I got some .224 77 TMK bullets recently for loading 223 , 1200 of them. This weekend I loaded up 20 with my same recipe  for SMK , the bullets were longer so I had to seat them deeper, and I could tell there was some variation in length. With 23 g H4895. Shout horrible, best group was 1.12 and the worst was 2.4 at 100 yards.

Today I decided to sort them and found about 1/3 are 1.055 in length , 1/3 are 1.063 to 1.065 in length and another third are 1.056 in length.

It seems Sierra is having some issues with quality control. I loaded up some more test loads with the 1.055 bullets I sorted out today . Hopefully I can update this next week with how they do.

I found a similar issue with OAL length with Remington 55gr projectiles and resultant diminished accuracy.  I switched to Hornady.

Best bet is to ask around for a better choice in your desired bullet weight.

I tried some 77 smk's when they first came out thinking they would be pretty close to spot on in length due to them being tipped but I was wrong.

They were just like op's, all over the place in length.

I've had similar measurements with other tipped projectiles.

I'm only worried about base to ogive.  As long as that's consistent, I generally don't have accuracy issues.

The base to ogive on the 1.055 and 1.056 bullets seem to be about the same , I’m guessing the difference in length is due to plastic tip variation.

I just can’t figure out how they are having bullets 10 thousands longer with the 1.065 ones pass QC. Seems QC should have caught those.

Never the less I’m happy to get to play with these even if I’m having a near 1/3 rejection rate for my SPR.  I’ll just use the rejected ones in my sbr. I’ve been wanting to try these out on deer and coyote.

If I find a can of XBR locally I will grab it. I don’t like paying hazmat for just 1lb to try.

I just opened up a 500ct box of the TMK’s and measured about 100 before giving up. All measured between 1.065 and 1.067, I wonder why the 100 rd box I was using has so much more variation?

I length sorted all the 80 grain SMKs I had and packed them in like groups of 100. I figure I'll load them together so any variation from a different length is consistent in the box of ammo. No idea if it actually made a difference but it made me feel better about my reloads.

H4895 seems like an unusual choice for 77 grain 223. Have you tried Varget, N140, XBR, or R15? Those are the powders I see most service rifle shooters gravitate towards for .223.

Just set your seating die to push the LONGEST bullet deep enough into the case to ensure you don’t have magazine-length issues.

Adjust powder charge slightly if necessary.

Unless you are the upper echelon of God’s-gift-to-marksmanship-excellence, you won’t notice any effect on target.

Exactly.

Nay. 23.5gr is sparks of Mjolnir.

What twist barrel do you have?

I've been shooting the 77 TMKs and they have shot incredibly well for me. Much better than the regular SMKs.

I didn’t think of that , I loaded up some at 2.260 and I had a bunch that were 2.270 and wouldn’t fit in a mag.

It’s a 1/7 stainless Douglas barrel.

H4895 is my favorite powder. I think the AMU uses it for their teams hand loads. It’s maybe one of the most versatile powders out there, dose not meter very well though.

I found them to not be as accurate as the SMK but they still shoot good.
I use TAC and found H322 to shoot heavies very well. I would've never thought to try it but seen someone else on another forum writing about it so decided to try it. It's very accurate.

This issue of seating to accomodate the LONGEST bullet in the box came up when I started messing around with "seconds."

"Seconds" from Midway are usually Sierras which vary in overall length by a considerably greater amount than the premium stuff that Sierra sells in their green boxes.

Sierra MatchKing bullets (the premium version) typically vary in overall length by only about 0.010"

By comparison, the "seconds" usually vary about 0.050" (OMG... five times as much variation!)

Well anyway, I decided I wanted to stil use them, and they all shot very well. But if you are loading to magazine-length, you gotta account for it.

So the $64,000 question is, "How much does 0.050" variation in seating depth change pressure?"

I other words, what is the pressure of the shortest one versus the pressure of the longest one? And how much does that affect point of impact downrange.

