Im trying to decide between the two for use in a 8.5 inch barrel and whether the higher muzzle velocity from the 69 grain will ultimately give me similar results but also add a bit more range.

I know that black hills has tested the 77 grain TMK to reliably fragment down to at least 1900 fps, a likely will do so at a lower velocity.

Does the 69 grain yield the same results?

How does the lighter weight affect total penetration in velocities under 2300 fps?

Which would you choose and why?

Both of those sound like terrible choices for a short barrel.

Really, you want lighter projectiles for shorter barrels so you can get some velocity:
https://rifleshooter.com/2015/12/223-remington-5-56mm-nato-barrel-length-and-velocity-26-inches-to-6-inches/

For example, XM193 is getting 2500fps from an 8", vs 2121fps for a 68gr.

So far the best projectile I've seen for velocity threshold is the Federal Fusion 62gr, which is rated for 1700fps.

I'd check out PoBoy's special on Youtube, he has a ton of 7.5" barrel gel tests (like over 30.)

I already have seen all his tests. I also buy the Fusion in the MSR version. I was looking for a fragmenting round to go along with the fusion.

I don't think that either of the TMK's are bad choices.

in poboy special he got about 2215 fps from a 70 grain TSX loaded by BH at 5.56 pressure.... The TSX requires at least 2300 fps to expand. So it didn't in his tests. In the case of the TMK, it is supposed to be about 1900 or less. If that's the case then a bullet of similar weight (69 and 70 grain) loaded by the same company (Black Hills) at the same pressures should yield similar velocities....


and if the 69 grain also expands or fragments at 1900 or less, like the 77 grain... then from an 8.5 inch barrel I have a round that has a muzzle velocity of roughly 2300 fps and it is good for reliable fragmentation out to 200+ yds, with a higher velocity at close ranges where it will most likely be used, and presumably better terminal performance from that higher velocity....  I want to know if the forum members agree or disagree with that assertion.

The figure you quoted for the 26 to 6 inch velocities was for a .223 pressure 68 grain OTM and a 5.56 pressure 55 grain FMJ. Neither of those would be good choices. But its very hard to find a 55 grain Bonded SP loaded to 5.56 pressures for civilian sales.

I have done my research I just want to know if the quote figure of 1900 for the 77 grain TMK applies to the 69 grain TMK also. and if that is a bad selection why?

8.5" 5.56 barrels are really just for range toys. 69 grain TMK underpenetrates at any velocity. The 77 TMK is great at 1900 FPS. At 1600 FPS is just yaws.

and

Bullet construction is more important than just velocity

OP:

I run 77TMKs. I would rather have penetration than velocity for a "possible" extended frag range.

If youre this worried about terminal effects, you should get a longer barrel, IMO 12" is best, 10" is the min.

I agree. Im just trying to get the best possible performance from what I currently have. I got a good price on a 8.5 5.56 So I Bought it. I will probably end up getting either a 10.5 inch 5.56 or an 8.5 300 blackout, but for right now, I know its not ideal but its what I have.... and (using a phrase from blue falcon here...) an 8.5 for use in self defense ranges isn't a nerf dart

The 5.56mm NATO/.223 Remington was not designed for an 8.5" barrel. The propellants/ chamber pressures/gas system was not tuned for that. Bullet manufactures spend a lot of time trying to get the end user a sweet spot for the best performance in the most widely used conditions.

I you like a 8.5" barrel setup, I would suggest leaning more towards the .300. The round was designed around what you want and the bullets that come out of the barrel and hit things away from you are specifically designed for your need.

ETA: Andrew is also good at showing in his videos (excellent by the way) that bullets are very unpredictable based on variables that effect the way the bullet impacts the gel.

ETA: You have the 8.5" barrel. Let me ask you. Is it a 5.56mm chamber or a .223?

