6mm build

Sorry if I'm derailing the thread, didn't wanna start another thread on similar topic. Does anyone know what the differences are between 6 mm slr and 6 cm? To my amature mind they are almost identical and barrel life under similar use should be similar but people are claiming to get 4000 rounds out of CM, compared to 2000-2500 of slr . Is it just slow burning powder & shoulder angle in 6 cm ? If yes, shoulder angle is only one degree different and why can't you use same powder in slr (it has very similar capacity)and have longer barrel life? Just trying to learn.
Dies and forming brass seems much easier for slr.
 
4000 round barrel life is suspicious to me, especially if you are pushing north of 3000 fps. May depend on what kind of accuracy is acceptable before you consider the barrel "done".
 
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The 6mm SLR give you a longer neck and effectively the same case capacity as the 243. The longer neck gives you more flexibility in seating bullets and you aren't really loosing any case capacity since the bullet is pushed back into the shoulder area with the 243 and 105/115 gr. bullets. A 243 reamer designed for 115 gr. bullets may not work as well for 105s and vice-versa. It definitely won't work as well for lighter bullets. Putting aside arguments about neck length and shoulder geometry affecting barrel life, I did find one definite advantage of the longer neck when testing rounds to decide on what will replace my 6mm Crusader. I loaded up some duds in 243, 6 SLR, 6x47L and 6mm Creedmoor. I measured the runout and then proceeded to cycle them violently from the magazine into the chamber of a 308 barrel. Alll fed well, but the runouts on the 243 were terrible afterwards compared to the others. Not only that, after a few cycles, the bullets in the 243 got loose and fell out or got pushed in. Kind of make sense. Those 105/115s are sticking way out and put a lot of torque on the neck when they hit the feed ramp. In engineering, we have a rule of thumb that when you put a rod into a hole, you want the depth of the hole to be at least 1.5x its diameter for it to stay aligned. The 243 neck does not provide that.

I didn't look at the 6mm Competition Match because it requires you to blow out the shoulder. I already do that with my 6mm Crusader, which is a 6mm Rem with a blown out shoulder. I don't see an advantage for me, and don't like the short neck. I'm skeptical of the 4000 round claim. I run Retumbo in in the Crusader, which is just as cool as H1000. I only shoot the 115s are 3125 fps, because there is a nice node there. I'm running at pretty low pressure (the Crusader can launch them WAY faster). Some of my cases have been loaded over 20 time. Yet, after shooting out several barrels, all have been between 2100-2400 rounds before I start getting vertical flyers. One went south on me in a match and at 900 yards. It was: shoulder, knee, shoulder, knee, shoulder, knee on the Fig. 11. Still would have been hitting a steel IPSC silhouette... so I guess it depends on what you consider shot out. Could the 6mm CM make it to 3000 rounds? Maybe. But, I wouldn't go with another round that requires fire-forming for a match that I'm going to loose up to half my brass in and step on a quarter of the cases I do get back. I don't want to do anything more than size down a neck or change the shoulder angle with a single pass though a die (which I do on any case to straighten out the necks on new cases)
 
Thanks kombayotch. Good point about forming brass. To be honest I can't see any difference big enough between 6 slr and 6cm to cause such dramatic difference in barrel life. I can live with 2500 round barrel life especially when you factor in time and components involved in fire forming.
 
For comparison between the 6mm Crusader and the 243:

PICT0002.jpg

6.5x284, 6mm Crusader, 6mm Rem, 243, 6.5x47, 6BR

I will take some pics of the 6mm Crusader next to 6 SLR, 6 Creedmoor and 6x47L when I get home.
 
For a reference, F Open shooters retire a 6BR barrel around 2500rds... that is around 29gr of Varget for a 105 at 2850'ish fps.

4000rds with so much more powder.. even slow powder? Depends on what accuracy means to you.

I am expecting 2000 to 2500rds for the 6XC with a limit of 2/3 min at distance. Likely under 40gr of H4350 for 3000fps and the 105/107/108gr family.

When reading accuracy claims vs bore life, always look at the frame of reference. Barrel can last a great long time if you only need a great group to show friends and family once in a while. Say best out of 10....

We find that barrels wear out real fast when EVERY shot is scored on a target.

simple test to prove to yourself - with a new bore at 100yds, better 200yds with ideal conditions, shoot 5X5rds groups. That is 25rds spaced how you like with the best load and chance of success. Measure best and worst group and average.. no excuses like "pull" shots or flyers. Shoot your best for every pull.. ACCEPT where every shot actually lands. Take your time....

I would keep that same 25 cases, powder, bullet and primer aside so you know all components are the same.

Now repeat the test after 1000rds, 1500rds, 2000rds and see what you get. Same thing... mark EVERY shot regardless of where it lands. No excuses. Compare the numbers... I bet you are no where near as accurate on average.

I compete with a 308 and it still eat barrels... a 6mm with a bunch of powder behind it.... bore wear will happen faster then many will like to believe.

Jerry
 
Here are the pics:

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6.5 SAUM, 6mm Crusader, 243 Win., 6mm SLR, 6mm Creedmoor, 6x47L

All with Berger Hybrids loaded 0.05" in from of the neck-shoulder junction, except for the 6mm Crusader that is loaded to mag length. The pressure ring in the Crusader goes down below the neck-shoulder junction, but just barely with the 105.


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6mm Crusader, 6mm SLR, 6mm Creedmoor with 115 DTAC and 117 Matrix VLD loaded 0.05" in from of the neck-shoulder junction, except for the 6mm Crusader that is loaded to mag length. The pressure ring in the Crusader goes down below the neck-shoulder junction.


