115 DTAC BN and my T2K

[hoverp]

I am having a real problem with getting the 115 BN coated DTAC's even close to the listed 38-39 grains of H4350. I can only safely (due to sticky bolt lift ) get 34-35 grains max. I have done an 20 shot test at 69 OAT. I load with the SSS dies and full size .003 casehead setback, Wolf Primers, Norma new brass, neck tension is .002 and the 115's loaded to just kiss the lands(ive tried set off and further into as well) at 34 grains Im fine no bolt lift problems, at35 ok but close....36 out of the question for rapid fire ....I dont want any sticky bolt lift at all. The primer pockets are NOT loosening at all and case growth is .003 at the head consistantly. I have not chronoed these yet but was very curious as to why Im only good with 34-35max??? The barrel is a stock schneider 26 inch from Tubb. Its clean and the chamber is clean as well. cases trimmed to 1.90 as well chamferred and deburred.... case and bullet runout is awesome at .001

any others having sticky bolt at these low charge weights?

 

[mikecr]

Not sure I understand 3thou casehead setback.
But 3thou undersize in the webs is huge IMO. 3thou growth there is huge.
Are you sure about this?

 

[hoverp]

case growth measured off the .375 datum line on the shoulder...sorry, just realized I should have said case shoulder!!! not case head..... Sorry.

 

[mikecr]

Ok, after FL sizing, are you measuring the headspace, and have you checked that the bolt cycles easily on reloaded cases?
Does the bolt turn stiff all the way on extraction? Or is it easy until the top of it's lift, then pops the rest of the way?

 

[watercam]

Had the same problem with a Tikka/6XC. Some barrels are just like that! Tried H4350, Reloader 17 to no avail. Polished the chamber a bit and that helped to a point but basically never could climb past the 2980 fps ceiling. Shot well though...

 

[RIFLE1]

Try making your brass from Lapua 22/250,.... I'm just saying,....

Seriously,... some of the lots of brass vary greatly in hardness. I wouldn't suspect this to entirely be the problem,... but it could be in large part a contributing factor.

 

[hoverp]

no luck so far tried Remington 22-250 fireformed and same results...barrel is back at SSS getting the chamber polished....

*****Question for you T2K owners out there...what is the measurement you get when measuring the post shot( not resized yet) case for headspace on the .375 datum line to the base of the case ***

Mine measures 1.514 post firing. 6xc dimensions off the SSS website say 1.520 min headspace.

 

[hoverp]

no luck so far tried Remington 22-250 fireformed and same results...barrel is back at SSS getting the chamber polished....

*****Question for you T2K owners out there...what is the measurement you get when measuring the post shot( not resized yet) case for headspace on the .375 datum line to the base of the case ***

Mine measures 1.514 post firing. 6xc dimensions off the SSS website say 1.520 min headspace.

Bump for the schneider barreled T2K owners out there to please measure the post fired case headspace dimension and post if you would please.

thank you.!

 

[rcw3]

I have had sticky bolt lift like that in three situations I can identify:

1. A too fast barrel twist which can cause pressure even with moderate loads - if you tell me it's a 7" twist 6mm barrel, I would say there's a high likelihood that's a potential source of what's going on; and

2. Norma brass is on the fat side (diameter wise) at the web, and if you look at some of the 6XC reamers, they really are too tight in the rear for that brass, and the sizing die cannot remedy that (since the die cannot size down the part of the web or the brass just forward of it that typically is in the back end of the chamber). The best remedy there is to remove the barrel and have the back end of the chamber worked over to open up the diameter a little more. If this is the situation, using Lapua 22-250 brass will likely not help, since Lapua brass runs on the max side diameter wise at the web as well. Try Winchester 22-250 brass as a base 6xc brass, if you think this is the issue and it can help you identify if that's the issue; and

3. Hot loads with pressure - but at only 34 gr of H4350, that is not likely, unless you are using the wrong powder or there was a mix up at the factory and you really don't have H4350 and are really using something like Varget.


For what it's worth, .003" shoulder set back is workable, you can run a little less in a bolt gun (i.e. .0015" - .002" is fine in a bolt gun), but that is not likely the cause of anything you are experiencing at this time.

Robert Whitley

 

[Mudcat]

Since I stopped using Norma/Tubb brass and Schnieder bbls, I have not had the sticky bolt lift unless I went over 40.0+ grains of H4350 and a 107 class bullet. Been there, done that, learned my lesson, solved the problem.

John

 

[Bob3700]

My first thought on your situation was "I'll be he has a Schneider bbl" and then Norma brass.

Almost every T2K factory Schneider bbl I have seen has had premature pressure problems, even with 107 SMKs.

Throw the 115 DTAC into the mix and I don't know of any local T2K shooters who can get them up to 2950 - 3000 fps without ruining brass.

Have some of the Norma 6XC brass and immediately had bolt clicks on opening. Went back to Rem/Win formed 22/250 brass and the problem of bolt clicks went away. There is .001-.002" difference in the base diameter of Norma vs Rem/Win brass.

You need a reamer that is sized for the Norma brass. Mine was ground for Rem/Win brass so didn't work very well.

IMHO, the 6XC is sized perfectly for the 105-107 gr 6mm bullets. Just not enough boiler room (velocity)for the 115 DTAC or Berger to get the BC advantage over the 105-107 gr bullets.

For the heavier bullets, you need something 243 sized like the std 243, 243 SLR or the 6 CM.

