223 with 77gn Nosler cc and TMK

[ShrpShooterSer]

HI

I have shot more than 400 rounds total of these two through my CZ527 with 600 mm bull barrel - 1:8, chromed (aftermarket), which has enormous freebore - with 65 mm coal and tmk still not touching the lands. Still cant get it to shoot .3, only occasionally I get .5 groups at 300 meters. I use cci400 and n140 as power charge. Cant even remember what I tried. Can it be that so much freebore is giving me a hard time to achieve better results? Should I try to minimize jump, or to increase it to the max (I ve read it somewhere?) Any thoughts?

[Richiew]

Hi there 

65 mm seems long . I run 2.26” or 2.3 with longer hornady 75 grain bullets . The nosler looks to be more tangent shape design which are jump tolerant so try loading these a bit longer or try the big gap way  . A hornady tool with threaded case would help to find the lands properly . TMKs usually need to be closer to the lands  to hit their sweet spot poss 10 thou gap ??  . 23 to 24 grain of n140 ? Try starting low and also download the Vihtavuori app . Hope this makes sense . Cheers 

[VarmLR]

As above.  I loaded my 77 TMKs to 2.29" using RS50 and at 100 yds they shoot into bug holes.  Sako brass, Muron KVB 223 M primers.

I have never found TMK needed loading close to lands.  My loads all use quite a jump(77 thou)  (custom barrel chambered for heavies).  I keep the same seating for all loads and once I find the best load, I move back in 3 or 4 thou steps until I see the group tighten or open and seat accordingly.  If you can provide your barrel details (length) and your powder details together with your load and the tested MV and case capacities I will see if I can run a GRT model for you to estimates best OBT.  I have been using this, calibrated to measured MVs to successfully load dev in short order.  It usually gets me very close indeed.

a 1/8 twist should be fine for these .  

 

My own data:  TMK77's/sako brass/23.8gr RS50/2737fps/ES11/0.38"@100m -  from last outing with them.  I have shot better using a lower node of 23gr for 2641fps and a 0.33" group (1/3moa) based on 5 shots.  In botyh cases, COL was 2.29"/58.17mm

[Bangbangman]

I load 77TMK, SMK and Nosler CC to an overall length of 2.260" (ie. Loads of jump!). 

Originally N140 (24gr), then Varget, then RS52 (dropped to 23.8.) 

In other words, I've found them both jump and powder tolerant. Not only this, they shoot to almost exactly the same POI at 100m.

 

Edit: at this length there is a lot of bullet in the case: vibratory settling avoids compressed load, though.

[shoppe]

Maybe you have loaded them too long and there is not a decent amount of the bullet in the case? 

The bullet will still need to be well supported in the case. Try a " normal " coal and see how you get on? 

Cheers

Shoppe

[Richiew]

I’ve been getting primer cratering with cci400s  so last load was with cci 450 primers and it has fixed the problem . 
Nothing wrong with your group sizes . 
My tikka 20” varmint stainless barrel 1:8” twist is happy with the heavier bullets at 24 grain of n540 for lapua 77, hornady 75 eldms and 73 grain Berger s . 

[Richiew]

Done some more digging ( 308 TMKs are secant sorry for Mis info  ) TMKs in this calibre seem to be tangent ogive shape so should be jump tolerant so loading to 2.26” should be good. N140 max is 25.5 grain and N540 25.2 so similar to your powder . 
1.894” case base to ogive fits all the 73-77 grain bullets in my barrel ( yours could be different though) 

[Laurie]

The Rt/R factor ratio of 0.96 as measured by Litz and seen in the top section of the pic in the previous post is a nearly perfect tangent form. (Rt/R is a numerical description of the ogive to shank junction form: 1.0 = true tangent; 0.5 is the original Knox/Berger VLD aggressive secant form and you can have anything in between leaning one way of the other.)

The TMK version of the 77gn is identical to that of its elderly 77gn MK version bar a fancy coloured tip, tiny BC improvement and additional tenner / 100 on the price. As the original MK was designed to operate at magazine length (2.25-2.26") in the Colt AR-15 HBar civilian match rifle with a chamber that produces c.2.5" COALs for such bullets when seated to just short of the lands with excellent precision, it can fairly be described as one of the most jump-tolerant bullets ever designed, and is moreover capable of superb precision in the right rifle and barrel.

The use of such a chamber on an aftermarket barrel suggests it was produced with a so-called '5.56 NATO' chamber in line with that adopted by Colt for its HBar model. The problem with such chambers is that there are as many takes on them as there are suppliers / machine-shops and many are frankly designed to take 62gn 5.56X45mm military spec ammo and make it reliably go bang in semi-auto AR-15s in the US market with 1-2 MOA or so precision being acceptable. One of the main differences between a true NATO chamber and civilian match versions is in the throat section's diameter. Today's match chambers have throats barely large enough for bullets to pass through whilst the military version is decidedly 'slack' by comparison which improves reliability in combat conditions but degrades precision.