I have no way to physically test this, but I do have Quickload on my computer.

Quickload tells me this:
A 77 grain Sierra MatchKing seated to 2.250" overall length (I never try to seat to 2.260" - that's how you sign up for feeding malfunctions) and 24.0 grains of TAC makes 57,357 PSI (SAAMI max for 5.56 is 62,366 PSI).

This is an excellent accuracy load. I have no desire to push the load any harder. Over my chronograph, I get low 2700's for velocity.

OK, so what happens if I push the bullet 0.050" deeper in the case.
That would put the overall length at 2.200"
Quickload says that boosts the pressure 59,840 PSI

That means if you play around with varying overall lengths, your pressure variations will be about 2,500 PSI.

What is the difference in TOTAL DROP at 600 yards when you have 2,500 PSI variation in velocity?

Quicktarget (companion program to Quickload) tells us this:
77 SMK at 57,357 PSI drops 122.9"
77 SMK at 59,840 PSI drops 120.5"

So the difference in drop (fastest bullet versus slowest bullet) when shooting those "seconds" is half the height of the X-ring on the 600 yard target.
I don't know about y'all, but that's way inside my mediocre ability to hold. I'll never see the difference on the target.

So yeah, push that longest bullet deep enough in the case that it won't hang up on feeding.
Push all the other bullets from that batch even deeper.

I'll close on a comment about 2.260" overall length.
I don't hold nearly hard enough that I can see any difference in accuracy based on how much the bullet "jumps" to reach the rifling. I know people like to talk about "jump" as though its as critical as making sure you don't include your sister in what goes on in the dark room at a frat party.
I'm just not that good. And I know I'll never be.

On 9/11/01 I was still of the mind that I had to load to 2.260"
The Pentagon plane flew over my kid's school a mile or so from the crash.
Which made me mad.
So I grabbed the kid out of school, and went home to start loading magazines.
Being a competition shooter mostly, my ammo was vetted already in 20-round magazines.
I began trying to load those 2.260" rounds into 30 round magazines.
Guess what.
TOO LONG.
dammit!

You don't want to get caught in the apocalypse (or out on the range when its 100 degrees) only to discover that you should have seated your bullets deeper.

So SEAT YOUR BULLETS DEEPER.

If you get so good that you can truly see a worthwhile difference by seating bullets longer ("0.015" off the rifling"... "just kissing the rifling" and such), then disregard my remarks.
Othewise, please bring ammo that actually works to muster.

There is SO MUCH about hobby ammunition-making that people *think* matters - but doesn't.
And equally as much that hobbyists refuse to accept as reality.

I've made some BAD AMMO in the decades I've been playing.
I try to make less of that sort these days. I learned my limitations early. Took decades to accept them.

Ok , I loaded some more , at 1.245 , 1.255, and 1.260 ( the latter won’t work with the longer 1.065 bullets and still fit in a mag) had a decent result with 23 grains of H4895 loaded at 1.045 it gave me a .894” group, I figured I would try short as black hills loads them that way. Best group was 23 grains H4895 loaded to 2.260 at .763”

I’m going to see if I can tune the 1.245” load in a bit more.

Attached File
Attached File

I've had great results with them...............


https://www.ar15.com/forums/AR-15/Another-200yd-test-The-77TMK-s-Reload-vs-PSA-vs-BHA/16-782209/

Mag length, I use R15 but H4895 is great for it!
Get them up around 2750fps...........golden!

In my testing, the COL sweet spot was 2.245” with the 77 TMK, which is the same as Black Hills. While I’m at it, 77 SMK sweet spot is 2.240”… which is the same as 77 FGMM. It’s almost like these big companies have already found all of this out and that’s why their ammo is so accurate!

The 77 TMK + XBR combo is awesome!

In my rifles, I have not seen an optimized load yet that’s at a COL of 2.260”. I’ve stopped doing load development at that length because of this and the obvious mag fitment issues. Seating depth does matter for accuracy if you and your rifle are capable of seeing it. YMMV