Terminal performance: 69tmk vs 77tmk?

[SDHNTR]

Is there a legit difference in construction? Like a thicker jacket to the 77?

For example, there is a genuine construction difference in the 168gr .308 TTSX and the 180gr TTSX that is far more meaningful than 12 grains.

 

[sierracharlie338]

I'm going to be a little careful here, as 2 whitetails is a pretty small sample size. My observation would be that they may not penetrate quite like the 77 gr. Hard to argue with dead deer, though.

This aligns with something someone else said earlier that there weren’t a lot of exits with their experience shooting 69s

 

[Pickettpuncher]

The comparison from a 308 168 and a 175 and the 22 cal 69 vs 77 is not apples to apples. That 8 grain difference is more than a 10% weight difference where in a 308 is much less. Penetration is probably the downfall.

 

[sierracharlie338]

Is there a legit difference in construction? Like a thicker jacket to the 77?

For example, there is a genuine construction difference in the 168gr .308 TTSX and the 180gr TTSX that is far more meaningful than 12 grains.

Not sure I’ve never seen a cut away of the two but it could be a factor

 

[SDHNTR]

Not sure I’ve never seen a cut away of the two but it could be a factor

Call Sierra and ask.

 

[dieselchessy]

Another thing to consider is that twist rate (rotational RPM) also plays a role in penetration.
Your losing weight of the projectile as well as RPM’s.

 

[xsn10s]

I use the 69 TMK’s out of a AR with a 16inch barrel + suppressor. I haven’t hit anything with them other than Kansas Whitetail and some coyotes. Ranges have 25-350ish. They perform very well as far as I can tell. I probably have 8-10 deer with them and never really felt like I needed anything bigger. I wouldn’t rebarrel over not being able to use the 77’s, just my opinion.

What velocity were you getting with your 16"? I have a 1-9 M4 that would work once I developed a load. TIA

 

[sierracharlie338]

Another thing to consider is that twist rate (rotational RPM) also plays a role in penetration.
Your losing weight of the projectile as well as RPM’s.

Interesting theory that I’ve never heard before. Have you seen this tested or discussed somewhere? I’d like to look into this more

 

[dieselchessy]

If you google “bullet rpm affect on terminal performance” or “bullet spin affect on terminal performance” you’ll find lots of reading.
I didn’t easily find a scientific type article. I’ll look more later. I don’t recall if it was Litz that wrote about it, or someone else.

 

[RyanT26]

What velocity were you getting with your 16"? I have a 1-9 M4 that would work once I developed a load. TIA

2825ish, I think it’s 24.5gr of SW precision.

 

[xsn10s]

2825ish, I think it’s 24.5gr of SW precision.

Thanks bud! You guys are killing me lol. Now I gotta fined a new scope for the M4 and some 69 gr TMK's.

 

[xsn10s]

Not sure I’ve never seen a cut away of the two but it could be a factor

We could probably get petey to do a cross section. RC hardness could be done but I doubt any manufacturer would spend extra money getting a different jacket hardness. The logistics would raise costs.

 

[Pickettpuncher]

We could probably get petey to do a cross section. RC hardness could be done but I doubt any manufacturer would spend extra money getting a different jacket hardness. The logistics would raise costs.

Being a match bullet, would you expect there to be any difference between the two as far as bullet construction.

 

[xsn10s]

Being a match bullet, would you expect there to be any difference between the two as far as bullet construction.

No I wouldn't. But when we're talking about terminal performance I don't like to assume anything. If it were purely for punching paper or steel I wouldn't waste my time. But the time spent on a lathe is well spent for this type of application.

 

[Pickettpuncher]

No I wouldn't. But when we're talking about terminal performance I don't like to assume anything. If it were purely for punching paper or steel I wouldn't waste my time. But the time spent on a lathe is well spent for this type of application.

I guess my point is it’s a match bullet. Why would Sierra alter the jacket for a match bullet. I would expect both the be the same, just the 77 gr started out with a longer cup. I do understand your concern on performance tho, I’m curious as well

 

[xsn10s]

I guess my point is it’s a match bullet. Why would Sierra alter the jacket for a match bullet. I would expect both the be the same, just the 77 gr started out with a longer cup. I do understand your concern on performance tho, I’m curious as well

They could change the thickness for reasons other than punching paper. Say a multi purpose bullet with different tip colors.

 

[idahodave]

I've killed deer with both, and have noticed little difference honestly. I suppose I'd prefer a 77 all things considered, but I certainly wouldn't re-barrel an accurate .22 chambering if it shot the 69s well.

Dave

 

[sierracharlie338]

I guess my point is it’s a match bullet. Why would Sierra alter the jacket for a match bullet. I would expect both the be the same, just the 77 gr started out with a longer cup. I do understand your concern on performance tho, I’m curious as well

I do happen to know that Hornady for example made the 55g Vmax and 55g zmax. Both identical right minus the color tip? Nope two different jacket thicknesses. I have seen the cross section of them side by side.

 

[Formidilosus]

The only real difference is 69gr TMK penetrates about 20-30% less than the 77gr TMK.

 

[DJL2]

I do happen to know that Hornady for example made the 55g Vmax and 55g zmax. Both identical right minus the color tip? Nope two different jacket thicknesses. I have seen the cross section of them side by side.

The Zmax is an Amax in different clothes... which I'd prefer to the Vmax anyway. Good option for folks that can get 'em cheap because of the cringy marketing.