If grouping isn't good enough (and I for one am confused by the original post as what standards are actually being achieved by the rifle), fiddling around with COALs might improve things, but given the bullet's inherent vast tolerance in this respect, would suggest that playing with COALs is more likely to simply burn powder and waste barrel life.

This matter of 223/5.56 chambers is quite confusing and difficult to tease out although there is a lot available online. This feature

 

https://www.luckygunner.com/labs/5-56-vs-223/

 

has some good insights and note the chamber reamer dimensions table. It shows true 5.56 chambers have around 0.0025" bullet clearance in the throat ('freebore') over a nominal 0.224" dia bullet whilst true match chambers are nil or virtually so.

Having said all that, there can be 50 different reasons why a rifle isn't performing as well as expected. I'm only cautioning that with this bullet, COAL / seating depth is an unlikely cause, and the allowable near 2.6" COAL suggests an extremely strange chamber has been provided as this is considerably longer than the commonly used Wylde match form would allow for instance.

[Bangbangman]

3 hours ago, Laurie said:

The Rt/R factor ratio of 0.96 as measured by Litz and seen in the top section of the pic in the previous post is a nearly perfect tangent form. (Rt/R is a numerical description of the ogive to shank junction form: 1.0 = true tangent; 0.5 is the original Knox/Berger VLD aggressive secant form and you can have anything in between leaning one way of the other.)

The TMK version of the 77gn is identical to that of its elderly 77gn MK version bar a fancy coloured tip, tiny BC improvement and additional tenner / 100 on the price. As the original MK was designed to operate at magazine length (2.25-2.26") in the Colt AR-15 HBar civilian match rifle with a chamber that produces c.2.5" COALs for such bullets when seated to just short of the lands with excellent precision, it can fairly be described as one of the most jump-tolerant bullets ever designed, and is moreover capable of superb precision in the right rifle and barrel.

The use of such a chamber on an aftermarket barrel suggests it was produced with a so-called '5.56 NATO' chamber in line with that adopted by Colt for its HBar model. The problem with such chambers is that there are as many takes on them as there are suppliers / machine-shops and many are frankly designed to take 62gn 5.56X45mm military spec ammo and make it reliably go bang in semi-auto AR-15s in the US market with 1-2 MOA or so precision being acceptable. One of the main differences between a true NATO chamber and civilian match versions is in the throat section's diameter. Today's match chambers have throats barely large enough for bullets to pass through whilst the military version is decidedly 'slack' by comparison which improves reliability in combat conditions but degrades precision.

If grouping isn't good enough (and I for one am confused by the original post as what standards are actually being achieved by the rifle), fiddling around with COALs might improve things, but given the bullet's inherent vast tolerance in this respect, would suggest that playing with COALs is more likely to simply burn powder and waste barrel life.

This matter of 223/5.56 chambers is quite confusing and difficult to tease out although there is a lot available online. This feature

 

https://www.luckygunner.com/labs/5-56-vs-223/

 

has some good insights and note the chamber reamer dimensions table. It shows true 5.56 chambers have around 0.0025" bullet clearance in the throat ('freebore') over a nominal 0.224" dia bullet whilst true match chambers are nil or virtually so.

Having said all that, there can be 50 different reasons why a rifle isn't performing as well as expected. I'm only cautioning that with this bullet, COAL / seating depth is an unlikely cause, and the allowable near 2.6" COAL suggests an extremely strange chamber has been provided as this is considerably longer than the commonly used Wylde match form would allow for instance.

Always informative, Laurie.

 

Speaking of which, when can we expect the next installment of your 223Rem post-REACH powder choices?!

[Laurie]

40 minutes ago, Bangbangman said:

Speaking of which, when can we expect the next installment of your 223Rem post-REACH powder choices?!

H4895 / VarGet alternatives Part 3 (4 x Viht v VarGet) is written. I'll do some pics and scans this week and get the piece off to The Gun Pimp (Vince) who is editor / compiler.

H4895 alternatives follow as all range-testing has been completed, also some eight powders in two parts. I've still to load and test the seven or eight Reach-compliant ball-type powders that are available here, a job for this autumn.

[Bangbangman]

4 hours ago, Laurie said:

H4895 / VarGet alternatives Part 3 (4 x Viht v VarGet) is written. I'll do some pics and scans this week and get the piece off to The Gun Pimp (Vince) who is editor / compiler.

H4895 alternatives follow as all range-testing has been completed, also some eight powders in two parts. I've still to load and test the seven or eight Reach-compliant ball-type powders that are available here, a job for this autumn.

Excellent