Load Data for 155 TMK?

[ColinR]

I just picked up a box of 155 TMK's but can't find any load data. The TMK is slightly longer than the standard MK so not sure where to start with COL. I will check where it sits relative to the lands as the ogive is clearly different. My AI has a long throat so probably a compromise on COL with a longer than normal jump while still having a cartridge that will fit the mag. I usually use 44.5 of N140 with the 2155 MK and will use this as a starting point, but any further info from anyone who has already used the TMK 155 will be useful.

[DW58]

I moved over from the 155gr Palma SMK (2156) to the 155gr TMK (7755) a few months ago. In my experience the loads I have ended up using for the TMK are the same as that previousy used for the SMK.

I would also point out that the TMK has been tested by Brian Litz - he has found the G7 BC of the 155gr TMK to be the same as that of the Palma TMK (2156) at 0.237.

[ColinR]

I moved over from the 155gr Palma SMK (2156) to the 155gr TMK (7755) a few months ago. In my experience the loads I have ended up using for the TMK are the same as that previousy used for the SMK.

I would also point out that the TMK has been tested by Brian Litz - he has found the G7 BC of the 155gr TMK to be the same as that of the Palma TMK (2156) at 0.237.

Correct me if I am wrong but don't the Palma SMK and TMK have a similar ogive design i.e. quite different to the 2155? I have used the 2155 very successfully in my AI and never really tested the 2156 to any extent other than loading up a couple of batches, from a box given me, to the same spec as the 2155. I think maybe now is the time to explore the 7755 and do a bit more load development from scratch.

[Laurie]

The 2156 usually needs a long jump to work well, US Fullbore and Palma shooters who have adopted this model in a big way say that 40 thou' minimum is needed even in their very short freebore chambers, Palma 95 and Bisley 150 and the more recent one. The old 2155 basically works with everything you throw at it from 10 thou' and larger. As the 2156 is pretty 'fussy', a super-large jump in your AI may or may not suit the design, likewise the TMK variant - the only way to find out is to try it / them.

I'm unsure of Sierra's strategy here with the TMK. One motive I'm pretty sure is to appear more 'modern' and that's certainly working given the amount of interest on shooting forums on both sides of the Atlantic, and being more 'modern' to command a higher price which also applies. Whilst other TMK models in other calibres offer higher BCs than their older stablemates, the 155 thirty doesn't against the 2156. What I do suspect though is that with the 2156 as originally introduced had its tip very sharply 'pointed', the introduction of the 7755 may see this dropped and the 2156 will lose 4 or 5% BC value as a result. More to the point (no pun intended), it'll reduce Sierra's production costs on the 2156 as pointing is an extra production step and will be a relatively expensive one at that. There are mixed reports from the US now about whether the 2156 is or isn't pointed suggesting that it's been missed out on some production lots.

[James K]

I've used them and have stuck with the same loads as the untipped bullets.

[ColinR]

The 2156 usually needs a long jump to work well, US Fullbore and Palma shooters who have adopted this model in a big way say that 40 thou' minimum is needed even in their very short freebore chambers, Palma 95 and Bisley 150 and the more recent one. The old 2155 basically works with everything you throw at it from 10 thou' and larger. As the 2156 is pretty 'fussy', a super-large jump in your AI may or may not suit the design, likewise the TMK variant - the only way to find out is to try it / them.

I'm unsure of Sierra's strategy here with the TMK. One motive I'm pretty sure is to appear more 'modern' and that's certainly working given the amount of interest on shooting forums on both sides of the Atlantic, and being more 'modern' to command a higher price which also applies. Whilst other TMK models in other calibres offer higher BCs than their older stablemates, the 155 thirty doesn't against the 2156. What I do suspect though is that with the 2156 as originally introduced had its tip very sharply 'pointed', the introduction of the 7755 may see this dropped and the 2156 will lose 4 or 5% BC value as a result. More to the point (no pun intended), it'll reduce Sierra's production costs on the 2156 as pointing is an extra production step and will be a relatively expensive one at that. There are mixed reports from the US now about whether the 2156 is or isn't pointed suggesting that it's been missed out on some production lots.

Thanks Laurie, that is very informative and almost, almost, puts a case for sticking with 2155 on the basis 'if it ain't broke.....' Seems the way to go is forget the 2156 and see what, if any, improvements can be rung out of the 7755. I just hope Sierra continue with 2155 and 2200 (168) as both these shoot exceptionally well through the AI. However, ultimately marketing and margin rule the day so one wonders how many 155 MK's Sierra need in their range

[ColinR]

I just measured various bullet types with the Hornady tool to give COL when touching lands of my AI as follows:

155 Amax 2.875"
155 2156 2.958"
155 2155 2.857"
155 LockBase 2.857
155 7755 2.973" (New TMK)
168 2200 2.890

This rifle obviously has a long throat and why LockBase and 2155 seem to shoot best even when loaded to 2.800 COL - still a jump of 0.057", but it seems this rifle shoots everything pretty well almost irrespective of COL. However, the 2156 and TMK would need to be loaded considerably longer to be even in the region of 0.060", probably leaving too little of the bearing surface in the neck.

I have a box of 155 TMK so will try them at different COL's to see how they work, but reading Laurie's post I don't have any great expectations.