Bob

 

[hoverp]

Thanks for all the input fellas, Here is where I am at right now, SSS wanted the barrel back after I sent them the rifle and they put in a reamer that opened the neck to .276,
my loaded round is .270, SSS shot the gun and chronoed the velocities and I was right in the ballpark for 38-39.5 grains H4350 giving me right around 3000 FPS with 115 BN DTAC , Norma Brass, and wolf primers, bullet set just touching the lands with .002 long range load single load tension on the bullet.

when I got the rifle back from them I loaded up 38 and 39 grain test loads.

I did this for Remington 22-250 brass (I fireformed it as part of the test)

I can only get one shot out of the Norma brass and the Rem 22-250 brass prior to tough sticky bolt lift.

the first shot on new brass it extracts fine and then I resize the case with SSS 6XC dies and everything measures great and the rounds slide right in there NO problem, bolt is very easy to open and close , one more shot and instantly the bolt is hard to open. If I resize the same case again its easy and smooth operation going in , post firing really tough comming out.
I have paid particular attention to web growth and primer pocket growth and ,ejector marks, primer condition..all of that. but no go. the only load I can shoot over and over again with the same piece of brass is right around 34 grains....I can shoot and reload this all day long...anything over that and progressively worse the few times I resize the case..., I sent the barrel back to SSS and they are polishing the chamber...dont know if that will help. I would like to know what reamer is made for Norma brass..i would buy one in a heartbeat.

I can shoot a new Norma case with 40 grains of H4350 and velocity is right around 3025 it extracts just fine for the first firing, but once resized... second shot...no go upon extraction. what is weird is all measurements are the same for the post shot 39 grainer and the post shot 34 grainer...down to the .0005 everywhere on the case

 

[Klong]

You need the equivalent of a small base or a body die. I have the same issue in one of my 6mm BRX barrels. If I use the standard die, it does not seem to size all the way down even with the full length die. I can fire the brass a second time and still extract, but it is difficult. I do not have a small base die just for this cartridge, but use a 308 die that is on the small side. Works just fine that way in my rifle.

 

[hoverp]

You need the equivalent of a small base or a body die. I have the same issue in one of my 6mm BRX barrels. If I use the standard die, it does not seem to size all the way down even with the full length die. I can fire the brass a second time and still extract, but it is difficult. I do not have a small base die just for this cartridge, but use a 308 die that is on the small side. Works just fine that way in my rifle.

with the standard die on yours does it chamber really easily, mine does , after I resize a extremly hard to extract case it chambers effortlessly. but it sticks upon extraction.

 

[Bob3700]

I feel that the only way you are going to solve your problem is to ream the chamber with a reamer that has a larger dimension at the head of the case.

All the small base sizing in the world won't change the case head dimension. That is solid brass.

Your brass already chambers easily, it is the extraction of the fired case that seems to be the problem. I fought the same problem with my rifle and changing brass (getting away from the Norma 6XC stuff) was the answer. A correctly dimensioned reamer would have had the same effect.

Probably not what you wanted to hear but you will spend a lot of time and effort trying other remedies.

Bob

 

[hoverp]

Bob, how do I go about getting a reamer that is proper for my Norma brass, I would think that with all the 6xc shooters out there and all the Norma brass there would be PTG or someone who has made one up properly...thoughts?

Thanks

Patrick

 

[gmitchell]

I had a similar problem in a 6X47, bad pressure issues with not alot of powder, I sent barrel back and the barrel company said there was too much taper in it sent me a new one. fixed problem maybe your problem also. If it shoots maybe they can relap

 

[Bob3700]

My question to you would be. Do you have any problems with Rem/WIn brass firing the higher pressure loads?

If the answer is NO, then the base of the chamber is too small for the Norma brass.

I would call Dave Kiff and tell him of my problem. See if he has a reamer in stock that will cut a chamber specifically for the Norma brass.

The sized cases are chambering with no problem, upon firing, the brass at the head has no where to go and is creating a lot of friction between the chamber and the case.

That is my .02 worth.

Bob

 

[hoverp]

BoB ,yes the Remington fireformed brass has the exact same issue, initial fireforming load was 38 grains H4350, no issue on extraction. once resized (Tubb die) it chambered effortlessly. second shot with 38 grains and extraction issue. no case growth at web, no primer issue, no oal issue, brass measured same as Norma post fired on the base and shoulder, headspace was fine as well.1.514, sized back .003.

115 DTAC BN cold barrel

Only thing I noticed on the Remington 22-250 brass was the base of the case stretches(first 1/4 inch above the web) and makes a thin section(that is visible to the naked eye) about .0015 inches smaller then it expands back out. It looks like it stretched at this point to grow in length to fit chamber.

Chamber headspace is under 1.520 min...brass measures 1.514 post firing so I figured its about 1.515 headspace.

 

[Bob3700]

Headspace should actually be no more than .001"-.003". Usually the difference between a go and a no-go gauge.

Boy, you've got me. Why the second firing generates extraction problems doesn't make sense.

Have you looked into the chamber with a bore scope to see if the chamber is free of any rings? Chips can get caught between the reamer and the chamber and score it making extraction difficult.

Also, you might want to make a chamber cast to see if the case length is what you think it is (as well as neck diameter). I have seen reamers and their prints that say one thing and the actual chamber they cut is another.

Can you tell if the case mouth on the second firing is still straight? I am thinking that perhaps the neck length on your chamber is a little short and your brass is too long? You might try cutting a case .010" shorter and fire it twice and see if the extraction problem persists.

Bob