DTA Covert Mystery

[Hoser]

I have a DTA A-1 Covert chambered in 300 Whisper.

The barrel is a Benchmark 7 twist chambered by TS Customs.

Working up loads with Berger 215 Hybrids, Vhit N-110 and Lapua brass. S&B 5-25 and TBAC Magnus-SR.

I found a solid load going about 1065 with a single digit ES/SD. I played with seating depth a bit and found a depth that was about 5/8-3/4 MOA out to 300 yards which is a far as I was planning to go.

The first first shot at 300 goes about 2.3 mils low. The rest are fine. Nice little round group. If I let the rifle sit for 4-5 minutes, shot #1 again goes 2.3 mils low and the rest are back normal.

Seeing as how it is the first round on a "cool-ish" barrel that goes low and no others makes me think it is a gun issue and not an ammo issue.

I re-torqued all the barrel screws, checked the brake and can, scope mount, completely cleaned the barrel, etc. I even checked the loose nut behind the scope and had another solid shooter shoot 10 shots. 1st one low. 2-10 were normal.

I dont speak DTA that well, I am fluent in AI rifles.

What am I missing or not checking? Or am I just a dumbass?

 

[Hondo1]

Are you hitting the front cap of your suppressor with that first round? Look for copper tracking.

 

[Hoser]

Nope. No baffle strikes of any sort.

 

[John_in_WYO]

Shoot round #1 into the berm then shoot 5 @ 300 yards and how does it group?

I shoot an SRS A1 Covert 1/8 16” .308.

Mine is OD Green.


Or hold 2.3 mils up for the first shot on a cool barrel and center for the next 4 and see how it groups.

 

[Dogtown]

I’ve been shooting this platform since late 2008 and have never seen that behavior. The only time I ever had an inconsistent POI shift was a bent index pin in a Gen 1, which is a non-issue for only the earliest models pre-2010.

 

[Hoser]

Shoot round #1 into the berm then shoot 5 @ 300 yards and how does it group?

I shoot an SRS A1 Covert 1/8 16” .308.

Mine is OD Green.


Or hold 2.3 mils up for the first shot on a cool barrel and center for the next 4 and see how it groups.

It puts the next five into about a 3 inch group.

 

[kthomas]

Is it an issue with your rear bag control?

I'm wondering if the rifle doesn't fully "settle" into the rear bag until after the recoil of the first shot.

 

[Hoser]

Is it an issue with your rear bag control?

I'm wondering if the rifle doesn't fully "settle" into the rear bag until after the recoil of the first shot.

Could be. But with another shooter having the exact same issue I doubt it.

I will try a different bag. I have a hard Edgewood bag that I will try tomorrow.

Later today I will yank the barrel completely out and take a look inside the receiver to see if there is something going on in there.

 

[Reload10]

I’m curious to know as well. I have a LMT MWS that is having this same phenomenon. Maybe a high stress point in the barrel and after a small heat is dissipates?

 

[TimK]

Does that first round chrono the same as the others or is it slow?

 

[soflastg]

try a group without the suppressor

 

[Dogtown]

Try a group while standing on one leg.

 

[soflastg]

Try a group while standing on one leg.

which leg?

 

[SupressYourself]

try a group without the suppressor

+1. I've noticed this phenomenon before with certain combos of rifle, load, and can. Although in my case, the first round is usually high.

 

[spife7980]

It doesnt do it at 100, only at distance 300?

I would zero it without the can, let it cool and then take a shot at distance with out the can and see if it still keeps up the same behavior. First round pop behavior etc.

 

[Hoser]

Does that first round chrono the same as the others or is it slow?

I didnt think to chrono them as it is always shot #1 after the gun has sat for a few minutes.

Might try that tomorrow evening if I have time/energy after the match.

 

[Hoser]

It doesnt do it at 100, only at distance 300?

I would zero it without the can, let it cool and then take a shot at distance with out the can and see if it still keeps up the same behavior. First round pop behavior etc.

Does it at all distances. Enough to drive me crazy.

 

[John_in_WYO]

It puts the next five into about a 3 inch group.

Nice shooting.

 

[PRDRIVER]

Do you have a different barrel that you can test to see if you are experiencing the same issue with another barrel?

If not, I'd pull the barrel and remount it to see if it continues. Maybe shoot it without the suppressor to see if you are seeing the same issue.

I'd also double check torque settings on your scope mount. If you have another mounted optic, maybe put it on there and see if you're still seeing the same issue.

I'd try to rule out everything possible.

I've not seen anything like what you are describing on a DT SRS.

Out of curiosity, what is the overall diameter of your barrel shank?

 

[bachelorjack]

Ever get this figured out?

 

[Hoser]

I went to the range last Sunday to try it without the suppressor.

I had pulled the barrel, cleaned the shank with acetone just in case and re torqued it all again. I also pulled and retorqued the scope mount.

Same damn thing.

Let it sit more than a few minutes and the first shot goes low.

I am going to try one or two last things.

I am using naked bullets. I will try some Hbn coated and not virgin Lapua brass.

Maybe switch to Sierra 220s or Berger 230s if this doesent fix it.

 

[Hoser]

Tried it again yesterday. This time over a CED chronograph with IR screens.

First shot, perfectly low. Second shot, right where they should be. Let the gun cool for a few minutes, first shot low. Same drill as always.

However, the first shot is also slow. About 100 fps.

So it appears to be an ammo issue.

I dont know how it can be an ammo issue as every powder charge was thrown with a V4 and I only used charges that were exactly what I was looking for.

All I can guess is it is a powder gunk in the barrel issue that gets "normal" as soon as a shot warms it up.

Going to try a different powder.

Its a pity as this load is really accurate and quiet, but that 1st round bullshit makes it a no-go.

 

[bachelorjack]

What powder were you using?

 

[Hoser]

What powder were you using?

Vhit N-110

 

[secondofangle2]

100 fps at 300 explains it.

My guess is that it's a temperature sensitivity issue. I'd change powders.

 

[secondofangle2]

What ever happened here?

 

[Dragoon300]

Tried it again yesterday. This time over a CED chronograph with IR screens.

First shot, perfectly low. Second shot, right where they should be. Let the gun cool for a few minutes, first shot low. Same drill as always.

However, the first shot is also slow. About 100 fps.

So it appears to be an ammo issue.

I dont know how it can be an ammo issue as every powder charge was thrown with a V4 and I only used charges that were exactly what I was looking for.

All I can guess is it is a powder gunk in the barrel issue that gets "normal" as soon as a shot warms it up.

Going to try a different powder.

Its a pity as this load is really accurate and quiet, but that 1st round bullshit makes it a no-go.

I see this is an old posting, but if you figured this out please let us know. In my opinion it's the empty, cool can. If all of the ammo is consistent, but velocity is low on the first round I would say the gas has cooled and changed things. Cans normally increase velocity, at least after the first round.

 

[Hoser]

It does it with and without the can.

I finally stopped worrying about it and have come to almost accept the fact that shot #1 will consistently suck.

 

[Dragoon300]

It does it with and without the can.

I finally stopped worrying about it and have come to almost accept the fact that shot #1 will consistently suck.

Sorry to hear that. Just a weird cold bore anomaly