Sierra TMK

[Heman]

The first 2156s were tipped, although it was a very conservative tip. Can someone post a picture of the current production as I would like to see how the tipping has changed.
I always went ahead and finished pointing mine which were purchased two years ago and last year.

Thanks in advance,
Shawn Agne

 

[Bryan Litz Ballistics]

Bryan, in your book applied ballistics for long range shooting, sierra 2156 is listed as having a g7 bc of .229. The file you attached list the 2156 as g7 of .237. Did further test revel a higher bc, or did sierra change something? Thanks!

The page I posted above is based on more recent lots than the data page in Applied Ballistics for Long Range Shooting. I think there's been some variation in the amount of pointing done on the 2156's from the factory, as well as normal lot variations to account for the .229 vs. .237 G7 BC.

The 155 TMK measured at 0.237.

-Bryan

 

[MLC]

I take it that Sierras introduction of the tipped bullet with an equal BC indicates that production of forming a tipped bullet vs a pointed bullet is either simpler or less expensive?

 

[Berger.Fan222]

I take it that Sierras introduction of the tipped bullet with an equal BC indicates that production of forming a tipped bullet vs a pointed bullet is either simpler or less expensive?

I think that may be the case, but it is also possible that the tipped bullet is in response to customer demand. If Sierra is losing customers and needs a new feature to bring them back, the TMK is a good idea.

So there seem to ba a combination of advantages: higher BC, more consitent BC, less expensive to make, more reliable expansion, customer demand. I know I've been tempted to try tipped bullets in matches, so a TMK is a natural attraction.

 

[siracusap]

Can someone who has the 155 TMK's post the length of the bullets? The bearing surface length would be a plus too.

Thanks

 

[Bryan Litz Ballistics]

The 155 TMK's are 1.279" long.
Nose length is .804"
BT is 0.200"
Bearing Surface is 0.275"

-Bryan

 

[XTR]

My nunbers are a little different:

oal=1.268
Bearing surface = 0.398 using my Hornady ogive attachment on my calipers
BT=0.162
Ogive=0.708

Keep in mind I am using an the 8-30 insert from Hornady that is probably a bit under .300 for my measurements, but the OAL is definitely different to what Bryan has

 

[TZaun]

Call it a hunch, but, I don't think Mr. Litz is using a Hornady tool.

 

[XTR]

Call it a hunch, but, I don't think Mr. Litz is using a Hornady tool.

I'm certain that he is not. Bryan posted that response while I was typing mine, and for comparison sake a lot of shooters do use that tool. I'm not disputing the difference in bearing surface, just noting the method by which the one I measured was determined.

The difference in OAL is however significant. My calipers probably aren't off my .010

 

[Bryan Litz Ballistics]

that's a good distinction to make; what is bearing surface?

My measurements are based on the portion of the bullet that is a full .308" in diameter. The dimensions you'll get from comparators like XTR used will tell you how much is over bore diameter (.300"), more or less. Not all comparators have ID's equal to bore diameter for the respective calibers. To work as a comparator, it just has to have an ID 'less than' groove diameter.

As for OAL difference, it's most likely lot variation.

-Bryan

 

[Berger.Fan222]

The 155 TMK's are 1.279" long.
Nose length is .804"
BT is 0.200"
Bearing Surface is 0.275"

-Bryan

Based on those numbers, the 155 TMK may not be adequately stable from a 1 in 12" or slower barrel. One may need a faster twist to get the full BC from this bullet.

 

[XTR]

I traded a box of 155TMKs for a box or 2156s at the match this weekend, and I talked to a couple of the Palma guys about the loads they are using with the 2156.

I'm going to take some of my Lapua Palma brass and a dose of Varget and I'm going to make up two lots of bullets seated identically from the lands in one of my rifles. Then I'm going to go to the range, zero both at 300. then on the same target back up to 600 and use the the same target and aiming point and shoot groups at 600 yards and see if there is any difference in a side by side same barrel comparison.

I'm expecting this load to be making close to 3000. The Palma guys are getting that but this rifle has a 28 not a 30 inch tube. I'll post up pictures and numbers when I get results.

JBM predicts that the TMK will have about 3" less drop. I think we should be able to see that if it's there.

I have to use 300 and not 100 for the test because the drop from 100 is more than the height of a target frame.

 

[minnesotamulisha]

Thanks, XTR. I'm looking forward to your review..

