77 TmK jump sensitive?

[masterblaster1]

I am have a newly built 7 twist 223 bolt gun, it's a shorty at 20 inches so I can use my suppressor. I been shooting the 77 smk forever with good results in all my other 223's, AR and bolt. I picked up some 77 TmK's to try out and found that my lee seater die in my coax press would only seat them down to 2.270 and I had to screw the die all the way downtown the plate with the adjuster ll the way down. I measured the chamber with the hornady tool and case and I have a max of 2.290 I can seat them to.I loaded up a bunch at .2 grain increments and the best load fell where my smk was at 23.5 8208xbr but the group is about 3/4 at 100 I want to get it down to 1/2 or better. I am wondering if the 77 tmk is sensitive to distance to lands and what die should I get for seating them all the way down to Sami spec?

 

[Park ranger]

I jump them a full .100" in my service rifle and they do just fine.

 

[dkhunt14]

I would start at .005 in the lands and go to 30 off in .010 increments. Some place in there they should shoot better. Once you find that place fine tune in between in smaller increments. Matt

 

[tenring]

They shoot well in my 7 twist savage jammed .005.

 

[Catfish]

They shoot best in my 224 TTH jamed into the land also.

 

[Shynloco]

masterblaster1,
You must be hand loading each round as opposed to magazine feeding (needs 2.260 Oal). But have you tried a different powder....say like VVN140 which is shown as the Accurate Load powder in the Sierra Manual for 77gr MK's? I suspect your rifle will shoot much better groups using VVN 140, 135, or 133. As for the die, I've found best seating is achieved using a Wilson In-Line Seater Die. Bruno's has then selling for $59 without the Micro adjustment and $84 with the new style Micro Adjustment.

Alex