will test to change the powder, at home i've a little of N140; next time i shall see what happen. I think that also the work of the bedding i shall be to do.

[P52]

After a year of test we have obtained the best results with the following tuning :
Full floating barrel
Glass bedding
Lapua Scenar 155 gn.; 41,5 gn. N140; GM210; shell Winchester; AOL 71 mm. (2,8")

200 m. (220 yrd)
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