Sierra MK 155gr 2156,new style)

[daes42]

I managed to get some Sierra MK 155gr,2156) for my 308 and found out they seem to be shaped differently than other bullets. The minimum jump I can get is 0.085', with a a cartridge overall length of 2.875', which is the max the AI magazine on my rifle can take,the interior magazine measurement is 2.890' but I want to leave some room for cartridges to feed properly). This jump is quite large but I do not know if it is excessive. In order for the bullet to touch the lands, the cartridge overall length is 2.965 and the straight shank of the bullet has maybe 0.020' of contact, so it literally falls out of the case neck. I do not have this problem with any other bullet I tried, which includes AMax 155 and 178, Sierra 155s,2155, old style) and 175 and Lapua Scenar 155 and 185.

By comparison the Lapua 155, when it is touching the lands,cartridge overall length of at 2.875'), has full length contact with the cartridge neck, with the boat tail starting just at the base of the case neck and protruding into the case. I generally shoot them at 0.010' from the lands, with cartridge overall length of 2.865'. All measurements have been checked with a comparator and overall length gauge.

This means that:

a. the throat of the rifle is a little long, but I can live with it for other bullets; and

b. This bullet,2156) is really shaped differently.

My question is: Should I even bother to try to shoot the 2156 SMK bullets with a 0.085' jump or am I wasting my time? Is it even possible to expect decent accuracy out of a jump this large? This may be acceptable but I have no feel for it. I was planning to shoot 25 or 30 to see. Any pointers would be appreciated. Thanks!

 

[fdshuster]

daes42: I also tried the 155 Palma #2156 and had similar experience. My throat is a little shorter than yours, and the bullet shank/neck contact length is .083', not enough that I'm comfortable with it. Tried that length,carefully, hoping it would not fall out), and back in .010' increments. Never could get it to shoot and have since given up on it. The good old reliable 155 HPBT MatchKing# 2155 continues to be the 'winner', loaded with 45 grs. of Varget.

 

[spclark]

daes42, I'd load 'em & shoot 'em.

There's been a lot of discussions this year on various forums about jump vs. no-jump. I learned by experience this year I can accurately jump one 6mm bullet,DTAC115) far farther,.060'!) than I ever thought possible strictly as a result of running out of ammo at a local match & shooting some cartridges I'd loaded for another rifle with a shorter chamber.

Yes, the 2156 is a vastly different shape than the 2155 but when they were first introduced late last year the AMU at Raton merely swapped out the 2155's they'd loaded for the newly-arrived 2156's & shot awesome!

If they don't shoot in your rifle let me know! I'll take 'em off your hands for what you paid for 'em & I'll pay the USPS freight.