88 TMK Loading Thread

[43.6N]

any help/advice on diagnosing my issue or what you’d try next?

tikka 22cm
PBB 16.25” 1-7.5tw .120 FB (brand new)
rs1.2
scythe ti
DA 3,150 ft

first 6 rnds thru the barrel were factory 80 ELDX to zero scope avg 2,932 fps

load 1
-88 tmk
-43.5 gr stball hd
-peterson lrp (unfired)
-cci 200
-2.7 coal
-2,600fps

load 2
-88 tmk
-38.5 gr h4381sc
-peterson lrp (unfired)
-cci 200
-2.7 coal
-2,524 fps

only shot a couple rnds of each hand load bc i saw light ejector swipes and heavier bolt lift. shots were spaced out 1-2 minutes. bullets were seated to 30 thou jump in my chamber based on modified case and hornady oal gauge.
lots of new variables at play so not sure if i just need the barrel to break in more or if i should be looking at one specific element on the loads/rifle system.

Sometimes with this super tough premium brass, it can take 1-2 firings before the brass fully expands and fire forms to your chamber.

Annealing the necks helps.
But until they fully seal against the chamber walls, they will push back against the bolt face, leading to early pressure signs like in your post.

I’ve seen it with alpha and Peterson virgin brass.
Hornady is soft enough of an alloy, that I’ve never seen it happen.

Take a virgin brass shoulder measurement, and compare it to your fired brass. If you can, just size the neck without bumping back the shoulder at all. Then reload those brass pieces and fire again. They will be much tighter in the chamber, and you won’t have as much thrust onto the bolt face because the walls of the chamber are gripping the case. Finally measure the shoulder of your twice fired brass, and compare it to the other two measurements.

 

[43.6N]

Edit to add measurements:
ADI Unfired Shoulder: 1.361
Fired Shoulder: 1.365

NAS3 Unfired: 1.351 - 1.355
Fired: 1.359 - 1.362

So now your fired nas3 cases are just barely the same length as your resized ADI brass?
I think excessive headspace is what led to the pierced primers.

How does the reloading process for the nas3 cases go? Based on the measurements, the once fired brass looks like a good candidate to neck size only before firing a second time.

 

[wind gypsy]

Well,
A couple days ago I ran a pressure test with ADI Brass, Fed 205 primers, N150 and the 88 TMK’s. I went up to 26.0 then backed off to 25.0 and shot another 15 of them. No issues, no sticky bolt lift. Some cratering of the primer, but I generally get some of that even on the factory ADI ammo. Velocity is 2686 fps.

I loaded up the NAS3 cases with 25, 26 and 27.0 of N150, based on the appx 10% larger case capacity stated by Shell Shock.
I fired all three rounds and got 2704, 2764 and 2840 fps. However, all three primers were pierced.

Edit: on further inspection and research, these are “cookie cutter” holes, often associated with the excessive headspace by a shoulder that is set back too far. These cases have a shoulder that is as much as .014” shorter than a fire formed case.

Now I’m not sure where the issue is, seeing how 25 & 26 were ok in the Adi brass. Maybe something to do with the characteristics of the alloy cases? Too much headspace? But I’ve never pierced a primer in a brass case at the same pressure.

Below is a photo showing, from left to right, 25.0 - 26.0 - 27.0. The ADI is a 25.0 load.
View attachment 1038954

This post made me look at SAAMI spec, there's only 0.007" tolerance available to remain in spec for case length to shoulder. Are the ADI cases you measured virgin?

Also, buzzkill. I ordered some NAS3 cases off the forum hype about them yesterday..

 

[wind gypsy]

Now I’m not sure where the issue is, seeing how 25 & 26 were ok in the Adi brass. Maybe something to do with the characteristics of the alloy cases? Too much headspace? But I’ve never pierced a primer in a brass case at the same pressure.

How I picture the issue happening (meaning i'm hypothesizing) - Length to shoulder is short so there is excessive head space, case head moves off of boltface when firing pin hits primer, case walls grip chamber walls with case head still not pressing back against bolt face, high pressure pushes primer to the rear more since case head is not firmly against bolt face and it results in more force against the firing pin -> pierced primer.

 

[nm.otter]

Getting the gripping the chamber part right has to be tricky with steel walls.

 

[B_Reynolds_AK]

Good insights everyone. I’ll start a separate thread so as to not clutter this one more than I have already.

@43.6N Your recommendations are helpful on re sizing.. if I was using brass cases. These NAS are one and done. Single use. They cannot be re sized.