 

[XTR]

I've loaded up the rounds for my test. First thing I notice is that the TMK has a shape that is visibly more of secant than the 2156, the nose taper is straighter than the 2156 and the transition to the bearing surface is more visible.

Checking the length in the rifle I'm going to shoot them in confirms some of this. Both have about the same OAL, but using the .30 insert on the Hornady tool the ogive measurement on the 2156 is 40 thou longer.

TMK touching lands:
2.935 OAL
2.228 ogive
2156 touching lands:
2.930 OAL
2.269 ogive

Which makes sense if you consider that my tool measures at about the .300 datum line so a bullet that has a more tangent shape that line is pushed further forward on the bullet.

Bearing surfaces look to be very similar on the two bullets.

They are loaded in Lapua Palma brass with 46.5gr of Varget. This rifle has a 26" barrel.

If I can swing it and I can find some good conditions I may try to back them both up to 1000 and measure the difference in drop between the two.

edit: I was thinking one thing and writing another, corrected my secant/tangent errors above, and just to to make clear, both bullets are seated .010 off of the lands by my comparator.

 

[Down South]

I've loaded up the rounds for my test. First thing I notice is that the TMK has a shape that is visibly more of tangent than the 2156, the nose taper is straighter than the 2156 and the transition to the bearing surface is more visible.

Checking the length in the rifle I'm going to shoot them in confirms some of this. Both have about the same OAL, but using the .30 insert on the Hornady tool the ogive measurement on the 2156 is 40 thou longer.

TMK touching lands:
2.935 OAL
2.228 ogive
2156 touching lands:
2.930 OAL
2.269 ogive

Which makes sense if you consider that my tool measures at about the .300 datum line so a bullet that has a more secant shape that line is pushed further forward on the bullet.

Bearing surfaces look to be very similar on the two bullets.

They are loaded in Lapua Palma brass with 46.5gr of Varget. This rifle has a 26" barrel.

If I can swing it and I can find some good conditions I may try to back them both up to 1000 and measure the difference in drop between the two.

Curious to see the outcome......

 

[CAU]

I've tested some of the 175 TMK's and I started the bullets out at .015" off the lands. My groups closed up considerably as I moved toward the factory length of 2.810." I wound up at 2.810" with 44 grains of Varget, 2654 fps over the CE chronograph (out of a 25" barrel, 11.25 twist), and .3" at one hundred for five shots. I'm in the process of testing at 500 now having shot just one group with 6 shots. Four of the five shots went into two inches and the other two dropped out of the group equally (about 1"+/-) though they were side by side, virtually touching. These two shots opened the group to three inches. The vertical dispersion on the four shots was around .6" and 3" for all six shots. I was shooting with a Harris bipod, loading the legs slightly, and a triad rear wedge. I plan to shoot more groups at five with a Sinclair FTR bipod and a Protektor rear bag to see if the groups close up. If not I will move on or retest with another powder. I like the bullets and they do appear promising at factory length in my gun.

 

[terryperkins]

CAU, how many MOAs did you come up from a 100 yard zero to 500 yards?

 

[DW58]

Thanks for all of the info on this topic, I've just started using the 155gr TMK (they've just arrived here in the UK in very limited quantities), desperately needed the G7 BC.

 

[CAU]

Terry, on a sunny day my come up is 11 moa at 500. The AB app calls for 10.6 moa up at that distance but I had to have eleven. I know that the velocity isn't correct but I haven't had the chance to true it.

Chris

 

[liltank]

I've loaded up the rounds for my test. First thing I notice is that the TMK has a shape that is visibly more of secant than the 2156, the nose taper is straighter than the 2156 and the transition to the bearing surface is more visible.

Checking the length in the rifle I'm going to shoot them in confirms some of this. Both have about the same OAL, but using the .30 insert on the Hornady tool the ogive measurement on the 2156 is 40 thou longer.

TMK touching lands:
2.935 OAL
2.228 ogive
2156 touching lands:
2.930 OAL
2.269 ogive

Which makes sense if you consider that my tool measures at about the .300 datum line so a bullet that has a more tangent shape that line is pushed further forward on the bullet.

Bearing surfaces look to be very similar on the two bullets.

They are loaded in Lapua Palma brass with 46.5gr of Varget. This rifle has a 26" barrel.

If I can swing it and I can find some good conditions I may try to back them both up to 1000 and measure the difference in drop between the two.

edit: I was thinking one thing and writing another, corrected my secant/tangent errors above, and just to to make clear, both bullets are seated .010 off of the lands by my comparator.

Any updates to the bullet test?