vertical shot problems 2 and one high..

[fordwrench]

searching for a excellent load for my ar 15 heavy barrel varminter and am having issues i believe from front or rear bags. shooting from a sinclair front pedestal and bunnie ear rear protector. what causes unexplained vertical? counted 5 or 6 groups that are 2 in one hole and 1 usually high opening the group to 5/8 - 3/4. what gives????

 

[fdshuster]

fordwrench: Don't know if you've tried different front rest locations on your AR handguard, but it is believed to make a difference. M.L.McPherson did an article on AR front rests in the October 2001 issue of "Precision Shooting". His findings indicate that the front rest/bag must be as close as possible to the front of the receiver. Float tube handguards are said to be even more of a problem if the front rest/bag is at the front of the handguard. I'm not able to use my Sinclair front rest with my ARs, but instead, use a hard packed large bunny eared front bag placing it almost touching the front of the receiver: it works/ for me. I've seen smaller group sizes using this method. Tried my Harris bi-pd, but groups opened up compared the the sand bag. Name of the article is " A ? of bag placement and gun design".

 

[fdshuster]

fordwrench: Got to thinking overnight, I do that sometimes) about the vertical stringing. Keep a close check on your gas rings: if the 3 gaps lineup during firing, it will create vertical. I personnally believe in and have the "McFarland" one piece gas ring in all four of my uppers. Sold by "Sinclair" for $3.60 each/ installs in 30 seconds. Would go to a 50 or 60 rd. match w/ gaps set at 120 degrees apart, fire the match, come home, take bolt apart for cleaning, and 2 of the gaps would be lined-up with the third very close. With the McFarland--fagetabowtit, doesn't happen. I've also sealed the gap between the rear of the receiver and the "half-moon" cut-out on the charging handle, using silicon, as suggested by Glen Zediker in his excellent book " The Competitive AR15", page 57. If you have the rear sling stud mounted on the butt, be very careful it's not making contact with the rear bag. I picked-up a spare, filed it down to the contour of the butt, and use it when doing some serious shooting for groups, off the bench. I've even removed the bottom butt-plate mounting screw, and sling stud, and fired without them: butt-plate held-on with top screw only has never been a problem. A favorite "do-all" load combo for me has been 25 grs. Varget w/ 55 gr. V-max/ used for max. 300 yd. For longer distances the 69 gr. Sierra #1380 with Varget and/or RL15 works, both loads used in: Bushmaster CMP 1-8, 2 uppers with Krieger 1-7.8, and even a BM 1-9 chrome-lined, they will shoot!) Just some thoughts, of what little I know: hope it may help.

 

[fordwrench]

thank you so much. i went again last night . i moved the front rest and held the gun a little tighter. it helped. i have 2 really nice shooting loads 69 mk and vv 540 and hornady 75bthp w/ rl15 they will one hole and small. thanks for the info. i think it would be wise to look in other places for group improvement. ie your rec. and or stock and rifle handling on the bench. i'm finding out its not a bolt gun. thanks for your help!