RPM experience with 108 ELDM and 110 MK

[Frankm]

Looking for guys with big 6mm cartridge experience with the above 2 bullets. (Other target bullet info ok too)

Before we turn reamer manufacturer loose on a 6-280AI project looking to figure out what rpm s these bullets will tolerate without blowing up. Plan to use a 30"+ barrel so 3400-3500 fps is a possibility.

Hornady tech said 300K rpm typically safe but 310K or more and blowups could be possible.

Goal is high velocity with max type BC bullets for Rockchucks and targets out to 1200-1400 yds.

Much appreciate any experiences of others. Thank you.

 

[Doug Beach]

I’ve no experience with the cartridge, but 300,000 rpm at 3500fps is an 8.4 twist. 310,000 rpm is an 8.1 twist.

 

[dstoenner]

I’ve no experience with the cartridge, but 300,000 rpm at 3500fps is an 8.4 twist. 310,000 rpm is an 8.1 twist.

And the 110 smk requires a 1:7 to be stable at sea level

david

 

[Frankm]

Problem with a recommended twist is it's given to cover all cartridges; ones with 2800 fps, etc. when you turn up the velocity RPM goes up. Also manufacturers recommendation based on low elevation such as sea level.

Kind of a fine line thus my interest in others experience with high velocity cartridges and these bullets.

As dstoenner mentions altitude also plays a role so if anyone shares their experiences please mention your altitudes.
Thx

 

[Evan]

I use this guy to rough in where I'm at: https://bergerbullets.com/twist-rate-calculator/

If you choose the 115 VLD (longest 6mm bullet they make), 3500fps, 8.5 twist, 10ft elevation at 80deg, you get an Sg of 1.3 which I've always found to work despite Berger saying it's marginal. This puts your RPM at 296k - right at the edge for my taste.

After my 7 twist 22BR experience, I will never put together a combo that exceeds 300k ever again. Blowing up bullets ruins everything, even when you're just shooting for fun.

 

[Frankm]

Evan, I hear you! That's why I m concerned.

We ve been blowing up 88 Eldms at 3275-3300 out of a 30" 22 CM with an 8 twist, but at 3175 fps in an 8 twist 26" barrel they work !

Had same happen with a 180 ELDM in a 7 STW Improved with a 7 twist 36" barrel. 3100 fps and they disappear. Found that 175 Eld X s will stay together at 3350 fps in same rifle due to thicker base and heavier jacket just above base. I tried to tell guy with rifle to use an 8 twist but he wanted a long, long barrel and with Lilja you had to do a 7 twist for longer than 30".

It is definitely a fine line. I m like you and think < 300K rpm is wise; plus we re at 3000 ft elevation. Probably need to give a 9 twist some serious consideration with this pending 6mm build if we really believe 3400-3500 fps is attainable with a 30" barrel.

 

[M14AMU]

Here's a simple solution!

Work with what's available!!

 

[Frankm]

That's like everyone driving a Yugo ...... No thanks!

 

[Spook]

108's blew up for me in a 1:8 bartlen chambered in 6 x 47, faster than 2900 but slower than 3000fps, with unbelievable consistency,slowed down to 2700 they stayed together.

 

[Frankm]

Spook, that's on the low velocity side of what I ve heard... how many groove was your 8 twist barrel?

Thx!

 

[ormandj]

That sounds like something else was going wrong, I would not expect that at those velocities with that twist. That’s only 270k rpm at 3000fps. Maybe a burr or something damaging the jacket/weakening it? I know the smaller caliber bullets tend to be more sensitive, but that seems awfully low unless the jackets are compromised.

 

[Spook]

Spook, that's on the low velocity side of what I ve heard... how many groove was your 8 twist barrel?

Thx!

5R ,switched to Berger 108 and didnt lose any at all.
the barrel shot 590+ scores pretty regularly.
It would have done better if my wind skills werent crap.

Had the same thing happen with Hornady 147's out of an 8 twist chambered in 6.5X55 Swede BJAI.
Switched to Berger Hybrids and never lost a single one.
The Hornady brass for the Swede blew primer pockets pretty regularly as well. Lapua brass solved that problem.

Ive shot the 80 amax and 80 eld through a 22-243 Middlestead (Benchmark 8T) for years @ very near 3400 fps without a problem though. Funny that ?

 

[Rob01]

Yeah something doesn't sound right. I run the 108s in a 7.7 5R twist Bartlein in my 6 Creed at over 3000fps and they all make target. Run the 147 in a 6.5 Creed 8 twist at 2820fps and no issues. Guess Hornady bullets just don't like you. LOL

 

[Ranger188]

Your 6-280 is overbore, and would expect barrel life to be shorter.
Maybe not as bad as a 22 creed. but I'd run a 8 - 8.5 twist and should
still stabilize the 110's or even more the 108's
I'd look at the Berger 109's also. High BC and a newer design for this problem.
You could do a gain twist.
I ran the 110's in a 7.5 twist @3140 for awhile and no problems.
Your at 3000 ft. a bonus.

 

[Frankm]

Thx all for the input. Friend went ahead and chambered 2 test mule rifles for this. ( actually rechambered two guns)

Did a 26" Rem 9.125 twist factory 243 barrel and a 30" Lilja 8 twist.

Remington didn't blow up a bullet! Shot 105 RFD, 108 ELDM, 110 MK and 115 RFD. Not sure that the 115 s weren t becoming unstable as they got squirrelly at 1140 yds. ( farthest steel we shot)
Got 3275 fps with 115 and R26. 105 s went 3450 with R26 and 108 and 110 went 3350-3375 fps also with R26.

Shot 30" just today and it was unreal... R26 with 105 s were going 3400+ with mild FF loads but blew up 1 out of 5 !! 110 MK s did 3430 with R26 but here's the crazy part.... thought what the heck we ve got the Labradar setup so let's try a couple 110 MK s with R33 and US869; 869 first shot was 3555 fps so we backed off 2 grains ( to 69) and still did easy 3500 fps. Bolt opened like butter and primers were still round! R33 first shot was 3598 fps at 66 grs and fairly flat Primer so went down to 64 grs and 3520 fps.

This thing was a lazer! Took 17 MOA with a 300 yd zero to shoot 1150 yd plate! It ll be really tough on barrels but talk about a LR chuck, Antelope or deer gun...!!

Thought a few of you might be interested and thanks again for input. To summarize I d say 9 twist with 105 grain bullets and 8 twist with 110 MK s.

 

[Hohn]

How does that performance compare to what you could get from a 6.5-06 or AI version of such?

 

[Frankm]

It is 6 s .... 280 AI vs 06 AI... advantage with using 280 AI brass to start is no fireforming.

 

[13red56]

I had a straight 6-06 for a while and ran 107 SMK’s at 3400 in an 8 twist with no issues. I have run the 110 SMK in a 9-7.7 gain twist barrel chambered in 6Creed run them to 3120 with no issues. With the speed you will be able to get an 8 twist I feel will be enough to stabilize the 110.

 

[Frankm]

Thanks 13red56..... last week we did testing with 110 MK and worked well with 8 twist. 3400 fps out of 30" bench gun, 3325 fps out of 27" sporter.

Cartridge sure likes R33 and US869 for velocity. Hard to believe Retumbo and H1000 are on fast side!!

 

[Frankm]

We got more velocity in earlier testing but upon reloading saw pressure issues in Primer pockets thus backed it off a little ...