308 Pressures (1:10 vs 1:11.25) Hornady TAP 168s

[Boltgun7443]

I'm at a loss.

I'm on a police team that specifically shoots Hornady TAP 308 168 AMAX rounds.

I have a 20 inch Lilja barrel in 1:10. Its one of out new new builds with 600 rounds through it. There is significant pressure signs on the brass (the small circular indentation)
Significant brass shavings are falling back into the firing pin hole, to the extent of "seemingly" blocking the firing pin from getting a full strike on the primer. It also is sometimes difficult to unlock the bolt and eject the round. It feels "stuck."

My Bartlein 20 inch in 1:11.25 has had zero issues in 3200 rounds of the TAP. I mean ZERO.

Both are blueprinted Rem 700 actions. Both had the same bulder, reamer, machining.

FPS is averaging 2640-2648.

***Can a tighter twist cause MORE pressure in regards to the 1:10 vs the 11.25? Can more pressure result in pushing the brass "back" into the bolt face and helping to create so much shaved brass / firing pin blockage?

Builder says Hornady's round is a hotter round, thus creating more pressure.
Hornady says that the chamber must be too tight thus creating issues ejecting, extracting etc...

I hope some of the above makes sense or has been seen before.

 

[Dave62677]

any pictures ?

 

[Boltgun7443]

Heres the brass, no pics of the bolt face...waiting on pics from other team members...

 

[natdscott]

First and foremost: what dimension do you get on FIRED casings from that rifle, with calipers across the mid-portion of the neck? They better be at least 0.002-0.004" larger than the same dimension across the neck of a loaded round, or that can be a serious issue on it's own. I doubt that's it, but it bears checking first.

Is it having any issue on chambering rounds easily?

Twist rate is not known to cause drastic changes in pressure, though the verdict is still out on that a bit, and Bartlein is entering testing soon-ish in that regard, for both .308 and 6.5 Creedmoor, using Hornady's testing equipment.

That said, bore diameter can VERY much affect chamber pressures, and Dan's barrel may be on the tighter side. The answer to that is a call to Lilja, and/or a set of pin gauges to judge bore dimensions. It only takes a few 0.0001" to make a helluva difference, even with conventional jacketed lead bullets.

Hornady does load a little hotter than some others, but those are not symptoms you can tolerate in a duty rifle. Put those rounds in the chamber on a hot day in the upper 90's, put the rifle and shooter on a rooftop across the street from a barricade, and then let both of them sit there for 4 hours. Not good.


At the end of the day, your solutions will depend on the department, but I see them as:

1) You need to change ammo types for the whole department and all rifles so that the one Lilja tube can digest FGMM or similar more easily.

or more possibly,

2) If bore dimensions are not to blame, have a slightly different reamer with a little longer throat run into the Lilja rifle to help drop chamber pressures. You're not going for hotdog-in-hallway effect, but you NEED a copy of the print for the original reamer to see if maybe the Hornady TAP is into the lands. Doubt it, but "doubt" is not an allowable answer.

-Nate

 

[ballisticdaddy]

I have found similar pressure signs with Hornady Superformance and TAP factory ammo also in my .308 bolt guns in both 1:10 and 1:11.25 twist rates.

 

[Dave62677]

deprime the case then measure the headspace with hornady comparator. it might give you more clues for the chamber

i had fired 168 Tap from my R700 blueprinted chamber Match 308 & AI AX 308, i don't recall i have experienced any pressure sign

 

[Supersubes]

No way is the twist causing that. If you went from 11.25 to an 8 twist, I’d still say it wasn’t the twist. I also wouldnt chalk it up to land profile.

If the Smith is sure that the reamer is the same, it’s gotta come down to bore dimensions. Is it a three groove Lilja? Have your smith cast or slug the bore. Maybe even cast /slug the old barrel. That would probably explain it. Bartlein bores have a land/groove ratio of around 70/30. I think the three groove Lilja’s are similar.

 

[Boltgun7443]

 

[spife7980]

I'm on a police team that specifically shoots Hornady TAP 308 168 AMAX rounds.

Heres the brass, no pics of the bolt face...waiting on pics from other team members...

Hornady TAP is loaded in a PPU case?

 

[Boltgun7443]

I didn't have pics of the my actual brass....These are the same markings that I could find online.

 

[Sniperstud]

Is your rifle suppressed? I also shoot an accurized Remington 700 for work. It has a 20" Hart, 1:10" barrel. I shoot it exclusively suppressed with Hornady 168gr TAP. Normally everything runs smooth, but if I shoot more than a couple hundred rounds without cleaning, I start getting hard bolt lift and ejector swipes on the case heads. So far, every time I have experienced this, cleaning the carbon out of the bore and chamber has taken care of the problem.

 

[Sniperstud]

I should add that before the rifle I'm currently using, I used an accurized Remington 700 with a 26", 1:11.25" barrel. That rifle was never suppressed. I also shot it exclusively with Hornady 168gr TAP, but never had any of these symptoms.