Its a 1 in 7 5.56 chamber.
Right now Im keeping the 62 grain fusion MSR and the 5.56 Black Hills 50 grain TSX in my SD/HD mags. Those two seem to yield the best penetration and expansion from shorter barrels and in the case of the Fusion, expand at lower velocities. I was looking to add a fragmenting round to the mix also.

As far as calibers and barrel lengths go I don't really feel that the difference of being 2 inches shorter (between 8.5 and 10.5) is enough to justify the loss in performance, so that is my plan and it makes more sense to me to stick with 1 caliber vs buying an upper for two calibers.

That makes more sense to me, because all of the rounds I buy now, will work as well or better from the 10.5 inch upper in 5.56 that I will get in the near future... so the investment I make in 5.56 ammo for the 8.5 I have now, will still benefit me with the 10.5 that I plan to buy down the road... Im not trying to pinch pennies but that BH 50 grain TSX isnt exactly cheap and im not exactly rich either

I am just trying to find another round that will fragment and still meet or come close to the 12 inch minimum in the mean time. I was just wondering how well the TMK's would fit that bill

Fragmentation is dependent on velocity.

Being at 8.5 inches puts you at a disadvantage out of the gate.

I would buy a box of M193 in as many different manufacturers as you can afford and chrono YOUR barrel to see which is the fastest in YOUR barrel.

That is your answer. If you want a fragmenting round. The fastest is M193.

ETA: Give Mk318 mod 0 a look also. Made for short barrels in the mil.

This is bad advice and shows a total lack of wound ballistics knowledge. Fastest is meaningless. M193 my be fastest round, but highest necessary velocity to achieve fragmentation. So it is the least likely to fragment, other than M855. Anything under 2700 fps and it wont fragment well, anything under 2400 fps and it wont fragment at all. 77 TMK will fragment at 500 fps lower velocity. If your barrel pushes 5.56 77 grain Black Hills over 1900 fps you are golden.

When you get a 10.5" barrel 5.56 77 grain TMK will fragment at the furthest distance of any loading, while still reacginger 12" minimum penetration. The 69 TMK may fragment at a longer range but who cares? It does not reach 12" penetration.

I don't have a total lack of knowledge. So your insult is invalid. Thanks for your personal attack though. You have done that to many people over the years on this site. So. I really shouldn't be surprised.



So.... back to the OP.

Here is the best answer. Go buy a box of what ever ammo you want to use or think you want to use. Chrono it out of YOUR barrel and see what velocity you get out of YOUR barrel and then use some ballistics charts to decide if it fits your need. You can also call the great folks at Black Hills and run these questions by them. They are great people to get info from.

What do you want to use your rifle for? and at what distance?

DevL just told you whats up. The OP is asking about the difference between the two rounds.

as stated by more than 1 person, the 77TMK is better in his barrel due to penetration due to retained weight, both of which have nothing to due with min frag velocity

ETA: TaylorWSO is right,

I miss read the thread and interjected M193 without reading the question.

My bad. And my apologies to him for my response.

No problem. I never even noticed until you pointed it out. I got the answer I was looking for and its what I already figured it would be....

Go with the 77 grain TMK.

I agree with the reasons for why and they make sense to me.

so Im good... besides, Im also on M4carbine.net
and over there you cant even ask a question without being attacked for asking it. That's much worse then whatever the debate was between the to two members above from this fourm.

In general I'd prefer the 77 over the 69 assuming your rifle stabilizes it. The shortest barrel I've killed something with while using TMK 77's was 12.5", though in the future I may use my 10.3".

I took a doe last year with a 12.5" shooting 77gr TMKs as loaded by BH, hit her broadside at about 40m. She ran about 40m and piled up, was dead in the few seconds it took to walk over to her. It hit a rib, dragged violently throughout the entire depth of the chest cavity, and had a small exit on the opposite side. The whole chest cavity was shredded, like someone took a blender to it, like soup. I say this in pretty much every TMK thread, but TMKs fuck shit up.

Excellent!

Both bullets are winners, so you really can't go wrong.