243 w DTAC .....

[kycamtrakker]

i just had a new rifle built in 243win and told him i wanted to shoot the DTAC. When i got it i loved the look and finish, took it home and measure the chamber. Its coal to the lands is only 2.7710.... seems very short for the DTAC, with .015 jump i think .567 of my bullet is still in the case. Just seems like a lot in there. Does anyone see a problem with this? The builder said mine was the 3or4 rifle built with this reamer and said the other rifles shot in the .2's. Does anyone think this is way to short????

 

[jhelmuth]

...to the lands that seems about right.

Why not load 'em up and go out and shoot a few and see what happens?

 

[Dgd6mm]

That's an ok lenght for a hunting round. If it was mine , I'd want it longer for a 115 DTAC. The .243 can spit this bullet out pretty quick if you have room for a good load of powder, of course following load work up safely with your choice of powder.

 

[Steve Blair]

If your intent is to avoid seating past the neck-shoulder junction, the freebore is way too short. Your freebore calculates to ~.022. That is correct for light, varmint weight bullets but wrong for 115 DTAC. I recommend a freebore of .150" that would give shank engagement of .226" touching and allow a little flexibility for both jump and throat wear.

 

[TimP]

If your intent is to avoid seating past the neck-shoulder junction, the freebore is way too short. Your freebore calculates to ~.022. That is correct for light, varmint weight bullets but wrong for 115 DTAC. I recommend a freebore of .150" that would give shank engagement of .226" touching and allow a little flexibility for both jump and throat wear.

sleepygator,
I am in the process of building a .243Win to run the 115gn DTAC's as well. The reamer my smith uses has .122 freebore. Can I get away with that or should I order a new reamer which is something I have been thinking about anyway. The neck dimension of his reamer is .277 which is OK but I might speck it at .275 or .276 which would allow me to clean up the necks a bit. Your opinion would be appreciated.
Thanks, TimP

 

[kycamtrakker]

i have shot it a few times and was decent groups with it. And i know its gonna wear the throat anyway, i just wondered if it would hurt seating that bullet that far into the case.

 

[Steve Blair]

sleepygator,
I am in the process of building a .243Win to run the 115gn DTAC's as well. The reamer my smith uses has .122 freebore. Can I get away with that or should I order a new reamer which is something I have been thinking about anyway. The neck dimension of his reamer is .277 which is OK but I might speck it at .275 or .276 which would allow me to clean up the necks a bit. Your opinion would be appreciated.
Thanks, TimP

[br]
The problem with the .243 is that the short neck does not allow much wiggle room, if you want to avoid the Dreaded Doughnut®. A .122" freebore will still put you into the junction. The neck is only .241" long and .122" would put you at .254 shank depth when touching. My 6mm SLR and 6mm Rem reamers have .271 necks and .130" freebores, but both have long necks that allow more depth. I would go with .150" freebore for the 115 DTAC. You may also consider shooting the Berger 105 Hybrid which would be fine at .122". It gives up nothing to the 115 DTAC in B.C. Neck diameter of .275 will probably not allow a full cleanup but is certainly a valid way to go. A .271 neck requires turning to ~.0123 neck thickness to provide .003" diametral clearance.

 

[TimP]

sleepygator,
I am in the process of building a .243Win to run the 115gn DTAC's as well. The reamer my smith uses has .122 freebore. Can I get away with that or should I order a new reamer which is something I have been thinking about anyway. The neck dimension of his reamer is .277 which is OK but I might speck it at .275 or .276 which would allow me to clean up the necks a bit. Your opinion would be appreciated.
Thanks, TimP

[br]
The problem with the .243 is that the short neck does not allow much wiggle room, if you want to avoid the Dreaded Doughnut A .122" freebore will still put you into the junction. The neck is only .241" long and .122" would put you at .254 shank depth when touching. My 6mm SLR and 6mm Rem reamers have .271 necks and .130" freebores, but both have long necks that allow more depth. I would go with .150" freebore for the 115 DTAC. You may also consider shooting the Berger 105 Hybrid which would be fine at .122". It gives up nothing to the 115 DTAC in B.C. Neck diameter of .275 will probably not allow a full cleanup but is certainly a valid way to go. A .271 neck requires turning to ~.0123 neck thickness to provide .003" diametral clearance.

Thanks again I appreciate your reply.

 

[kycamtrakker]

i reload my own ammo but all the loaded ammo ive seen with a dtac is 2.86 so is this the norm? I just cant help but to think im gonna have problems

 

[Steve Blair]

i reload my own ammo but all the loaded ammo ive seen with a dtac is 2.86 so is this the norm? I just cant help but to think im gonna have problems

[br]
2.86" OAL puts the shank ~.060" past the junction. That does not mean you will automatically have problems. There are two reasons to seat the bullet forward of the neck-shoulder junction. The first is to avoid the Dreaded Doughnut® and the second is to maximize powder capacity. In order to seat the DTAC out far enough, the freebore must be long enough to make using shorter bullets problematic. Short necks always have this flexibility problem. It is not unique to the .243 Win. Why not try shooting it as is and, if you do have problems and want to continue shooting the DTAC 115, have the freebore extended?

 

[kycamtrakker]

but what im saying is that at 2.77 im way past/into that junction

 

[Steve Blair]

but what im saying is that at 2.77 im way past/into that junction

[br]
.243 Winchester cartridges loaded with 115 DTAC bullets must have an OAL >=2.95 to reliably clear a doughnut if it forms. What I meant in the previous post was that they do not always form. I like to make certain of clearance as well as having the additional case capacity. The price paid is often a dedicated barrel, good only for a narrow bullet weight range. [br]
I understand the implications of your current freebore length. What I am saying is try shooting it as is and reevaluate if you see problems. Many people claim to never see doughnuts form. I'm not that lucky.

 

[kycamtrakker]

i dont get the doughnut but even with 42gr of H4350 i am seeing some slight pressure. I havent ran them thru the chrono yet either

 

[Steve Blair]

i dont get the doughnut but even with 42gr of H4350 i am seeing some slight pressure. I havent ran them thru the chrono yet either

[br]
While not necessarily what your barrel is producing, QuickLOAD says that 42.0 H4350 behind a 115 DTAC seated 2.755 produces 65311 PSI, over five thousand above max. If that is correct, I have no doubt you are seeing pressure signs. Shoot them over a chrono and see what it is doing. I would back down and work up again, watching for pressure indications.

 

[jcampbellsmith]

i just had a new rifle built in 243win and told him i wanted to shoot the DTAC. .....

I suggest making up a couple of dummy rounds that give you the seating that you want and then go back to your smith and ask him to adjust the chamber to match your dummy round. I had advice from a couple of forum members when I was trying to work out the seating for 105 AMax in 6XC.
You don't say what make of rifle you have, but if it's a Remington, then a Wyatt's Extended Magazine is worth considering too. That's what I had fitted to my 260 Rem to allow me to use 140gr AMax.
http://www.midwayusa.com/product/993148/wyatts-outdoors-extended-magazine-box-remington-700-bdl-short-action?cm_vc=2271BrandPopProd
Persist and get the rifle set the way you want it. Good luck. JCS

 

[kycamtrakker]

its a stiller tac 30 with a 26" Brux barrel 7.5twist and its got Badger M5 DBM