with a 7.5 being so short i would think the lighter bullet moving faster than the loved 75 gr would be better. the 75 grain makrs sense for 10 inch sbrs but 7.5 is SO short. ani ideas or info?

You have it backwards.

A heavier bullet spends more time in the barrel.

.... more energy put into the bullet and less wasted.

I recommend either 77 grain Sierra matchking or 75 grain TAP

Thank you.

75/77 gr offerings flat out do not expand at all in a 7".

Only at 2000fps at the muzzle.

Check out Hornady 55gr SP, 64gr Power Point, 62gr Fusion. 50-65gr SP is what you want in that barrel length. There's gel testing out there.

This was info I was looking for, thank you

Projectile performance is usually pretty heavily dependent on velocity.  Whether it be an expanding projectile (Gold Dot, Fusion, TAP SBR, TSX, etc.) or a FMJ/BTHP/etc. projectile which relies on yaw/fragmentation to dramatically increase terminal effectiveness, they all have a minimum velocity at which they perform as desired.  Typically, minimum velocities for desired performance are going to be lower with expanding projectiles than they will be with fragmenting projectiles that rely on yaw to initiate fragmentation.

It's also important to understand that heavier projectiles will be traveling at slower velocities than lighter projectiles everything else being equal (barrel length, etc.).

Knowing this, yes, when you start getting down into extremely short barrels, a lighter projectile is going to be the better choice in a lot of cases because the heavier projectiles will offer extremely limited range inside their performance envelope, with some never reaching their required velocity thresholds at all.

A heavier projectile spending more time in the bore (due to the projectile traveling at a slower velocity) has fuck all to do with how the projectile actually performs on target.  I'm not even sure what you mean by "having more energy put into it."  

Also, those projectiles you're recommending are never going to reach their required fragmentation thresholds out of a 7.5" barrel.  The generally accepted fragmentation threshold for the 77gr SMK is somewhere around 2250fps.  You're barely getting there with a 10.5" barrel and you'll never reach that velocity number with a 7.5" barrel, even at the muzzle.  

ETA:  OP, a high quality expanding load designed to work at lower velocities commonly found with shorter barrels is what you should be looking for (as already mentioned).  Speer Gold Dot, Federal Fusion, TAP SBR, etc. are all great choices.  I'm not entirely sure on the 55gr TAP Urban, but IIRC, that specific load uses a VMAX projectile which is more of a varmint bullet.  You'll see impressive expansion/fragmentation, but penetration isn't exactly great.

I think what the guy was saying is that typically a heavier bullet is longer, and may add a little dwell time. IDK how that would really help with velocity though. Seems the heavier weight would offset any gain with the additional dwell.

This guy has several videos testing a 7.5" ar with various loads.

7.5" Hornady Tap Test

7.5" MK262 77g

Rjeff I agree with your post 99.9% but give the Vmaxes another look they may surprise you. At the velocities produced by shortys (or extended range in a 16-20) the Vmax acts more like a controlled expansion SP. The 300blk 110gr Vmax is a good example of this.

I halfway think a 55gr Vmax loaded very very light to about 2550 in a 16" carbine gas w/ carbine buffer (in hopes of cycling)  could  be a great HD round and like shooting a .22 recoil wise, the reduced velocity would actually increase performance IMO on 2 leg targets.

Here's the 55gr in a 7".

I'm actually disappointed in the velocity because I chronoed Federal .223 55gr ball at 2300 from a 7".

Interesting.  Admittedly, I was going off memory on the Vmax projectiles, but I thought I remembered when doing research on .300BLK loads that gel tests comparing the 110gr VMAX to the 110/120gr TTSX showed the VMAX having considerably less penetration depth than the Barnes loads (probably due to the projectiles fragmenting and not retaining a lot of their weight).  

I'll definitely look into them some more.

SBR Ammo

50 or 55gr Barnes TSX bullets are supposed to perform well in the velocity ranges produced by short barrels.

Attached File


12" may be a tad shy for hunting but perfect for self defense and as that velocity sheds we will see less dramatic expansion retaining more weight and penetrating deeper. Its only 12" right there at the muzzle at its very fastest.

The Barnes blacktip are fantastic, can't recall their pen numbers but my wallet knows the Vmax is $12 a box cheaper and good enough for me

That is interesting. You may be on to something.

This video shows an mk318 out of a 7.5" mushrooming like a SP instead of fragmenting.

Fast forward to 5:00.

As556, you got me interested in the v-max.

What is the difference between the 'custom' and the 'black' in 300blk?

Honestly haven't looked into it much I would imagine they're the same.

Not sure the custom load has a cannelure but the Black definitely does.

There used to be an awesome pdf by Brassfetcher online about 300 but its gone now. They used Vmax and it did very well as did the Hornady 110gr SP not unlike their 55gr offering.

Crazy to say but even some 125s are not pushed fast enough to perform the 125gr SMK for instance.  Im sticking with 115 and under for the time being.

The 125 TMK is an exception though.

Excellent info; thanks.  This is a good candidate for my 10.5" if I ever get the bolt-over issue squared away.

I am in the same boat and from what I have found out, the list of rounds that seem to perform reasonably well at velocities from a 7.5 inch barrel are...



5.56 55 grain GMX - Hornady
5.56 50 grain TSX - Black hills (2300fps)
5.56 77 grain TMK - Black Hills * (1900 fps)
5.56 69 grain TMK - Black hills * (1900 fps)
5.56 64 grain Ranger - Winchester * (1600 fps)
5.56 MK 318 sost mod 0 - Federal * (1900 fps)
5.56 64 grain Bonded tactical LE - Federal * (1600 fps)
.223 62 grain Fusion MSR - Federal * (1700 fps)
.223 64 grain Gold dot - Speer * (1600 fps)
.223 55 grain Gold Dot - Speer *
.223 55 grain PSP - Fioccoi


The ones with the asterisk (*) all have expansion or fragmentation thresholds below 2000 fps and will give you the best performance from a 7.5 inch barrel at distances beyond 50 yds
In parenthesis is either the manufactures listed velocity threshold for fragmentation/expansion... or the lowest velocity I could find for those rounds in gel tests where they fragmented or expanded



The 77 and 69 grain above are the sierra TMK ("tipped match king) version loaded by Black hills 1900 probably isn't its threshold but Black Hills only tested down to 1900 fps

They also load the SMK OTM (open tip Sierra match king) version in the same weight (69 and 77 grain) but the OTM wont give the same results at the velocity of a 7.5 that the tipped one will

There are other rounds that will expand or fragment but may not be suitable for defense  like the VMAX
these are all listed on the recommended defense ammo list and/or performed well in tests at 7.5 inch velocities

No problem. I think since it got 19" in the 7" you could get a perfect mix of fragmentation and penetration at the velocity a 10" will produce.  The 7" test also gives you a rough minimum expansion floor to calculate your effective range.

One thing I think people underestimate with rifles especially is the loads that only get 9-10" of penetration in common gel tests in 16" guns. That means its getting 10" right there at the muzzle which is a hair shy of "minimum" (still insane to have 1k ft lbs dissipated in 10" of tissue)  but as range extends and velocity bleeds off that bullet is going to exhibit the classic behavior of less expansion and deeper penetration making it a viable load at further distances. This is a desirable trait IMO. Those lighter weight bullets that are driven just a liiiiittle too fast at the muzzle actually do quite well at lower velocity. These same bullets are good in SBRs as well for this reason as we saw with the 55gr Vmax/7" I posted above.

Reminds me of a test with 5.45 Vmax everyone said it sucked but in reality it just barely underpenetrated at the muzzle which means it would be perfect at 50-300m.