TMKs - Seating distance off the lands

[VarmLR]

Will report back later on lower loads for the 69TMK at book seating depth (which happens to be 100 thou = tightest group at 24.7gr N140). Have started at 22.8 and gone up .4gr/step all at 100 thou). There's a little breeze but at 100 yds, it shouldn't play too much havoc today (famous last words!). I've taken the opportunity to do the same for my 55 and 60gr loads too, and will be picking the lowest accurate load in each chase for taking forward.

 

 

 

My groupings are all luck.

I will try and find the arrival and mail it to you. It was a while ago I read it.

 

Thanks Phil. Nothing lucky about those groups ...I know how much care you've taken with sorting your rifles and your loads and that it pays off, shows.

[VarmLR]

Some promising results this afternoon. I know that these are just two shot groups, but ammo was running low, but this gives a good indication of what a few disciplined shots brought today. Wind was 3 Oclock at 4mph, distance 100 yds:

 

 

 

23.6gr means not quite so hot. I did shoot off a few at 70 thou seating I'd prepared and 3 shot groups averaged 0.25 inches, pretty much equi-distant spacing between centres, so the 100 thou seating resulted in the tightest (albeit small) group, as with previous trials.

 

I'll shoot a few 5 shot groups at this load once I've re-stocked on TMks but this appears to be the load. I knew that the rifle was more capable than me and if I can keep groups around 0.2 inches, that'll do for my shooting, which isn;t competition level.

 

The only other change made to the set up was replacing the M18 scope with Nightforce scope which I much prefer...great optics...makes a heck of a difference being able to make out a knat's whsikers at 100 yds to precision!

[Si-Snipe]

Anyone else had issues with Sierra TMKs seated close to the lands (say up to 10 thou?). I can't seem to find a node for 69gr 224 bullets...most groups are similar (all around 1 moa or slightly more) i.e. poor. I seated 10 thou off lands and am beginning to think that the TMK might be sensitive to jump. Anyone tried them with much larger jump? At the same time, I tried some 60gr Vmax, again, 10 thou off lands and was looking at a group less than half the size. Barrel is 1/8 twist 223 so should favour the heavier bullet. I normally start load dev with 10 thou jump and vary powder charge but am now thinking that I should start at book seating length, get the tightest group and then try altering leade. Any advice welcome.

Hi mate. We have found the TMK prefer a jump. Around 30 thou has given the best results with the 77's.

[VarmLR]

Hi mate. We have found the TMK prefer a jump. Around 30 thou has given the best results with the 77's.

 

I'm loading mine to 100 thou now (2.26 inches COAL) and when not messing groupings up by making schoolboy errors (tightest group competition yesterday!!) am getting the tightest groups I've ever shot. Got lucky and shot 0.18 inches yesterday whilst shooting a few practice groups. I now have to work on technique and discipline!

 

Here we go:

 

[22lrman]

Chris Long Optimal Barrel Time concept is a very good for developing a starting load IMO. Choose your target node time.Then tweek up and down from there by 0.2gn increments to fine tune.

Quickload saves so much time and cost infinding barrel times, and will probably pay for itself in that respect. The more accurate the inputs the better. Case volume etc

Changing seating changes pressure profiles and subsequently barrel times. So maybe thats the correlation you are seeing.

Good luck it seems like you are getting there anyway

[VarmLR]

Chris Long Optimal Barrel Time concept is a very good for developing a starting load IMO. Choose your target node time.Then tweek up and down from there by 0.2gn increments to fine tune.

Quickload saves so much time and cost infinding barrel times, and will probably pay for itself in that respect. The more accurate the inputs the better. Case volume etc

Changing seating changes pressure profiles and subsequently barrel times. So maybe thats the correlation you are seeing.

Good luck it seems like you are getting there anyway

 

This is a bit out of date now, but yes. What I'm seeing is barrel time effects on harmonics. For new loads, I start with a load ladder, dismiss the loads that are off vertical and keep those which group roughly to the same place. They're refined to the tightest few, then seating distances are worked back from 5 or 10 thou in 20 or 30 thou jumps to get the seating that corresponds to optimum barrel time. QL wasn't much of a help as it happens; at least not initially as what it didn't model was barrel bore dimensions and how polished the bore was (may be less significant) and QL-MVs were significantly different to measured. I'm happy to work up loads without QL. I can get into the ballpark pretty quickly without it now and optimise the loads pretty precisely without it too. I can see its uses, but it isn't for me. I'm not a LR comp shooter.

[22lrman]

I know what you mean about QL. Sometimes a marmite thing. But definitely sounds like you know what you are doing and enjoying it to boot. Cant get much better than that.!

Be interested to hear what you get to with your best load.