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6mm Crusader x2, 6mm SLR x2, 6mm Creedmoor x2
 

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As usual, no free lunch. Pay the barrel man for the extra case capacity.
Accuracy diminished a barrel in about 700 rds for top accuracy in .243 Ackley I made up back in the 90's.
Shooting a 6BR now and enjoying that.

If I want real long distance I pick a larger bore.
 
"But, I wouldn't go with another round that requires fire-forming for a match that I'm going to loose up to half my brass in and step on a quarter of the cases I do get back."

For me its the opposite. I would far rather lose cheap Winchester .243 brass that you simply load and shoot to fireform than expensive Norma 6XC Brass that is hard to get. I have a 6 Competition Match in the cooker. Got the reamer and the dies already and am assembling the rest. There's plenty of top end shooters on other sites that have run the 6CM well past 3500rds and still get good accuracy including Joe Hendricks himself. We shall see. Even if it doesn't get that much life it doesn't matter. The brass is what sold it for me.
 
Winchester 6mm Rem brass is just as cheap as the 243, as is the 257 Roberts brass that can also be used and has never gone out of stock at the local shop. The forming loads never gives as good of accuracy or velocity though, and you're still burning up components. While I can do short range practice while forming with cheap varmint bullets, that is still more expensive than using my 223 trainer, which is also more accurate. The way I look at it, I can use the same cheap Winchester brass with the SLR, and simply run it through the die to form it, them fire it at normal velocity. The difference in velocity is meaningless since you still need to download the SLR due to the 3100-3150 fps velocity limit matches have in place to protect their steel (that came about because of the 6mm Crusader, btw). Many people even see the SLR as wasting powder because of that. But, I'm looking at it for the same reason: cheap available brass that I can find in Canada.

I haven't completely decided on what to change to, because at this point, I can't find a good supply of 6.5 Creedmoor brass or even the cheap and supposedly available 243 brass. So, I'm going to run the Crusader again this year because I have a good supply of powder and components on hand, and replacements have always been easy to find. If I was just going to do paper punching matches, I wouldn't mind. You don't lose brass in stuff that's shot on a square range and my brass is lasting forever shooting those matches. As it stand, I barely have time to load, let alone form cases... but, it's that or nothing.
 
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LS, you must have a stash of some really old brass. I haven't seen Win component brass in YEARS. I gave up waiting for 308 brass after 2.5yrs.

243, I didn't track but since all 308 family cases have been off line from Win, I can only suspect so was the 243. And this is still ongoing.

So yes, BRASS is the reason I went with the 6XC. Even with the last 4yrs of US consumption and recent "we have no troops in your country stupidity", 22250 was always available.. at least far more often then other chamberings.

Varminters are a massive market in the US and will be supplied. They get brass.. I get brass... life is good.

I also switched to PRVI.. great, tough stuff, well priced.. they are a very large ammo maker and supply is only limited by demand. When all other US brands were backordered, they supplied and in big quantities.

If barrels lasted as long as some say, why is there a rapidly growing market for barrel nut type prefit barrels for custom actions?

Can there be barrels and set ups that last longer then the norm? Of course. Bet your match on it? I hope so.... :)

Jerry
 
If you need 257Roberts brass, get it all NOW.

Sounds like Win and Rem have discontinued this... Nosler is it and bring $$$$$.

You can form from Mauser family with the 7x57 the closest.

PRVI now makes - 243, 7x57 and 8X57, 22-250, 7-08 and 308 - and others of course. I am just listing in case you are looking into the future for more brass. The Canadian supply chain likely has stock from years ago but right now, win and Rem are getting out of the component brass business.

Norma, PRVI, Hrn are filling the void. Lapua is there too but not growing listings are much as they were... not sure what is happening here. Nosler just strikes me as really pricey brass.

So, if you are playing a game where you are going to loss brass, plan accordingly.

Personally, if I wanted the easiest no brainer chamber, it would be 243. Is it the best for the PRS game? Obviously not but for ease of components.. easy, well, kind of.

Jerry
 
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Got out to test the new 6XC put together by Terry of Black Art Rifle. Looks like it will be an easy rifle to tune and set up. All shots at 100yds on a very calm day... about 6C.

Shilen SS Select Match 6mm #4 contour, 8 twist, 24" finished, brake from a 338 cannon. Savage repeater receiver with accutrigger set around 2.5lbs.

This was the first high pressure loads the brass had seen since being formed so I think there is room to tweak things a bit more. Group D is 0.242" for 3 rds... nice start.

Hrn 105gr BTHP, H4350, Fed 210M, PRVI 22-250 brass

I would expect speeds to be around 3000fps given the loads mimic others in load manuals... get a magnetospeed on the rifle next time. Look forward to LR tuning.

Jerry

PS.. for those interested in barrel break in.. the first shot marked is literally the first shot of the barrel. Adjusted scope and started shooting groups A to E without stopping at a slowish cadence. No cleaning yet. Give it a swab next time out and see what the fouling is like.
 
Jerry,
These loads were shot "fireforming" brass, correct?
You would never guess by looking at the crushed 22-250 case that they would shoot excellent, but they always seem to.
You will love the 6XC.
Why did you decide to go with a brake? Just to see hits easier?
 
The cases had been rough formed using Cornmeal and Titegroup. So they are like 95% formed. I will not shoot a case with a secondary shoulder and a bullet. Too many things to go wrong.

Brake so I can spot my own hits. With UKD targets, if you don't see the miss, well... you are going to repeat until you do. Recoil is best described as light so seeing the impact, maybe even the trace should be possible.

More testing but so far at 100yds, the chamber has been a pussycat. Throat length is perfect for the 105 family and the mag. THIS I was very pleased with.

Jerry
 
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